Analog modeling of the Mexican Fold-and-Thrust Belt in central México Alberto Vásquez Serrano, Posgrado en Ciencias de laTierra. Universidad Nacional Autónoma de México. (
[email protected]) Gustavo Tolson, Depto. de Geología Regional, Instituto de Geología. Universidad Nacional Autónoma de México. (
[email protected]) Abstract In central Mexico, the Mexican Fold-and-Thrust Belt (MFTB) presents particular characteristics different to other fold-thrust belts. The presence of important sedimentary facies changes in the pre-tectonic units plays an important role in the deformation style, shortening accommodation and kinematic evolution. Field observations and direct dating of deformation have contributed to our understanding of the development of this orogenic wedge. Nevertheless, there are some fundamental aspects that we need to know: What is the importance of the facies changes in the history of deformation? How is deformation accommodated near the borders of the facies changes? What is the influence of lateral mechanical characteristics of the pre-tectonic units on the deformation of the syntectonic deposits? What is the role of superficial processes (erosion and sedimentation) in the deformation of the orogenic wedge in central Mexico? To answer these questions we used scaled analog models to study the kinematic evolution of fold-and-thrust belts. Sand-box modeling is frequently used to generate scaled orogenic wedges in natural gravity conditions. For the models, we used different sands with different friction angles to model the lateral mechanical variation in pretectonic rocks, product of the facies changes. Our results indicate that the kinematic evolution, deformation style (dominance of folds in the basins and thrusts in the platforms) and strain variations (more in the basins and less in the platforms) of the MFTB are related spatially with the mechanical properties in the pre-tectonic rocks, the geometry of the borders between platforms and basins, and the weight of syntectonic deposits. The deformation within syntectonic deposits depends on its position in the wedge, with high simple shear strain concentrated on the border zone between platforms and basins, while pure shear dominates in the middle part of the basins. These results are congruent with the field observations and shortening estimations reported in previous work.
Introduction
Model setup
Location and geology Cordilleran Hinterland
a evad ra N Sier tholith Ba
In foreland fold and thrust belts (FFTB) lateral facies variations of pretectonic units are commonly observed. Lateral stratigraphic variations cause lithological and therefore mechanical variations that highly control styles of deformation within a FFTB (Suter, 1987; Fitz-Díaz et al., 2012). Due to the presence of different paleogeography elements, the Mexican fold and thrust belt (MFTB) in central México offers an excellent opportunity to explore the effect of the lateral mechanical variation of pre-tectonic rocks and the superficial procesess on the kinematic, strain distribution and deformation style of the FFTB, through the systematic analysis of scaled analog models and compared with the field observations in previos works (Fitz-Díaz et al., 2012; Vásquez-Serrano & Tolson, 2015).
0.8 cm 1.1 cm
MSMS: Mega Shear Mojave-Sonora. SMF: San Marcos Fault. MGP: Morelos-Guerrero Platform. MPF: Motagua-Polochic Fault. MFTB: Mexican Fold-Thrust Belt
Speed Motor
Modified from Fitz-Díaz et al., 2012
Toliman Sequences
Colorado Plateaou
El Doctor Platform Basalt Sand
Quartz fine Sand
Valles-SLP Platform
Zimapán Basin
Quartz Sand
Quartz Sand
Width Movement direction
0.1 cm
velocity =0.8 mm/min
Tampico-Misantla Basin
Height Displacement
11 cm
Glass Microspheres
Angle
M
SM
S
Results B’
P
Study Area
F
MP
Tampico-Misantla Basin
Valles-San Luis Platform
Homogeneous quartz sand F1
9.5°
F2 F3
F4 F6
F5
F7
Detachment zone
Zimapan Basin
Legend
500 000 Faults
Tolimán Sequences El Doctor Platform B
Thrusts
Late Cretaceous turbidites Cretaceous carbonate basins
Roads
Cretaceous carbonate platforms
Towns
Early Cretaceous volcaniclastics
Q alluvial deposits
Late Jurassic carbonaceous limestone
Tertiary volcanics Tertiary intrusives
Middle Jurassic redbeds Triassic siliciclastic melange
Eocene redbeds
Triassic peri-continental siliciclastics
Paleogene turbidites
Cross section 1
Shortening: 78%
56%
Toliman Sequences
F1 F2
F3
El Doctor Platform
61%
45%
15%
Zimapan Basin
Valles-SLP Platform
Tampico-Misantla Basin
10°
F4
F6
F5
F7
F8
F9
El Doctor Platform
~35%
~43% 13%
Valles-SLP Platform
Zimapan Basin
F12
Tampico-Misantla Basin B’
B
α=3-3.8°
(α+β)Max=6.3°
V V V V
V V
V
V
V
V
V
V V
V
V
V
V
V
V
V
V
V
V
V
V
10 km
Shortening: 68%
54%
Toliman Sequences
where da/dt is the rate of change of the cross-sectional area of the wedge, vT is the erosive flux, ka is an area-length coefficient, S is the slope of the sand wedge, W is the width of the orogen, h is an exponent in area-length relationship, m is an area exponent, n is a slope exponent and K is the erodibility constant . The erosion events were applied episodically as material was being accreted to the wedge.
Fine basalt Sand (size=0.5-0.9 mm)
50% Quartz Sand- 50% Glitter
Fine quartz Sand (size~0.25 mm)
Basalt Sand (size=1-2 mm)
Pomez Sand (size=0.3-0.5 mm)
Glass microspheres
Basin rocks Quartz Sand-small dough balls
0
Quartz-Feldspar Sand (size=0.25-0.45 mm)
10
Quartz-Feldspar Sand (size=0.5-0.75 mm)
20
Quartz Sand (size=0.5-0.75 mm)
30
F3
El Doctor Platform
F4
45%
38%
Zimapan Basin
Valles-SLP Platform
Tampico-Misantla Basin
8.4°
F5
F7
F6
F8
F9 F10
Shortening: 74%
66%
Toliman Sequences
El Doctor Platform
Angle of repose
55%
17%
Zimapan Basin
Valles-SLP Platform
Tampico-Misantla Basin
F2
1 mm
Summary of materials properties and parameters used in phisical experiments. Physical Experiment 1500 33° 1900 42°
Erosion parameters m 0.4 n 1 h 1.4 K 0.0000005 Ka 4 S 0.265 vT (km/yr) 0.001114
1500 30°
F1
F3
F4
Quartz Sand
20
30 40 Displacement (cm)
50
60
10
20
30 40 Displacement (cm)
50
60
10
20
30 40 Displacement (cm)
50
60
10
20
30 40 Displacement (cm)
50
60
20 10 0 20
t (min)
500
15 10 5
700
F5
F7
300 t (min)
500
10 0
15 10 5
40
F1 F2
30 20 10 0 30
F7 F8
25 20 15 10 5
F9 0
20
0 0
700
F6
F8
20
25
F5
F6
30
200
t (min)
400
600
00
Observations Results from our physical experiments show that the lateral mechanical variations have an important influence in the shortening distribution (more in the basin and less in the platforms), with a deformation concentration in the border between platforms and basin. This behavior is different in the case of a homogeneous wedge without mechanical variations. The number of thrust faults and their activity depend on the syntectonic sedimentation, on the erosion and the lateral mechanical variations; for an homogeneous wedge, the activity of faults is congruent with the Coulomb-Mohr wedge, but for the other models the pattern is different, for example, in the experiment with syntectonic strata several faults are active in many stages. The variation of the wedge width and angle during the deformation depend strongly on the erosion, syntectonic strata and the facies changes. Our results are relevant to hydrocarbon exploration, where there are mechanical variations in orogenic wedges.
References.
1400 24
10
30
0 0
F4
F9
Basalt Sand
5
40
100
80%
10.2°
33°
Quartz Sand Density (kg/m3) Angle of repose Basalt Sand Density (kg/m3) Angle of repose Fine Quartz Sand Density (kg/m3) Angle of repose Glass microspheres Density (kg/m3) Angle of repose
300
F1 F2 F3 F4 F5 F6 F7 F8 F9 F10
Heterogeneous sand with syntectonic erosion
44°
Parameter
t (min)
10
600
F3
Angle of repose
1 mm
400
15
40
100
65%
F1
Platform rocks Quartz-Feldspar Sand (size=0.25-0.75 mm)
Deformable materials consisted of a 2.1 cm layer of sand placed at the base of a teflon coated box. The total thickness of deformable materials was designed to represent ~5.3 km of brittle sedimentary package (Fitz-Díaz et al., 2012). Using this length, the model was scaled to a natural orogenic wedge using scaling rules utilized in other analog models (Hubbert 1951; Ramberg, 1967), in which the vertical stress and cohesion of the model and nature have the same units and are scaled similary. In our experiments, the model/nature vertical stress ratio is 4.03 X 10-6. In the case of erosion, we applied a rule in which mass removal is limited by the rate of fluvial bedrock incision (Hilley & Strecker, 2004; Hilley et al., 2004), using the following equation:
Angle of repose
An important parameter that characterized mechanically the rocks in the Coulomb failure criterion is the internal friction angle. This parameter is different between massive carbonate plataform rocks (36-43°) and thinly bedded basinal rocks (27-33°, Donath, 1961; Handin, 1969; Fitz-Díaz et al., 2011). In analog modeling, the noncohesive granular material has an angle of repose that is similar to the friction angle (Hubbert, 1951).
F2
Angle of repose of some granular materials 40
200
20
V
β=2-2.5°
Model Method and Materials
0
00
F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12
Heterogeneous sand with syntectonic depositation
10
Wedge Width
Toliman Sequences
~70%
~55%
>70%
F11
F10
20
25
F10 0
Heterogeneous sand without syntectonic deposits
450 000
400 000
F10
30
Wedge ange
2300 000
F8 F9
40
F1 F2 F3 F4 F5 F6 F7 F8 F9
Wedge Width
MG
Fault activity vs time Wedge Width
k
Wedge ange
loc
Wedge ange
aB
Wedge Width
F
uil
2350 000
ah
Wedge ange
SM
Co
Geological Settings In the Vizarrón-Tamazunchale cross-section, the rocks are mostly Cretaceous carbonates, with lateral facies changes associated with different paleogeographical elements across the region. These elements are, from west to east: the El Doctor Platform, the Zimapán Basin, the Valles–San Luis Potosí Platform and the Tampico-Misantla Basin (Fitz-Díaz et al, 2012; Carrillo-Martínez, 1997; Suter, 1987). To the west, the Cretaceous rocks are in fault contact with a suite of rocks here grouped as the Tolimán sequences. Unconformably overlying these rocks, the syntectonic turbidites are represented by the late cretaceus sedimentary Soyatal and Méndez Formations.(Hernández-Jáuregui, 1997).
0.5 cm 0.4 cm
Carrillo-Martínez, M., 1990. Geometría estructural de la Sierra Madre Oriental entre Peñamiller y Jalpan, estado de Querétaro: Sociedad Geológica Mexicana, Convención Geológica Nacional, 6, México D.F. Libro-guía de la excursión geológica a la región de Zimapán y áreas circundantes, estados de Hidalgo y Querétaro, p. 1-20. Donath, F. A., 1961Experimental study of shear failure in anisotropic rocks. Geological Society of America Bulletin 1961;72, no. 6;985-989. Fitz-Díaz E., Hudleston P., Siebenaller, L., Kirschner, D., Camprubí, A., Tolson, G., Pi, T., 2011. Insights into fluid flow and water-rock interaction during deformation of carbonate sequences in the Mexican Fold-Thrust Belt. Journal of Structural Geology, v.33, n. 8, p.1237-1253.
Fitz-Díaz, E., Tolson, G., Hudleston, P., Bolaños-Rodríguez, D., Ortega- Flores, B., Vásquez-Serrano, A., 2012. The role of folding in the development of the Mexican FoldThrust Belt. Geosphere, v. 8, no. 4, p. 931-949. Hernández-Jáuregui, R., 1997. Sedimentación sintectónica de la Formación Soyatal (Turoniano Medio-Campaniano) y modelado cinemático de la Cuenca de Flexura de Maconí, Querétaro. Instituto Politécnico Nacional, ESIA, Master Thesis. 94 p. Hubbert, M. K., 1951, Mechanical basis for certain familiar geologic structures: Geol. Soc. America Bull., v. 62, p. 355-372. Handin, J., 1969. On the Coulomb-Mohr Failure Criterion. Journal of Geophysical Research. v. 74, no. 22. 5343-5348. Hilley, G. E., Strecker, M. R., 2004. Steady state esosion of critical Coulomb wedges with application to Taiwan and the Himalaya, J. Geophys. Res., 109.
Hilley, G. E., Strecker, M. R. Ramos, V. A., 2004. Growth amd erosion of fold-and-thrust belts with an application to the Aconcagua fold-and-thrust belt, Argentina, J. Geophys. Res., 109. Ramberg, H.,1967. Model experimentation of the effect of gravity on tectonic processes, The Geophysical Journal of the Royal Astronomical Society, 14, 307-329. Suter, M., 1987. Structural traverse across the Sierra Madre Oriental fold-thrush belt en east-central México: Geological Society of America Bulletin, v. 98, p. 246-264. Vásquez-Serrano A., Tolson, G. 2015. Deformation patterns of syntectonic strata in the Vizarrón-Tamazunchale cross-section of the Mexican Fold and Thrust Belt of Central México. Cordilleran Section - 111th Annual Meeting. Session No. 22--Booth# 3.
