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1
He, Yuqing, Teng Wang, Lihua Fang, and Li Zhao. "The 2020 Mw 6.0 Jiashi Earthquake: Coinvolvement of Thin-Skinned Thrusting and Basement Shortening in Shaping the Keping-Tage Fold-and-Thrust Belt in Southwestern Tian Shan." Seismological Research Letters 93, no. 2A (December 15, 2021): 680–92. http://dx.doi.org/10.1785/0220210063.
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Abstract The Keping-tage fold-and-thrust belt in southwest Tian Shan is seismically active, yet the most well-recorded earthquakes occurred south of the mountain front. The lack of large earthquakes beneath the fold-and-thrust belt thus hinders our understanding of the orogenic process to the north. The 2020 Mw 6.0 Jiashi earthquake is an important event with surface deformation in the fold-and-thrust belt well illuminated by Interferometric Synthetic Aperture Radar, providing an opportunity to study the present-day kinematics of the thrust front through the analysis of satellite measurements of surface deformations. Here, we employ the surface deformation and relocated aftershocks to investigate the fault-slip distribution associated to this event. Further added by an analysis of Coulomb stress changes, we derive a fault model involving slips on a shallow, low-angle (∼10°) north-dipping thrust fault as well as on a left-lateral tear fault and a high-angle south-dipping reverse fault in mid-crust. Aftershocks at depth reflect the basement-involved shortening activated by a thin-skinned thrust faulting event. In addition, this earthquake uplifted the southernmost mountain front with relatively low topography, indicating the basin-ward propagation of the southwest Tian Shan.
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Zhang, Hong. "Accumulation Models of the Natural Gas in the Foreland Basins of China and their Physical Simulation Experiment." Advanced Materials Research 233-235 (May 2011): 2812–15. http://dx.doi.org/10.4028/www.scientific.net/amr.233-235.2812.
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The paper chooses foreland basin as its research object. after summarizing the accumulation characteristics of the different phases and different parts of them, the common models of the whole foreland basin are given and the physical simulation experiments are carried out. It shows that the foreland basins experience three phases of evolution. Phase 1 is the period that the source rock and structure oil and gas traps form. Phase 2 is the period that multi-cycle reservoir and lithologic oil and gas pool form. phase 3 is the period that foreland uplift belt and fault anticline pool form. Then a foreland basins has three different belts including of thrust belt, foredeep and foreland slope belt, foreland uplift belt, and the belts have different accumulation models. With regard to the hydrocarbon accumulation period of the foreland basin, the thrust belt have precedence to other belt. foredeep and foreland slope belt forms the secondary pools. Foreland uplift belt accumulates hydrocarbon very quickly.
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Connors, Karen A. "Unraveling the boundary between turbidites of the Kisseynew belt and volcano-plutonic rocks of the Flin Flon belt, Trans-Hudson Orogen, Canada." Canadian Journal of Earth Sciences 33, no. 5 (May 1, 1996): 811–29. http://dx.doi.org/10.1139/e96-062.
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The Flin Flon – Kisseynew boundary in the eastern Trans-Hudson Orogen is interpreted here as an early thrust fault that places 1.86–1.84 Ga Kisseynew belt turbidites over previously deformed 1.91–1.88 Ga arc and ocean-floor assemblages of the Flin Flon belt. The basin in which sedimentary rocks of the Kisseynew belt were deposited has been interpreted to have formed partly within the Flin Flon belt. The fault that juxtaposes the two belts is interpreted to have been localized near the ancestral basin margin, resulting in development of a major ramp zone during basin closure. This interpreted ramp zone provides an explanation for the steep to shallow structural transition that corresponds to increasing metamorphic grade. Collapse of the Kisseynew sedimentary basin and juxtaposition of the two belts are attributed to southwest-verging folding and thrusting that initiated prior to emplacement of 1.83 Ga plutons. This magmatism was followed by regional greenschist- to upper-amphibolite-grade metamorphism (1.82–1.805 Ga) and renewed southwest-directed folding and thrusting. Late backfolds developed at the leading edge of the fold-thrust belt. Postpeak metamorphic deformation resulted in large-scale, upright folding of the fold–thrust stack (including the Flin Flon – Kisseynew boundary). This stage of deformation is interpreted to record a transition from southwest-directed transport to northwest-southeast-directed shortening at ~1.8 Ga.
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Pei, Yangwen, Douglas A. Paton, Rob J. Knipe, W. Henry Lickorish, Anren Li, and Kongyou Wu. "Field-based investigation of fault architecture: A case study from the Lenghu fold-and-thrust belt, Qaidam Basin, NE Tibetan Plateau." GSA Bulletin 132, no. 1-2 (June 19, 2019): 389–408. http://dx.doi.org/10.1130/b35140.1.
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AbstractThe fault zone architecture of a thrust fault zone is critical for understanding the strain accommodation and structural evolution in contractional systems. The fault architecture is also important for understanding fluid-flow behavior both along and/or across thrust fault zones and for evaluating potential fault-related compartmentalization. Because mesoscale (1–100 m) structural features are normally beyond seismic resolution, high-resolution outcrop in situ mapping (5–10 cm resolution) was employed to study the deformation features of a thrust fault zone located in the Qaidam Basin, northeastern Tibetan Plateau. The excellent exposure of outcrops enables the detailed investigation of the Lenghu thrust fault zone and its architecture. The Lenghu thrust fault, a seismically resolvable fault with up to ∼800 m of throw, exhibits a large variation of fault architecture and strain distribution along the fault zone. Multiple structural domains with different levels of strain were observed and are associated with the fault throw distribution across the fault. Based on previously proposed models and high-resolution outcrop mapping, an updated fault zone model was constructed to characterize the structural features and evolution of the Lenghu thrust. The possible parameters that impact fault architecture and strain distribution, including fault throw, bed thickness, lithology, and mechanical heterogeneity, were evaluated. Fault throw distributions and linkages control the strain distribution across a thrust fault zone, with local folding processes contributing important elements in Lenghu, especially where more incompetent beds dominate the stratigraphy. Mechanical heterogeneity, induced by different layer stacking patterns, controls the details of the fault architecture in the thrust zone. The variations in bed thicknesses and mechanical property contrasts are likely to control the initial fault dips and fault/fracture density. Large fault throws are associated with wide strain accommodation and damage zones, although the relationship between the development and width of the fault zone and the throw accumulation remains to be assessed. By presenting the high-resolution mapping of fault architecture, this study provides an insight into the subseismic fault zone geometry and strain distributions possible in thrust faults and reviews their application to assessments of fault zone behavior.
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Li, Bin, Qiqi Li, Wenhua Mei, Qingong Zhuo, and Xuesong Lu. "Analysis of accumulation models of Middle Permian in Northwest Sichuan Basin." Earth Sciences Research Journal 24, no. 4 (January 26, 2021): 419–28. http://dx.doi.org/10.15446/esrj.v24n4.91149.
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Great progress has been made in middle Permian exploration in Northwest Sichuan in recent years, but there are still many questions in understanding the hydrocarbon accumulation conditions. Due to the abundance of source rocks and the multi-term tectonic movements in this area, the hydrocarbon accumulation model is relatively complex, which has become the main problem to be solved urgently in oil and gas exploration. Based on the different tectonic backgrounds of the middle Permian in northwest Sichuan Basin, the thrust nappe belt, the hidden front belt, and the depression belt are taken as the research units to comb and compare the geologic conditions of the middle Permian reservoir. The evaluation of source rocks and the comparison of hydrocarbon sources suggest that the middle Permian hydrocarbon mainly comes from the bottom of the lower Cambrian and middle Permian, and the foreland orogeny promoted the thermal evolution of Paleozoic source rocks in northwest Sichuan to high maturity and over maturity stage. Based on a large number of reservoir physical properties data, the middle Permian reservoir has the characteristics of low porosity and low permeability, among which the thrust nappe belt and the hidden front belt have relatively high porosity and relatively developed fractures. The thick mudstone of Longtan formation constitutes the regional caprock in the study area and the preservation condition is good as a whole. However, the thrusting faults destroyed the sealing ability of the caprock in the nappe thrust belt. Typical reservoir profiles revealed that the trap types were different in the study area. The thrust fault traps are mainly developed in the thrust nappe belt, while the fault anticline traps are developed in the hidden front belt, and the structural lithological traps are developed in the depression belt. The different structural belts in northwest Sichuan have different oil and gas accumulation models, this paper built three hydrocarbon accumulation models by the analysis of reservoir formation conditions. The comprehensive analysis supposed the hidden front belt is close to the lower Cambrian source rock, and the reservoir heterogeneity is weak, faults connected source rock is developed, so it is a favorable oil and gas accumulation area in the middle Permian.
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Karaca, Sukru O., Ismail A. Abir, Shuhab D. Khan, Erman Ozsayın, and Kamil A. Qureshi. "Neotectonics of the Western Suleiman Fold Belt, Pakistan: Evidence for Bookshelf Faulting." Remote Sensing 13, no. 18 (September 9, 2021): 3593. http://dx.doi.org/10.3390/rs13183593.
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The Suleiman Fold-Thrust Belt represents an active deformational front at the western margin of the Indian plate and has been a locus of major earthquakes. This study focuses on the western part of the Suleiman Fold-Thrust Belt that comprises two parallel NW–SE oriented faults: Harnai Fault and Karahi Fault. These faults have known thrust components; however, there remains uncertainty about the lateral component of motion. This work presents the new observation of surface deformation using the Small Baseline Subset (SBAS), Interferometric Synthetic Aperture Radar (InSAR) technique on Sentinel-1A datasets to decompose displacement into the vertical and horizontal components employing ascending and descending track geometries. The subsurface structural geometry of this area was assessed using 2D seismic and well data. In addition, geomorphic indices were calculated to assess the relative tectonic activity of the area. InSAR results show that the Karahi Fault has a ~15 mm right-lateral movement for descending and ~10 mm/for ascending path geometries. The Harnai Fault does not show any lateral movement. Seismic data are in agreement with the InSAR results suggesting that the Harnai Fault is a blind thrust. This work indicates that the block between these two faults displays a clockwise rotation that creates the “bookshelf model”.
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Greenhalgh, Scott R., John H. McBride, John M. Bartley, R. William Keach, Brooks B. Britt, and Bart J. Kowallis. "Along-strike variability of thrust fault vergence." Interpretation 3, no. 3 (August 1, 2015): SX1—SX12. http://dx.doi.org/10.1190/int-2014-0182.1.
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The 3D kinematic evolution of thrust systems, in which vergence changes along strike, is poorly understood. This study uses 3D seismic data from Big Piney-LaBarge field, Wyoming, to examine the geometry and kinematics of two faults at the leading edge of the Hogsback thrust sheet, the frontal thrust of the Late Cretaceous Sevier fold-thrust belt. These thrusts lie along strike of each another and share an east-vergent detachment within the Cretaceous Baxter Shale. The two thrusts verge in opposite directions: The southern thrust verges eastward forming a frontal ramp consistent with major thrusts of the Sevier belt, whereas the northern thrust verges westward to form a type 1 triangle zone with the Hogsback thrust. The thrusts have strike lengths of 5 km (3.1 mi) and 8 km (5.0 mi), respectively, and they are separated by a transfer zone of less than 0.5 km (0.3 mi) wide. Strata in the transfer zone appear to be relatively undeformed, but reflections are less coherent here, which suggests small offsets unresolved by the seismic survey. Retrodeformable cross sections and a structure contour map on the Cretaceous Mesaverde Group indicate that shortening varies along strike, with a pronounced minimum at the transfer zone and greater shortening across the northern, west-vergent thrust (610 m [2000 ft]) than across the southern, east-vergent thrust (230 m [755 ft]). Mapping of these thrusts suggests that they propagated laterally toward each other to form a type 1 antithetic fault linkage in the transfer zone. Spatial patterns expressed in seismic attributes in and near the detachment horizon, which include waveform classification and spectral decomposition, suggest that stratigraphic variations may have pinned the detachment, thus localizing the transfer zone. Thickness variations in the thrust sheet also may have influenced the thrust geometry. Our study provides an analog for analysis of similar complex contractional belts around the world.
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Yong, Li, Yan Liang, Zhou Rongjun, Shao Chongjian, Zhao Guohua, Su Dechen, Yan Zhaokun, and Yun Kun. "Seismotectonic Mechanisms of Lushan (Ms7.0) Earthquake in the Frontal Propagation Belt of the Longmen Shan, Sichuan, China." Journal of Earthquake and Tsunami 09, no. 02 (June 2015): 1550005. http://dx.doi.org/10.1142/s1793431115500050.
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In recent years, the apparent seismic activity around Longmen Shan and its front has included the Wenchuan (Ms8.0) Earthquake and the Lushan (Ms7.0) Earthquake, occurring in 2008 and 2013, respectively. Based on the focal mechanism solution, rupture processes, seismic intensity, surface deformation, and aftershocks of the Lushan Earthquake and the active fault on Longmen Shan, we divided the Longmen Shan and its front into two tectonic deformation belts, the Longmen Shan thrust belt and the frontal propagation belt. By comparing the differences in the tectonic deformation styles, active faults, and earthquake histories of the two belts, we propose two kinds of seismotectonic models: one is a thrusting belt characterized by napping and detachment, and the other is a frontal propagation belt characterized by thrusting and detachment folding. By analyzing the seismogenic mechanisms of thrusting and detachment folding in the frontal propagation belt during the Lushan Earthquake, we have inferred that the Lushan Earthquake was formed by thrusting and detachment folding in the frontal propagation belt. The seismogenic fault of the Lushan Earthquake was the Dayi Fault, which dips NW with a listric surface, and converges on the detachment surface. The detachment surface is the seismic source layer of the Lushan Earthquake.
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SINGH, V. P., and D. SHANKER. "On the seismicity and tectonic activity Of the Bengal basin." MAUSAM 43, no. 4 (December 31, 2021): 371–78. http://dx.doi.org/10.54302/mausam.v43i4.3504.
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The tectonic activity of the Bengal basin for years 1850-1988 of seismicity and 16 years (1970-1985) of P-wave first motion data have been studied. The seismicity studies reveal three seismic belts such as Dhubri fault (striking N-S), Calcutta hinge zone (striking NE-SW) and the central region of the Bengal basin (striking NW-SE). Dauki fault is comparatively less seismically active than Dhubri fault. The seismicity of Dhubri fault and Calcutta hinge zone are confined to limited extension. The seismic activity along the central portion of the Bengal basin is extending from the Himalayan region (27°N, 88.5°E) to eastern plate margin (23.8°N, 92°E). .This appears to be a tectonic belt and is associated with the northeast drifting of Indian plate. The focal, mechanism studies reveal thrust faulting showing the stresses to be perpendicular to the proposed belt.
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Qian, Jun Feng. "Structural Deformation of Southern Tien Shan Fold-Thrust Belt — Take the North Margin of Kashi for Example." Advanced Materials Research 1010-1012 (August 2014): 1419–24. http://dx.doi.org/10.4028/www.scientific.net/amr.1010-1012.1419.
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The Structural and deformational features of fold-thrust belt in the north margin of Kashi，southern Tian Shan were disclosed based on various data such as two dimensional seismic profile and field geologic survey. The results show that the fold-thrustbelt can be divided into several rows of anticlines, includingKalaboketuoer-Wenguer, Tuopa-Kangxiweier, Atushi and Kashi on plane,and the development of Atushi anticlines and its north side was controlled by the activity of the thrust system originated along the middle Cambrian Awatage Group from north to south. The fold-thrust belt can be divided into two different spatial levels: the shallow tectonic is a large scale imbricate thrust system, the detachment surface is uplifted from Cambrian system to Neogene system; the deep structure is a buried duplex structure system, the fault in floor and fault in roof are located at gypsic horizon in Cambrian and Neogene systemrespectively. Based on structural deformation analyzing and balanced section technology, the distribution of each anticlinal belt and the structure style of the low and deep thrust systems are confirmed. In this area the distance is shortened by 32.64～49.1km from north to south since Pliocene with the scalage of 40.5%～50.51%，and its average crustal shortening rate is 9.11～13.71mm/a.
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Lacroix, S., and E. W. Sawyer. "An Archean fold-thrust belt in the northwestern Abitibi Greenstone Belt: structural and seismic evidence." Canadian Journal of Earth Sciences 32, no. 2 (February 1, 1995): 97–112. http://dx.doi.org/10.1139/e95-009.
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An integration of structural field data and Lithoprobe seismic reflection line 28 in the northwestern Abitibi Greenstone Belt (AGB) reveals a crustal-scale, south-to southwest-vergent thrusting event that developed "in sequence" above a shallowly (15°) north-dipping sole thrust at a mid-crustal level. Seismic reflector geometry above this décollement suggests a mid crust (6–20 km depth) dominated by low-angle thrusts with smooth trajectory ramps and culmination folds or antiformal stacks, similar to the structural style of neighbouring high-grade plutonic–gneissic (Opatica) and sedimentary (Pontiac) subprovinces. In contrast, low-to high-angle east–west-trending thrusts at the upper-crust greenstone belt level (6–9 km depth) are interpreted to be listric. They occur in two fault systems, the Chicobi and Taibi, that resemble "imbricate fan" systems. The contrasting structural geometry of the upper and mid crust is interpreted as variations in level through the thrust stack, and resembles Paleozoic mountain belts where the upper AGB would represent a ductile–brittle fold–thrust belt. However, the structural evolution of the AGB has been complicated by earlier intrusive–metamorphic contacts or set of thrusts beneath it, and (or) younger out-of-sequence thrusts with north-vergent backthrusts. Also, south-to southwest-vergent thrusts were reactivated, folded, and steepened during a younger dextral strike-slip event.
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YANG, KENN-MING, RUEY-JUIN RAU, HAO-YUN CHANG, CHING-YUN HSIEH, HSIN-HSIU TING, SHIUH-TSANN HUANG, JONG-CHANG WU, and YI-JIN TANG. "The role of basement-involved normal faults in the recent tectonics of western Taiwan." Geological Magazine 153, no. 5-6 (August 5, 2016): 1166–91. http://dx.doi.org/10.1017/s0016756816000637.
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AbstractIn the foreland area of western Taiwan, some of the pre-orogenic basement-involved normal faults were reactivated during the subsequent compressional tectonics. The main purpose of this paper is to investigate the role played by the pre-existing normal faults in the recent tectonics of western Taiwan. In NW Taiwan, reactivated normal faults with a strike-slip component have developed by linkage of reactivated single pre-existing normal faults in the foreland basin and acted as transverse structures for low-angle thrusts in the outer fold-and-thrust belt. In the later stage of their development, the transverse structures were thrusted and appear underneath the low-angle thrusts or became tear faults in the inner fold-and-thrust belt. In SW Taiwan, where the foreland basin is lacking normal fault reactivation, the pre-existing normal faults passively acted as ramp for the low-angle thrusts in the inner fold-and-thrust belt. Some of the active faults in western Taiwan may also be related to reactivated normal faults with right-lateral slip component. Some main earthquake shocks related to either strike-slip or thrust fault plane solution occurred on reactivated normal faults, implying a relationship between the pre-existing normal fault and the triggering of the recent major earthquakes. Along-strike contrast in structural style of normal fault reactivation gives rise to different characteristics of the deformation front for different parts of the foreland area in western Taiwan. Variations in the degree of normal fault reactivation also provide some insights into the way the crust embedding the pre-existing normal faults deformed in response to orogenic contraction.
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Lyu, Chengfu, Xixin Wang, Xuesong Lu, Qianshan Zhou, Ying Zhang, Zhaotong Sun, Liming Xiao, and Xin Liu. "Evaluation of Hydrocarbon Generation Using Structural and Thermal Modeling in the Thrust Belt of Kuqa Foreland Basin, NW China." Geofluids 2020 (December 18, 2020): 1–18. http://dx.doi.org/10.1155/2020/8894030.
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The Kuqa Basin is a typical foreland basin in northwest China, characterized by compressive foreland fold-and-thrust belts and a regionally distributed huge salt layer. A large number of overthrust faults, fault-related folds, and salt-related structures are formed on the thrust belt due to strong compression and structural deformation, causing difficulty in simulation of the basin. In this study, modeling of the thermal history of the complicated compressional structural profiles in the Kuqa foreland basin was successfully conducted based on the advanced “Block” function introduced by the IES PetroMod software and the latest geological interpretation results. In contrast to methods used in previous studies, our method comprehensively evaluates the influence of overthrusting, a large thick salt layer with low thermal conductivity, fast deposition, or denudation on the thermal evolution history. The results demonstrate that the hydrocarbon generation center of the Kuqa foreland basin is in the deep layers of the Kelasu thrust belt and not in the Baicheng Sag center, which is buried the deepest. A surprising result was drawn about the center of hydrocarbon generation in the Kuqa foreland basin, which, although not the deepest in Baicheng Sag, is the deepest part of the Kelasu thrust Belt. In terms of the maturity of the source rock, there are obvious temporal and spatial differences between the different structural belts in the Kuqa foreland basin, such as the early maturation of source rocks and the curbing of uplift and hydrocarbon generation in the piedmont zone. In the Kelasu thrust belt, the source rock made an early development into the low mature-mature stage and subsequently rapidly grew into a high-over mature stage. In contrast, the source rock was immature at an early stage and subsequently grew into a low mature-mature stage in the Baicheng Sag–South slope belt. The time sequence of the thermal evolution of source rocks and structural trap formation and their matching determines the different accumulation processes and oil and gas compositions in the different structural belts of the Kuqa foreland basin. The matching of the multistage tectonic activity and hydrocarbon generation determines the characteristics of the multistage oil and gas accumulation, with the late accumulation being dominant. The effective stacking of the gas generation center, subsalt structural traps, reservoir facies of fine quality, and huge, thick salt caprocks creates uniquely favorable geological conditions for gas enrichment in the Kelasu foreland thrust belt.
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NEBOT, MARINA, and JOAN GUIMERÀ. "Kinematic evolution of a fold-and-thrust belt developed during basin inversion: the Mesozoic Maestrat basin, E Iberian Chain." Geological Magazine 155, no. 3 (October 4, 2016): 630–40. http://dx.doi.org/10.1017/s001675681600090x.
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AbstractThe Maestrat basin was one of the most subsident basins of the Mesozoic Iberian Rift system, developed by a normal fault system which divided it into sub-basins. Its Cenozoic inversion generated the N-verging Portalrubio–Vandellòs fold-and-thrust belt in its northern margin, detached in the Triassic evaporites. In the hinterland, a 40 km wide uplifted area, in the N–S direction, developed, bounded to the N by the E–W-trending, N-verging Calders monocline. This monocline is interpreted as a fault-bend fold over the ramp to flat transition of the E–W-trending, N-verging Maestrat Basement Thrust, and also indicates the transition from a thick-skinned (S) to a thin-skinned (N) style of deformation. This paper presents a kinematic evolutionary model for the northern margin of the basin and a reconstruction of the Maestrat Basement Thrust geometry, generated by the inversion of the Mesozoic normal fault system. It contains a low-dip ramp (9°) extended southwards more than 40 km, attaining a depth of 7.5 km. As this thrust reached the Mesozoic cover to the foreland, it propagated across the Middle Muschelkalk evaporitic detachment, generating a nearly horizontal thrust which transported northwards the supra-salt cover, and the normal fault segments within it, for c. 11–13 km. The displacement of the basement in the hanging-wall of the low-dip basement ramp generated the 40 km wide uplifted area, while the superficial shortening was accumulated in the northern margin of the basin – which contains the thinnest Mesozoic cover – developing the Portalrubio–Vandellòs fold-and-thrust belt.
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Smeraglia, Luca, Nathan Looser, Olivier Fabbri, Flavien Choulet, Marcel Guillong, and Stefano M. Bernasconi. "U–Pb dating of middle Eocene–Pliocene multiple tectonic pulses in the Alpine foreland." Solid Earth 12, no. 11 (November 9, 2021): 2539–51. http://dx.doi.org/10.5194/se-12-2539-2021.
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Abstract. Foreland fold-and-thrust belts (FTBs) record long-lived tectono-sedimentary activity, from passive margin sedimentation, flexuring, and further evolution into wedge accretion ahead of an advancing orogen. Therefore, dating fault activity is fundamental for plate movement reconstruction, resource exploration, and earthquake hazard assessment. Here, we report U–Pb ages of syn-tectonic calcite mineralizations from four thrusts and three tear faults sampled at the regional scale across the Jura fold-and-thrust belt in the northwestern Alpine foreland (eastern France). Three regional tectonic phases are recognized in the middle Eocene–Pliocene interval: (1) pre-orogenic faulting at 48.4±1.5 and 44.7±2.6 Ma associated with the far-field effect of the Alpine or Pyrenean compression, (2) syn-orogenic thrusting at 11.4±1.1, 10.6±0.5, 9.7±1.4, 9.6±0.3, and 7.5±1.1 Ma associated with the formation of the Jura fold-and-thrust belt with possible in-sequence thrust propagation, and (3) syn-orogenic tear faulting at 10.5±0.4, 9.1±6.5, 5.7±4.7, and at 4.8±1.7 Ma including the reactivation of a pre-orogenic fault at 3.9±2.9 Ma. Previously unknown faulting events at 48.4±1.5 and 44.7±2.6 Ma predate the reported late Eocene age for tectonic activity onset in the Alpine foreland by ∼10 Myr. In addition, we date the previously inferred reactivation of pre-orogenic strike-slip faults as tear faults during Jura imbrication. The U–Pb ages document a minimal time frame for the evolution of the Jura FTB wedge by possible in-sequence thrust imbrication above the low-friction basal decollement consisting of evaporites.
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Hussain, Hamid, and Zhang Shuangxi. "Structural Evolution of the Kohat Fold and Thrust Belt in the Shakardarra Area (South Eastern Kohat, Pakistan)." Geosciences 8, no. 9 (August 21, 2018): 311. http://dx.doi.org/10.3390/geosciences8090311.
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The Kohat fold and thrust belt, located in North-Western Pakistan, is a part of Lesser Himalaya developed due to the collision between the Indian and Eurasian plates. The structural evolution records of this area indicate that it consists of tight anticlines and broad syncline structures. Previous studies show that the structural pattern of this area has been produced due to multiple episodes of deformation. In the present research, 2D seismic data has been integrated with our field surveys to clarify the role of active strike-slip faulting in reshaping the surface structures of Shakardarra, Kohat. At the surface, doubly plunging anticlines and synclines are evolved on evaporites as detachment folds, truncated by thrust faults along their limbs. Seismic data show that the thrust faults originate from basal detachment located at the sedimentary-crystalline interface and either cut up section to the surface or lose their displacement to splay or back thrusts. At the surface, the Shakardarra Fault, the Tola Bangi Khel Fault, the Chorlaki Fault, and the axial trend of fold change their strike from EW to NS showing that the thrust and axial trend of folds are rotated along the vertical axis by the influence of the Kalabagh strike-slip fault. Strike-slip motion dominates the style of deformation at the northern segment. The current deformation is concentrated on the splay faults in the northern segment of the Kalabagh Fault. We propose that Shakardarra is sequentially evolved in three episodes of deformation. In the first phase, the detachment folds developed on Eocene evaporites, which are truncated by thrust faults originated from the basal detachment in the second phase. In the third phase, early formed folds and faults are rotated along the vertical axis by the influence of Kalabagh strike-slip fault.
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Chandonia, William, and John Hogan. "The Kanarra fold-thrust structure—the leading edge of the Sevier fold-thrust belt, southwestern Utah:." Geology of the Intermountain West 10 (January 25, 2023): 1–64. http://dx.doi.org/10.31711/giw.v10.pp1-64.
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The multiple origins proposed for the Kanarra anticline in southwestern Utah as a drag-fold along the Hurricane fault, a Laramide monocline, a Sevier fault-propagation fold, or a combination of these processes, serve to muddy its tectonic significance. This in part reflects the structural complexity of the exposed eastern half of the fold. The fold evolved from open and up-right to overturned and tight, is cross-cut by multiple faults, and was subsequently dismembered by the Hurricane fault. The western half of the fold is obscured because of burial, along with the hanging wall of the Hurricane fault, beneath Neogene and younger sediments and volcanics. We present the results of detailed bedrock geologic mapping, and geologic cross sections restored to Late Cretaceous time (prior to Basin and Range extension), to demonstrate the Kanarra anticline is a compound anticline-syncline pair inextricably linked with concomitant thrust faulting that formed during the Sevier orogeny. We propose the name Kanarra fold-thrust structure to unambiguously identify the close spatial and temporal association of folding and thrusting in formation of this prominent geologic feature. We identify a previously unrecognized thrust, the Red Rock Trail thrust, as a forelimb shear thrust that was in a favorable orientation and position to have been soft-linked, and locally hard-linked, with the thrust ramp of the basal detachment to form a break thrust. The east verging Red Rock Trail thrust is recognized by a distinctive cataclasite in the Lower Jurassic Navajo Sandstone. The hanging wall of the Red Rock Trail thrust is displaced eastward over the Middle Jurassic Carmel Formation and Upper Cretaceous formations and can be traced for at least 27 km and possibly farther. We contend the Kanarra fold-thrust structure unambiguously defines the leading edge of the Sevier fold-thrust beltin southwestern Utah. Stratigraphic relationships in the southern and northern part of the Kanarra fold-thrust structure constrain its development between the early and late Campanian (about 84 to 71 Ma) but possibly younger. In southwestern Utah, initial movement along the Iron Springs thrust at about 100 Ma (Quick and others, 2020) and subsequent eastward advancement of the Sevier deformation front to the Red Rock Trail thrust at about 84 to 71 Ma coincided with well-documented magmatic flare ups in the Cordilleran arc in the hinterland of the Sevier fold-thrust belt. This temporal relationship between magmatic flare ups and thrusting is consistent with a close correspondence between arc-related processes and episodic foreland deformation.
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Lebinson, Fernando, Martín Turienzo, Natalia Sánchez, Vanesa Araujo, María Celeste D’Annunzio, and Luis Dimieri. "The structure of the northern Agrio fold and thrust belt (37°30’ S), Neuquén Basin, Argentina." Andean Geology 45, no. 2 (March 5, 2018): 249. http://dx.doi.org/10.5027/andgeov45n2-3049.
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The Agrio fold and thrust belt is a thick-skinned orogenic belt developed since Late Cretaceous in response to the convergence between the Nazca and South American plates. The integration of new structural field data and seismic line interpretation allowed us to create two balanced cross-sections, which help to analyse the geometry of both thick and thin-skinned structures, to calculate the tectonic shortenings and finally to discuss the main mechanisms that produced this fold and thrust belt. The predominantly NNW-SSE structures show varying wavelengths, and can be classified into kilometer-scale first order basement involved structures and smaller second, third and fourth order fault-related folds in cover rocks with shallower detachments. Thick-skinned structures comprise fault-bend folds moving into the sedimentary cover, mainly along Late Jurassic evaporites, which form basement wedges that transfer the deformation to the foreland. Thus, shortenings in both basement and cover rocks must be similar and consequently, by measuring the contraction accounted for thin-skinned structures, is possible to propose a suitable model for the thick skinned deformation. The balanced cross-sections indicate shortenings of 11.2 km (18%) for the northern section and 10.9 km (17.3%) for the southern section. These values are different from the shortenings established by previous works in the region, reflecting differences in the assumed model to explain the basement-involved structures. According to our interpretation, the structural evolution of this fold and thrust belt was controlled by major basement-involved thrust systems with subordinate influence of inversion along pre-existing normal faults during the Andean compression.
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Giorgadze, Anzor, Victor Alania, and Levan Gorgidze. "Structure of the Rioni Foreland Fold-and-thrust Belt: A Review." Works of Georgian Technical University, no. 2(524) (June 6, 2022): 56–65. http://dx.doi.org/10.36073/1512-0996-2022-2-56-65.
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The article presents an overview of the structural structure of the Rioni Forland Fold-and-thrust Belt. The structures are mainly represented by folds and duplexes associated with south-vergent faults. The synclines are overlaid by Middle Miocene-Pleistocene syntectonic sediments and are represented by piggy-back basins. Faultrelated folds are mainly represented by growing fault-propogation folds. The kinematic evolution of the Rioni Forland Basin in the Late Alpine period is related to the structural wedge (or duplexes) of the Caucasus foundation moving southwards, and its modern structure is represented by a thin-skinned fold-and-thrust belt.
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Cheng, Feng, Andrew V. Zuza, Peter J. Haproff, Chen Wu, Christina Neudorf, Hong Chang, Xiangzhong Li, and Bing Li. "Accommodation of India–Asia convergence via strike-slip faulting and block rotation in the Qilian Shan fold–thrust belt, northern margin of the Tibetan Plateau." Journal of the Geological Society 178, no. 3 (January 29, 2021): jgs2020–207. http://dx.doi.org/10.1144/jgs2020-207.
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Existing models of intracontinental deformation have focused on plate-like rigid body motion v. viscous-flow-like distributed deformation. To elucidate how plate convergence is accommodated by intracontinental strike-slip faulting and block rotation within a fold–thrust belt, we examine the Cenozoic structural framework of the central Qilian Shan of northeastern Tibet, where the NW-striking, right-slip Elashan and Riyueshan faults terminate at the WNW-striking, left-slip Haiyuan and Kunlun faults. Field- and satellite-based observations of discrete right-slip fault segments, releasing bends, horsetail termination splays and off-fault normal faulting suggest that the right-slip faults accommodate block rotation and distributed west–east crustal stretching between the Haiyuan and Kunlun faults. Luminescence dating of offset terrace risers along the Riyueshan fault yields a Quaternary slip rate of c. 1.1 mm a−1, which is similar to previous estimates. By integrating our results with regional deformation constraints, we propose that the pattern of Cenozoic deformation in northeastern Tibet is compatible with west–east crustal stretching/lateral displacement, non-rigid off-fault deformation and broad clockwise rotation and bookshelf faulting, which together accommodate NE–SW India–Asia convergence. In this model, the faults represent strain localization that approximates continuum deformation during regional clockwise lithospheric flow against the rigid Eurasian continent.Supplementary material: Luminescence dating procedures and protocols is available at https://doi.org/10.17605/OSF.IO/CR9MNThematic collection: This article is part of the Fold-and-thrust belts and associated basins collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts
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SAALMANN, K., and F. THIEDIG. "Thrust tectonics on Brøggerhalvøya and their relationship to the Tertiary West Spitsbergen Fold-and-Thrust Belt." Geological Magazine 139, no. 1 (January 2002): 47–72. http://dx.doi.org/10.1017/s0016756801006069.
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The Tertiary fold-and-thrust belt on Brøggerhalvøya is characterized by a NE-vergent pile of nine thrust sheets. The sole thrust of the pile is located in Precambrian phyllites and climbs up-section to the northeast. Four lower thrust sheets consisting predominantly of Upper Palaeozoic sediments are overlain by two thrust sheets in the central part of the stack which contain a kilometre-scale syncline and anticline. The fold is cut by juxtaposed thrusts giving rise to the formation of three structurally higher basement-dominated thrust sheets. A multiple-stage kinematic model is proposed including (1) in-sequence foreland-propagating formation of the lower thrust sheets in response to N–S subhorizontal bedding-parallel movements, (2) a change in tectonic transport to ENE and out-of-sequence thrusting and formation of the kilometre-scale fold-structure followed by (3) truncation of the kilometre-scale fold and stacking of the highest basement-dominated thrust sheets by hind-ward-propagating out-of-sequence thrusting. The strain of the thrust sheets is predominantly compressive with the exception of the structurally highest thrust sheets, reflecting a temporal change to a more transpressive regime. Thrusting was followed by (4) N–S extension and (5) W–E extension. Comparison of the structural geometry and kinematic evolution of Brøggerhalvøya with the data reported for the fold belt further south allows us to assume a coeval evolution with the fold belt. A latest Paleocene/Early Eocene age for the main phase of thrusting is suggested for the West Spitsbergen Fold-and-Thrust Belt; the main phases therefore pre-date the separation of Svalbard and Greenland due to right-lateral movements along the Hornsund Fault Zone. The fold belt's temporal evolution followed by the formation of the Forlandsundet Graben can be linked with the plate-kinematic framework in the span between latest Paleocene and Middle Eocene times.
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Shah, Syed Tallataf Hussain, Nangyal Ghani Khan, Muhammad Imran Hafeez Abbasi, Kamran Tabassum, and Syed Khaizer Wahab Shah. "The Mineralization and Structural Geology of the Porphyry Copper Deposits of Pakistan." Nepal Journal of Science and Technology 19, no. 2 (October 10, 2021): 130–36. http://dx.doi.org/10.3126/njst.v20i1.39449.
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The purpose of this review is to shed light on copper deposits found in different regions of Pakistan. The geological attributes of copper deposits have been considered with their tectonic context. The porphyry copper deposits can be traced in Pakistan from the north through Kohistan Island Arc (KIA) up to the south to Chaghi Magmatic Arc (CMA). These deposits are mainly found in and around the Late Tertiary–Early Tertiary Himalayan Belt, Kohistan magmatic arc, Karakorum Block Foreland fold and thrust belt, Ophiolite Thrust belt, Suture zone and Chaghi Magmatic Arc. These deposits in Pakistan are chiefly established in different episodes of tectonic regimes, including subduction processes, oceanic island arc, continental arc, along with Chaman- OrnachNal Fault system and post-collisional settings.
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Higgins, Simon, Richard J. Davies, and Benjamin Clarke. "Antithetic fault linkages in a deep water fold and thrust belt." Journal of Structural Geology 29, no. 12 (December 2007): 1900–1914. http://dx.doi.org/10.1016/j.jsg.2007.09.004.
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Savchuk, Yu S., and A. V. Volkov. "The Role of a Detachment Fault in the Spatial Distribution of Ore-Bearing Paleofluid Flows in the Central Kolyma Region: A Nonconventional Approach to Predictive Metallogenic Modeling." Geology of Ore Deposits 64, no. 4 (August 2022): 163–79. http://dx.doi.org/10.1134/s1075701522040055.
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Abstract— The Central Kolyma region is the main gold-bearing part of the Verkhoyansk–Kolyma fold-and-thrust belt. Analysis of the developed geodynamic models of fold and thrust belt formation mechanisms, the Verkhoyansk–Kolyma belt in particular, suggests the leading role of subhorizontal movements on the detachment zone (decollement) at the base of an orogen as the “sole,” on which nappes detached at an early stage and with which major reverse strike-slip listric faults were directly associated at the collisional stage. In our opinion, the role of a detachment fault, the most important regional structure, is obviously underestimated in predictive metallogenic models. The detachment fault zone is complicated by transverse NE-trending faults, where its thickness and the fluid permeability can occur. The paper proposes a variant that links previously discovered gold deposits and occurrences in five gold mineralization strips along the inferred paleofluid flow routes. Here, the paleofluid flow route is the horizontal projection of the most probable migration pathway of released fluids from their generation zone to the ore deposition zone, which is drawn across the largest ore accumulations.
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Charlesworth, H. A. K., S. T. Johnston, and L. G. Gagnon. "Evolution of the triangle zone in the Rocky Mountain Foothills near Coalspur, central Alberta." Canadian Journal of Earth Sciences 24, no. 8 (August 1, 1987): 1668–78. http://dx.doi.org/10.1139/e87-160.
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A triangle zone, which commonly occurs along the external margin of a foreland thrust and fold belt with a buried thrust front, is underlain by a subhorizontal, blind, foreland-verging thrust that ends against a foreland-dipping, hinterland-verging thrust. These contemporaneous thrusts, active towards the end of orogenesis, enclose an intercutaneous wedge that moved towards the foreland. During orogenesis, a triangle zone evolves through periodic replacement of faults bounding the active wedge. Replacements occur in cycles during each of which a lower fault tends to be replaced by one in a lower stratigraphic horizon, an upper fault by one farther away from the foreland. Each cycle ends with the lower fault moving to a younger horizon where it joins a new, more external upper fault.Near Coalspur, the triangle zone exposes the remnants of several wedges involving Upper Cretaceous and Paleocene molasse. Most of these wedges developed during the last cycle but one and have a combined displacement of about 5 km. Within this cycle, the younger the wedge, the older the strata at its extremity. The upper fault of each wedge cuts the lower fault of the preceding wedge. The upper fault of one of the wedges has a lateral ramp.
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Cao, Kai, Philippe Hervé Leloup, Guocan Wang, Wei Liu, Gweltaz Mahéo, Tianyi Shen, Yadong Xu, Philippe Sorrel, and Kexin Zhang. "Thrusting, exhumation, and basin fill on the western margin of the South China block during the India-Asia collision." GSA Bulletin 133, no. 1-2 (April 30, 2020): 74–90. http://dx.doi.org/10.1130/b35349.1.
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Abstract The pattern and timing of deformation in southeast Tibet resulting from the early stages of the India-Asia collision are crucial factors to understand the growth of the Tibetan Plateau, but they remain poorly constrained. Detailed field mapping, structural analysis, and geochronological and thermochronological data along a 120 km section of the Ludian-Zhonghejiang fold-and-thrust belt bounding the Jianchuan basin in western Yunnan, China, document the early Cenozoic tectonic evolution of the conjunction between the Lanping-Simao and South China blocks. The study area is cut by two major southwest-dipping brittle faults, named the Ludian-Zhonghejiang fault and the Tongdian fault from east to west. Numerous kinematic indicators and the juxtaposition of Triassic metasedimentary rocks on top of Paleocene strata indicate thrusting along the Ludian-Zhonghejiang fault. Similarly, structural analysis shows that the Tongdian fault is a reverse fault. Between these structures, fault-bounded Permian–Triassic and Paleocene rocks are strongly deformed by nearly vertical and upright southwest-vergent folds with axes that trend nearly parallel to the traces of the main faults. Zircon and apatite (U-Th)/He and apatite fission-track data from a Triassic pluton with zircon U-Pb ages of 237–225 Ma in the hanging wall of the Ludian-Zhonghejiang fault, assisted by inverse modeling, reveal two episodes of accelerated cooling during 125–110 Ma and 50–39 Ma. The Cretaceous cooling event was probably related to crustal thickening during the collision between the Lhasa and Qiangtang terranes. The accelerated exhumation during 50–39 Ma is interpreted to record the life span of the fold-and-thrust belt. This timing is corroborated by the intrusive relationship of Eocene magmas of ca. 36–35 Ma zircon U-Pb age into the fold-and-thrust belt. Early Cenozoic activity of the deformation system controlled deposition of alluvial-fan and braided-river sediments in the Jianchuan basin, as evidenced by eastward and northeastward paleoflows and terrestrial clasts derived from the hanging wall of the Ludian-Zhonghejiang thrust. Since 39 Ma, decreasing cooling rates likely reflect cessation of activity on the fold-and-thrust belt. Early Cenozoic compressive deformation on the western margin of the South China block together with geological records of contraction in central, northern, and eastern Tibet document Eocene upper-crustal shortening located in the Himalaya, Qiangtang terrane, and northern plateau margins together with contractional basin development in the intervening Lhasa, Songpan-Garze, and Kunlun terranes, coeval with or shortly after the onset of the India-Asia collision. This suggests that moderate crustal shortening affected a large part of Tibet in a spaced way, contrary to models of homogeneous crustal thickening soon after the collision, and prior to the main crustal thickening, propagating progressively from south to north. This complex deformation pattern illustrates the complexity of Asian crustal rheology, which contrasts with assumptions in existing geodynamic models.
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McMechan, M. E. "Walker Creek fault zone, central Rocky Mountains, British Columbia-southern continuation of the Northern Rocky Mountain Trench fault zone." Canadian Journal of Earth Sciences 37, no. 9 (September 1, 2000): 1259–73. http://dx.doi.org/10.1139/e00-038.
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Walker Creek fault zone (WCFZ), well exposed in the western Rocky Mountains of central British Columbia near 54°, comprises a 2 km wide zone of variably deformed Neoproterozoic and Cambrian strata in fault-bounded slivers and lozenges. Extensional shear bands, subhorizontal extension lineations, slickensides, mesoscopic shear bands, and other minor structures developed within and immediately adjacent to the fault zone consistently indicate right-lateral displacement. Offset stratigraphic changes in correlative Neoproterozoic strata indicate at least 60 km of right-lateral displacement across the zone. WCFZ is the southern continuation of the Northern Rocky Mountain Trench (NRMT) fault zone. It shows a through going, moderate displacement, strike-slip fault system structurally links the NRMT and the north-central part of the Southern Rocky Mountain Trench. Strike-slip motion on the WCFZ occurred in the Late Cretaceous to Early Eocene at the same time as northeast-directed shortening in the fold-and-thrust belt. Thus, oblique convergence in the eastern part of the south-central Canadian Cordillera was apparently resolved into parallel northwest-striking zones of strike-slip and thrust faulting during the Late Cretaceous to Early Eocene. The change in the net Late Cretaceous to Early Eocene displacement direction for rocks in the Rocky Mountain trenches from north (56-54°N) to northeast (52-49°N) suggests that the disappearance of strike-slip displacement and increase in fold-and-thrust belt shortening in the eastern Cordillera between 56° and 49°N is largely the result of a north-south change in relative plate motion or strain partitioning across the Cordillera, rather than the southward transformation of right-lateral strike-slip displacement on the Tintina - NRMT fault system into compressional deformation.
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Chen, Guihua, Xun Zeng, Zhongwu Li, and Xiwei Xu. "Active Faulting of Landforms along the Tuosuhu-Maoniushan Fault and Its Seismotectonic Implications in Eastern Qaidam Basin, China." Seismological Research Letters 93, no. 2A (January 12, 2022): 897–913. http://dx.doi.org/10.1785/0220210110.
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Abstract The fold-and-thrust belt along the northern margin of the Qaidam basin is a typical active tectonic belt located in the northeast Tibetan Plateau. This belt is at a high risk of strong earthquakes with magnitudes larger than 6, as shown by multiple recorded events during 1962–2009. The lack of detailed late Quaternary surficial faulting data and systematic seismotectonic studies has posed difficulties in properly assessing the seismic risks and understanding the ongoing geodynamics in this region. In this study, we mapped the geomorphic features and fault traces from high-resolution satellite images and field investigations of the Tuosuhu-Maoniushan fault (TMF). Field photogrammetry was conducted to obtain deformation measurements using a DJI M300 real-time kinematic (RTK) drone. The TMF displaces the Holocene and late Pleistocene alluvial terraces in the eastern Qaidam basin. This fault dips to the south in the west and central segments (as a boundary of the Denan depression) and to the north in the eastern segment along the piedmont of the Maoniushan Mountains. The vertical slip rate is estimated to be 0.37 ± 0.08 mm/yr, which is similar to that of the active southern Zongwulongshan fault. By integrating our investigations with the previously published studies on deep structures and Cenozoic geology of the region, we propose a deep-seated thrust model for the seismotectonics of the northern margin of the Qaidam basin. The Aimunike, Tuosuhu-Maoniushan, southern Zongwulongshan, and Zongwulong faults, along with many folds, form an active compressional zone. The complex across-strike structures and along-strike segmentation could facilitate the release of strain through earthquakes of magnitude 6–7 in this broad seismotectonics belt, rather than through strong surface-rupturing events resulting from a single mature large fault.
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Kastelic, Vanja, and Michele M. C. Carafa. "Fault slip rates for the active External Dinarides thrust-and-fold belt." Tectonics 31, no. 3 (June 2012): n/a. http://dx.doi.org/10.1029/2011tc003022.
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Khalili, Marzieh, and Yildirim Dilek. "The 9 April 2013 Kaki earthquake (Mw 6.3) in SW Iran occurred along a blind backthrust in the Fars geological province of the Zagros Fold and Thrust Belt." Geological Society, London, Special Publications 501, no. 1 (2021): 71–85. http://dx.doi.org/10.1144/sp501-2021-20.
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AbstractThe Zagros Fold and Thrust Belt (ZFTB) in southern Iran is a seismically active tectonic zone, where SW-vergent thrust faults and NW–SE- and NE–SW-oriented strike-slip fault systems accommodate crustal shortening, resulting from the active Arabia–Eurasia collision. The majority of earthquakes in Iran occur within the ZFTB, posing a major hazard for society. The 9 April 2013 Kaki Earthquake (Mw 6.3) in the southern part of the ZFTB took place along a fault that was previously unknown regarding its surface expression, geometry and kinematics. We have used surface–subsurface distributions and focal mechanism solutions of the Kaki Earthquake aftershocks to characterize the fault system responsible for the quake. Our results indicate that it was a NE-vergent thrust fault with a minor dextral component that slipped c. 7–17 km at depth, causing the Kaki Earthquake. There were no surface ruptures, although some surface fissures developed in fluvial terraces during the main shock. We interpret this fault as a blind backthrust, which probably represents a reactivated Mesozoic basement fault emanating from the Zagros detachment surface. An upper shallow décollement zone within the Miocene Gachsaran Salt facilitated its upward propagation on the back-limb of an overturned syncline.
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Ortner, Hugo, and Sinah Kilian. "Thrust tectonics in the Wetterstein and Mieming mountains, and a new tectonic subdivision of the Northern Calcareous Alps of Western Austria and Southern Germany." International Journal of Earth Sciences 111, no. 2 (November 20, 2021): 543–71. http://dx.doi.org/10.1007/s00531-021-02128-3.
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AbstractWe investigate the tectonic evolution of the Wetterstein and Mieming mountains in the western Northern Calcareous Alps (NCA) of the European Eastern Alps. In-sequence NW-directed stacking of thrust sheets in this thin-skinned foreland thrust belt lasted from the Hauterivian to the Cenomanian. In the more internal NCA major E-striking intracontinental transform faults dissected the thrust belt at the Albian–Cenomanian boundary that facilitated ascent of mantle melts feeding basanitic dykes and sills. Afterwards, the NCA basement was subducted, and the NCA were transported piggy-back across the tectonically deeper Penninic units. This process was accompanied by renewed Late Cretaceous NW-directed thrusting, and folding of thrusts. During Paleogene collision, N(NE)-directed out-of-sequence thrusts developed that offset the in-sequence thrust. We use this latter observation to revise the existing tectonic subdivision of the western NCA, in which these out-of-sequence thrusts had been used to delimit nappes, locally with young-on-old contacts at the base. We define new units that represent thrust sheets having exclusively old-on-young contacts at their base. Two large thrust sheets build the western NCA: (1) the tectonically deeper Tannheim thrust sheet and (2) the tectonically higher Karwendel thrust sheet. West of the Wetterstein and Mieming mountains, the Imst part of the Karwendel thrust sheet is stacked by an out-of-sequence thrust onto the main body of the Karwendel thrust sheet, which is, in its southeastern part, in lateral contact with the latter across a tear fault.
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Jiao, L., and N. V. Koronovsky. "Geological background of the 12 May 2008 Wenchuan catastrophic earthquake (Longmen Shan, Western China)." Moscow University Bulletin. Series 4. Geology, no. 6 (December 28, 2016): 37–45. http://dx.doi.org/10.33623/0579-9406-2016-6-37-45.
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Longmen Shan fault zone is located in the special joint between the Triassic Songpan-Ganzi orogen of the Qinghai-Tibetan Plateau and the stable Sichuan basin of the Yangtze platform. In this region there are four major active faults and three tectonic nappes. According to the analysis of neotectonics and historical earthquakes the Longmen Shan fault zone is a dangerous earthquake belt. The rupture system of the Wenchuan earthquake is characterized by thrust and dextral strike-slip movement.
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Wennberg, Ole Petter, Arild Andresen, Sigurd Hansen, and Steffen G. Bergh. "Structural evolution of a frontal ramp section of the West Spitsbergen, Tertiary fold and thrust belt, north of Isfjorden, Spitsbergen." Geological Magazine 131, no. 1 (January 1994): 67–80. http://dx.doi.org/10.1017/s0016756800010505.
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AbstractThe geometry and kinematic evolution of a frontal ramp section associated with the Tertiary West Spitsbergen Orogenic Belt has been investigated in a small area (Lappdalen) north of Isfjorden. The previously recognized thrust front corresponds to a complex step or ramp in the position of the sole-thrust in the area. The sole-thrust is localized to the evaporites of the Permian Gipshuken Formation to the west of the footwall ramp, whereas to the east it continues as a bedding-parallel thrust in Triassic shales (Sassendalen Group). The area to the west of the footwall ramp is characterized by large scale thrusts and folds involving the Permian Gipshuken and Kapp Starostin formations and the lower part of the Triassic Sassendalen Group. East of the footwall ramp both Permian and Triassic strata are sub-horizontal and apparently undeformed. Three major thrust sheets are recognized. Based on the geometric relationship between folds and faults in the area, both fault-bend and fault-propogation mechanisms of folding are inferred. Restoration of the Kapp Starostin Formation to its pre-deformational state indicates a minimum of 35% shortening. Structural observations within the Sassendalen Group in the study area and on Dickson Land suggest that some of this shortening is transmitted eastwards along one or more bedding parallel thrusts in the Sassendalen Group.
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MacDonald, Justin, Guillaume Backé, Rosalind King, and Richard Hillis. "The Hammerhead Delta—deepwater fold-thrust belt, Bight Basin, Australia: 2D kinematic and geomechanical reconstructions." APPEA Journal 51, no. 2 (2011): 739. http://dx.doi.org/10.1071/aj10119.
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The Hammerhead Delta—deepwater fold-thrust belt is located in the Ceduna Sub-basin of the Bight Basin, offshore southern Australia. It is a short lived gravity gliding system, Late Santonian-Maastrichtian in age. It exhibits a distinctive spoon shape in cross-section and detaches on a master horizon above Santonian marine shales of the Tiger Supersequence. Here, we have interpreted a large seismic dataset—including the recently acquired regional two-dimensional seismic dataset provided by Ion Geophysical—to constrain the regional structural geometry of the Hammerhead Delta—deepwater fold-thrust belt. Two structural restorations were completed to quantify the amount of extension and shortening in the system. These restorations were: a two-dimensional kinematic restoration, using 2D MOVE; and a two-dimensional geomechanical restoration, using Dynel 2D. By comparing results from the two techniques we demonstrate that the amount of observed extension in the delta top is nearly balanced by the shortening in the delta toe. The near balance (< 2 % excess extension) of the system is a unique result. Other passive margin systems demonstrate larger amounts of extension compared to shortening, due to the regional-scale pro-gradational nature of the systems. These results suggest that the balanced geometry of the Hammerhead Delta—deepwater fold-thrust belt is consistent with either a sudden decrease in sediment supply during the upper Maastrichtian, resulting in a cessation of prograding fault activity, or a loss of extension to the underlying Cenomanian growth faults or some combination thereof. Thus, the system failed to develop into an extensive passive margin delta—deepwater fold-thrust belt.
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Di Fiori, Russell V., Sean P. Long, Anne C. Fetrow, Kathryn E. Snell, Joshua W. Bonde, and Jeff Vervoort. "Syncontractional deposition of the Cretaceous Newark Canyon Formation, Diamond Mountains, Nevada: Implications for strain partitioning within the U.S. Cordillera." Geosphere 16, no. 2 (January 6, 2020): 546–66. http://dx.doi.org/10.1130/ges02168.1.
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Abstract The timing of deformation and deposition within syntectonic basins provides critical information for understanding the evolution of strain in mountain belts. In the U.S. Cordillera, contractional deformation was partitioned between the Sevier thrust belt in Utah and several structural provinces in the hinterland in Nevada. One hinterland province, the Central Nevada thrust belt (CNTB), accommodated up to ∼15 km of shortening; however, in most places, this deformation can only be bracketed between Permian and Eocene. Cretaceous deposits of the Newark Canyon Formation (NCF), which are sparsely exposed along the length of the CNTB, offer the opportunity to constrain deformation timing. Here, we present mapping and U-Pb zircon geochronology from the NCF in the Diamond Mountains, which demonstrate deposition of the NCF during proximal CNTB deformation. Deposition of the basal NCF member was under way no earlier than ca. 114 Ma, a tuff in the middle part of the section was deposited at ca. 103 Ma, and the youngest member was deposited no earlier than ca. 99 Ma. Intraformational angular unconformities and abrupt along- and across-strike thickness changes indicate that NCF deposition was related to growth of an east-vergent fault-propagation fold. Clast compositions define unroofing of upper Paleozoic sedimentary rocks, which we interpret as the progressive erosion of an anticline ∼10 km to the west. CNTB deformation was contemporaneous with shortening in the Sevier thrust belt, which defines middle Cretaceous strain partitioning between frontal and interior components of the Cordillera. Strain partitioning may have been promoted by renewed underthrusting during a period of high-flux magmatism.
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Falcucci, Emanuela, Maria Eliana Poli, Fabrizio Galadini, Giancarlo Scardia, Giovanni Paiero, and Adriano Zanferrari. "First evidence of active transpressive surface faulting at the front of the eastern Southern Alps, northeastern Italy: insight on the 1511 earthquake seismotectonics." Solid Earth 9, no. 4 (July 18, 2018): 911–22. http://dx.doi.org/10.5194/se-9-911-2018.
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Abstract. We investigated the eastern corner of northeastern Italy, where a system of NW–SE-trending dextral strike-slip faults of western Slovenia intersects the south-verging fold and thrust belt of the eastern Southern Alps. The area suffered the largest earthquakes of the region, among which are the 1511 (Mw 6.3) event and the two major shocks of the 1976 seismic sequence, with Mw = 6.4 and 6.1. The Colle Villano thrust and the Borgo Faris–Cividale strike-slip fault have been here first analyzed by interpreting industrial seismic lines and then by performing morphotectonic and paleoseismological analyses. These different datasets indicate that the two structures define an active, coherent transpressive fault system that was activated twice in the past two millennia, with the last event occurring around the 15th–17th century. The chronological information and the location of the investigated fault system suggest its activation during the 1511 earthquake.
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Chamlagain, D., and D. Hayashi. "Numerical simulation of fault development in fold-and-thrust belt of Nepal Himalaya." Himalayan Journal of Sciences 2, no. 4 (January 29, 2008): 111. http://dx.doi.org/10.3126/hjs.v2i4.821.
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Erslev, Eric A., and Kyle R. Mayborn. "Multiple geometries and modes of fault-propagation folding in the Canadian thrust belt." Journal of Structural Geology 19, no. 3-4 (March 1997): 321–35. http://dx.doi.org/10.1016/s0191-8141(97)83027-1.
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Bombolakis, E. G. "Thrust fault mechanics and dynamics during a developmental stage of a foreland belt." Journal of Structural Geology 11, no. 4 (January 1989): 439–55. http://dx.doi.org/10.1016/0191-8141(89)90021-7.
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Jensen, S. M. "Lead isotope signatures of mineralised rocks in the Caledonian fold belt of North-East Greenland." Rapport Grønlands Geologiske Undersøgelse 162 (January 1, 1994): 169–76. http://dx.doi.org/10.34194/rapggu.v162.8259.
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Lead isotope analyses of samples with small accumulations of metals and incompatible elements from the Precambrian gneisses of North-East Greenland indicate that mineralisation mostly involved remobilisation of metals from local host rocks. Source ages of Iead fall in three groups: (I) 1700–2400 Ma for Lower Proterozoic skarns, Caledonian sulphide-bearing pegmatites and quartz veins, and post-Jurassic pyrite-mineralised fault breccias; (2) 900–1000 Ma for Caledonian shear zones and Caledonian(?) skarns in Middle-Late Proterozoic rocks; and (3) ~400 Ma for Caledonian thrust zones with associated relative uranium enrichment along thrust planes.
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Quick, J. Daniel, John P. Hogan, Michael Wizevich, Jonathan Obrist-Farner, and James L. Crowley. "Timing of deformation along the Iron Springs thrust, southern Sevier fold-and-thrust belt, Utah: Evidence for an extensive thrusting event in the mid-Cretaceous." Rocky Mountain Geology 55, no. 2 (December 1, 2020): 75–89. http://dx.doi.org/10.24872/rmgjournal.55.2.75.
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ABSTRACT The temporal and spatial distribution of strain associated with the Sevier orogeny in western North America is significantly different in the southern end of the belt, at the latitude of Las Vegas, Nevada, than farther to the north at the latitude of Salt Lake City, Utah. Reasons for these differences have been speculative as a lack of temporal constraints on thrusting in the intervening region hindered along-strike correlation across the belt. We determined a crystallization age of 100.18 ± 0.04 Ma for zircons extracted from a recently recognized dacite lapilli ash-fall tuff near the base of the synorogenic Iron Springs Formation. We propose the name “Three Peaks Tuff Member” for this unit, and identify a type stratigraphic section on the western flank of the “Three Peaks,” a topographic landmark in Iron County, Utah. Field relationships and this age constrain movement on the Iron Springs thrust and the end of the sub-Cretaceous unconformity in the critical intervening area to latest Albian/earliest Cenomanian. Movement on the Iron Springs thrust was synchronous with movement on multiple Sevier thrusts at ~100 Ma, indicating that the mid-Cretaceous was a period of extensive thrust-fault movement. This mid-Cretaceous thrusting event coincided with a period of global plate reorganization and increased convergence, and hence an increased subduction rate for the Farallon Plate beneath North America. The accelerated subduction contributed to a Cordilleran arc flare-up event and steepening of the orogenic wedge, which triggered widespread thrusting across the retroarc Sevier deformation belts. Additionally, based on temporal constraints and the strong spatial connection of mid-Cretaceous thrusts to lineaments interpreted as pre-orogenic transform faults, we suggest that temporal and spatial variations along the strike of the orogenic belt reflect tectonic inheritance of basement structures associated with the edge of the rifted Precambrian craton.
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Höy, Trygve, and P. van der Heyden. "Geochemistry, geochronology, and tectonic implications of two quartz monzonite intrusions, Purcell Mountains, southeastern British Columbia." Canadian Journal of Earth Sciences 25, no. 1 (January 1, 1988): 106–15. http://dx.doi.org/10.1139/e88-011.
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The Reade Lake and Kiakho stocks are posttectonic mesozonal quartz monzonite porphyries that intrude dominantly Middle Proterozoic Purcell Supergroup rocks in southeastern British Columbia. K–Ar dates of hornblende from the Reade Lake stock range from 103 to 143 Ma. However, a U–Pb date of 94 Ma from zircon concentrates is interpreted to be the age of emplacement of the stock, suggesting the range and older K–Ar dates are due to excess 40Ar. A K–Ar date of 122 Ma for the hornblende from the Kiakho stock is believed to be a more reliable intrusive age.Both stocks cut across and apparently seal two faults that have played roles in the tectonic evolution of the Purcell anticlinorium and Rocky Mountain thrust belt. The Reade Lake stock cuts the St. Mary fault, an east-trending reverse thrust that crosses the Rocky Mountain trench and links with thrusts in the Rocky Mountains; the Kiakho stock cuts the Cranbrook fault, an older east-trending normal fault. Hence, the 94 Ma date on the Reade Lake stock constrains the latest movement on the St. Mary fault to early Late Cretaceous; and the 122 Ma date on the Kiakho stock appears to limit latest movement on the Cranbrook fault to Early Cretaceous. These faults and the intrusions are part of an allochthonous package, displaced eastward by underlying thrust faults during formation of the Purcell anticlinorium and more eastern thrusts in the Rocky Mountains.
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Florez-Niño, Juan-Mauricio, Atilla Aydin, Gary Mavko, Marco Antonellini, and Asterio Ayaviri. "Fault and fracture systems in a fold and thrust belt: An example from Bolivia." AAPG Bulletin 89, no. 4 (April 2005): 471–93. http://dx.doi.org/10.1306/11120404032.
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Verwater, Vincent F., Eline Le Breton, Mark R. Handy, Vincenzo Picotti, Azam Jozi Najafabadi, and Christian Haberland. "Neogene kinematics of the Giudicarie Belt and eastern Southern Alpine orogenic front (northern Italy)." Solid Earth 12, no. 6 (June 15, 2021): 1309–34. http://dx.doi.org/10.5194/se-12-1309-2021.
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Abstract. Neogene indentation of the Adriatic plate into Europe led to major modifications of the Alpine orogenic structures and style of deformation in the Eastern and Southern Alps. The Giudicarie Belt is a prime example of this, as it offsets the entire Alpine orogenic edifice; its activity has been kinematically linked to strike-slip faulting and lateral extrusion of the Eastern Alps. Remaining questions on the exact role of this fold-and-thrust belt in the structure of the Alpine orogen at depth necessitate a quantitative analysis of the shortening, kinematics, and depth of decoupling beneath the Giudicarie Belt and adjacent parts of the Southern Alps. Tectonic balancing of a network of seven cross sections through the Giudicarie Belt parallel to the local NNW–SSE shortening direction reveals that this belt comprises two kinematic domains that accommodated different amounts of shortening during overlapping times. These two domains are separated by the NW–SE-oriented strike-slip Trento-Cles–Schio-Vicenza fault system, which offsets the Southern Alpine orogenic front in the south and merges with the Northern Giudicarie Fault in the north. The SW kinematic domain (Val Trompia sector) accommodated at least ∼ 18 km of Late Oligocene to Early Miocene shortening. Since the Middle Miocene, this domain experienced at least ∼ 12–22 km shortening, whereas the NE kinematic domain accommodated at least ∼ 25–35 km shortening. Together, these domains contributed an estimated minimum of ∼ 40–47 km of sinistral strike-slip motion along the Northern Giudicarie Fault, implying that most offset of the Periadriatic Fault is due to Late Oligocene to Neogene indentation of the Adriatic plate into the Eastern Alps. Moreover, the faults linking the Giudicarie Belt with the Northern Giudicarie Fault reach ∼ 15–20 km depth, indicating a thick-skinned tectonic style of deformation. These fault detachments may also connect at depth with a lower crustal Adriatic wedge that protruded north of the Periadriatic Fault and are responsible for N–S shortening and eastward, orogen-parallel escape of deeply exhumed units in the Tauern Window. Finally, the E–W lateral variation of shortening across the Giudicarie Belt indicates internal deformation and lateral variation in strength of the Adriatic indenter related to Permian–Mesozoic tectonic structures and paleogeographic zones.
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Zhazhlayi, Paiwast, and Ali Surdashy. "Neo-Tectonism and Quantitative Morphotectonic Analysis of Roste Valley at Imbricated-Suture Zones, Kurdistan Region, Iraq." Iraqi Geological Journal 55, no. 2E (November 30, 2022): 35–58. http://dx.doi.org/10.46717/igj.55.2e.3ms-2022-11-17.
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The morphotectonic analysis was done of the Roste valley, within the Imbricated and Suture zone of the Zagros Fold,Thrust Belt. The formations of the Imbricate Zone are of Jurassic and Cretaceous ages and the Suture Zone is covered by Zagros nappes of the Tertiary period. The Zagros Fold-Thrust Belt passes through several stages and tectonic phases. During the last stage of the Zagros Fold-Thrust Belt development from the Savian to Valahian and Pasadenian tectonic phases, the study area is influenced by active tectonic activity which is reflected by geomorphic properties in each subbasin. The migration of the Roste stream across oblique fault leaves 7 levels of the river terraces which are also signs of Neotectonics. The study area is divided into 18 subbasins for the morphotectonic analysis through applying geomorphic indices (HI, SL, Vf, Af, Smf, and Bs) and accordingly the index of relative active tectonics was indicted. The morphotectonic study reveals that the index of relative active tectonics is higher in the Suture Zone than in the Imbricated Zone. The index of relative active tectonics of the Suture Zone’s subbasins ranges from high to very high neotectonics activity (1.67-1.17), whereas of the Imbricate Zone’s subbasins ranges from medium to high active tectonic activity (2.33-1.67). The results are related to morphotectonic indices that show the balance between the tectonic and erosion process.
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Azmi, Azrin, Norasiah Sulaiman, Muhammad Ashahadi Dzulkafli, and Zaiton Harun. "Transpressional Deformation Of Bukit C, Guar Sanai: Lithostratigraphic Implication." Bulletin Of The Geological Society Of Malaysia 70, no. 1 (November 30, 2020): 77–86. http://dx.doi.org/10.7186/bgsm70202006.
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The upper part of the Setul Formation and the lower part of the Kubang Pasu Formation are well exposed in Guar Sanai, Perlis due to the earth quarry activities. However, compared to the Hill A and Hill B, the outcrops in Hill C clearly illustrates the influence of structure on the lithostratigraphy of the area. The boundary between the Setul Formation and the Kubang Pasu Formation is marked by the thrust fault generally trending north-south to northeast-southwest and mylonite. The thrust belt associated with folding and uplift clearly developed in the zone between parallel lateral faults (trending north-south and southeast-northwest) and is interpreted to accommodate slip along the transpression zone. The sinistral faults are then deformed by transpression movement of dextral faults (trending east-southwest and east-west) which amplified the earlier structures. The combination of lateral and thrust movements formed flower structure that associated with folding and uplift, commonly found in transpressional zone of the strike-slip region. Deformation has caused the older Setul Formation being uplifted to almost equivalent position to the younger Kubang Pasu Formation and led to the displacement of original bed position and repetition of similar sequences. The formation of folding and reverse faulting associated with left lateral strike-slip fault are interpreted to cause by movement of major fault in the northwest Peninsular Malaysia, known as the Bok Bak Fault.
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Yaghoubi, Ali, SeyedBijan Mahbaz, Maurice B. Dusseault, and Yuri Leonenko. "Seismicity and the State of Stress in the Dezful Embayment, Zagros Fold and Thrust Belt." Geosciences 11, no. 6 (June 12, 2021): 254. http://dx.doi.org/10.3390/geosciences11060254.
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This study focuses on determining the orientation and constraining the magnitude of present-day stresses in the Dezful Embayment in Iran’s Zagros Fold and Thrust Belt. Two datasets are used: the first includes petrophysical data from 25 wells (3 to 4 km deep), and the second contains 108 earthquake focal mechanisms, mostly occurring in blind active basement faults (5 to 20 km deep). Formal stress inversion analysis of the focal mechanisms demonstrates that there is currently a compressional stress state (Aφ=2.0–2.2) in the basement. The seismologically determined SHmax direction is 37° ± 10°, nearly perpendicular to the strike of most faults in the region. However, borehole geomechanics analysis using rock strength and drilling evidence leads to the counterintuitive result that the shallow state of stress is a normal/strike-slip regime. These results are consistent with the low seismicity level in the sedimentary cover in the Dezful Embayment, and may be evidence of stress decoupling due to the existence of salt layers. The stress state situation in the field was used to identify the optimally oriented fault planes and the fault friction coefficient. This finding also aligns with the prediction Coulomb faulting theory in that the N-S strike-slip basement Kazerun Fault System has an unfavorable orientation for slip in a reverse fault regime with an average SW-NE SHmax orientation. These results are useful for determining the origin of seismic activity in the basin and better assessing fault-associated seismic hazards in the area.
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Umhoefer, Paul J., Margaret E. Rusmore, and G. J. Woodsworth. "Contrasting tectono-stratigraphy and structure in the Coast Belt near Chilko Lake, British Columbia: unrelated terranes or an arc – back-arc transect?" Canadian Journal of Earth Sciences 31, no. 11 (November 1, 1994): 1700–1713. http://dx.doi.org/10.1139/e94-152.
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Stratigraphy and structural styles vary greatly in two areas of the Coast Belt near Chilko Lake (Chilcotin Ranges in the east and Coast Mountains in the west). No definite continuity between the two belts has been established in the pre-mid-Cretaceous geology, but this area may be a long-lived, episodic magmatic arc and nearby arc-related basin. The stratigraphic contrasts may reflect inherent differences between an arc and related basinal sequence. Triassic volcanic-arc sequences are part of the Stikine (western belt) and Cadwallader (eastern belt) terranes, which may be part of the same arc. The Jurassic is represented by one dated pluton in the west compared with almost continuous deposition of volcanogenic clastic rocks in the east. Lower Cretaceous sequences in the west and east may represent a volcanic arc and back-arc basin. The Taylor Creek Group (Albian) is the first definitive link between the two belts and represents an arc and intra-arc or back-arc basin. The structural evolution of the two belts also differs significantly. The early Late Cretaceous Eastern Waddington thrust belt comprises all major structures in the west, but only has minor expression in the east. Most of the structures in the east are part of the latest Cretaceous(?) to early Tertiary dextral-strike-slip, Yalakom fault system. These differences were most likely caused by the Late Cretaceous change from nearly orthogonal subduction to a dextral-oblique convergent margin.
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Jaiswal, Priyank, Colin A. Zelt, Rahul Dasgupta, and Kulendra K. Nath. "Seismic imaging of the Naga thrust using multiscale waveform inversion." GEOPHYSICS 74, no. 6 (November 2009): WCC129—WCC140. http://dx.doi.org/10.1190/1.3158602.
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This case study images the structural features related to the Naga thrust fault (northeast India) using a combination of multiscale waveform inversion and prestack depth migration (PSDM). The waveform model and the PSDM image complement each other: the former provides a physical-property map (P-wave velocity model) and the latter provides a structural image. The velocity model encompassing the starting model for waveform inversion is constructed using joint inversion of first and reflected traveltimes. The [Formula: see text] data are inverted consecutively in [Formula: see text] bandwidths to yield the final waveform model, which in turn is used for PSDM. The PSDM image and the waveform model are consistent with the lithological interpretation of an inline exploratory well. When interpreted jointly, the PSDM image and the waveform model reveal the presence of a conjugate fault system in the Naga thrust and fold belt.
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Ray, G. E. "The Hozameen fault system and related Coquihalla serpentine belt of southwestern British Columbia." Canadian Journal of Earth Sciences 23, no. 7 (July 1, 1986): 1022–41. http://dx.doi.org/10.1139/e86-103.
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The Hozameen Fault of southwestern British Columbia is associated with the Coquihalla serpentine belt and separates two distinct crustal units. Northeast of the fault are greenstones of the Early Triassic (?) Spider Peak Formation, which are unconformably overlain by Jurassic to Cretaceous turbidite and successor basin deposits of the Pasayten Trough. The oldest sedimentary rocks in the trough, the Ladner Group, contain a locally developed basal unit that hosts the Carolin mine gold orebody. Southwest of the fault, the Permian to Jurassic Hozameen Group represents a dismembered ophiolite succession comprising ultramafic rocks of the Petch Creek serpentine belt, overlain in turn by greenstone and chert units. The greenstones in the Hozameen Group and the Spider Peak Formation are geochemically distinguishable; the latter represent sodic, ocean-floor, subalkaline basalts formed in a spreading ridge environment, while the former include both arc tholeiites and oceanic island–seamount subalkaline basalts.Farther west, the major Petch Creek Fault separates the Hozameen Group from the Custer–Skagit Gneiss. This fault is locally associated with the Petch Creek serpentine belt and is considered to be a northern extension of the Ross Lake Fault of Washington State.The rocks in the Hozameen Group, Spider Peak Formation, and Pasayten Trough were probably deposited within a single basin that initiated as an extensive, multirifted, marginal back-arc basin and eventually evolved into the steadily narrowing Pasayten Trough.Following Early to Middle Cretaceous closure of the Pasayten Trough, oblique, easterly-directed movement along westerly-dipping thrusts caused the Custer–Skagit Gneiss to override the Hozameen Group, which in turn overrode rocks of the Pasayten Trough farther east; these boundary thrusts formed precursor structures for the Hozameen and Petch Creek faults. Ultramafic basement material underlying the Spider Peak Formation and the Hozameen Group was thrust up the bounding fractures, producing the Coquihalla and Petch Creek serpentine belts, respectively.Large-scale dextral transcurrent displacement, possibly related to movement along the Fraser Fault system, occurred subsequently along the Petch Creek and Hozameen faults. This wrench movement was preceded by the Mid-Eocene (?) intrusion of the Needle Peak pluton and was followed by emplacement of the 16–35 Ma Chilliwack batholith.