Recent advances in understanding the geological ...

Recent advances in understanding the geological development of the New England Province of the New England Orogen P. G. Floodl & J.e. Aitchison 2 1Department of Geology, ·University of New England 2Department of Geology, University of Sydney

INTRODUCflON Traditionally the New England Orogen is subdi vided into three regional provinces: Yarrol, Gympie and New England. The New England Province is composed of numerous fault-bounded tectonic fragments referred to as tectonostratigraphic terranes (Cawood and Leitch, 1985; Leitch and Scheibner, 1988; Flood and Aitchison, 1988; Aitchison and Flood, 1990a; Coney et al., 1990). Each terrane is characterised by a geological history which is distinct from that of neighbouring terranes. Stratigraphic terranes and disrupted terranes are the two most commOn types found within the New England Orogen. Post-accretionary tectonic processes have caused terrane dispersion further complicating the geometry of terrane distribution (Figure 1). Whilst the plate tectonic paradigm pervaded most geological research of the mid to late 1970's, its derivative, the terrane concept (Coney et al., 1980; Howell, 1989), has managed only limited application in deciphering the geological development of the New England Orogen. The terrane concept has highlighted the inadequate nature of the fixist stance of many plate tectonic models. The terrane concept cautions that the diverse assemblage of lithologic units within a fold belt - or orogenic system - cannot be assumed to have directly linked genetic relationships. The intrinsic mobility of each component (or terrane) reqUires that the geologic history of each unit must be evaluated On the information gleaned from each outcrop and not from regional generalizations. Most terranes should be considered suspect in regard to paleogeographic linkage, though this does not mean that all terranes are exotic, fartravelled crustal fragments. The purpose of this brief note is to provide a guide to recent literature pertaining to the regional geology and tectonic setting of the New England

NED '93 Conference Proceedings

60

NED '93 Conference Proceedings

Province of the New England Orogen. Selected highlights in several areas of research are detailed in the following account.

BIOSTRATIGRAPHY The application of Paleozoic radiolarian biostratigraphy to determining the age of the radiolarian-bearing siliceous sediments of the New England Orogen has progressed at a very rapid rate since 1988. New age constraints on the formation and accretion of various terranes have had important implications for tectonic reconstructions ( Aitchison, 1988; 1990; Aitchison and Flood, 1990, 1991; Aitchison, Flood and Spiller, 1992). Radiolarian-bearing rocks are widespread throughout the orogen and this form of study has enormous potential for future biostratigraphic studies.

GEOCHRONOLOGY Advances have been made in our understanding of the age of the ophiolitic rocks (Aitchison et al., 1992). A U /Pb age of 530 Ma from a plagiogranite witllin the Weraerai terrane indicates that it is the oldest rock identified. Clearly alternative explanations of the tectonic evolution of the New England Orogen are required to explain this age. The availability of single crystal dates using the SHRIMP ion microprobe at the Australian National University will provide the necessary incentive for researchers to reassess the precision of many of the earlier obtained whole rock dates and it will also point to the occurrence of 'inheritance' and the likelihood of older basement underneath the New England Orogen - something that has been suspected for the past decade and is now mappable using the SHRIMP as a remote sensing tool ( Roberts et al., 1991). Improvements in 40Ar/ 39Ar dating technique offer the potential to resolve

61

_.. __.._. .. ._ timing of multiple metamorphic events and lea.d to resolution of the geology in emgmatic zones such as the Nambucca Slate Belt. m~y

STRUcrURE AND TEcrONICS Attempts to decipher the tectonic history include many papers (Fergusson and Flood, 1984; Cawood and Leitch, 1985; Murray, 1986; Murray e/ al." 1987; Cross e/ al., 1987; Flood and Aitchison, 1988, 1990; Scheibner, 1989; Cawood and Flood, 1989; Glen and Beckett, 1989; Aitchison and Flood 1990a,b,c; Korsch e/ al." 1990; Coney e/ al.,: 1990; Collins, 1991; Aitchison and Flood 1991; Liang, 1991; Dirks e/ al., 1992; Aitchison e/ al." 1992; Flood and Aitchison, 1992). One significant result is the recognition of the Gamilaroi terrane as a rifted island arc (the missing Tamworth Belt arc) and that there must have been eastward-directed subduction pre late Devonian to have preserved the terrane above the Lachlan Fold Belt. A second significant result is the recognition of the docking of the Gamilaroi terrane as indicated by the presence of Lachlan Fold Belt derived quartzites within the Keepit Conglomerate. The presence of unconformity bounded sequences within the foreland basin. may reflect distinct accretion events. There is a growing awareness of the possible presence of 'thin-skinned' tectonic features, The recently completed Bureau of Mineral Resources deep seismic profile across the New England Province will necessitate further reassessment of the structural relationships of the foreland basin- fold and thrust belt- accretionary complex arrangement.

MINERALIZATION Several articles discussed the style of mineralization (Botti mer, 1986; Degeling e/ al." 1986; Ashley and Kleeman, 1988; Plimer and Kleeman, 1985; Murray, 1990; Ashley e/ al., 1990; Gilligan and Barnes, 1990; Ashley e/ al., 1991; Plimer e/ al., 1991). The recently published New South Wales Department of Mineral Resources meta~logenetic maps (Tamworth-Hastings, DOrrlgo-Coffs Harbour) and associated notes provide a very useful compilation of data for these 1:250000 map sheets.

62

CHERT GEOCHEMISTRY Aitchison & Flood, (1990) · propose that two distinct chert types may be recognised within the accretionary complex of the New England Orogen. Type I are ribbonbedded cherts displaying low AI/(AI+Fe+Mn), high Fe203, high MnO/Ti02, high Si/(Si+AI+Fe). These indicate possible hydrothermal contribution, accumulation far from a terrigenous source, and high biogenic component. Type II are tuffaceous cherts characterised by high AI/(AI+Fe+Mn), low MnO/Ti02 and Si/(Si+AI+Fe) which indicates formation in an environment more proximal to a terrigenous source. The abundance of Na20 and Al203 relative to Si02 in this type indicates dilution by volcanic ash. AI-Fe-Mn diagrams indicate that Type II cherts are non-hydrothermal. Both cherts were conveyed into a trench by subduction processes where hemipelagic sedimentation was swamped by terrigenous material from turbidity currents. Recent analyses of the Ce/Ce' anomaly of the chert sequences indicate similar results to those reported by Murray e/ al. (1990; 1991a,b; 1992a,b). Environment specific- geochemical indices, indicate by analogy with the Franciscan complex of California, a far · travelled history for the cherts. The values obtained from the cherts of the Djungati terrane include the spectrum of ridge-proximal through ' to continental margin-proximal environments. When combined with biostratigraphic age control these data prOVide the potential to resolve ocean basin histories.

LATE CARBONIFEROUS 'ANDEAN-MARGIN'VOLCANICS The stratigraphic succession and setting of the late Carboniferous ignimbritic and volcaniclastic succession exposed along the western part of the New England province of the New England orogen has been comprehenSively documented by McPhie (1983;1984, 1986a, 1987). More recently, the research of Flood (1987, 1991), Pecover (1987) and Flood and Taylor (1991) has demonstrated the importance of this area of continental margin arc volcanism as having enormous potential for exploration for natural zeolites.

NEO '93 Conference Proceedings

- - -------------

LATE PERMIAN VOLCANICS

explora lion. It has been clearly demonstrated that a genetic association exists between basalts and sapphires.

Widespread terrestrial and shallow marine volcanism in the Late Permian produced thick sequences of predominantly rhyolitic to rhyodacitic tuffs and ignimbrites (Barnes e/ al., 1991). Recent recompilation mapping by the New South Wales Geological Survey has led to revision of the volcanics and the name Wands worth Volcanic Group was introduced to encompass the Emmaville Volcanics, Wallangarra Volcanics, Drake Volcanics and Gilgurry Mudstone, Dundee Rhyodacite and units of the Coombadjha Volcanic Complex. The term also covers large tracts previously referred to as "undifferentiated Permian volcanics". Several Late Permian continental silicic volcanics are preserved in the eroded remnants of volcanic cauldrons at several sites between Dundee and Wallangarra (McPhie, 1986b, 1988). The youngest unit is the Dundee Rhyodacite, a widespread and distinctive crystal-rich ignimbrite. The Late Permian Volcanics, whilst forming an overlap sequence. to the terranes, are themselves intruded by the second pulse of comagmatic plutonism.

CONCLUSION Terrane analysis provides as ideal methodology for deciphering the geological history of complex orogens such as the New England Orogen. The present simplistic structural subdivision belies a much more complex history of geological development within the orogen. Radiolarians have provided age constraints for many of the previously undated rock sequences. Chert geochemistry now provides an index of the relative distance from spreading ridge and/or continental influence. Two continen.tal margin arc assemblages have been recognised; a late Carboniferous arc and a late Permian arc. Distinct periods of intrusion by Stype and I-type granite batholiths occur. The S-type may be related to an overthickening of the accretionary prism. The 1type are related to a late Permian continental arc distinct from the late Carboniferous' Andean-margin' continental

NEW ENGLAND BATHOLITH

arc.

The tectonostratigraphic terranes have been intruded by granitoids during two distinct phases of plutonism, the first during the Late Carboniferous (S-type) and the second during the Late Permian-Early Triassic (1- and A-type). It is not possible to cite any publications which advances our knowledge of the nature of plutonism within the orogen since the work of Shaw and Flood(1981) and Hensel et al.(1985). Recent summaries may be found in Kleeman(1988, 1991) and Plimer e / al.(1991).

ACKNOWLEDGEMENT Funding for studies in the New England Orogen was provided by the' Australian Research Council, BHP Minerals and CRA Exploration.

REFERENCES AITCHISON J.e. & FLOOD P.G., 1990a. Preliminary tectonostratigraphic terrane map of the southern part of the New Englan Orogen, eastern australia. In T.J. Wiley, D.G. c Howell and F.L. Wong (eds), Terrane analysis of China and the Pacific rim. Circum-Pacific Council for Energy and Mineral Resources, Earth Science Series 13, 81-85. AITCHISON J.e. & FLOOD P.G ., 1990b. Geochemical constraints on the depositional setting of Palaeozoic cherts from the New England orogen, NSW, eastern Australia. Mar. Ceol. 94, 79-95. AITCHISON J.e. & FLOOD P.G., 199Oc. Early Carboniferous radiolarian age constrain the timing of sedimentation within the Anaiwan

TERTIARY BASALTIC VOLCANISM AND ASSOCIATED SAPPHIRES The Tertiary basaltic volcanics of the Tablelands region have been the subject of extensive exploration effort by companies looking for commercial deposits of sapphires. In the Glen Innes-Inverell area these volcanics belong to the Central Volcanic Province. Recent research by Pecover and Coenraads (1989), Seward and Korsch (1989), Coenraads (1990), Coenraads et al. (1990a,b), and Pecover (1992) has provided a reference point for sapphire

63

NEO '93 Conference Proceedings I

,. •

terrane, New England orogen, eastern Australia. N. Tb. Geol. Palaont. Abh. 180,1-19. AITCHISON J.C & FLOOD P.G., 1991. New England Orogen. In M. MouIlade and A.E.M. Nairn (eds),

The Phanerozoic Geology of the World 1: The Palaeozoic, A. Elsevier, Amsterdam, pp. 301-309. AITCHISON J.C, 1988. Late Paleozoic radiolarian ages from the Gwydir terrane, New England orogen, eastern Australia. Geology 16, 793795. AITCHISON J.C, 1990. Significance of Devonian-Carboniferous radiolarians from accretionary terranes of the New England orogen, eastern Australia. Mar. Micropaleontol. 15, 365-378. AITCHISON J.e., FLOOD, P.G. & SPILLER, F.CP., 1992. Tectonic setting and paleoenvironment of terranes in the southern New England orogen, eastern Australia as constrained by radiolarian biostratigraphy.

Palaeo geography, Pa laeoc lima tolo g y, Palaeoecology 94,31-54. . AITCHISON J.C, IRELAND T.R., BLAKE M.e. Jr & FLOOD P.G., 1992. 530 Ma zircon age for ophiolite from the New England orogen: oldest known rocks from eastern Australia. Geology 20, 125c128. ASHLEY P.M. & KLEEMAN J.D., 1988. Drake and Emmaville areas, northern New South Wales. In L.H. Hamilton (ed.) Field Excursions

Handbook for the North Australian Geological Convention, pp. 143-161. Geo!. Soc. Aust., Qld Div., Brisbane. ASHLEY P.M., COOK N.D.J. & HILL R.L., 1990. Occurrence and significance of aurostibite in Sb-Au ore from Hillgrove, New South Wales, Australia. N. lb. Miner. Mh.12, 537551. BARNES R.G., BROWN R.E., BROWNLOW J.W. & STROUD W.J., 1991. Late Permian volcanics in New England -the Wandsworth Volcanic Group. Geological Survey

of New South Wales Quart. Notes 84, 1-36. BOTTOMER L.R., 1986. Epithermal silvergold mineralization in the Drake area, northeastern New South

64

Wales. Aust. J. Earth Sci. 33, 457473. COENRAADS R.R., 1990a. Key areas for alluvial diamond and sapphire exploration in the New England gem fields, New South Wales, Australia. Econ. Geol. 85, 1186-1207: COENRRADS R.R., 1990b. Palaeogeography of the Braemar Deep-Lead Sapphire Deposit, New South Wales. J. Proc. Roy. Soc. NSW 123,75-84. COENRAADS R.R., SUTHERLAND F.L. & KINNY P. D., 1990. The origin of sapphires: U-Pb dating of zircon inclusions sheds new light.

Mineralogical Mag.54, 113-122. COENRRADS R.R., 1990b. Palaeogeography of the Braemar Deep-Lead Sapphire Deposit, New South Wales. ,. Proc. Roy. Soc. NSW 123,75-84. COLLINS W.J., 1991. A reassessment of the 'Hunter-Bowen Orogeny': tectonic implications for the Southern New England .Fold Belt. Aust. J. Earth Sci. 38, 409-423. CONEY P.J., EDWARDS A., HINE R., MORRISON F. & WINDRIM D., 1990. The regional tectonics of the Tasman orogenic system, eastern Australia. J. Struct. Geol. 12, 519543. CONEY P.J., JONES D.L. & MONGER J.W.H., 1980. Cordilleran suspect terranes. Nature 239, 329-333. CROSS K.C, FERGUSSON CL. & FLOOD P.G., 1987. Contrasting structural styles in the Paleozoic subduction complex of the southern New England Orogen, eastern Australia. In E.e. Leitch & E. Scheibner (eds)

Terrane Accretion and Orogenic Bel/s, pp. 83-92. Am. Geophys. Un:, Geodyn. Ser. 19. DEGELING P.R ;, GILLIGAN L.B., SCHEIBNER E. & SUPPEL D.W., 1986. Metallogeny and tectonic development of the Tasman Fold Belt System in New South Wales. Ore Geol. Rev. 1, 259-313. FERGUSSON e.L. & FLOOD P.G., 1984. A late Palaeozoic subduction complex in the Border Rivers Area of southeast Queensland. Proc. R. Soc. Qld 95, 47-55. FLOOD P.G., 1987. Occurrence and nature of zeoli tic tuffs within the Late

continental growth.

Carboniferous Currabubula Formation, Werrie Syncline, New South Wales. Geol. Surv. NSW Sydney Report, 1987/146: 75-81. FLOOD P.G., 1991. Prospecting for natural zeolites: an exploration model based upon an occurrence in 300 Ma old rocks near Werris Creek, New South Wales, Australia. Trans Instn Min. Metall . (Sect B: App!. earth sci.) 100, B9-BI3. FLOOD P.G. & AITCHISON J.C, 1988. Tectonistratigraphic terranes of the southern part of the New England Orogen. In J.D. Kleeman (ed.), New •

Hall, London. KLEEMAN ).D., 1988. Constraints granitic intrusives and extrusives on the tectonics of the southern New England Orogen in the late Palaeozoic-early Triassic. In ).0. Kleeman (ed.), New England

Orogen Tectonics and Metallogenesis. Univ. New England, Armidale, Australia, pp. 129-133. KLEEMAN J.D., 1991. Paleozoic granitoids anq associated volcanics. In M. MouIlade and A.E.M. Nairn (eds),

England Orogen Tectonics and Metallogenesis. Univ. New

The Phanerozoic Geology of the world 1: the Palaeozoic, A.

England, Armidale, Australia, pp.

Elsevier, Amsterdam, pp. 309-325. KORSCH R.)., HARRINGTON H.J., MURRAY CG., FERGUSSON CL. & FLOOD P.G., 1990. Tectonics of the New England Orogen. Bureau Mill . Res., Geology & Geophysics Bull. 232, 35-52. LIANG T.CK., 1991. Fault-related folding:TuJcumba Ridge, western New England. Aust. I. Earth Sci. 38, 349-355. McPHIE )., 1983. Outflow ignimbrite sheets from Late Carboniferous calderas, Currabubula Formation, New South Wales, Australia. Geol. Mag. 120(5), 487-503. McPHIE L 1984. Permo-Carboniferous silicic volcanism and palaeogeography of the western edge of the New England Orogen, northeastern New South Wales. Aust. I. Earth Sci. 31, 133-146. McPHIE)., 1986a. Primary and redeposited facies from a large-magnitude, rhyolitic, phreatomagmatic eruption: Cana Creek Tuff, Late Carboniferous, Australia. I. Volcanol. Geotherm. Res . 28, 319350. McPHIE J., 1986b. Evolution of a nonresurgent cauldron·: the Late Permian Coombadjha Volcanic Complex, northeastern New South Wales, Australia. Geol. Mag. 123, 257-277. McPHIE J., 1987. Andean analogue for Late Carboniferous volcanic arc and arc flank environments of the western New England Orogen, New South Wales, Australia. Tectonophysics 138, 269-288.

7-10.

•

FLOOD P.G. & AITCHISON J.C 1992. Late Devonian accretion of the Gamilaroi terrane to eastern Gondwana: provenance linkage suggested by the first appearance of Lachlan Fold Belt-derived quartzites. Aust.J. Earth Sci.39, 539544. FLOOD P.G. and TAYLOR J.C, 1991. .,.. Mineralogy and geochemistry of Late Carboniferous zeolitites, near Werris Creek, New South Wales, Australia. N. lb. Miner. Mh. H2, 4962. GILLIGAN L.B. & BARNES R.G., 1990. New England Fold Belt in New South Wales - regional geology and mineralisation. In F.E. Hughes (ed.), . Geology of the Mineral

Deposits of Australia and Papua New Guinea, pp. 1417-1424 . Australasian Ins!. Mining Metallurgy Monography 14, Melbourne. R. A. & BECKETT )., 1989. Geological note: thin-skinned tectonics in the Hunter Coalfields of New South Wales. Aust. I. Earth Sci: 36, 589-593. i:.it:~ ""r.T H.D., McCULLOCH M.T. & CHAPPELL B.W., 1985. The New England Batholith: constraints on its derivation from Nd and Sr isotopic studies of granitoids and country rock. Geochimica et Cosmochimica Acta 49, 369-384. ): HO"~EI D.G., 1989. Tectonics of Suspect

Mountain building and

65

NEO '93 Conference Proceedings I

McPHIE J., 1988. Sourcc(s) of the Dunce Rhyodacite Ignimbrite: implications for the existance of Late Permian cauldrons in the southern New England Orogen. In J.D. Kleeman (ed.), New England

Orogen Tectonics and Metal/ogenesis. Univ. New England, Armidale, Australia, pp. 145-149. MURRAY CG., 1986. Metallogeny and tectonic development of the Tasman Fold Belt System in Queensland. Ore Geol. Rev. 1, 315-400. MURRAY CG., 1990. Tasman Fold Belt in Queensland. In F.E. Hughes (ed.),

Geology of the Mineral Deposits of Australia and Papua New Guinea, pp. 1431-1451. Australasian Inst. Mining Metallurgy Monograph 14, Melbourne. MURRAY CG., FERGUSSON CL., FLOOD P.G., WHITAKER W .G. & KORSCH R.J., 1987. Plate tectonic model for the Carboniferous evolution of the New England Fold Belt. Aust. J. Earth Sci. 34, 213-236. MURRAY R. W., BUCHHOLTZ TEN BRINK M. R., BRUMSACK H. J., M. R., GERLACH D. C, RUSS III G. P., 1991b. Rare earth elements in Japan Sea sediments and diagenetic behavior of Ce/Ce': Results from ODP Leg 127. Geochimica et Cosmochimica Acta, 55, 2453-2466. MURRAY R. W., BUCHHOLTZ TEN BRINK M. R., GERLACH D. C, RUSS III G. P., AND JONES D. L., 1991a. Rare earth, major, and trace elements in chert from the Franciscan Complex and Monterey Group, California: Assessing REE sources to fine-grained marine sediments, Geochimica et Cosmochimica Acta, 55, 1875-1895. MURRAY R. W., BUCHHOLTZ TEN BRINK M. R., GERLACH D. C, RUSS III G. P., AND JONES D. L., 1992. Interoceanic variation in rare earth, major, and trace element depositional chemistry of chert: perspectives gained from the DSDP and ODP record.Geochimica et Cosmochimica Acta, 56, 1897-1913.

66

MURRAY R. W., BUCHHOLTZ TEN BRINK M. R., JONES D. L., GERLACH D. C, PRICE RUSS III G., 1990. Rare earth elements as indicators of different marine depositional environments in chert and shale. Geology, 18, 268-271. MURRAY R. W., JONES D. L.,BUCHHOL TZ TEN BRINK M. R., 1992. Diagenetic formation of bedded chert: Evidence from chemistry of .the chert-shale couplet. Geology, 20, 271-274. PECOVER S.R., 1987. Zeolite occurrences in New South Wales:. Geology and Prospectivity. Geol. Surv. NSW Sydney Report, 1987/146,66-74. PECOVER S.R., 1992. A guide to the geology of economic sapphire deposits in the central volcanic province, northeastern N.S.W. In W.F. Will mont (ed .) Regional and

Economic Geology of the New England District. Geological Society of Australia, Queensland Division, Brisbane pp.55-73. PECOVER S.R. & COENRAADS R.R., 1989. Tertiary volcanism, alluvial processes, and the origin of sapphire deposists at "Braemar", near Elsmore, northeastern New South Wales. Geological Survey of New South Wales, Quart. Notes 77, 1-23. . PERKINS C, 1988a. Origin and provenance of submarine volcaniclastic rocks in the Late Permian Drake Volcanics, New South Wales. Aust. J. Earth Sci. 35, 325-337. PERKINS C, 1988b. The Red Rock deposit: Late Permian submarine epithermal precious metal system in northeastern New South Wales. Pacific Rim Congress 87, Gold Coast,

Granite,

Australia.

Min e r.

Deposita 26, 267-274. ROBERTS J. & ENGEL B.A., 1987. Depositional and tectonic history of the southern New England Orogen. Aust. J. Earth Sci. 34, 1-20. ROBERTS J., CLAOUE-JONES J.C & JONES P. L 1991. Calibration of the Carboniferous and Early Permian of the Sou thern New England Orogen by SHRIMP ion microprobe zircon analyses. In Diessel CF.K. (ed.) Twenty Fifth

Newcastle Symposium on "Advances in the study of the Syd n ey Bas in", pp. 38-43. Department of Geology, University of Newcastle. SCHEIBNER E., 1989. The tectonics of New South Wales in the second decade of application of the Plate Tectonic Paradigm. ,. Proc. Roy. Soc. NSW 122,35-74. SEWARD D. & KORSCH R.J., 1989. Fission track dating of alluvial zircons from the Inverell sapphire field, New England Orogen. Aust. ,. Earth Sci. 36, 475-477. SHAW S.E. & FLOOD R.H., 1981. The New England Batholith, Eastern Australia: Geochemical Variations in Time and Space. ,. Geophys. Res. 86, 10530-10544.

Australia, Australasian Institute of Mining and Metallurgy, Confr. Proc., 895-898. PUMER I.R. & KLEEMAN J.D., 1985. Mineralization associated with the Mole Granite, Australia. In. C Halls (ed.), High heat production

granites (HHP), hydrothermal circulation and ore genesis. London, Instn. Min. Metall., pp. 563-569. PUMER l.R., LU J. & KLEEMAN J.D., 1991. Trace and rare earth elements in cassiterite - sources of components for the tin deposits of the Mole



67