The Guanxian-Anxian fault zone in the Longmen Shan, Sichuan, China, exhibits long-term creep-slip but ruptured during the 2008 Wenchuan earthquake, challenging the view that creeping faults rarely generate strong earthquakes. To investigate the transition from creep-slip to stick-slip, we analyzed fault rocks from the WFSD-3, using microstructural observations, XRD, mu XRF, Raman spectroscopy, and quartz grain size statistics. Fault rocks show intense foliation, pressure-solution structures, and abundant clay minerals, reflecting long-term aseismic creep. At the interface between black and gray fault gouges at similar to 1249.98 m, microstructures indicate stick-slip behavior, including truncated grains, angular fragments, and finer grain sizes. Here, clay content drops sharply while strong minerals (quartz, feldspar, calcite, dolomite) increase. Elemental mapping shows Al and K enriched in black gouge, whereas Ca and Si in gray gouge; Raman spectroscopy indicates possible graphitization; the finest quartz grains occur in black gouge. These features mark co-seismic principal slip zone of the Wenchuan earthquake. We propose that fluid-driven transformation of strong minerals into clays facilitates creep-slip, whereas localized precipitation of strong minerals strengthens the fault, causing stress accumulation and controlling the creep-slip to stick-slip transition. This mechanism has implications for reassessing seismic hazards of creeping faults.

Abstract The Yingxiu–Beichuan Fault Zone (YBFZ), located in the Longmen Shan Thrust Belt (LSTB) on the eastern Tibetan Plateau, is highly seismically active. However, direct evidence of large earthquakes at depth is scarce. Here, we present rock magnetic, microstructural, and geochemical analyses of four fault zones from the Wenchuan Earthquake Fault Scientific Drilling borehole 2. Results show that fault gouges have high magnetic susceptibility, contain neoformed magnetite and monoclinic pyrrhotite, providing direct evidence for repeated large earthquakes with frictional heating temperatures of ∼500–900°C at depth. These earthquakes occurred in a reducing, sulfide‐bearing fluid environment throughout the seismic cycle. The increasing abundance of neoformed ferromagnetic minerals with depth could be related to more recent large earthquakes propagating at greater depths, supporting a structural model of vertical stacking and eastward propagation of the LSTB. This study provides key constraints on the deep seismic history and tectonic evolution of the LSTB.

The Yingxiu-Beichuan fault zone (YBFZ) has long been active and experienced repeated large earthquakes. The physicochemical properties of the deep fault zone (>1000 m) are the key to understanding the deformation mechanism of large earthquakes. This study uses rock magnetic, microstructural, and geochemical analyses of representative samples exposed in FZ1681 within the Wenchuan Earthquake Fault Scientific Drilling borehole 2 (WFSD-2) cores. Fault gouge and fault breccia have higher magnetic susceptibility values than wall rocks, and they contain abundant paramagnetic minerals and small quantities of magnetite and monoclinic pyrrhotite. The magnetite and monoclinic pyrrhotite in the fault gouge were mainly formed by coseismic frictional heating, indicating that large earthquakes with frictional heating temperatures of similar to 500-900 degrees C once occurred in the YBFZ. The seismogenic and coseismic environment was reducing with a relatively high sulfur content. The monoclinic pyrrhotite in the fault breccia was formed mainly by low-temperature hydrothermal fluid. This indicates that the fault zone experienced reducing and low-temperature (<400 degrees C) hydrothermal fluid with a relatively high sulfur content after the earthquake. The YBFZ, which experiences frequent large earthquakes, is weakly oxidizing environment at different depths, but the effect of the low-temperature hydrothermal fluid is weaker at depth.

Quantifying late Cenozoic extension in central Tibet is critical to models of the tectonic evolution of the Tibetan Plateau. A series of similar to NS-trending grabens in this region preserve important records of extensional deformation. Constraining their geometry and kinematics is essential for understanding the Cenozoic tectonic history of the plateau. In this study, we focus on the Yibug Caka graben (YCG), the most prominent graben system within the Qiangtang terrane, central Tibet. Using high-resolution satellite imagery, field investigations, and cosmogenic Be-10 dating (n = 16), we analyze the tectonic and geomorphic characteristics of the YCG to determine the late Quaternary throw rates of the normal faults bounding this graben. UAV surveys reveal vertical offsets of similar to 10 to 21 m on alluvial fans dated to similar to 100 and similar to 200 ka, yielding minimum throw and extension rates of similar to 0.08 and similar to 0.07 mm/yr, respectively. These rates are the first well-dated, late Quaternary constraints for the YCG, and indicate that extensional deformation in central Tibet is distributed on widespread normal and strike-slip faults, hence with significantly lower extension rates than those in southern Tibet. This difference is thus attributed to distinct extensional mechanisms between the two regions.

[Objective]The coseismic surface rupture formed by an earthquake is the most obvious geomorphological evidence of fault activity.Its spatial distribution and deformation characteristics record essential information about seismic ruptures and fault motion.This information not only aids in understanding the earthquake rupture process and seismogenic mechanism but also contributes significantly to a deeper comprehension of fault evolution and crustal deformation.Therefore,it is of great importance to promptly investigate coseismic surface rupture zones and acquire high-precision geomorphological data.[Methods]The November 18,1951 M 8.0 Beng Co earthquake in central Tibet ruptured the Beng Co fault and produced a well-preserved surface rupture zone.We obtained high-precision images by integrating field investigations with high-resolution orthomosaic images and digital elevation models(DEMs)derived from unmanned aerial vehicle(UAV)imagery based on the Structure from Motion(SfM)method.We measured both coseismic and cumulative displacements along the rupture zone to examine the kinematic characteristics of the Beng Co fault and the seismogenic background of the Beng Co earthquake.[Results and Conclusions]The earthquake ruptured the eastern segment of the Beng Co fault,forming an approximately 90-km-long coseismic surface rupture zone with an overall strike of 120°.A series of right-lateral offset gullies/terraces,push-ups,and pull-aparts along the rupture zone reveals that the Beng Co fault is an active right-lateral strike-slip fault.Cumulative offset probability distribution(COPD)analysis suggests that large earthquakes have occurred repeatedly along this fault and have been fairly regular in terms of slip accumulation,with a typical lateral slip of～4.0 m.The Beng Co earthquake occurred as a direct response to the fault's accommodation of regional extrusion deformation caused by the rapid eastward movement of the eastern Qiangtang block.[Significance]This work not only facilitates the timely preservation of high-resolution 3D data of the coseismic surface rupture associated with the Beng Co earthquake but also provides a basis for studying tectonic deformation and assessing seismic hazards in central Tibet.

Accurately estimating the duration of the Induan Stage (Early Triassic) is crucial for understanding biotic recovery and the rate of environmental upheavals following the Permian-Triassic mass extinction. However, there is considerable uncertainty because astrochronological and radiometric dating approaches have given substantially different durations. In this study, we establish a comprehensive chronological framework for the Induan Stage by integrating astrochronology, magnetostratigraphy, radiometric dating, biostratigraphy, and chemostratigraphy. Marine sections in South China, at Xiejiacao, Chaohu, and Daxiakou, preserve continuous Lower Triassic deposits, providing a unique opportunity for integrated stratigraphic studies. By analyzing new gamma ray series from the Xiejiacao section and gamma ray series from the Chaohu and Daxiakou sections, we construct a composite 405 kyr eccentricity cycle-calibrated time scale for the Induan Stage. Our results estimate the Induan duration at 1.57 +/- 0.2 Myr. By anchoring this timescale to the Permian-Triassic boundary (251.902 +/- 0.024 Ma), we propose an age of 250.33 +/- 0.2 Ma for the Induan-Olenekian boundary. The revised timescale reconciles previous discrepancies between astrochronological and radiometric dating, providing a robust foundation for improving global stratigraphic correlations and enhancing our understanding of key phenomena, including carbon cycle perturbations and environmental changes during the Induan. Moreover, it offers a new timeline for biotic recovery following the Permian-Triassic mass extinction and contributes to the ongoing refinement of the Geologic Time Scale.

To constrain the temporal and spatial evolution of the Ganzi-Litang Paleo-Tethys Ocean, this study presents the first paleomagnetic results from Late Triassic volcanic rocks in the Yidun terrane in the eastern Tibetan Plateau. The mean paleomagnetic direction for 27 sites is Ds = 39.2 degrees, Is = -52.9 degrees, kappa s = 42.2, alpha(95) = 4.3 degrees, and the paleomagnetic pole is located at 14.9 degrees N, 247.1 degrees E (kappa = 31.1 and A(95) = 5.1 degrees). Fold, reversal, and paleosecular variation tests, together with petrographic investigations, confirm the primary origin of the characteristic remanent magnetization. These results indicate that the Yidun terrane was situated at similar to 34.8 degrees N at similar to 231 Ma. Combined with available paleomagnetic and geological evidence, this suggests that: (a) the Ganzi-Litang Ocean closed no later than similar to 231 Ma; (b) the Paleo-Tethys Ocean finally closed during the early Late Triassic; and (c) the final closure of the Paleo-Tethys Ocean was nearly synchronous from east to west.

The Xianshuihe fault zone (XSHF) in southwestern China accommodates both aseismic creep and seismic slip, yet geological evidence constraining these processes remains limited. Hence, we conducted microstructural, geochemical, and rock magnetic analyses of fault‐zone materials from the Cuoniulongba River outcrop. Fault breccias and relatively undeformed sandstones adjacent to the principal slip zone (PSZ) exhibit elevated magnetic susceptibility (MS), likely reflecting monoclinic pyrrhotite precipitated from post‐seismic low‐temperature hydrothermal fluids. Creep‐related fault gouge within the PSZ is characterized by low MS. Notably, the gouge sample S4 within the PSZ shows high MS, reflecting magnetite neoformation induced by coseismic frictional heating (>500°C), consistent with the observation of thermal decomposed kaolinite due to fluid drainage. This study presents the geological evidence associated with the XSHF linked to aseismic creep, coseismic frictional heating, and post‐seismic hydrothermal alteration, and provides new insights into the seismic behavior of continental strike‐slip faults.

The geodynamic setting of the southwestern Yangtze Block in the latest Mesoproterozoic has been a controversial issue for decades, which confuses the relationship between the Yangtze Block and the assembly of Rodinia supercontinent. We here report an integrated dataset of petrology, whole-rock geochemistry, zircon U-Pb ages and Hf isotopes for the newly identified latest Mesoproterozoic granitoids from the Yonglang area, southwestern Yangtze Block. SHRIMP and LA-ICP-MS zircon U-Pb dating results suggest that these granitoids were mainly crystallized at ca. 1.02 Ga. These samples show typical geochemical signatures of I-type granite, such as negative correlation between P2O5 and SiO2 contents, positive correlation between A/CNK ratios and SiO2 contents, and zirconium saturation temperature (Tzr) of 748-818 degrees C. Their zircon epsilon Hf(t) values range from-3.0 to 0.8, with two-stage model ages of 2.0-1.8 Ga. These ca. 1.02 Ga granitoids were likely generated by the partial melting of amphibolites under H2O-rich conditions originated from hydrous fluids of the subduction components, reinforced a latest Mesoproterozoic arc-back-arc system in the southwestern Yangtze Block. Based on the spatial-temporal variations of the late Mesoproterozoic subduction-related magmatic records around the periphery of the Yangtze Block, it is suggested that this block may have started to drift towards the Rodinia supercontinent at least at ca. 1.02 Ga.

The Paleo-Asian Ocean's (PAO) closure timing and the Alxa Block's (ALB) tectonic affinity remain debated. We present new paleomagnetic and geochronologic data from Permian volcanic and sedimentary rocks in the ALB. Characteristic remanent magnetization (ChRM) directions from Early (similar to 282 Ma), Middle (similar to 268 Ma), and Late Permian (similar to 255 Ma) rocks pass fold, reversals, and conglomerate tests, confirming their primary origin. These results yield the first reliable Permian paleopoles for the ALB. The data indicate minor movement during the Early-Middle Permian, followed by rapid northward drift and similar to 53.8 degrees counterclockwise rotation in the Middle-Late Permian. Comparison with surrounding blocks suggests the ALB was tectonically linked to North China but independent of Tarim. A significant paleolatitudinal gap between North China-ALB and Siberian-South Mongolia blocks during the Late Carboniferous-Middle Permian implies a wide mid-eastern PAO, which closed during the Late Permian. These findings refine Permian paleogeographic reconstructions of Eastern Asia.

Pyrrhotite formed in pseudotachylyte is an important magnetic mineral for understanding earthquake mechanisms and seismogenic environments. To reveal the formation mechanism of pyrrhotite within pseudotachylyte, we conducted microstructural, geochemical, and rock magnetic (after heating) experiments on samples from the Wenchuan Earthquake Fault Scientific Drilling project Hole 2 (WFSD-2), in the Longmen Shan thrust belt on the eastern margin of the Tibetan Plateau. Metallic iron was formed by the thermal decomposition of iron oxide and sulfide at high temperatures (≥1300 °C) within a reducing environment. Then, monoclinic pyrrhotite was formed at a very high melting temperature (≥1500 °C) from the reaction between a limited amount of sulfur and metallic iron. Metallic phosphorus was formed at temperatures ≥1300 °C and was preserved as Fe-P alloy. We observed that the quantity of Fe-P alloy spherulites increased with increasing temperature, as did the complexity of their structure and composition. Isometric polyhedral Fe-P alloy spherulites began to form at 1500 °C. The spherulites that formed at 1750 °C had a more complex structure and a perfectly regular shape compared to those formed at 1500 °C. We suggest that metallic phosphorus from fault zones, along with carbon and metallic iron, could be a new indicator of large earthquakes. The monoclinic pyrrhotite and excess iron in the pseudotachylyte from WFSD-2 indicate a frictional temperature of ≥1500 °C and a strongly reducing seismogenic environment.

Knowledge of the tectonic and paleogeographic context of North China during the Proterozoic is pivotal for unraveling the origins of early multicellular eukaryotes and the dynamics of supercontinents like Nuna and Rodinia. However, stratigraphic correlations across basins, the tectonic framework, and North China's position within Nuna and Rodinia, particularly its relationship with the Congo-Sao Francisco plate, are contentious. To address these issues we conducted a detailed paleomagnetic and rock magnetic study of the red dolomite of the Duguan Formation in the Xiaoqinling-Luanchuan region, part of the Xiong'er block of North China. Thermal demagnetization revealed a high-temperature remanence component, with an unblocking temperature exceeding 670 degrees C, likely carried by detrital hematite. This component passed both fold and reversal tests. After tilt correction, the site-mean direction of the high-temperature component is Ds = 76.7 degrees, Is = 16.9 degrees, ks = 30.4, a95 = 7.3 degrees (14 sites). This corresponds to a paleomagnetic pole at 15.8 degrees N, 200.4 degrees E (dp/dm = 3.9 degrees/7.5 degrees). Comparison of this pole with previous high-quality Proterozoic poles from North China indicates that the Duguan pole falls between the Yangzhuang and Mengyin dykes (1630 Ma). Considering the existing zircon U-Pb dating results, we conclude that the Duguan Formation is older than the Yangzhuang Formation, equivalent to the upper part of the Gaoyuzhuang Formation. Comparison with the Proterozoic apparent polar wander (APW) paths of North China and Congo-Sao Francisco indicates that these two blocks could only have amalgamated after 1080 Ma, with no earlier connection. However, due to the limited quantity of Proterozoic paleomagnetic data from Congo-Sao Francisco, the details of this Neoproterozoic connection remain uncertain.

Knowledge of the seismogenic environment of fault zones is critical for understanding the processes and mechanisms of large earthquakes. We conducted a rock magnetic study of the fault rocks and protoliths to investigate the seismogenic environment of earthquakes in the Motuo fault zone, in the eastern Himalayan syntaxis. The results indicate that magnetite is the principal magnetic carrier in the fault rocks and protolith, while the protolith has a higher content of paramagnetic minerals than the fault rocks. The fault rocks are characterized by a high magnetic susceptibility relative to the protolith in the Motuo fault zone. This is likely due to the thermal alteration of paramagnetic minerals to magnetite caused by coseismic frictional heating with concomitant hydrothermal fluid circulation. The high magnetic susceptibility of the fault rocks and neoformed magnetite indicate that large earthquakes with frictional heating temperatures >500°C have occurred in the Motuo fault zone in the past, and that the fault maintained an oxidizing environment with weak fluid action during these earthquakes. Our results reveal the seismogenic environment of the Motuo fault zone, and they are potentially important for the evaluation of the regional stability in the eastern Himalayan syntaxis.

The collision of India and Asia formed the Himalayas and caused the uplift of the Tibetan Plateau. Greater India comprises the part of the Indian plate that was subducted beneath Asia and the Tethyan Himalaya. Quantitative constraints on the extent of Greater India are needed to study the process of the India-Asia collision. However, such constraints are lacking and the topic remains debated. We present paleomagnetic data from late Paleocene (similar to 58 Ma) mafic rocks from the western Tethyan Himalaya. The mean paleomagnetic direction is Ds/Is = 348.5 degrees/+6.5 degrees with k = 38.7 and a(95) = 5.2 degrees, which passed the fold, reversals, and paleosecular variation tests. The results define the paleolatitude of the Tethyan Himalaya as 3.3 +/- 4.5.N at similar to 58 Ma for the reference site of 29.9 degrees N/83.3 degrees E. A comparison of the Paleogene paleolatitudes of the Tethyan Himalaya shows that the terrane moved northward by 1540 +/- 290 km between similar to 60 Ma and similar to 50 Ma, with a rate of movement of 15.4 +/- 2 cm/yr. The new paleomagnetic result confirms that the extent of Greater India was 1130 +/- 400 km and was essentially uniform from east to west. This finding implies that the collision between India and Asia was nearly be quasi-synchronous from the middle-eastern to western segments along the Indus-Tsangpo suture zone.

AbstractThe Early Paleozoic paleolatitudinal position of the terranes in the northern Tibetan Plateau is the key to unraveling the evolution of the Proto‐Tethys Ocean. We present the first Late Cambrian paleomagnetic results from the Oulongbuluke terrane (OT), in the northern Tibetan Plateau. The mean paleomagnetic direction for 16 sites is Ds = 196.2°, Is = −36.9° with κs = 31.5, α95 = 6.7°, corresponding to a paleopole at 68.2°S/51.9°E with dp/dm = 4.6°/7.8°. Rock magnetic and petrologic analyses demonstrate the primary origin of the magnetic mineralogy. This paleomagnetic result defines the Late Cambrian paleolatitude of the OT as 20.6 ± 4.6°S (reference point: 37.2°N/96.6°E). Combined paleomagnetic and geological evidence suggests that the terranes in the northern Tibetan Plateau were located to the northwest of the Indian plate of Gondwana during the Late Cambrian.

Stress states near active fault zones are key to understand their seismogenic setting, geodynamic evolution and future seismic activity. The Longmen Shan Fault Belt (LSFB) is a prominent fault zone that has had a long history of activity and major recent earthquakes in the eastern Tibetan Plateau. However, we have no records of major events prior to the 2008 Wenchuan earthquake, and this hinders progress in understanding both the past and future seismicity of the LSFB. A Late Triassic pseudotachylyte, recently discovered and dated, provides an opportunity to compare modern stress states with those acting ca. 230 Ma ago. Here we use a new paleoseismological approach, based on the magnetic fabric of the fault rocks, to determine the focal mechanism of Late Triassic seismic events, each recorded in pseudotachylyte veins at the Bajiaomiao outcrop. The anisotropy of magnetic susceptibility (AMS) of pseudotachylytes and cataclasites arises from the shape preferred orientation of coseismic neoformed magnetite and monoclinic pyrrhotite, whereas that of protocataclasite arises mainly from the crystallographic preferred orientation of inherited clastic magnetite. The AMS of fault rocks shows well-defined magnetic foliation and lineation. The pseudotachylyte generation vein formed along the plane where seismic slip took place, while the AMS obliquity with respect to this plane indicates seismic slip with-248 degrees trend and 38 degrees dip. This result is consistent with the attitude of macroscopically visible subhorizontal striations on the pseudotachylyte plane itself. The consistent asymmetry of multiple injection veins with respect to the pseudotachylyte generation vein, along with the asymmetry of the AMS fabric, shows that seismic deformation resulted from left lateral, strike-slip motion. This study provides the oldest example, to date, of focal mechanism determination using the AMS method. The kinematics of the Late Triassic event departs from that of the 2008 Wenchuan earthquake thrust motion. Yet, with a displacement estimated between-4.4 and 17.4 m, the magnitude of the Late Triassic event was likely Mw 7.5-7.9.

The zircon provenances of the late Paleoproterozoic metasedimentary rocks are important for assembling Proto-Yangtze and its reconstruction in the Nuna supercontinent. We present a dataset involving 363 detrital zircon U-Pb dating and 165 Hf isotope analyses from the Laochanghe Formation of the Dahongshan Group in the southwestern Yangtze Block. New detrital zircon U-Pb ages, combined with the heterogeneity of sedimentary strata and available magmatic age data, suggest that the maximum depositional age of the Laochanghe Formation cloud be younger than 1.81 Ga and older than 1.74 Ga. The zircon U-Pb-Hf isotope compositions of the volcanic and metamorphic rocks overlap with those of the late Paleoproterozoic metasedimentary rock, suggesting the southwestern Yangtze Block provided provenance at 1.9, 2.3, and 2.7 Ga. This characteristic is significantly different from the northern Yangtze Block only provided partial provenance at 1.9 and 2.7 Ga. The northern and southwestern of the Yangtze Block jointly provide material for the late Paleoproterozoic metasedimentary rocks, combining synchronous late Paleoproterozoic magmatism and metamorphism, indicative of the formation of the proto-Yangtze Block in response to the accumulation of the Nuna supercontinent. Additionally, the potential provenance areas of the late Paleoproterozoic metasedimentary rock in the southwestern Yangtze include the northwestern Laurentia and southern Siberia, excluding the northern Australian, and Cathaysia. These findings indicate that the southwestern Yangtze may have been located between northwestern Laurentia and southern Siberia during the partial fragmentation of the Nuna supercontinent, enhancing our understanding of changes in the Nuna supercontinent over time.

Pseudotachylytes form in seismic fault zones at shallow depths down to typical seismogenic depths. Determining their formation depth is key to reconstruct the stress properties and seismogenic environment of the faults. To obtain the Late Triassic pseudotachylyte formation depth and seismogenic environment of faults in the Longmen Shan Fault Zone (LMFZ), we carried out rock magnetic, microstructural and geochemical analyses of pseudotachylyte, cataclasite and protocataclasite from the Bajiaomiao outcrop along the Yingxiu-Beichuan fault. The magnetic minerals in the pseudotachylyte and cataclasite are newly-formed magnetite, monoclinic pyrrhotite, and paramagnetic minerals, while those in the protocataclasite are paramagnetic minerals as well as primary magnetite. Pseudotachylytes have higher magnetic susceptibility values than wall rocks. The high temperature during frictional heating induces the thermal decomposition of paramagnetic minerals, forming magnetite and monoclinic pyrrhotite, and thus contributing to the higher magnetic susceptibility values of the pseudotachylytes and indicating a reductive seismogenic environment with weak fluid that contains few sulfides. The X-T results show that protocataclasite has never been subjected to heating over 275-300 degrees C in nature, which implies that the protocataclasite and pseudotachylyte were formed at a depth of 12.8-14.0km. From the seismogenic depths, the structure of the pseudotachylyte, and the seismic mechanism, we estimate the normal stress sigma as <= 240.2 similar to 264. IMPa and the shear stress a 144.1 similar to 158.5MPa for the LMFZ. Previous powerful earthquakes occurred repeatedly in the region, and the pseudotachylytes formed within the consolidated cataclastic rocks at the seismogenic depth (<14km) are relatively easy to be preserved. They also recorded strong stress and reduced seismogenic environments with weak fluid activity.

Present-day tectonic deformation in central Tibet is characterized by a series of -NS-trending grabens which accommodate EW extension. Quantifying the geometry and kinematics of these grabens is essential to understand Cenozoic tectonic deformation and Tibetan Plateau evolution. Here, we focus on the Norma Co graben (NCG), i. e., the southern segment of the Shuanghu-Norma Co graben (SH-NCG) system, which is the most prominent graben system within the Qiangtang terrane in central Tibet. We study its tectonic and geomorphologic characteristics to determine the late Quaternary throw rates of the normal faults bounding the graben, based on highresolution satellite images interpretation, field investigation, and cosmogenic 10 Be dating (n = 23). Using terrestrial LiDAR, UAV, and kinematic GPS, we precisely measure vertical offsets (up to 15 m) of -90 -120 ka-old alluvial surfaces, yielding a throw rate of 0.10( +0.04/-0.03) mm/yr. This rate is ten times lower than those published along other NS -trending grabens in southern Tibet, reflecting different deformation mechanisms, as previously suggested: grabens in eastern Qiangtang formed by rapid eastward block extrusion, those in western Qiangtang formed by distributed extension on numerous scattered normal faults, and those in southern Tibet result from divergent orthogonal thrusting along the curved Himalayan arc.