Accepted Manuscript Sandstone provenance and U–Pb ages of detrital zircons from Permian–Triassic forearc sediments within the Sukhothai Arc, northern Thailand: record of volcanic-arc evolution in response to Paleo-Tethys subduction Hidetoshi Hara, Miyuki Kunii, Yoshihiro Miyake, Ken-ichiro Hisada, Yoshihito Kamata, Katsumi Ueno, Yoshiaki Kon, Toshiyuki Kurihara, Hayato Ueda, San Assavapatchara, Anuwat Treerotchananon, Thasinee Charoentitirat, Punya Charusiri PII: DOI: Reference:
S1367-9120(17)30192-X http://dx.doi.org/10.1016/j.jseaes.2017.04.021 JAES 3057
To appear in:
Journal of Asian Earth Sciences
Received Date: Revised Date: Accepted Date:
23 September 2016 20 April 2017 21 April 2017
Please cite this article as: Hara, H., Kunii, M., Miyake, Y., Hisada, K-i., Kamata, Y., Ueno, K., Kon, Y., Kurihara, T., Ueda, H., Assavapatchara, S., Treerotchananon, A., Charoentitirat, T., Charusiri, P., Sandstone provenance and U–Pb ages of detrital zircons from Permian–Triassic forearc sediments within the Sukhothai Arc, northern Thailand: record of volcanic-arc evolution in response to Paleo-Tethys subduction, Journal of Asian Earth Sciences (2017), doi: http://dx.doi.org/10.1016/j.jseaes.2017.04.021
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Sandstone provenance and U–Pb ages of detrital zircons from Permian–Triassic forearc sediments within the Sukhothai Arc, northern Thailand: record of volcanic-arc evolution in response to Paleo-Tethys subduction
Hidetoshi Hara a,*, Miyuki Kunii b, Yoshihiro Miyake b, Ken-ichiro Hisada b, Yoshihito Kamata b,
Katsumi Ueno c, Yoshiaki Kon a, Toshiyuki Kurihara d, Hayato Ueda e, San Assavapatchara f,
Anuwat Treerotchananon f, Thasinee Charoentitirat g, Punya Charusiri g
a
Geological Survey of Japan, AIST, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan
b
Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8572,
Japan
c
Department of Earth System Science, Fukuoka University, Fukuoka 814-0180, Japan
d
Graduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan
e
Department of Geology, Faculty of Science, Niigata University, Niigata 950-2181, Japan
f
Department of Mineral Resources, Bangkok 10400, Thailand
g
Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330,
1
Thailand
* Corresponding author.
E-mail address:
[email protected] (H. Hara).
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ABSTRACT
Provenance analysis and U–Pb dating of detrital zircons in Permian–Triassic forearc sediments from the Sukhothai Arc in northern Thailand clarify the evolution of a missing arc system associated with Paleo-Tethys subduction. The turbidite-dominant formations within the forearc sediments include the Permian Ngao Group (Kiu Lom, Pha Huat, and Huai Thak formations), the Early to earliest Late Triassic Lampang Group (Phra That and Hong Hoi formations), and the Late Triassic Song Group (Pha Daeng and Wang Chin formations). The sandstones are quartzose in the Pha Huat, Huai Thak, and Wang Chin formations, and lithic wacke in the Kiu Lom, Phra That, Hong Hoi and Pha Daeng formations. The quartzose sandstones contain abundant quartz, felsic volcanic and plutonic fragments, whereas the lithic sandstones contain mainly basaltic to felsic volcanic fragments. The youngest single-grain (YSG) zircon U–Pb age generally approximates the depositional age in the study area, but in the case of the limestone-dominant Pha Huat Formation the YSG age is clearly older. On the other hand, the youngest cluster U–Pb age (YC1) represents the peak of igneous activity in
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the source area. Geological evidence, geochemical signatures, and the YC1 ages of the sandstones have allowed us to reconstruct the Sukhothai arc evolution. The initial Sukhothai Arc (Late Carboniferous–Early Permian) developed as a continental island arc. Subsequently, there was general magmatic quiescence with minor I-type granitic activity during the Middle to early Late Permian. In the latest Permian to early Late Triassic, the Sukhothai Arc developed in tandem with Early to Middle Triassic I-type granitic activity, Middle to Late Triassic volcanism, evolution of an accretionary complex, and an abundant supply of sediments from the volcanic rocks to the trench through a forearc basin. Subsequently, the Sukhothai Arc became quiescent as the Paleo-Tethys closed after the Late Triassic. In addition, parts of sediments of supposed Devonian–Carboniferous age within the Sukhothai Arc were revised as the Triassic Lampang Group, and the Early Cretaceous Khorat Group.
Keywords: Detrital zircon U–Pb dating; Forearc basin; Paleo-Tethys; Sandstone provenance; Sukhothai Arc; Indochina Block
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1. Introduction
The Sukhothai Arc in northern Thailand developed in response to the subduction of Paleo-Tethyan oceanic crust beneath the present western margin of the Indochina Block, and it is characterized by volcanic successions, the intrusion of I-type granitoids, and the deposition of Permian–Triassic forearc basin sediments (Barr and Macdonald, 1991; Ueno and Hisada, 2001; Sone and Metcalfe, 2008; Metcalfe, 2013). Reconstruction of igneous activity associated with Paleo-Tethys subduction is important in understanding Permian–Triassic convergence tectonics and the magmatism that occurred between the Indochina and Sibumasu blocks in Southeast Asia. However, the nature of the igneous activity and its precise timing has not been clarified in this area. In northern Thailand, the Permian–Triassic volcanic successions have been named the Chiang Khong and Lampang volcanic belts (e.g., Barr et al., 2000; Singharajwarapan and Berry, 2000; Panjasawatwong et al., 2003; Barr and Charusiri, 2011). In these belts, U–Pb dating of zircons from the volcanic rocks has only been done for the Middle to Late Triassic volcanic rocks (e.g., Barr et al., 2000; Srichan et al., 2009; Qian et al.,
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2013), and there are no data for the Permian to Early Triassic volcanic rocks still now, as these rocks have largely been eroded away. I-type granitoids have provided some evidence of the magmatic activity, but the data are few because of the limited distribution of these granitoids in the Sukhothai Arc (Gardiner et al., 2016). In contrast, Permian to Triassic sedimentary successions, which formed in the forearc basin of the Sukhothai Arc, are widely distributed in northern Thailand. The sediments are mainly sandstone, mudstone, and limestone, and are known as the Permian Ngao and Triassic Lampang and Song groups (e.g., Charoenprawat et al., 1994; Ishibashi et al., 1994; Chaodumrong and Burrett, 1997; Singharajwarapan and Berry, 2000; Kobayashi et al., 2006; Chonglakmani, 2011;Ueno and Charoentitirat, 2011; Sone et al., 2012). In this study, we focus on the provenance of these forearc sediments, as they possibly preserve continuous records of the Permian–Triassic magmatic evolution of the missing Sukhothai Arc. Sandstone petrography and geochemistry are useful in determining provenance, tectonic setting, and sediment recycling (e.g., Bhatia and Crook, 1986; Dickinson et al., 1983), and U–Pb dating of detrital zircons from sandstone enable the
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maximum depositional age to be determined from the youngest or peak age, and enable reconstruction of the tectonic evolution of sediment provenance (e.g., Fedo et al., 2003; Dickinson and Gehrels, 2009; Ernst et al., 2009; Hampton et al., 2010 Beranek and Mortensen, 2011; Cawood et al., 2012). Combining these methods potentially provides not only the maximum depositional age but also information on tectonic setting and the temporal and spatial variations in provenance (Eizenhöfer et al., 2015; Hu et al., 2015; Lee et al., 2016). Hara et al. (2012, 2013) studied the U–Pb ages of detrital zircons and the provenance of an accretionary complex in northern Thailand that developed during the time of Paleo-Tethys subduction, and they discussed the supply system of the sediment from provenance (continent and arc) to trench as well as the maximum depositional age of the accretionary complex during Late Permian to Middle Triassic. Hara et al. (2013) also outlined the activity of the Sukhothai Arc, based on detrital zircon U–Pb ages. In addition, the chemistry of detrital chromian spinels, obtained from several tectonic units in Thailand, provided specific information on the tectonic setting with respect to the occurrence of mafic and ultramafic rocks (Chutakositkanon et al., 2001; Hisada et al., 2004).
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Here, we adapt these techniques for a study of the Permian–Triassic forearc sediments within the Sukhothai Arc. In addition, we examined the ages of zircons from sediments of supposed Devonian and Carboniferous age within the Sukhothai Arc in an attempt to understand the initial tectonic framework of arc evolution; previously the depositional ages of these sediments were uncertain due to the lack of age-diagnostic fossils. The aim of this paper is to determine evolution of the Sukhothai Arc, as recorded in continuous sedimentary successions of Carboniferous and Permian–Triassic age, and to reconstruct the evolution of the arc system associated with Paleo-Tethys subduction and closure, by combining provenance analysis from petrography and geochemistry with detrital zircon U–Pb dating.
2. Permian–Triassic forearc sediments of the Sukhothai Arc
Northern Thailand is here divided into the following four geotectonic units (from west to east): the Sibumasu Block, the Inthanon Zone, the Sukhothai Arc, and the Indochina Block (Fig. 1). The Sukhothai Arc largely corresponds to the Sukhothai Zone
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of Barr and Macdonald (1991) and the Sukhothai fold belt of Bunopas (1981), and it is dominated by deformed Carboniferous to Triassic sedimentary rocks, volcanic rocks, and Early Permian to Triassic I-type granitoids. It is considered to represent a continental island arc that was produced by subduction (towards the present east) of the Paleo-Tethys under the Indochina Block (Ueno and Hisada, 2001; Sone and Metcalfe, 2008; Hara et al., 2009, 2012, 2013; Metcalfe, 2013). The Nan–Uttaradit Suture Zone separates the Sukhothai Arc from the Indochina Block, and is interpreted to be the remnant of a back-arc basin (Ueno and Hisada, 2001; Sone and Metcalfe, 2008). The Sibumasu Block, which belonged to the eastern part of the Cimmerian continent (Sengör, 1979), is characterized by a peri-Gondwanan stratigraphy of Lower Permian glaciogenic diamictites with Gondwanan fauna and flora, and Middle–Upper Permian platform carbonates (Metcalfe, 1988, 2006; Ueno, 2003). The Inthanon Zone, originally proposed by Barr and Macdonald (1991), is characterized by Paleo-Tethyan oceanic rocks, pre-Devonian basement rocks, and Late Triassic and Early Jurassic S-type granitoids and gneissic rocks. The Inthanon Zone is interpreted to represent nappes of Paleo-Tethyan rocks that were thrust westwards over a marginal part of the
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Sibumasu Block (Caridroit et al., 1992; Ueno and Hisada, 2001; Hara et al., 2009; Barber et al., 2011). The Indochina Block is part of the South China–Indochina Superterrane (Metcalfe, 2002, 2006), and it has remained within the paleo-equatorial region since its Early Devonian breakaway from Gondwana. Permian–Triassic forearc sediments within the Sukhothai Arc were first described by Piyasin (1971, 1972) in the Ngao–Lampang–Phareo area, northern Thailand (Fig. 2). These sediments were attributed to the Ngao Group by Bunopus (1981), the Lampang Group by Piyasin (1971), and the Song Group by Chonglakmani (2011). In this paper, we describe these sedimentary groups further, aided by the recent compilation of data by Ueno and Charoentitirat (2011) and Chonglakmani (2011), and information gained from provincial geological maps of the Phrae and Lampang areas by Charoenprawat et al. (1994) and Vimuktanandana (2006a, b). In particular, we describe the petrography of the sandstones based on thin-section observations, modal analyses, and the Q–F–L and Qm–F–Lt ternary diagrams with the tectonic field (Fig. 3) proposed by Dickinson et al. (1983). The Permian Ngao Group can be subdivided into three formations, which in
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ascending order are the Kiu Lom, Pha Huat, and Huai Thak formations (Fig. 2). The Kiu Lom Formation is dominated by tuffaceous sandstone and shales, and it also contains conglomerates with clasts of limestone and rhyolitic–andesitic volcaniclastics (Fig. 4a). Calcareous layers and thin limestone beds are intercalated with the clastic rocks. The sandstones are usually calcareous, very poorly sorted, and they can be classified as lithic wackes with abundant andesitic and felsic volcanic fragments (Fig. 4b). They plot as ‘lithic recycled’ field on the Qm–F–Lt diagram (Fig. 3). The formation was considered to represent the late Asselian–Sakmarian (early Early Permian) based on fusuline faunas (Ueno and Charoentitirat, 2011), but a more recent study by Miyahigashi et al. (2014) showed that it continued into the Yakhtashian (Artinskian) of the late Early Permian. The Pha Huat Formation is a succession of bedded sandstone with mudstone, siltstone, and bedded limestone (Fig. 4c), with the limestone often forming thick bodies in the upper part of the formation. The sandstone can be classified as lithic wacke, and it contains lithic fragments of felsic volcanic rocks, polycrystalline quartz, and metamorphic rocks such as micaceous and quartzose schist (Fig. 4d). The sandstone
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plots in the ‘transitional recycled’ field on the Qm–F–Lt diagram (Fig. 3). This formation can be assigned to the Middle to early Late Permian based on fusulines and conodonts (Ueno and Charoentitirat, 2011). The Huai Thak Formation is a thick-bedded succession of sandstone and mudstone with conglomerate (Fig. 4e), and it also contains massive, bedded, and locally lenticular limestone. The conglomerates are composed mainly of fragments of rhyolite and felsic tuff together with some polycrystalline quartz and quartzose schist (Fig. 4f). The sandstones are lithic wackes dominated by abundant felsic volcanic fragments (Figs. 4g and 4h). They range widely within the ‘transitional recycled’, ‘mixed’, and ‘transitional arc’ fields when plotted on the Qm–F–Lt diagram (Fig. 3). Brachiopod, ammonoid, and fusuline faunas in the limestone and shale of the Huai Thak Formation indicate Changhsingian age (latest Permian) (Sakagami and Hatta, 1982; Waterhouse, 1983; Ishibashi and Chonglakmai, 1990; Ueno and Sakagami, 1991; Ishibashi et al., 1994). The Early−Middle Triassic Lampang Group can be subdivided into the Phra That, Pha Kan, Hong Hoi, and Doi Long formations, and it is made up of a succession
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of repeated carbonate- and turbidite-dominant facies (Chonglakmani, 2011). For provenance analysis, we focused on the turbidite-dominant facies of the Phra That and Hong Hoi formations. The Phra That Formation consists of sandstone, siltstone, conglomerate with volcaniclastic fragments, and limestones. The sandstone, often lithic wacke, is calcareous, and poorly sorted. Siltstone and mudstone are abundant in the upper part of the formation (Figs. 5a and 5b), suggesting a fining-upwards sequence (Chaodumrong and Burrett, 1997). Bivalves indicate the depositional age to be Scythian (Induan) to early Anisian (Chonglakmani, 2011). The Hong Hoi Formation is a typical turbidite succession consisting of sandstone and mudstone, with some intervening conglomeratic beds (Figs. 5c and 5d). Sedimentary structures such as graded bedding, parallel lamination, and convolute lamination are well developed. Folds and minor thrusts, observed in the turbidite sequence on the outcrop scale, probably represent slump structures (Fig. 5e). The sandstones of this formation are lithic wackes with volcanic fragments dominant (Figs. 5f and 5g). The lithic sandstones fall in the ‘dissected arc’ to ‘transitional arc’ fields on the Qm–F–Lt diagram (Fig. 3). Bivalves and ammonoids indicate a Ladinian to early
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Carnian age (Chonglakmani, 2011), and siliceous mudstones associated with conglomerate in the basal part of the formation yield a radiolarian fauna of Ladinian age (Figs. 5g and 5h; Kamata et al., 2016). The Song Group, proposed by Chonglakmani (2011) for the Triassic sequence in the Phrae area, can be subdivided into the Pha Daeng, Kang Pla, and Wang Chin formations in ascending order. Of these, we investigated the Pha Daeng and Wang Chin formations, which are characterized by turbidites with minor limestone interbeds. The Pha Daeng Formation contains red to gray silty sandstone, siltstone, mudstone, and minor limestone and volcaniclastics (Fig. 6a). The sandstones are lithic wackes that are dominated by volcanic fragments (Fig. 6b), and they plot in the ‘dissected arc’ to ‘transitional arc’ fields on the Qm–F–Lt diagram (Fig. 3). This formation contains early to middle Carnian bivalves and ammonoids (Chonglakmani, 2011). The Wang Chin Formation consists of sandstone, mudstone, and interbedded sandstone, mudstone, and limestone (Fig. 6c). Graded bedding, parallel lamination, and convolute lamination are well preserved in the turbidites of this formation (Figs. 6d and 6e). Slaty cleavage is frequently developed in the mudstone (Fig. 6f). Most of the
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sandstones are lithic wackes with dominated by volcanic fragments, and they are sometimes calcareous and quartzose; they plot in the ‘quartzose recycled to transitional recycled’ fields on the Qm–F–Lt diagram (Fig. 3). Bivalves, ammonoids, and conodonts indicate a middle Carnian to early Norian age (Chonglakmani, 2011). Miyahigashi (2014) reported that foraminifera from the limestone of this formation suggest an age range from Norian to Rhaetian.
3. Sediments of supposed Devonian–Carboniferous age from between the Sukhothai Arc and the Inthanon Zone
The marine succession of supposed Carboniferous age, called the Dan Lan Hoi Group, is distributed in the southern part of the Sukhothai Arc (Fig. 1) and it contains thick volcaniclastic beds (Bunopas, 1981). The inference of a Carboniferous age was based solely on stratigraphic relationships with the adjacent and possibly Devonian Khao Khieo Formation, and the assigned age is therefore questionable (Ueno and Charoentitirat, 2011). The Dan Lan Hoi Group can be subdivided into three
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formations: the Khao Khi Ma, Lan Hoi, and Khao Luang (Bunopus, 1981; Ueno and Charoentitirat, 2011). The Khao Khi Ma and Khao Luang formations include large amounts of volcaniclastic material and were deposited in a submarine-fan environment close to a volcanic source, whereas the Lan Hoi Formation represents a shallow-marine facies with provenances that are both volcanic and continental. We collected samples for zircon dating from the felsic tuff of the supposedly Devonian Khao Khieo Formation and from the sandstone of the supposedly Carboniferous Khao Khi Ma and Lan Hoi formations. In addition, we collected Carboniferous sandstone from the Mae Tha Formation and Carboniferous quartzose sandstone from the Inthanon Zone in the Chiang Mai area. The Khao Khieo Formation, assigned a Devonian age by Bunopus (1981), consists mainly of sandstone, slate, and felsic and andesitic tuffs. The true age of deposition is uncertain because of a lack of age-diagnostic fossils (Wongwanich and Boucot, 2011). The felsic tuffs are well foliated (Fig. 7a) and usually accompanied by slates that are dominated by quartz, plagioclase phenocrysts, and volcanic matrix alternated to chlorite (Fig. 7b; sample PT01).
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The Khao Khi Ma Formation is a succession of greenish volcaniclastic agglomerates with interbedded volcaniclastic sandstone and tuffaceous shale. The volcaniclastic agglomerates are composed of poorly sorted and weakly bedded andesitic conglomerates (Fig. 7c). The volcaniclastic sandstone is dominated by andesitic volcanic fragments, plagioclase, abundant pyroxene, and rare quartz, set in an argillaceous matrix (Fig. 7d; sample PT02). The Lan Hoi Formation consists of quartzose sandstone, siltstone, and shale, with minor tuff and conglomerate. The quartzose sandstone is massive (Fig. 7e) and interbedded with siltstone and tuff (Fig. 7f). The quartzose sandstone is dominantly quartz and calcite with minor volcanic and micaceous lithic fragments (Fig. 7g; sample PT03). The Mae Tha Formation is made up mainly of quartzose and feldspathic sandstone, and gray shale. Age-diagnostic fossils have not been reported from this formation, although a few unidentified plant remains have been found (Ueno and Charoentitirat, 2011). The sandstone contains abundant quartz and minor amounts of volcanic fragments, plagioclase, and mica (Fig. 7h; sample PT04).
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The quartzose sandstones within the Inthanon Zone contain abundant quartz and minor amounts of volcanic fragments, and the petrography and geochemistry of the sandstones were described by Hara et al. (2012) (Fig. 7i; sample PT05, equivalent of QS04 of Hara et al., 2012). The mudstones in this formation contain Late Carboniferous ammonoids (Fujikawa and Ishibashi, 1999). These Carboniferous sediments are interpreted to be part of the Sibumasu domain, and they are imbricated with Paleo-Tethyan rocks within the Inthanon Zone (Barber et al., 2011; Ueno and Charoentitirat, 2011).
4. Analytical methods
Thirty-six samples of sandstone and siltstone from the Permian–Triassic forearc sediments within the Sukhothai Arc were crushed for geochemical analysis. Concentrations of 10 major elements and trace elements were determined from glass beads using X-ray fluorescence (XRF; Rigaku RIX3000) at Niigata University, Japan. The total Fe contents are given as Fe2O3. Loss on ignition (LOI) was measured by
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weighing the samples before and after 2 h of heating at 850 °C. Concentrations of Sc, Hf, U, and the REEs were analyzed by inductively coupled plasma–mass spectrometry (ICP–MS) using an Agilent 7500a instrument housed at Niigata University. Samples were prepared using a combined acid digestion procedure (HCl and HF) and alkali fusion by dissolution with a combination of HF–NHO3 and HF–HCl at 150 °C after adding anhydrous Na2CO3. Analytical accuracy, as estimated by deviations from the geological reference material W-2 (U.S. Geological Survey; Eggins et al., 1997) and JB-1a (Geological Survey of Japan; Imai et al., 1995), was better than 8%. Analytical precision, estimated from relative deviation values, was better than 5%. Detrital chromian spinels were analyzed using a field emission–electron probe microanalyzer (FE–EPMA; JEOL JXA8530F) housed at the Research Facility Center for Science and Technology, University of Tsukuba, Japan. Analyses were performed with a spot size of 5 μm under an accelerating voltage of 15 kV, and with a beam current of 10 nA. We assumed that all the Ti is in the form of an ulvöspinel phase (Fe2TiO4) in the chromian spinel. The Fe2+–Fe3+ partitioning in the spinel was calculated by spinel stoichiometry.
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Detrital zircons were separated from the sandstones using isodynamic magnetic and sodium polytungstate (SPT) heavy liquid separation techniques. Zircon grains were picked randomly from the concentrates and then mounted and embedded in a Teflon sheet. Most of the zircons were 50–100 m in size, generally transparent and light violet to light yellow in color, and with euhedral, prismatic, and subrounded shapes. Cathodoluminescence (CL) imaging, using an SEM–EDS (JEOL JSM-6610 LV) equipped with a CL system (Gatan Mini CL) at the Geological Survey of Japan, AIST (Tsukuba, Japan), was performed to observe the internal structures and zonation patterns of the zircons, and to select suitable sites for U–Pb dating. Most of the zircons exhibited clear oscillatory zoning, faint zoning, and high Th/U ratios (mostly >0.2, Tables S1 and S2), which indicate a magmatic origin (Corfu et al., 2003; Hoskin and Schaltegger, 2003). U–Pb isotope analyses of zircons from the Permian–Triassic forearc sediments, and from sample PT03, were determined by laser ablation–ICP–MS (LA–ICP–MS; Agilent 7500cx at the Geological Survey of Japan), and we followed the analytical methods of Kon and Takagi (2012) and Kon et al. (2015). Analyses were
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performed with a spot size of 15 μm, a 10 Hz repetition rate, a pulse energy of 5 μJ/cm 2, and using a Ti:S femtosecond laser ablation system operating at a wavelength of 260 nm. Zircon U–Pb isotope analyses for four samples (PT01, PT02, PT04, and PT05) were performed with LA–ICP–MS (Agilent 7500a at Niigata University). Analyses were performed with a spot size of 30 μm, a 5 Hz repetition rate, a pulse energy of 12–13 μJ/cm2, and using a New Wave UP213 laser ablation system operating at a wavelength of 213 nm. Calibrations, data quality control were undertaken using the standard silicate glass NIST SRM610 (Walder et al., 1993), 91500 standard zircon (Wiedenbeck et al., 1995). We verified the accuracy of our analyses using the Plešovice standard zircon (Sláma et al., 2008). The weighted mean U–Pb age of the Plešovice zircon were 338 ± 2 Ma at the Geological Survey of Japan, and 335 ± 2 Ma at Niigata University during operation respectively, consistent with reference data (337.13 ± 0.37 Ma, Sláma et al., 2008). All discordant data and common-Pb detected data were not used to determine detrital zircon U–Pb ages during this study. All detrital zircon U–Pb ages and concordia diagrams were calculated using Isoplot v.3.75 (Ludwig, 2012). The geological timescale is based on Gradstein et al. (2012).
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5. Geochemistry of the clastic rocks
XRF and ICP–MS analyses were carried out to determine the major, trace, and rare earth element (REE) concentrations in the clastic rocks. The results are given in Table 1. Variation diagrams between (SiO2 + CaO) and TiO2, Cr, and V are shown in Fig. 8; we used (SiO2 + CaO) contents because most of the clastic rocks are calcareous in the study area. The (SiO2 + CaO) contents for the Ngao and Song groups vary from 70 to 90 wt.%, and the contents are slightly lower (60 to 80 wt.%) for the Lampang Group. The geochemical data generally exhibit a negative correlation between (SiO 2 + CaO) and major element oxides (e.g., TiO2, Fe2O3, MgO, and K2O) and compatible elements such as Cr and V (Table 1 and Fig. 8). Moreover, within the Song Group the clastic rocks from the Pha Daeng Formation have low (SiO2 + CaO) contents and high TiO2, Cr, and V contents. These geochemical characteristics of the Pha Daeng Formation are similar to those of the Lampang Group. Fig. 9 shows the mean values of trace elements normalized to Post-Archean
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Australian Shale (PAAS; Taylor and McLennan, 1985; McLennan, 1989) as well as the mean values of REEs normalized to chondrite for each formation (Sun and McDonough, 1989). Compared with PAAS, the clastic rocks from all the formations have low concentrations of trace elements. In addition, large-ion lithophile elements (LILEs; Ba and Rb) and compatible elements (Cr and V) are depleted relative to PAAS. Here, we selected three igneous rocks as candidate source rocks, based on data from Srichan et al. (2009): basalt–andesite (BA), felsic volcanic rock (F), and diorite (D) from the Sukhothai Zone. The REE patterns of the clastic rocks show enrichments in light REEs, flat patterns of heavy REEs, and negative Eu anomalies. Among the three candidate source rocks, this pattern fits with the felsic volcanic rock and diorite rather than the basalt–andesite.
6. Geochemistry of the chromian spinels
We obtained 28 detrital chromian spinel grains from five sandstone samples: N03_Ph from the Pha Huat Formation, L03_Hh and L04 from the Hong Hoi Formation,
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S01_Pd from the Pha Daeng Formation, and S08 from the Wang Chin Formation. The sample localities are shown on Fig. 2. The analytical results obtained using FE–EPMA are listed in Table 2. Detrital chromian spinels from the Pha Huat Formation have values of Cr# [= Cr/(Cr + Al) atomic ratios] of 0.45 to 0.54, and low TiO 2 contents of 0.03 to 0.24 wt.% (Fig. 10a). The chromian spinels from the Hong Hoi and Pha Daeng formations are characterized by relatively high values of Cr# (0.25 to 0.84) and variable TiO2 contents of 0.10 to 1.13 wt.% (Fig. 10a). The Wang Chin Formation contains detrital chromian spinels with low Cr# values and TiO 2 contents (Fig. 10a). In addition, most of the detrital chromian spinels present a broad positive correlation between YFe [= 100Fe3+/(Cr + Al + Fe3+) atomic ratios] and TiO2 contents (Fig. 10b). Based on the discrimination diagram proposed by Arai (1992), most of the detrital chromian spinels from the Hong Hoi and Pha Daeng formations fall in the field of ‘island arc basalts’ (Figs. 10a and 10b). On the other hand, detrital chromian spinels from the Pha Huat and Wang Chin formations show unclear trends, but most plot in the mixing field between ‘island arc basalts’ and ‘MORB’ (Arai, 1992; Ghosh et al., 2012).
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7. U–Pb ages of detrital zircons from the Permian–Triassic forearc sediments within the Sukhothai Arc
The detrital zircons from seven sandstone samples of the Permian–Triassic forearc sediments were dated using LA–ICP–MS U–Pb analysis. The samples were N01_Kl from the Kiu Lom Formation, N03_Ph from the Pha Huat Formation, N06_Ht from the Huai Thak Formation, L03_Hh and L05_Hh from the Hong Hoi Formation, S01_Pd from the Pha Daeng Formation, and S09_Wc from the Wang Chin Formation (see Fig. 2 for sample localities). The U–Pb ages are presented as relative age probability plots in Figs. 11 and 12, and are listed in Table 3 and Table S1. The majority of the ages are concordant within 2 analytical uncertainties, and for this paper we used the concordant data for our interpretation of the detrital zircon U–Pb ages. The sandstone samples from the six formations can be grouped into two types with respect to the zircon U–Pb ages: one type shows a single distinct cluster of Permian–Triassic peak ages with only small numbers of Paleozoic and Proterozoic zircons (N01_Kl, N06_Ht, L03_Hh, L05_Hh, and S01_Pd), whereas the other type has
25
multiple clusters of zircon ages, not only with a Permian–Triassic peak but with several other smaller Paleozoic and Proterozoic peaks (N03_Ph and S09_Wc; Fig. 13). This study used two younger age values to determine whether detrital zircon U–Pb ages represent depositional ages by combining youngest single grain zircon ages with 1 uncertainty values (YSG) and the weighted mean age of the youngest cluster that overlap in age at 1 uncertainty values (YC1) following the quantitative interpretation approach for detrital zircon U–Pb age data of Dickinson and Gehrels (2009). The YSG and YC1 U–Pb ages for each sample are summarized in Table 3. With regard to the Permian Ngao Group, sample N01_Kl from the Kiu Lom Formation yielded YSG and YC1 U–Pb ages of 279 ± 8 and 294 ± 4 Ma, sample N03_Ph from the Pha Huat Formation yielded YSG and YC1 ages of 282 ± 9 and 361 ± 9 Ma, and sample N06_Ht from the Huai Thak Formation yielded YSG and YC1 ages of 251 ± 7 and 258 ± 2 Ma, respectively (Table 3). The YSG and YC1 ages for sample N01_Kl are broadly within the range of the depositional age of the Kiu Lom Formation, as determined from fossil evidence, although the YSG age is close to the youngest limit of the depositional age; the YC1 age coincides with the age of the
26
lower part of the Kiu Lom Formation. The YSG and YC1 ages for sample N03_Ph from the Pha Huat Formation are clearly older than the depositional age. The YSG age for sample N06_Ht from the Huai Thak Formation approximates the depositional age within a range of 1 error, whereas the YC1 age is slightly older. The sandstones of the Triassic Lampang and Song groups yielded detrital zircon YSG and YC1 U–Pb ages that included, respectively, 231 ± 7 and 244 ± 3 Ma for sample L03_Hh from the Hong Hoi Formation, 229 ± 8 and 242 ± 2 Ma for sample L05_Hh from the Hong Hoi Formation, 219 ± 5 and 240 ± 3 Ma for sample S01_Pd from the Pha Daeng Formation, and 220 ± 8 and 249 ± 6 Ma for sample S09_Wc from the Wang Chin Formation (Table 3). The YSG ages for samples L03_Hh and L05_Hh coincide with the younger depositional age of the Hong Hoi Formation. The YSG age of sample S01_Pd from the Pha Daeng Formation is clearly younger than the depositional age, as determined from fossil evidence. The second youngest single grain zircon age of sample S01_Pd is 221 ± 6 Ma, presenting a similar age for YSG age of 220 ± 8 Ma. Both zircon grains are constituent of youngest cluster determined YC1 age, presenting no hydrothermal alternation based on CL observation, and no effect of common Pb. For
27
that reason, we consider that YSG age of 220 ± 8 Ma is suitable for interpretation of depositional age. In the present study, combining fossil and YSG age data, the depositional age of the Pha Daeng Formation determined ranging from the Carnian to the Norian. The YSG age presents the younger limit of depositional age in this case. The YSG age of sample S09_Wc falls within the Late Triassic depositional age of the Wang Chin Formation. In contrast, almost all of the YC1 ages from the Lampang and Song groups are older than the depositional ages of each formation, as determined from fossil evidence. Burrett et al. (2014) examined detrital zircon U–Pb ages obtained from the Hong Hoi, Pha Deang, and Wang Chin formations, and which were presented as merged data from several samples. They suggested that the data from the Hong Hoi Formation showed a single cluster, whereas those from the Pha Daeang and Wang Chin formations were in multiple clusters. However, the results are unclear because of a lack of information about stratigraphic relationships and the location of each sample.
8. Revision of the Devonian and Carboniferous ages previously assigned to
28
sediments in northern Thailand in the light of new U–Pb age data
The following four samples of sandstone and one of tuff were dated using LA–ICP–MS
U–Pb
analysis
of
detrital
zircons
from
the
supposedly
Devonian–Carboniferous-aged sediments: PT01 (tuff) from the Khao Kieo Formation, PT02 (sandstone) from the Khao Khi Ma Formation, PT03 (sandstone) from the Lan Hoi Formation, PT04 (sandstone) from the Mae Tha Formation, and PT05 (sandstone) from the Inthanon Zone (see Fig. 1 for sample localities). The U–Pb age results are presented as relative age probability plots in Figs. 12 and 13, and listed in Tables 4 and S2. The felsic tuff sample PT01 from the Khao Kieo Formation yielded a YSG U–Pb age of 215 ± 4 Ma and a YC1 U–Pb age of 229 ± 2 Ma. For the sandstones from the Dan Lan Hoi Group we obtained the following YSG and YC1 U–Pb ages: 235 ± 4 and 254 ± 3 Ma for sample PT02 from the Khao Khi Ma Formation, and 133 ± 4 and 137 ± 5 Ma for sample PT03 from the Lan Hoi Formation. For the sandstones from the Mae Tha Formation and the Inthanon Zone the YSG and YC1 U–Pb ages were 331 ± 5
29
and 337 ± 6 Ma for sample PT04, and 494 ± 6 and 515 ± 7 Ma for sample PT05, respectively. The age data for the tuff and volcaniclastic sandstone samples PT01 and PT02 present a clear single peak, suggesting that almost all the zircons came from a single volcanic source, whereas the quartzose sandstone samples PT03, PT04, and PT05 present multiple clusters of age data due to a variety of provenances. In the light of these new U–Pb age data, it is necessary to re-examine the previously assigned ages of Devonian–Carboniferous for the sediments between the Sukhothai Arc and the Inthanon Zone in northern Thailand. The Khao Kieo Formation was assigned a Devonian age by Bunopus (1981), but the new zircon U–Pb age data (a single cluster) for the felsic tuffs indicates a Late Triassic age. In the Dan Lan Hoi Group, detrital zircon U–Pb ages of Early to Middle Triassic were obtained for the volcaniclastic sandstone of the Khao Khi Ma Formation, and an Early Cretaceous age for the quartzose sandstone of the Lan Hoi Formation. Based on the Triassic U–Pb ages for the Khao Kieo and Khao Khi Ma formations, the tuffs and volcaniclastic sandstones in the Sukhothai area should be correlated with the volcanic members in the Lampang volcanic belt. On the other hand, the quartzose sandstones of the Lan Hoi Formation,
30
which yielded Early Cretaceous zircon age data, should now be assigned to the Cretaceous formation that was deposited within the basin on the Khorat Plateau (Carter and Bristow, 2003; Meesok, 2011). The new data and observations indicate a lack of Devonian–Carboniferous sediments within the Sukhothai Arc in the present day. The detrital zircon U–Pb age data for the quartzose sandstone of the Mae Tha Formation exhibit clear peaks at 337, 437, and 530 Ma as well as minor Proterozoic peaks (Fig. 12), and the 337 Ma YC1 age probably corresponds to a maximum depositional age around the middle of the Carboniferous. Recent studies of zircon ages have confirmed the existence of Silurian and early Carboniferous volcanism at 434–428 Ma at Loei (Khositanont et al., 2008), 424 Ma at Loei (Zhao et al., 2016), and 350–330 Ma in Laos (Qian et al., 2015). These new data suggest that the clusters of zircon peak ages at 337 and 437 Ma in the Mae Tha Formation can be related to volcanic sources within the Indochina Block, which indicates in turn that the Mae Tha Formation was deposited near the block, and can be interpreted as part of the Indochina domain. However, any interpretation of its present position within the Inthanon Zone remains uncertain. Along the western margin of the Indochina Block, Late Carboniferous
31
arc-like volcanic rocks are found around the Loei (Northeast Thailand) and Pak Lay (northern Laos) areas (Fig. 1), for which zircon U–Pb ages of ca. 315 Ma (Qian et al., 2015) and 306–304 Ma (Kamvong et al., 2014) have been reported. Zircons with these ages are not found in the quartzose sandstone of the Mae Tha Formation, and we take this to mean that the Mae Tha Formation had already been deposited before 315 Ma. We propose, therefore, that the Mae Tha Formation was deposited between 337 and 315 Ma, in the middle Carboniferous. On the other hand, the U–Pb ages of detrital zircon from the Carboniferous quartzose sandstone within the Inthanon Zone have several clear peaks at 515, 556, 858, 1160, and 1531 Ma, and no Carboniferous zircons from the Indochina Block (Fig. 12), presenting same character from the Carboniferous sandstones from the Sibumasu Block (Burrett et al., 2014; Cai et al., 2017). Thus, the U–Pb age data support that quartzose sandstones within the Inthanon Zone belong to part of the Sibumasu domain.
9. Source rock composition and sediment provenance
32
The geochemistry of clastic rocks is useful for understanding the composition of the source rocks (e.g., McLennan et al., 1993). In particular, trace elements in clastic rocks can be used to constrain the nature of the source rock, because incompatible elements are enriched in felsic volcanic rocks, LILEs are abundant in the continental crust, and compatible elements are dominant in mafic and ultramafic rocks (Feng and Kerrich, 1990; McLennan et al., 1990). The petrographic (Fig. 3) and geochemical characteristics (Fig. 8) of our sandstone samples indicate that they can be divided into two types: quartzose sandstones in the Pha Huat, Huai Thak, and Wang Chin formations, and lithic sandstones in the Kiu Lom, Phra That, Hong Hoi, and Pha Daeng formations. Our data also show that the trace elements in these clastic rocks have no consistent trend from incompatible to compatible elements relative to PAAS (Fig. 9a), probably indicating mixed sources with basalt–andesite, felsic volcanic rocks, and other igneous rocks from the Sukhothai Arc. In addition, the patterns of REEs with negative Eu anomalies in the clastic rocks suggest that the source rocks were felsic volcanic rocks and diorite, but the data indicate no information in detail (Fig. 9b). In clastic rocks, increasing V and Sc concentrations suggest an increase in
33
volcanic components (Ryan and Williams, 2007; Surpless, 2015). On Fig. 14a, we can recognize a high contribution of volcanic material to the lithic sandstones. Bracciali et al. (2007) proposed the use of the V–Ni–Th*10 ternary diagram for determining the relative contributions of source material from mafic, ultramafic, and felsic sources. In similar fashion, we use here a V–Cr–Th*10 ternary diagram, replacing Ni with Cr as a proxy for ultramafic rocks (Fig. 14b). In addition, the trends from mafic to felsic volcanic rocks in the Sukhothai Arc were estimated from the mean values of geochemical data for basalt–andesite (BA), felsic volcanic rock (F), and diorite (D) from the Sukhothai Arc (Srichan et al., 2009), and Phanerozoic granite (G; Condie, 1993). On the V–Cr–Th*10 ternary diagram, the lithic sandstones plot between the fields of ‘basalt–andesite’ and ‘felsic volcanic rock’, while the quartzose sandstones plot around the fields for ‘felsic volcanic rock’ and ‘diorite to granitic rock’ (Fig. 14b). McLennan et al. (1993) proposed the Zr/Sc–Th/Sc diagram for determining the source compositions of clastic rocks, employing Th as a typical incompatible element, Sc as a compatible element, and Zr as a recycling element. According to this diagram (Fig. 14c) the source rock compositions of the lithic sandstones are more or less consistent with
34
basalt–andesite and felsic volcanic rock. In contrast, the source rock compositions of the quartzose sandstones fall in the fields of ‘felsic volcanic rock’ and ‘diorite to granitic rock’. Bhatia and Crook (1986) proposed tectonic discrimination diagrams based on immobile trace elements to understand the tectonic setting of sedimentary basins. Based on their La–Th–Sc ternary diagram (Fig. 14d), most of our clastic rock samples cluster within the ‘continental island arc’ field, with a few samples from the Wang Ching Formation plotting in the ‘passive continental margin’ field. We conclude, therefore, that the dominant sources for the sandstones of the Pha Huat, Huai Thak, and Wang Chin formations were felsic volcanic and plutonic rocks, whereas the dominant sources for the sandstones of the Kiu Lom, Phra That, Hong Hoi, and Pha Daeng formations were basalt, andesite, and felsic volcanic rocks. Chaodumrong (1994) described the lithofacies and sandstone petrography of the Hong Hoi and Wang Chin formations. The Hong Hoi Formation is characterized by lithic sandstone consisting abundant volcanic fragments and plagioclase with minor quartz, whereas the Wang Chin Formation presents quartzose sandstone, as well as this study. In addition, he reported that the REEs patterns of both formations are similar and
35
plotted between andesite and rhyolite field. In the present study, we identified different source rock compositions between both formations based on geochemical results focus on volcanic rock input (Fig. 14), although the REEs patterns of both formations present similar pattern presenting negative Eu anomalies (Fig. 9). The lithic sandstones of the Hong Hoi Formation were mainly sourced from ‘basalt–andesite’ and ‘felsic volcanic rock’, while the source rocks of the quartzose sandstones of the Wang Chin Formation were mainly from the ‘felsic volcanic rock’ and ‘diorite to granitic rock’.
10. Evolution of volcanic activity within the Sukhothai Arc
By integrating information from the regional geology and sandstone provenance with the U–Pb ages of detrital zircons in the Permian–Triassic forearc sediments, we propose the following model for the evolution of the Sukhothai Arc in response to Paleo-Tethys subduction, as well as for the development of an accretionary complex and a back-arc basin during the Permian–Triassic. A summary of the stratigraphy and the evolutionary model of the Sukhothai Arc are shown in Figs. 15 and
36
16, respectively. During the middle Carboniferous, the Mae Tha Formation was deposited along the western margin of the Indochina Block. This formation is characterized by quartzose sandstones that were sourced from almost all the continental cratonic areas within the Indochina Block, as well as from some minor Silurian and early Carboniferous volcanic rocks. The Sukhothai Arc did not exist during this period, and only continental signatures are evident at this time in northern Thailand. The arc-like volcanic rocks occurred along the western margin of the Indochina Block during the Late Carboniferous (Kamvong et al., 2014; Qian et al., 2015). During the Early Permian, the Kiu Lom Formation was deposited in a forearc basin that developed along the present western margin of the Indochina Block. This formation is characterized by felsic to andesitic volcaniclastics and conglomerate, although the geochemistry of some of the sandstones suggests a dominantly basaltic to felsic volcanic influence (Fig. 14). When compared with potential source rocks, the clastic rocks of the Kiu Lom formation show no Eu anomalies and no enrichment in heavy REEs, and have a similar pattern to basalt–andesite (Fig. 9). On the basis of
37
sedimentary structures and clast-supported conglomerates, Miyahigashi et al. (2014) suggested that the volcaniclastics were mainly gravity flow deposits that formed in a channel that was cut into a submarine slope. This would mean that the felsic–andesitic source volcanic rocks were distributed in and around these sites of sediment deposition. Detrital zircon U–Pb age data exhibit a clear cluster of ages in the range 310 to 280 Ma, with a YC1 age of 294 Ma, corresponding to the depositional age of this formation (Fig. 15). The volcaniclastics and the detrital zircons were probably supplied from volcanoes that were erupted contemporaneously with sediment deposition. However, these supposed volcanic source rocks have now been eroded away. As mentioned above, Late Carboniferous arc-like volcanic rocks are distributed along the western margin of the Indochina Block, and the U–Pb ages of zircons from these rocks are ca. 315 Ma (Qian et al., 2015) and 306–304 Ma (Kamvong et al., 2014). Thus, continental arc volcanism intensified in the Late Carboniferous (Qian et al., 2015). Additionally, in the Nan suture zone between the Sukhothai Arc and the Indochina Block, Yang et al. (2016) examined U–Pb ages of zircons from oceanic crustal rocks and noted the presence of 311 Ma gabbro and 316 Ma metabasalt in the
38
Nan area of northern Thailand. These dates are similar to those of the arc-like volcanism. Qian et al. (2016a) obtained U–Pb ages of 336 and 305 Ma for zircons from the basaltic rocks in the Luang Prabang area of Laos, and they concluded from these dates that the Nan back-arc basin opened in the Late Carboniferous. However, this back-arc basin was located to the west of the Late Carboniferous arc-like volcanic rocks in their present position, and developed in front of the continental arc volcanoes. There are, however, major regional problems in interpreting the relationships of the geological setting of the continental arc and back-arc volcanic belts. Nevertheless, the volcanic activity preserved in the Kiu Lom Formation can probably be considered to represent the initial development of a continental island arc along the front of a back-arc within the Sukhothai Arc (Fig. 16-1). These volcanic events probably occurred locally, because the general paucity of geological evidence points to a scattered distribution of Carboniferous volcanic rocks and the Kiu Lom Formation. We conclude that the Sukhothai Arc developed initially as a continental island arc during the Late Carboniferous to Early Permian, and that the Nan back-arc basin was spreading locally. Subsequently, the Pha Huat Formation was deposited in the forearc area of the
39
Sukhothai Arc during the Middle to early Late Permian. Sandstones of this formation are derived mostly from a felsic volcanic, diorite and granite source (Fig. 14). Their detrital zircon YSG and YC1 U–Pb ages are 282 and 361 Ma, respectively, and there is a cluster of zircons with ages in the range 389–335 Ma, clearly older than the depositional age. Moreover, Proterozoic detrital zircons are found in the sandstones of this formation (Fig. 12 and Table S1). These data indicate that Early Paleozoic felsic volcanic rocks were presented in the source area, probably along the western margin of the Indochina Block where felsic volcanic rocks of an appropriate age were reported by Qian et al. (2015) around the Loei area and in Laos. The scarcity of detrital zircons with ages corresponding to the age of sediment deposition is noteworthy, because it means that the Sukhothai Arc was inactive during the Middle to early Late Permian. Gardiner et al. (2016) reported a U–Pb age of 266 Ma for zircons from granite (inferred to be an I-type) in the Sukhothai Arc of eastern Myanmar. According to a compilation of zircon U–Pb ages by Searle et al. (2012), the intrusion of I-type granites, associated with the subduction of the Paleo-Tethyan oceanic crust during the period 267–227 Ma, was widespread within the Central and Eastern belts of the East Malaya
40
Block (the southern geotectonic extension of the Sukhothai Arc; Metcalfe, 2013). Similar (but perhaps minor) I-type granites are therefore likely to have been emplaced elsewhere in the Sukhothai Arc during the Middle–Late Permian, but those plutonic rocks may not have been uplifted and eroded at the time of deposition of the Pha Huat Formation. We note that the Nan back-arc basin was already open and inactive by the Late-Middle Permian, based on the presence of radiolarian cherts (Hada et al., 1999), so clearly at this time there was a deep-sea environment between the Sukhothai Arc and the Indochina Block. We conclude, therefore, that the Middle to early Late Permian the Sukhothai Arc was characterized by minor igneous activity within the arc and the chert deposition at inactive back-arc basin (Fig. 16-2). During the latest Permian to early Late Triassic, the detrital zircon age data and the geochemical evidence from the Huai Thak, Hong Hoi, and Pha Daeng formations indicate that the Sukhothai volcanic arc was active at this time (Figs. 16-3 and 16-4), and the Triassic Lampang and Chiang Khong volcanic belts provide direct evidence of this activity. Recent U–Pb dating studies have recorded volcanic activity at 241–240 Ma (Barr et al., 2000; Qian et al., 2017) in the Lampang volcanic belt and at
41
242–238 Ma (Qian et al., 2013), 233 Ma (Barr et al., 2006), 231 Ma (Qian et al., 2016b), 229 Ma (Qian et al., 2016c), and 223–220 Ma (Srichan et al., 2009) in the Chiang Khong volcanic belt. In addition, I-type granitoids within the Sukhothai Arc have yielded Ar–Ar ages of 245–210 Ma (Charusiri et al., 1993), and Middle Triassic U–Pb ages (245–227 Ma) were obtained for zircons from granitoids on Peninsular Malaysia (Searle et al., 2012). Moreover, mafic-ultramafic rocks were emplaced at the lower crustal depth during latest Permian, associated with subduction of Paleo-Tethys (257 Ma; Fanka et al., 2016). The U–Pb ages of detrital zircons from the Huai Thak, Hong Hoi, and Pha Daeng formations form young single cluster distributions, suggesting that the zircons were derived from a single source in the Sukhothai Arc. This result indicates that intensive volcanic arc and back-arc activity created an important barrier to the supply of sediment from the continent. Felsic volcanic rocks dominated the source area for sandstones in the Huai Thak Formation during the latest Permian, and basaltic–felsic volcanic rocks dominated the source for the Phra That, Hong Hoi, and Pha Daeng formations during the Early to early Late Triassic. Therefore, the nature of the
42
volcanism in the source area changed from felsic to more mafic between the Permian and Triassic (Fig. 14, Figs. 16-3 and 16-4). In addition, the geochemical characteristics of detrital chromian spinels in the Hong Hoi and Pha Daeng formations provide further evidence of an island arc basaltic provenance (Fig. 9). During the Early to Middle Triassic, arc-type volcanic activity associated with subduction of the Paleo-Tethys also occurred around the Loei and Petchabun areas (Loei–Petchabun volcanic belt) of Thailand and western Laos, proposed by Kamvong et al. (2014) and Qian et al. (2016d). These volcanic rocks have yielded zircon U–Pb ages of 259 and 249–246 Ma (Salam et al., 2014), 244–241 Ma (Kamvong et al., 2014), and 238 Ma (Qian et al., 2016d). The Early to Middle Triassic volcanic activity constituted a continental island arc, and its volcanic front probably extended through the Sukhothai Arc to the Indochina Block (Figs. 16-3 and 16-4). At present, the Chiang Khong and Lampang volcanic belts in the Sukhothai Zone are almost parallel to the Loei–Petchabun volcanic belt in the Indochina Block, and they represent a series of coeval volcanic belts of Early to Middle Triassic age that may possibly have been rearranged during the Cenozoic as a result of strike-slip movements along structures such as the Uttaradit fault zone (Morley et al.,
43
2011), although further detailed study is needed. During this period of intensive Early to Middle Triassic volcanic activity, the youngest limits of the depositional ages of the Huai Thak, Hong Hoi, Pha Daeng formations are given by the U–Pb YSG ages, (Fig. 15). On the other hand, the YC1 ages for these formations are older than the depositional ages (Fig. 15). The YC1 ages of 244–240 Ma for the Hong Hoi and Pha Daeng formations correspond to the U–Pb ages of zircons from volcanic rocks in the Lampang volcanic belt (240 Ma; Barr et al., 2000), and it is likely that the YC1 U–Pb ages of detrital zircons correspond to the peak age of volcanic activity. The YC1 age of 258 Ma for the Huai Thak Formation suggests that the volcanic rocks from the initial stage of development of the Sukhothai Arc are now missing. In addition, we note that the YC1 U–Pb ages of 251 and 243 Ma for sandstones from an accretionary complex (Hara et al., 2013) are similar to the YC1 ages in the forearc sediments, and that the sediment supply from the volcanic arc to the trench through the forearc basin took place during the development of an accretionary complex that evolved at the same time as the Lampang volcanic belt was active during Middle Triassic (Fig. 16-4).
44
Subsequent to this intensive Early–Middle Triassic volcanic activity, the Wang Chin Formation was deposited within the forearc basin of the western Sukhothai Arc during the Late Triassic (Fig. 16-5). The Nan back-arc basin was closed until the Late Triassic, judging from the occurrence of limestones, cherts, and hemipelagic sediments within the basin during the Permian to Middle Triassic (Ueno and Charoentitirat, 2011). In addition, it has generally been thought that the Paleo-Tethys Ocean closed after the Middle Triassic, since siliceous radiolarian-bearing sediments occur on the continental slope of the Sibumasu Block (Kamata et al., 2014). Moreover, an even younger age for closure after the early Late Triassic has been suggested, given the ca. 230 Ma zircon U–Pb ages for S-type granite intrusions associated with collision between the Sibumasu and Indochina blocks (Gardiner et al., 2016), and closure as the latest Triassic is possible based on the widespread deposition of the non-marine Khorat Group, which covered both the Indochina and Sibumasu blocks (Hada et al., 1999). The petrography and geochemistry of sandstones of the Wang Chin Formation indicate a provenance dominated by felsic volcanic rocks and other igneous rocks. The U–Pb ages of detrital zircons from the Wang Chin Formation are characterized by
45
multiple peaks, a YSG age of 220 Ma, and a YC1 age of 249 Ma (Fig. 15). The 220 Ma YSG age coincides with the depositional age of this formation, but the YC1 age is clearly older, and this means that zircons from the Sukhothai Arc with the same age as the depositional age of the Wang Chin Formation are rather rare. Most of the zircons providing the YC1 ages were supplied from older felsic volcanic and plutonic rocks, and the ages reflect the intensive igneous activity in the Sukhothai Arc during Early to Middle Triassic. In addition, Early Paleozoic and Proterozoic zircons are abundant in the Wang Chin Formation, suggesting a substantial contribution of continental material from the Indochina Block (Fig. 12). These detrital zircon U–Pb ages suggest a low level of volcanic activity in the Sukhothai Arc just before the closure of the Paleo-Tethys Ocean in the Late Triassic. The probable tectonic and paleogeographic settings at the time would have facilitated the supply of sediment from the continent (Fig. 16-5). We conclude that magmatic activity in the Sukhothai Arc commenced by Late Carboniferous to Early Permian, presented an inactive period at Middle Permian, marked an intensive period during Late Permian to early Late Triassic. The episodic and transitional magmatic activity was explained by change in nature of the subducted
46
oceanic crust such as temperature associated with slab age, and the movement direction (e.g., Kimura et al., 2005; Sagong and Kwon, 2005; Imaoka et al., 2011). The Paleo-Tethyan oceanic crust was not simple nature, probably composed of several heterogeneous crusts presenting diversities of slab age and movement direction.
9. Conclusions
Based on U–Pb dating of detrital zircons, as well as sandstone petrography and geochemistry, we have elucidated the evolution of volcanic activity in the Sukhothai Arc of northern Thailand, and determined the provenance of the Permian–Triassic forearc sediments. The sediments are dominated by turbidites, and include the Permian Ngao Group (Kiu Lom, Pha Huat, and Huai Thak formations), the Early to earliest Late Triassic Lampang Group (Phra That and Hong Hoi formations), and the Late Triassic Song Group (Pha Daeng and Wang Chin formations).
(1) On the basis of sandstone petrography and geochemistry, the sandstones can be
47
subdivided into quartzose sandstones (Pha Huat, Huai Thak, and Wang Chin formations) and lithic sandstones (Kiu Lom, Phra That, Hong Hoi, and Pha Daeng formations). The quartzose sandstones are characterized by an abundant supply of quartz, materials from felsic volcanic and plutonic rocks, whereas the lithic sandstones were supplied with materials from basaltic to felsic volcanic rocks.
(2) In the sandstones, the youngest single-grain zircon U–Pb age (YSG) generally approximates the depositional age, although the YSG age for the Pha Huat Formation, which is dominated by limestone, is clearly older than the depositional age. In each formation, the youngest cluster U–Pb zircon age (YC1) indicates the peak of igneous activity in the source area.
(3) The geochemical signatures and U–Pb ages of the sandstones, together with direct geological evidence, have allowed us to reconstruct the evolution of the Sukhothai Arc, the nature of its volcanic activity, its periods of quiescence or intensive magmatism, the evolution of an associated accretionary complex, and the tectonic history and closure of
48
the Paleo-Tethys Ocean during the Permian–Triassic. The information on provenance recorded in the forearc sediments proved useful in understanding the evolution of this volcanic arc.
(4) Sediments of supposed Devonian–Carboniferous age within the Sukhothai Arc were revised as the Triassic volcaniclastics of the Lampang Group, and the Early Cretaceous quartoze sandstone of the Khorat Group, based on U–Pb ages of the sandstone and tuff.
Acknowledgments
Part of the fieldwork for this study was supported by a Grant-in-Aid (No. 25302010) from the Overseas Research Fund of the Japan Society for the Promotion of Science (JSPS), by the JSPS Institutional Program for Young Researcher Overseas Visits, and by Chulalongkorn University Fund for Visiting Professor in Department of Geology, Faculty of Science. This study is a contribution to IGCP516 and IGCP589. We would like to thank Dr P. Chaodumrong and Dr W. Srichan for valuable comments on the
49
geology and tectonics of northern Thailand; Prof S. Arai for suggestions and valuable comments on detrital chromian spinels; Dr Y. Adachi and Ms R. Nohara for support with ICP–MS and XRF analyses at Niigata University; Dr T. Danhara and Dr H. Iwano of Kyoto Fission Track Co. Ltd, Japan, for assistance during zircon separation for U–Pb dating; Ms M. Hirano for support with LA–ICP–MS for U–Pb dating at Niigata University; Dr W. Wiwegwin, Ms J. Vivatpinyo, Dr Y. Horiuchi, Dr S. Nakae, Dr J. Kuroda, Mr A. Miyahisgashi, and the International Coordinate Office at the Department of Mineral Resources, Thailand, for their support during field survey and sampling; and Mr A. Owada, Mr T. Sato, Mr K. Fukuda, and Ms E. Hirabayashi for their expertise in thin section preparation. Thanks are also due to the Prof Mei-Fu Zhou, the Prof C. Morley and anonymous reviewer for their constructive and valuable comments of the manuscript. Ternary plots were made using the freely distributed software CoDaPack 2.0, programed by Thió-Henestrosa and Martín-Fernández (2005), and Comas-Cufí and Thió-Henestrosa (2011), and which is available at http://ima.udg.edu/codapack/.
Appendix A. Supplementary material
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Supplementary data associated with this article can be found in the online version, at http://……/. These data include Google map of the most important areas described in this article.
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Figure and Table Captions
Fig. 1. (a) Tectonic map of Thailand and surrounding regions. (b) Distribution of Devonian to Triassic strata in northern Thailand between the Sukhothai Arc and the Inthanon Zone according to the 1:1,000,000 geological map of Thailand by the Department of Mineral Resources (1999), compiled by Barr and Charusiri (2011), Chonglakmani (2011), Ueno and Charoentitirat (2011), and Wongwanich and Boucot (2011).
Fig. 2. Simplified geological map of the Lampang–Ngao–Phrae area in northern Thailand, showing sample localities (see Fig. 1 for map location). The map is based on the quadrangle geological map of the Lampang area (Charoenprawat et al., 1994), the provincial geological maps of the Phrae and Lampang areas (Vimuktanandana, 2006a, b), and the present study.
Fig. 3. Qt–F–L and Qm–F–Lt ternary diagrams with the tectonic fields of Dickinson et
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al. (1983). Qt = total quartz (mono- and polycrystalline grains), Qm = monocrystalline quartz, F = feldspar (plagioclase and K-feldspar), L = lithic fragments, Lt = lithic fragments and polycrystalline quartz.
Fig. 4. Outcrop photographs and photomicrographs of clastic rocks of the Ngao Group (see Fig. 2 for sample localities). (a) Matrix-supported and poorly sorted conglomerate of the Kiu Kom Formation (N01_Kl). (b) Lithic sandstone with calcite in pore spaces, the Kiu Kom Formation (N01_Kl). (c) Succession of interbedded sandstones and mudstones, and bedded limestone, the Pha Huat Formation (N02). (d) Lithic sandstone with lithic fragments of Lv, Qp, and Lm, the Pha Huat Formation (N03_Ph). (e) Bedded succession of sandstone and mudstone with conglomerate, the Pha Huat Formation (N11). (f) Close-up view of conglomerate (N14). (g) Lithic sandstone with abundant quartz and lithic fragments of Lv and Qp, the Huai Thak Formation (N06_Ht). (h) Close-up view of Lv and Qp fragments (N06_Ht). All photomicrographs were taken under crossed polarized light. Cg-ls = limestone conglomerate, Cg-v = rhyolitic to andesitic volcaniclastics conglomerate, Cg = conglomerate bed, Q = quartz, Qp =
75
polycrystalline quartz, P = plagioclase, Lm = metamorphic lithic fragment, Lv = volcanic lithic fragment, Ca = calcite.
Fig. 5. Outcrop photographs and photomicrographs of clastic rocks of the Lampang Group (see Fig. 2 for sample localities). (a) Bedded silty sandstone of the Phara That Formation (L02). (b) Siltstone with a calcite layer of the Phara That Formation (L01). (c) Coherent turbidite sequence of the Hong Hoi Formation (L05_Hh). (d) Conglomerate of limestone (Cg-ls) and volcaniclastic (Cg-v) fragments, the Hong Hoi Formation (L03_Hh). (e) Fold and thrust developed in the Hong Hoi Formation (L10). (f) Lithic wacke with calcite in pore spaces, the Hong Hoi Formation (L05_Hh). (g) Lithic wacke dominated by volcanic fragments (L10). All photomicrographs were taken under crossed polarized light. Q = quartz, P = plagioclase, Lv = volcanic lithic fragment, Ca = calcite.
Fig. 6. Outcrop photographs and photomicrographs of clastic rocks of the Song Group (see Fig. 2 for sample localities). (a) Bedded gray silty sandstone and red siltstone of the
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Pha Daeng Formation (S02). (b) Lithic wacke sandstone of the Pha Daeng Formation (S01_Pd). (c) Bedded calcareous sandstone of the Wang Chin Formation (S07). (d) Bedded sandstone and mudstone of the Wang Chin Formation (S11). (c) Convolute lamination observed in sandstone (S11). (f) Slaty cleavage developed in mudstone (S09_Wc). (g) Quartzose sandstone dominated by quartz and volcanic fragments, the Wang Chin Formation (S07). (h) Lithic sandstone with calcite in pore spaces (S09_Wc). All photomicrographs were taken under crossed polarized light. Q = quartz, P = plagioclase, Lv = volcanic lithic fragment, Ca = calcite.
Fig. 7. Outcrop photographs and photomicrographs of sediments in northern Thailand that had previously been assigned Devonian–Carboniferous ages (see Fig. 1 for sample localities). See the text for information on the revised ages for these formations. (a) Foliated felsic tuff of the Khao Kieo Formation (now assigned a Late Triassic age). (b) Felsic tuff with quartz and plagioclase phenocrysts, the Khao Kieo Formation (PT01). (c) Volcanic conglomerate of the Khao Khi Ma Formation (now assigned an Early–Middle Triassic age). (d) Volcaniclastic sandstone with andesitic volcanic clasts,
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plagioclase, and abundantly heavy minerals, the Khao Khi Ma Formation (PT02). (e) Massive sandstone of the Lan Hoi Formation (now assigned an Early Cretaceous age). (f) Interbedded tuff and shale of the Lan Hoi Formation. (g) Quartzose sandstone of the Lan Hoi Formation composed mainly of quartz and calcite (PT03). (h) Quartzose sandstone of the Mae Tha Formation (PT04). (i) Quartzose sandstone from the Inthanon Zone (PT05). All photomicrographs were taken under crossed polarized light. Q = quartz, P = plagioclase, Lv = volcanic lithic fragment, M = micaceous fragment, Ca = calcite, Hm = heavy mineral, Qv = quartz vein.
Fig. 8. Variation diagrams of (SiO2 + CaO) versus TiO2, Cr, and V for clastic rocks of the Ngao, Lampang, and Song groups.
Fig. 9. PAAS-normalized trace element plot (a) and chondrite-normalized REE plot (b). Gray areas represent the ranges for potential source rocks of basalt–andesite, felsic volcanic rocks, and diorite, using data from Srichan et al. (2009).
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Fig. 10. Geochemistry of the detrital chromian spinels. (a) Cr# [= Cr/(Cr + Al) atomic ratios] versus TiO2 content. (b) YFe [= 100Fe3+/(Cr + Al + Fe3+) atomic ratios] versus TiO2 content. The magmatic fields bearing chromian spinels are after Arai (1992).
Fig. 11. Relative
206
Pb/238U age probability plots and age distribution histograms for
detrital zircons with ages younger than 400 Ma in the Permian to Triassic forearc sediments.
Fig. 12. All age distribution histograms for multiple-cluster-type detrital zircons from the various samples.
Fig. 13. Relative
206
Pb/238U age probability plots and age distribution histograms for
detrital zircons with ages younger than 1000 Ma in the sediments that had previously been assigned Devonian to Carboniferous ages.
Fig. 14. Discrimination diagrams showing source rock compositions and tectonic
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setting. (a) Sc versus V concentrations. (b) V–Cr–Th*10 ternary diagram. (c) Zr/Sc versus Th/Sc diagram. (d) La–Th–Sc diagram. BA = basalt and andesite, F = felsic volcanic rock, D = diorite of the Sukhothai Arc (average values are from Srichan et al., 2009), and G = Phanerozoic granite (after Condie, 1993). OIA = oceanic island arc, CIA = continental island arc, ACM = active continental margin, PCM = passive continental margin. See the text for details.
Fig. 15. Summary stratigraphic column showing depositional ages, detrital zircon U–Pb ages, and reconstruction of the volcanic activity within the Sukhothai Arc. Age data for I-type granitoids are from Charusiri et al. (1993), Seale et al. (2012), and Gardiner et al. (2016). U–Pb ages of detrital zircons from the accretionary complex are from Hara et al. (2013). U–Pb ages of zircons from the Pha Huat Formation were excluded from this figure because they are clearly older than the depositional age. Kl = Kiu Lom Formation, Ph = Pha Huat Formation, Ht = Huai Thak Formation, Pt = Phra That Formation, Pk = Pha Kan Formation, Hh = Hong Hoi Formation, Dl = Doi Long Formation. Pd = Pha Daeng Formation, Kp = Kang Pla Formation, Wc = Wang Chin Formation. YSG =
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youngest single-grain zircon U–Pb age, YC1 = weighted mean U–Pb age of youngest cluster. See text for details.
Fig. 16. Schematic model of the evolution of the Sukhothai Arc reconstructed from sandstone provenance and U–Pb ages of detrital zircons from Permian–Triassic forearc sediments. Right-hand panels show paleogeographic reconstructions of the Sukhothai Arc and the western margin of the Indochina Block. Left-hand panels show cross-sections (along the black lines in the right-hand panels) through the Paleo-Tethys, the Sukhothai Arc, and the Indochina Block. AC = accretionary complex. FA = forearc. See text for details.
Table 1 Major element, trace element, and REE compositions of the sandstones.
Table 2 Results of FE–EPMA analyses of detrital chromian spinels.
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Table 3 Summary of U–Pb ages for detrital zircons from Permian–Triassic sediments within the Sukhothai Arc.
Table 4 Summary of the U–Pb ages of detrital zircons from sediments within the Sukhothai Arc that had previously been assigned Devonian–Carboniferous ages.
Interactive Map for this article Localities of U–Pb dating samples
Appendix A. Supplementary material
Table S1 Results of LA–ICP–MS U–Pb dating of detrital zircons from sandstones of the
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Permian–Triassic forearc sediments.
Table S2 Results of LA–ICP–MS U–Pb dating of detrital zircons from tuffs and sandstones that had previously been assigned Devonian–Carboniferous ages.
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Figure1
Fig. 1. Hara et al.
Fig. 1. Hara et al.
Figure2
Fig. 2. Hara et al.
Fig. 2. Hara et al.
Figure3
Fig. 3. Hara et al.
Fig. 3. Hara et al.
Fig. 4. Hara et al. Figure4
Fig. 4. Hara et al.
Fig. 5. Hara et al. Figure5
Fig. 5. Hara et al.
Fig. 6. Hara et al. Figure6
Fig. 6. Hara et al.
Fig. 7. Hara et al. Figure7
Fig. 7. Hara et al.
Figure8
Fig. 8. Hara et al.
Fig. 8. Hara et al.
Fig. 9. Hara et al. Figure9
Fig. 9. Hara et al.
Figure10
Fig. 10. Hara et al.
Fig. 10. Hara et al.
Fig. 11. Hara et al. Figure11
Fig. 11. Hara et al.
Figure12
Fig. 12. Hara et al.
Fig. 12. Hara et al.
Figure13 Fig. 13. Hara et al.
Fig. 13. Hara et al.
Figure14
Fig. 14. Hara et al.
Fig. 14. Hara et al.
Figure 15
Figure 16
Table1
Table 1 Major element, trace element, and REE compositions of the sandstones. LOI: weight loss on ignition. Fe2O3* is total iron as Fe2O3. Ngao Group Sample N01_Kl N02 N03_Ph N04 N05 N06_Ht N07 N08 N09 N10 N11 N12 N13 N14 Formation Kui Lom Fm. Pha Huat Fm. Pha Huat Fm. Pha Huat Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm Lithology Sandstone silt Sandstone silt Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone silt Sandstone Sandstone Major element (wt.%) SiO2 65.45 75.52 65.09 54.04 76.47 83.73 84.35 52.54 68.17 68.93 89.97 69.35 82.56 89.43 TiO2 0.24 0.59 0.56 0.58 0.36 0.33 0.31 0.20 0.55 0.18 0.35 0.61 0.33 0.25 Al2O3 11.10 10.70 9.35 9.47 9.75 10.10 9.93 6.35 14.58 6.13 6.54 13.45 8.15 6.75 FeO* 2.01 5.41 4.52 3.88 3.62 0.34 1.18 1.89 3.17 1.69 0.63 5.02 4.03 0.74 MnO 0.04 0.01 0.23 0.25 0.08 0.00 0.00 0.06 0.06 0.06 0.00 0.01 0.02 0.00 MgO 1.01 1.43 2.14 2.00 1.56 0.14 0.12 1.06 1.21 0.73 0.16 2.34 0.81 0.05 CaO 7.39 0.12 6.09 13.92 1.32 0.04 0.02 19.38 2.70 10.30 0.03 0.81 0.03 0.03 Na2O 4.78 0.48 0.05 1.47 2.10 0.04 0.05 1.60 5.78 1.17 0.07 0.64 0.15 0.05 K2O 0.48 1.63 1.91 1.32 1.11 0.83 0.82 0.62 0.74 0.61 0.98 2.66 0.29 0.26 P2O5 0.05 0.07 0.12 0.13 0.05 0.01 0.02 0.03 0.07 0.03 0.04 0.11 0.02 0.02 L.O.I 6.61 3.69 9.46 12.88 3.04 3.42 3.56 16.39 1.81 9.87 2.13 4.16 4.37 2.65 Total 99.39 100.23 100.03 100.37 99.84 99.02 100.50 100.34 99.20 99.89 100.97 99.72 101.22 100.31 Trace element determied by XRF (ppm) Ba 111.6 287.8 331.7 203.9 208.7 261.7 169.4 182.3 100.2 89.4 308.2 422.3 66.1 55.3 Cr 11.0 45.2 53.5 53.5 9.7 8.2 8.3 8.3 6.3 5.1 26.1 49.5 7.4 11.9 Nb 3.2 12.1 9.4 8.9 6.3 5.2 5.7 4.1 4.9 5.2 6.9 11.6 5.3 4.1 Ni -3.8 11.4 23.5 22.1 7.8 0.0 2.3 0.0 0.0 0.4 0.8 21.3 3.3 0.0 Rb 18.5 81.0 70.7 54.5 43.2 30.6 29.8 24.1 9.7 23.2 47.9 115.5 14.2 19.6 Sr 584.5 69.9 229.1 813.8 184.7 40.6 44.3 258.8 112.6 444.0 33.8 69.1 18.1 92.6 V 31.4 75.2 86.1 90.6 29.6 19.6 20.3 22.0 46.8 11.2 35.8 89.8 27.7 23.5 Y 20.3 30.2 30.0 34.3 29.8 39.3 26.5 26.4 20.5 34.2 20.0 26.6 27.3 12.9 Zr 81.8 193.1 198.8 176.1 126.9 138.0 122.2 96.3 72.1 102.2 138.7 188.6 142.4 79.4 Th 5.7 8.8 6.8 7.3 8.5 9.1 8.9 4.8 4.4 4.5 8.4 10.3 7.3 7.3 Pb 10.8 20.2 21.8 8.3 17.9 8.2 8.4 7.5 8.4 12.8 16.8 21.2 12.5 4.2 Trace element and REE compositions determied by ICPMS (ppm) Li 14.9 41.9 20.0 24.9 20.8 15.8 18.7 15.9 10.9 14.4 16.6 43.0 54.2 30.7 Sc 12.1 12.1 12.8 14.5 9.4 7.3 7.0 7.9 16.2 6.6 5.0 14.1 7.7 5.6 Co 10.6 13.8 24.7 16.5 13.4 12.4 15.4 11.4 20.6 14.9 29.7 12.4 26.4 21.4 Zn 64.7 64.8 70.6 63.7 32.7 102.3 24.9 214.1 -34.5 1.3 8.0 80.0 81.7 10.9 Ga 9.3 14.2 11.8 12.5 10.1 10.5 9.1 7.5 19.7 6.7 7.8 18.3 8.3 6.6 Cs 2.1 6.2 4.9 2.2 1.7 0.8 0.9 0.6 0.5 1.9 3.0 5.7 0.7 2.1 La 7.9 20.3 25.8 37.8 15.7 18.0 8.3 10.5 9.4 10.4 28.6 32.4 10.8 10.1 Ce 15.7 37.4 55.5 67.1 32.0 24.7 15.8 21.0 19.6 23.1 38.0 64.5 20.5 17.5 Pr 2.0 4.7 7.0 8.9 4.4 4.5 1.9 2.7 2.5 3.0 6.0 7.8 2.6 2.0 Nd 8.5 16.8 26.6 33.3 17.9 18.4 8.0 11.5 11.3 13.5 22.9 28.2 10.7 7.9 Sm 2.1 3.6 6.1 7.3 4.6 4.3 1.9 3.1 2.9 3.8 5.1 5.5 2.5 1.4 Eu 0.6 0.8 1.1 1.6 1.1 1.0 0.5 0.7 1.5 0.9 1.0 0.9 0.7 0.3 Gd 2.6 4.2 6.0 6.9 4.5 4.3 2.4 3.5 3.3 4.8 3.9 4.9 3.4 1.2 Tb 0.4 0.7 0.9 1.0 0.8 0.7 0.5 0.6 0.6 0.9 0.6 0.8 0.6 0.2 Dy 3.1 4.6 5.2 6.3 5.1 4.8 3.3 4.0 3.5 5.6 3.3 4.6 4.1 1.4 Ho 0.7 1.0 1.1 1.3 1.1 1.1 0.8 0.9 0.8 1.2 0.7 1.0 1.0 0.3 Er 2.3 3.1 3.1 3.7 3.2 3.5 2.5 2.6 2.3 3.6 1.9 3.0 3.1 0.9 Tm 0.4 0.4 0.5 0.5 0.5 0.6 0.4 0.4 0.3 0.5 0.3 0.4 0.4 0.2 Yb 2.4 3.1 3.0 3.3 3.2 3.5 2.6 2.5 2.3 3.3 2.0 3.2 3.6 1.1 Lu 0.4 0.4 0.4 0.5 0.5 0.5 0.4 0.4 0.3 0.5 0.3 0.5 0.4 0.2 Hf 2.5 5.0 5.3 5.0 3.4 3.3 3.1 2.6 2.1 2.8 3.4 5.0 3.8 1.7 Ta 0.2 0.8 0.7 0.7 0.4 0.3 0.3 0.3 0.2 0.2 0.4 0.9 0.3 0.2 U 1.6 2.3 2.3 1.9 1.7 0.8 0.8 1.5 1.6 0.9 1.1 3.0 1.4 0.6
Lampang Group Sample L01 L02 L03_Hh L04 L05_Hh L05 L06 L07 L08 L09 L10 Formation Phra That Fm. Phra That Fm. Hong Hoi Fm Hong Hoi Fm Hong Hoi Fm Hong Hoi Fm Hong Hoi Fm Hong Hoi Fm Hong Hoi Fm Hong Hoi Fm Hong Hoi Fm Lithology Sandstone silt Sandstone Sandstone Sandstone silt silt Sandstone silt Sandstone Sandstone Major element (wt.%) SiO2 59.66 65.16 43.02 57.00 61.90 60.74 62.71 60.07 60.62 64.70 54.18 TiO2 0.42 0.65 0.75 0.60 0.59 0.79 0.33 0.68 0.68 0.59 0.68 Al2O3 13.56 18.66 11.67 10.85 12.35 14.27 11.99 13.92 13.12 15.50 16.64 FeO* 4.68 3.34 6.25 5.06 4.07 8.04 3.70 6.76 5.64 5.12 8.28 MnO 0.05 0.00 0.26 0.28 0.09 0.14 0.09 0.21 0.17 0.06 0.15 MgO 2.12 0.45 2.75 2.42 1.28 2.67 0.98 2.29 2.24 1.66 2.82 CaO 4.46 0.12 15.90 8.15 8.15 2.71 6.42 3.50 5.43 1.64 4.23 Na2O 1.34 0.42 3.80 3.04 2.86 1.63 0.71 2.04 2.32 4.13 4.30 K2O 2.18 2.28 0.65 0.67 1.01 1.48 1.91 1.35 1.36 2.45 0.64 P2O5 0.06 0.02 0.14 0.08 0.07 0.14 0.06 0.10 0.14 0.07 0.11 L.O.I 9.89 8.96 14.58 11.15 6.70 5.92 10.11 7.28 7.62 2.84 6.25 Total 98.94 100.43 100.45 99.87 99.53 99.42 99.43 98.96 99.98 99.34 99.22 Trace element determied by XRF (ppm) Ba 440.0 605.4 397.7 194.5 308.3 190.8 329.7 213.5 225.0 609.8 144.1 Cr 26.0 38.9 61.4 44.2 23.0 58.5 27.8 51.0 50.6 21.4 19.3 Nb 8.2 8.1 7.1 5.6 7.3 12.0 10.1 10.9 7.9 6.7 6.7 Ni 15.3 8.5 11.7 9.8 4.3 28.7 23.9 21.0 14.1 3.6 6.5 Rb 86.3 93.0 24.9 30.7 39.3 75.4 96.1 68.4 66.0 83.7 21.3 Sr 288.1 390.8 356.3 271.0 356.3 94.1 159.2 100.1 138.5 184.0 291.7 V 66.1 110.6 133.5 120.7 85.0 115.1 61.7 109.1 105.5 85.5 126.2 Y 36.4 47.8 35.6 26.3 24.2 31.2 28.8 28.5 26.9 22.7 23.5 Zr 168.6 175.3 159.8 126.0 131.9 205.2 145.6 187.7 173.5 144.5 158.0 Th 7.5 9.8 4.6 6.5 7.7 7.5 9.4 7.8 6.9 10.5 6.4 Pb 26.7 21.0 5.1 9.5 20.6 23.8 15.3 13.4 25.0 22.9 15.6 Trace element and REE compositions determied by ICPMS (ppm) Li 28.8 20.0 23.9 34.6 33.4 57.7 31.2 56.7 32.1 38.7 56.5 Sc 15.8 24.0 18.3 14.1 13.2 16.1 12.6 17.2 15.6 13.0 17.3 Co 15.6 19.6 18.0 18.3 26.2 39.2 8.8 21.3 26.4 16.7 20.7 Zn 107.6 42.5 98.1 129.6 82.9 127.5 105.6 95.0 96.4 57.4 82.0 Ga 18.1 23.5 17.2 13.1 13.3 16.9 19.7 18.0 14.9 16.5 17.4 Cs 3.7 4.4 1.4 2.5 3.5 7.5 11.4 9.3 6.5 5.3 2.1 La 21.7 29.7 18.8 18.8 24.7 25.5 44.6 25.5 30.5 27.2 20.1 Ce 42.4 32.9 36.9 35.2 46.3 50.9 81.6 51.4 55.6 53.4 38.8 Pr 5.5 5.6 4.8 4.5 5.1 6.1 10.4 6.1 7.1 6.5 4.8 Nd 22.3 22.0 19.5 17.9 19.8 23.3 38.3 22.6 26.5 23.3 18.5 Sm 4.6 4.8 4.7 3.9 4.0 5.6 6.4 4.8 6.0 4.8 3.7 Eu 0.9 1.0 1.3 1.1 1.0 1.3 0.9 1.2 1.4 1.2 0.8 Gd 4.7 5.5 5.1 4.2 3.8 5.8 5.4 4.9 5.7 4.7 3.7 Tb 0.8 1.0 0.8 0.7 0.6 0.9 0.8 0.8 0.9 0.7 0.6 Dy 5.2 6.3 5.1 4.2 3.9 5.5 4.7 4.7 4.8 3.9 3.3 Ho 1.1 1.4 1.1 0.9 0.8 1.2 1.0 1.0 1.0 0.8 0.7 Er 3.4 4.7 3.1 2.4 2.6 3.3 2.7 2.7 3.0 2.5 1.9 Tm 0.6 0.6 0.5 0.4 0.4 0.4 0.4 0.4 0.4 0.3 0.3 Yb 3.5 4.2 2.8 2.2 2.5 3.2 2.6 2.6 2.8 2.7 1.8 Lu 0.5 0.7 0.4 0.3 0.4 0.4 0.4 0.4 0.4 0.4 0.3 Hf 4.5 4.5 3.7 3.0 3.3 5.2 4.1 5.0 4.7 3.9 3.3 Ta 0.6 0.6 0.4 0.4 0.4 0.9 0.8 0.8 0.6 0.7 0.4 U 2.1 2.1 1.3 1.9 2.2 2.7 2.1 2.4 2.5 3.5 1.7
Song Group Sample S01_Pd S02 S03 S04 S05 S06 S07 S08_Wc S09 S10 S11 Formation Pha Daeng Fm.Pha Daeng Fm.Pha Daeng Fm.Pha Daeng Fm.Pha Daeng Fm.Wang Chin FmWang Chin FmWang Chin FmWang Chin FmWang Chin FmWang Chin Fm Lithology Sandstone Sandstone silt Sandstone silt Sandstone Sandstone Sandstone Sandstone silt Sandstone Major element (wt.%) SiO2 59.14 57.63 55.06 69.28 61.30 88.12 85.35 68.87 58.19 71.19 60.31 TiO2 0.91 0.75 0.52 0.91 0.71 0.27 0.52 0.40 0.32 0.45 0.30 Al2O3 14.81 13.82 11.99 13.70 15.13 6.91 7.82 6.11 8.67 14.56 5.42 FeO* 4.60 5.90 3.49 3.81 5.36 0.43 0.93 2.80 2.49 2.67 2.20 MnO 0.17 0.17 0.21 0.09 0.05 0.00 0.00 0.11 0.10 0.02 0.10 MgO 4.63 3.44 2.00 0.82 2.55 0.40 0.38 1.06 1.14 1.13 1.06 CaO 3.77 4.96 11.11 1.83 2.95 0.10 0.05 9.08 13.43 0.95 15.25 Na2O 3.27 3.39 2.99 6.25 1.72 0.07 0.11 0.75 2.69 3.02 1.48 K2O 1.56 1.31 1.51 0.52 2.56 1.87 2.15 1.18 0.68 2.49 0.48 P2O5 0.23 0.20 0.14 0.14 0.17 0.05 0.02 0.08 0.08 0.08 0.06 L.O.I 5.89 7.51 11.07 2.14 5.88 1.93 1.93 8.87 11.83 3.17 13.25 Total 99.51 99.76 100.49 99.91 98.99 100.22 99.37 99.62 99.91 100.03 100.14 Trace element determied by XRF (ppm) Ba 313.0 238.3 341.8 200.5 321.5 99.1 196.6 262.5 85.3 257.2 98.9 Cr 94.0 64.2 71.8 28.5 74.6 20.9 46.1 38.9 28.4 31.5 29.1 Nb 15.3 14.8 10.5 13.2 9.2 9.2 11.2 9.9 4.7 10.2 5.5 Ni 27.9 33.0 24.2 2.5 35.1 0.0 -1.3 23.4 11.9 9.6 8.5 Rb 66.8 63.9 86.3 28.7 114.5 72.2 103.4 64.5 34.0 109.9 24.9 Sr 358.5 147.0 268.6 364.1 109.9 153.6 13.8 227.5 593.3 167.9 646.0 V 115.7 107.2 83.9 93.6 127.2 24.7 44.8 39.1 51.2 56.4 41.6 Y 29.9 33.6 26.1 37.7 30.2 14.4 19.0 27.6 15.1 22.8 21.1 Zr 239.1 201.4 172.1 183.1 178.8 114.8 290.5 264.1 97.6 168.7 94.5 Th 11.2 9.6 7.9 13.0 10.1 14.5 14.6 9.0 5.0 13.1 4.3 Pb 10.1 20.6 11.4 19.8 9.5 13.9 9.3 72.9 10.4 16.3 11.4 Trace element and REE compositions determied by ICPMS (ppm) Li 95.7 77.0 67.7 36.8 49.7 42.1 13.9 36.1 23.2 20.8 17.5 Sc 15.4 15.3 12.4 10.4 17.2 5.2 5.6 6.1 8.7 10.9 8.5 Co 21.8 28.6 24.9 22.7 18.0 27.5 28.3 21.4 16.0 14.2 19.8 Zn 511.8 54.5 85.7 79.0 81.2 13.4 9.5 66.5 40.3 49.0 41.1 Nb 16.9 16.1 12.0 15.2 11.4 8.4 13.2 12.5 4.1 11.3 5.9 Cs 14.8 11.1 30.9 6.4 8.6 7.1 7.5 9.2 2.1 8.7 1.7 La 34.4 45.5 45.2 72.5 30.6 19.5 25.8 27.5 16.0 35.9 17.5 Ce 72.9 93.0 91.7 93.4 61.2 31.4 48.6 59.4 30.7 67.1 34.8 Pr 8.9 10.9 11.1 15.0 7.2 3.8 5.8 7.8 3.9 8.3 4.8 Nd 34.6 42.3 40.6 55.6 27.4 13.5 21.1 30.1 14.8 29.5 19.0 Sm 6.7 8.2 7.9 10.7 5.4 2.1 3.9 6.8 3.3 6.1 4.8 Eu 1.6 1.7 1.7 2.6 1.1 0.4 0.6 1.3 1.0 1.1 1.2 Gd 5.9 7.1 6.8 9.2 5.0 1.6 2.9 6.1 3.1 4.8 4.4 Tb 0.9 1.0 0.9 1.3 0.8 0.3 0.5 0.9 0.5 0.7 0.6 Dy 5.0 5.9 5.0 6.8 4.7 1.8 2.9 4.9 2.7 3.8 3.7 Ho 1.0 1.1 1.0 1.3 1.0 0.4 0.6 1.0 0.6 0.8 0.7 Er 3.0 3.2 2.9 3.8 2.7 1.1 2.0 2.9 1.7 2.4 2.1 Tm 0.5 0.5 0.4 0.5 0.4 0.2 0.3 0.4 0.2 0.3 0.3 Yb 2.9 3.0 2.5 3.4 2.7 1.2 2.0 2.5 1.7 2.6 1.8 Lu 0.4 0.4 0.4 0.5 0.4 0.2 0.3 0.4 0.2 0.4 0.3 Hf 5.9 5.2 4.8 4.7 4.7 2.5 7.6 6.4 2.3 5.2 2.4 Ta 1.1 1.1 0.9 0.9 0.8 0.6 1.0 1.0 0.3 0.9 0.4 U 4.6 2.9 3.1 4.1 2.9 2.0 2.4 3.4 1.2 3.4 1.3
Table1
Table 1 Major element, trace element, and REE compositions of the sandstones. LOI: weight loss on ignition. Fe 2O3* is total iron as Fe2O3. Ngao Group Sample N01_Kl N02 N03_Ph N04 N05 N06_Ht N07 N08 N09 N10 N11 N12 N13 N14 Formation Kui Lom Fm. Pha Huat Fm. Pha Huat Fm. Pha Huat Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm. Huai Thak Fm Lithology Sandstone silt Sandstone silt Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone Sandstone silt Sandstone Sandstone Major element (wt.%) SiO2 65.45 75.52 65.09 54.04 76.47 83.73 84.35 52.54 68.17 68.93 89.97 69.35 82.56 89.43 TiO2 0.24 0.59 0.56 0.58 0.36 0.33 0.31 0.20 0.55 0.18 0.35 0.61 0.33 0.25 Al2O3 11.10 10.70 9.35 9.47 9.75 10.10 9.93 6.35 14.58 6.13 6.54 13.45 8.15 6.75 FeO* 2.01 5.41 4.52 3.88 3.62 0.34 1.18 1.89 3.17 1.69 0.63 5.02 4.03 0.74 MnO 0.04 0.01 0.23 0.25 0.08 0.00 0.00 0.06 0.06 0.06 0.00 0.01 0.02 0.00 MgO 1.01 1.43 2.14 2.00 1.56 0.14 0.12 1.06 1.21 0.73 0.16 2.34 0.81 0.05 CaO 7.39 0.12 6.09 13.92 1.32 0.04 0.02 19.38 2.70 10.30 0.03 0.81 0.03 0.03 Na2O 4.78 0.48 0.05 1.47 2.10 0.04 0.05 1.60 5.78 1.17 0.07 0.64 0.15 0.05 K2O 0.48 1.63 1.91 1.32 1.11 0.83 0.82 0.62 0.74 0.61 0.98 2.66 0.29 0.26 P2O5 0.05 0.07 0.12 0.13 0.05 0.01 0.02 0.03 0.07 0.03 0.04 0.11 0.02 0.02 L.O.I 6.61 3.69 9.46 12.88 3.04 3.42 3.56 16.39 1.81 9.87 2.13 4.16 4.37 2.65 Total 99.39 100.23 100.03 100.37 99.84 99.02 100.50 100.34 99.20 99.89 100.97 99.72 101.22 100.31 Trace element determied by XRF (ppm) Ba 111.6 287.8 Cr 11.0 45.2 Nb 3.2 12.1 Ni -3.8 11.4 Rb 18.5 81.0 Sr 584.5 69.9 V 31.4 75.2 Y 20.3 30.2 Zr 81.8 193.1 Th 5.7 8.8 Pb 10.8 20.2
331.7 53.5 9.4 23.5 70.7 229.1 86.1 30.0 198.8 6.8 21.8
203.9 53.5 8.9 22.1 54.5 813.8 90.6 34.3 176.1 7.3 8.3
Trace element and REE compositions determied by ICPMS (ppm) Li 14.9 41.9 20.0 Sc 12.1 12.1 12.8 Co 10.6 13.8 24.7 Zn 64.7 64.8 70.6 Ga 9.3 14.2 11.8 Cs 2.1 6.2 4.9 La 7.9 20.3 25.8 Ce 15.7 37.4 55.5 Pr 2.0 4.7 7.0 Nd 8.5 16.8 26.6 Sm 2.1 3.6 6.1 Eu 0.6 0.8 1.1 Gd 2.6 4.2 6.0 Tb 0.4 0.7 0.9 Dy 3.1 4.6 5.2 Ho 0.7 1.0 1.1 Er 2.3 3.1 3.1
24.9 14.5 16.5 63.7 12.5 2.2 37.8 67.1 8.9 33.3 7.3 1.6 6.9 1.0 6.3 1.3 3.7
208.7 9.7 6.3 7.8 43.2 184.7 29.6 29.8 126.9 8.5 17.9
261.7 8.2 5.2 0.0 30.6 40.6 19.6 39.3 138.0 9.1 8.2
169.4 8.3 5.7 2.3 29.8 44.3 20.3 26.5 122.2 8.9 8.4
182.3 8.3 4.1 0.0 24.1 258.8 22.0 26.4 96.3 4.8 7.5
100.2 6.3 4.9 0.0 9.7 112.6 46.8 20.5 72.1 4.4 8.4
89.4 5.1 5.2 0.4 23.2 444.0 11.2 34.2 102.2 4.5 12.8
308.2 26.1 6.9 0.8 47.9 33.8 35.8 20.0 138.7 8.4 16.8
422.3 49.5 11.6 21.3 115.5 69.1 89.8 26.6 188.6 10.3 21.2
66.1 7.4 5.3 3.3 14.2 18.1 27.7 27.3 142.4 7.3 12.5
55.3 11.9 4.1 0.0 19.6 92.6 23.5 12.9 79.4 7.3 4.2
20.8 9.4 13.4 32.7 10.1 1.7 15.7 32.0 4.4 17.9 4.6 1.1 4.5 0.8 5.1 1.1 3.2
15.8 7.3 12.4 102.3 10.5 0.8 18.0 24.7 4.5 18.4 4.3 1.0 4.3 0.7 4.8 1.1 3.5
18.7 7.0 15.4 24.9 9.1 0.9 8.3 15.8 1.9 8.0 1.9 0.5 2.4 0.5 3.3 0.8 2.5
15.9 7.9 11.4 214.1 7.5 0.6 10.5 21.0 2.7 11.5 3.1 0.7 3.5 0.6 4.0 0.9 2.6
10.9 16.2 20.6 -34.5 19.7 0.5 9.4 19.6 2.5 11.3 2.9 1.5 3.3 0.6 3.5 0.8 2.3
14.4 6.6 14.9 1.3 6.7 1.9 10.4 23.1 3.0 13.5 3.8 0.9 4.8 0.9 5.6 1.2 3.6
16.6 5.0 29.7 8.0 7.8 3.0 28.6 38.0 6.0 22.9 5.1 1.0 3.9 0.6 3.3 0.7 1.9
43.0 14.1 12.4 80.0 18.3 5.7 32.4 64.5 7.8 28.2 5.5 0.9 4.9 0.8 4.6 1.0 3.0
54.2 7.7 26.4 81.7 8.3 0.7 10.8 20.5 2.6 10.7 2.5 0.7 3.4 0.6 4.1 1.0 3.1
30.7 5.6 21.4 10.9 6.6 2.1 10.1 17.5 2.0 7.9 1.4 0.3 1.2 0.2 1.4 0.3 0.9
Table2
Table 2 Results of FE–EPMA analyses of detrital chromian spinels. *: high-Ti group of chromian spinel. Formation Pha Huat Fm. Sample N03_Ph grain No 1 2 3 wt.% SiO2 0.06 0.04 0.11 TiO2 0.05 0.24 0.03 Al2O3 23.96 23.98 29.52 Cr2O3 39.98 41.22 36.49 FeO 20.46 20.92 16.05 MnO 0.32 0.34 0.30 MgO 11.75 8.81 13.13 CaO 0.01 0.09 0.03 Na2O 0.01 0.00 0.00 K2O 0.02 0.01 0.01 NiO 0.10 0.00 0.13 Total 96.71 95.65 95.80 Atomic ratios Ti 0.001 0.006 0.001 Al 0.904 0.921 1.078 Cr 1.012 1.062 0.894 Fe2+ 0.450 0.565 0.394 Fe3+ 0.104 0.002 0.028 Mg 0.560 0.428 0.606 Mn 0.009 0.009 0.008 Cr# 0.528 0.536 0.453 Mg# 0.555 0.431 0.606 YFe
0.052 0.001 0.014
Hong Hoi Fm L03_Hh 3* 4
1
2*
0.10 0.37 17.24 47.30 21.58 0.40 10.76 0.11 0.00 0.00 0.09 97.96
0.14 0.67 19.74 37.13 31.12 0.47 7.00 0.15 0.05 0.01 0.07 96.56
0.11 1.13 19.32 39.13 23.85 0.35 10.72 0.72 0.03 0.00 0.08 95.43
0.009 0.667 1.226 0.475 0.110 0.526 0.011 0.648 0.525
0.017 0.793 1.001 0.649 0.217 0.356 0.014 0.558 0.354
0.029 0.762 1.035 0.449 0.171 0.534 0.010 0.576 0.543
5
6
7*
Hong Hoi Fm L04 1 2
0.14 0.20 15.16 42.95 26.65 0.58 9.94 0.24 0.02 0.00 0.06 95.95
0.07 0.10 16.49 49.67 21.83 0.47 8.13 0.48 0.04 0.00 0.09 97.36
0.16 0.45 16.60 45.17 21.62 0.42 11.55 0.14 0.00 0.00 0.18 96.30
0.17 0.56 15.99 40.93 29.95 0.42 5.66 0.33 0.00 0.00 0.06 94.08
0.03 0.04 0.23 0.32 11.86 9.64 53.37 53.50 21.31 28.64 0.43 0.52 8.66 5.07 0.00 0.00 0.00 0.02 0.03 0.00 0.10 0.06 96.02 97.82
0.09 0.60 22.12 36.09 26.63 0.38 10.61 0.00 0.00 0.03 0.02 96.57
0.20 0.14 0.12 0.12 0.05 0.35 0.38 0.37 0.42 0.51 19.15 7.07 7.52 11.97 18.27 47.67 55.71 57.48 50.12 43.13 11.85 23.66 22.19 21.64 23.44 0.67 0.80 0.57 0.35 0.37 16.10 7.81 9.02 10.61 11.83 0.06 0.08 0.00 0.02 0.03 0.04 0.03 0.01 0.00 0.03 0.03 0.00 0.00 0.00 0.00 0.05 0.13 0.08 0.12 0.08 96.16 95.82 97.36 95.37 97.74
0.37 0.25 16.64 34.72 21.49 1.08 20.98 0.00 0.12 0.03 0.15 95.82
0.12 0.96 20.65 35.47 23.29 0.31 14.76 0.00 0.01 0.01 0.05 95.63
0.12 0.70 17.43 43.64 23.34 0.30 11.72 0.05 0.00 0.00 0.20 97.50
0.00 0.15 42.33 23.54 14.01 0.20 16.47 0.07 0.01 0.02 0.26 97.06
0.18 0.15 44.44 20.72 16.04 0.24 13.44 0.00 0.13 0.00 0.28 95.62
0.005 0.615 1.169 0.512 0.261 0.510 0.017 0.655 0.499
0.003 0.649 1.312 0.590 0.028 0.405 0.013 0.669 0.407
0.011 0.653 1.192 0.429 0.163 0.575 0.012 0.646 0.572
0.015 0.672 1.153 0.700 0.175 0.300 0.013 0.632 0.300
0.006 0.483 1.457 0.555 0.061 0.446 0.013 0.751 0.445
0.015 0.859 0.940 0.491 0.224 0.521 0.011 0.523 0.515
0.008 0.717 1.197 0.235 0.081 0.762 0.018 0.625 0.764
0.006 0.642 0.899 0.033 0.574 1.024 0.030 0.583 0.969
0.024 0.798 0.919 0.292 0.308 0.721 0.009 0.535 0.712
0.017 0.677 1.138 0.427 0.190 0.576 0.008 0.627 0.574
0.003 1.428 0.533 0.296 0.037 0.703 0.005 0.272 0.703
0.003 1.521 0.476 0.407 -0.02 0.582 0.006 0.238 0.588
0.111 0.041 0.064 0.055 0.077 0.097 0.271 0.152 0.095
0.019
-0.01
0.055 0.108 0.087 0.128 0.014 0.081 0.088
0.009 0.402 1.496 0.737 0.109 0.267 0.016 0.788 0.266
0.031 0.054
1*
2
3
0.010 0.298 1.577 0.584 0.127 0.417 0.024 0.841 0.416
Pha Daeng Fm. S01_Pd 4 5 6*
7
8*
9*
0.010 0.309 1.583 0.533 0.111 0.469 0.017 0.837 0.468
0.011 0.487 1.369 0.459 0.155 0.546 0.010 0.738 0.544
0.013 0.706 1.118 0.432 0.196 0.578 0.010 0.613 0.573
Wang Chin Fm S08 1 2
Table3
Table 3 Summary of U–Pb ages for detrital zircons from Permian–Triassic sediments within the Sukhothai Arc. Formation Sample Depositional age Detrital zircon U-Pb data Number of concordant data (N) Number of concordant data
