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Geological settings of southern Tibet. Distribution of major faults, focal mechanism of recent earthquakes, and surface topography in the research area are shown. The black lines of nearly N-S trending indicate rifts in southern Tibet. The black dotted lines represent sutures (BNS: Bangong-Nujiang suture, IYS: Indus-Yarlung suture, and JSS: Jinsha suture). Focal mechanisms (beach balls) are earthquakes of M w > 6.0 since 1975 from the GCMT catalog (www.globalcmt.org) (Dziewonski et al., 1981; Ekström et al., 2012). The low seismic velocity zones are acquired from Hetényi et al. (2011). The magma extrusions are Miocene adakites (Chung et al., 2005). The inset panel shows the approximate location of the India and Eurasia plates. The blue box shows the location of the Tibetan Plateau, and the red line represents the Main Boundary Thrust between the Indian and Eurasian plates.
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N–S trending rifts are widely distributed in southern Tibet, suggesting that this region is under E–W extension, behind the N–S collision between the Eurasia and India plates. Geophysical anomalies and Miocene magma extrusions indicate the presence of dispersed weak zones in the mid-lower crust in southern Tibet. These weak zones are partially loca...
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... variety of tectonically and seismically active faulting zones are formed in different regions of Tibetan Plateau, with NW-SE and NE-SW trending conjugate strike-slip faults in central Tibet and N-S normal faulting systems in southern Tibet. The N-S trending rifts, initiated in the middle to late Miocene, are distributed almost equi- distantly in southern Tibet, as shown in Figure 1 ( Armijo et al., 1986;Burchfiel et al., 1992;Cogan et al., 1998;Molnar & Tapponnier, 1978;Tapponnier et al., 1981;Woodruff et al., 2013;Yin et al., 1994). These rifts are formed in the upper crust, accommodated by ductile deformation in the middle crust (e.g., Coleman & Hodges, 1995;Kapp et al., 2008). ...
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... the first stage (2.5 Ma), deformation is heterogeneous in the upper crust (Figures 4a-4b1), with incipient strain localization above the weak layer. Small-scale upwelling of the weak crust nucleates below the incipi- ent strain localized zones (Figure 4c1). ...
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... the first stage (2.5 Ma), deformation is heterogeneous in the upper crust (Figures 4a-4b1), with incipient strain localization above the weak layer. Small-scale upwelling of the weak crust nucleates below the incipi- ent strain localized zones (Figure 4c1). Surface uplift of approximately 0.9 km is predicted above the weak layer due to the buoyancy of the low-density layer (Figure 4d1). ...
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... upwelling of the weak crust nucleates below the incipi- ent strain localized zones (Figure 4c1). Surface uplift of approximately 0.9 km is predicted above the weak layer due to the buoyancy of the low-density layer (Figure 4d1). In the area without such weak middle crust, surface subsides (<1.0 km) because of the E-W extension of the model. ...
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... topography indicates that rifts always develop above the weak zones, despite of the variations in Moho temperature and thermal state of the lithosphere. In hot lithosphere with high Moho temperature (800°C, ModelR), several N-S rifts develop regularly in the upper crust and evolves into magma extrusion at 4.35 Ma (Figures 10a-10c). Whereas in the colder lithosphere with lower Moho temperature (i.e., 700°C in ModelT1 and 600°C in ModelT2), rifts are more disperse and slightly oblique to the N-S direction (Figures 10d-10i). ...
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... hot lithosphere with high Moho temperature (800°C, ModelR), several N-S rifts develop regularly in the upper crust and evolves into magma extrusion at 4.35 Ma (Figures 10a-10c). Whereas in the colder lithosphere with lower Moho temperature (i.e., 700°C in ModelT1 and 600°C in ModelT2), rifts are more disperse and slightly oblique to the N-S direction (Figures 10d-10i). Pronounced rifts initiate in the upper crust at 2.5 Ma and evolve with substantial weak Table 2). ...
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... extensional velocity leads to slower development of normal faults, and no normal fault is generated when the extensional velocity less than 2.2 cm/a. Figure 11 shows the model results for low extensional velocity (2.2 cm/a in ModelV, Table 2), in which the ratio of the extensional to shortening strain rate is 1.5. Only one dominant rift and several short- trending incipient normal faults develop above the weak middle crustal layer, striking oblique to the N-S direction (Figures 11a and 11d). ...
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... 11 shows the model results for low extensional velocity (2.2 cm/a in ModelV, Table 2), in which the ratio of the extensional to shortening strain rate is 1.5. Only one dominant rift and several short- trending incipient normal faults develop above the weak middle crustal layer, striking oblique to the N-S direction (Figures 11a and 11d). Strain heterogeneity initiates at approximately 4.8 Ma, which develops much slower than models with larger E-W extension (Figure 11a). ...
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... one dominant rift and several short- trending incipient normal faults develop above the weak middle crustal layer, striking oblique to the N-S direction (Figures 11a and 11d). Strain heterogeneity initiates at approximately 4.8 Ma, which develops much slower than models with larger E-W extension (Figure 11a). Slight strain localization of faulting system con- centrates within the upper crust (Figure 11b), similar to that in the reference model. ...
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... heterogeneity initiates at approximately 4.8 Ma, which develops much slower than models with larger E-W extension (Figure 11a). Slight strain localization of faulting system con- centrates within the upper crust (Figure 11b), similar to that in the reference model. Surface uplifts approxi- mately 1.0 km above the weak middle crust at 4.8 Ma and tends to subside along the incipient strain localized zones (Figure 11c). ...
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... strain localization of faulting system con- centrates within the upper crust (Figure 11b), similar to that in the reference model. Surface uplifts approxi- mately 1.0 km above the weak middle crust at 4.8 Ma and tends to subside along the incipient strain localized zones (Figure 11c). At 6.3 Ma, strain heterogeneity in the upper crust develops into rifts, with surface subsi- dence along the rifting zones oblique to N-S direction. ...
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... 6.3 Ma, strain heterogeneity in the upper crust develops into rifts, with surface subsi- dence along the rifting zones oblique to N-S direction. Surface uplifts in the predominant rifting zone due to extrusion of weak layer (Figure 11f). Surface expression of the rift is similar to that in the reference model at earlier stage (4.0 Ma, Figure 4d4). ...
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... expression of the rift is similar to that in the reference model at earlier stage (4.0 Ma, Figure 4d4). In regions without weak middle crustal layer, upper crust deforms uni- formly, and the stress state favors conjugated strike-slip joints (Figures 11a and 11d). ...
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... parameters of the weak crustal layer greatly influence the topography evolution and development of normal faults. The comparison of average topography at 2.5 Ma in models with different densities or depths of the weak layer is illustrated in Figure 12. Driven by upwelling of the weak middle crustal layer with the low- est density (2,500 kg/m 3 in modeR), the average surface topography is 0.9 km with some variations. ...
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... by upwelling of the weak middle crustal layer with the low- est density (2,500 kg/m 3 in modeR), the average surface topography is 0.9 km with some variations. An increase in density and hence decrease in buoyancy of the weak layer leads to a decrease in topography above it (Figure 12a). Conversely, an increase in the depth of the weak layer results in lower surface topogra- phy, likely due to the increased strength of thicker upper crustal layer above the weak layer. ...
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... an increase in the depth of the weak layer results in lower surface topogra- phy, likely due to the increased strength of thicker upper crustal layer above the weak layer. However, this effect is not systematic and the average topography is nearly similar to that in the reference model, when the weak layer is located much deeper (20 km deeper than the reference model, Figure 12b). In this case, the weak layer is embedded in the deep lower crust, which potentially imposes larger buoyancy to the weak layer. ...
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... middle to late Miocene magma and geophysical anomalies indicate the continuous presence of the hot and weak middle to lower crust in southern Tibet since the rift initiation, which may be sustained by the continuous convergence of the thickened crust ( Liao et al., 2017). While in central Tibetan, there is no synchronous magmatic activity or middle to lower crustal partial melting (Figure 13a). ...
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... our numerical models with the prescribed weak middle to lower crustal layer, the lithospheric deformation is characterized by extension-orthogonal rifts above the weak layer and incipient conjugate strike-slip faults in the adjacent areas beyond the weak layer (e.g., Figure 4a). These results show similarities to the observed N-S rifts and partial melting in the middle to lower crust in southern Tibet and strike-slip faults in central Tibet ( Figure 13). In addition, the normal faults in southern Tibet are limited to the upper crust and gradually evolve into low angle in the rift systems. ...
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Citations
... Zhang et al., 2023) and that the N-S-trending rifts are perpendicular to the orogenic belt, the ideal crustal flow model and gravity collapse model may not explain the formation of the TYR and PXR. Nevertheless, the lower viscosity of the middle crust is likely to promote rifting within an extensional background (Bischoff & Flesch, 2018;Pang et al., 2018). The N-S-compression between the Indian and Eurasian plates and the effect of gravitational potential energy are causing the plateau crust to elongate in an E-W direction. ...
... In models of rift formation dominated by a weak mid-crust, the larger the scale of the weak layer is, the greater the scale of rift surface development (Pang et al., 2018). The YGR, the largest rift in the STRS, is characterized by low-Vs features that are smaller and more confined than those of other rifts. ...
Plain Language Summary
The rifts in the southern Tibetan Plateau are closely related to the growth and evolution of the plateau. These rifts are often considered as a whole in studies on their developmental modes. However, different rifts exhibit variations in terms of the timing of magmatism (before or after rifting). This implies that the developmental modes of different rifts are likely to involve different crustal deformation processes. To further investigate the formation modes of different rifts, we used the ambient noise method to obtain the crustal shear wave velocity structure. The presence of a low‐velocity layer in the mid‐crust indicates a vertical layering of crustal strength, which reveals that the upper crustal segmentation together with ductile deformation of the weak mid‐crust contributed to the formation of some rifts. In contrast, the presence of an isolated low‐velocity anomaly extending to the mid‐crust implies that a disruption of the lateral crustal strength caused the formation of another rift. Our findings will change the traditional understanding of the formation of N–S‐trending rifts and the evolution of the Tibetan Plateau.
... According to the distribution and focal mechanisms of local earthquakes ( Figures 1B, C), the middle crust was an aseismic zone and the normal faults were generally associated with north-trending rifts (Shi et al., 2020). The earthquakes in lower crust were triggered by the strong interactions between the crust and mantle (Molnar and Chen, 1983;Pang et al., 2018;Shi et al., 2020). ...
Although the Himalayan-Tibetan orogen is a result of compressional tectonics, the orogen also hosts active rifts accommodating east-west extension orthogonal to the north-south India-Asia convergence. In this study we address the question of how the north-trending rifts were formed by conducting high-resolution seismic imaging survey across southeastern Tibet where the Cona rift is exposed. Our work shows that the crustal structures of this youngest rift in southern Tibet was constructed by multiple-scale structures that are decoupled with depth and long rift trend. We suggest this deformation style to have resulted from eastward extrusion of the middle and upper crust with increasing speeds to the north towards the Yarlunbg-Zangpo suture. The differential eastward extrusion in turn may have contributed to the formation and evolution of the eastern Himalayan syntaxis.
... Considerable evidence has indicated that the formation of NAS trending rifts is related to deep dynamic processes (Hoke et al., 2000;Hou et al., 2006). Furthermore, numerical simulation results have shown that the generation of rifts or conjugate strike-slip fault systems depends on the distribution of LVZs in the crust (Pang et al., 2018). Areas with LVZs are prone to rifting formation, while areas without LVZs are more likely to develop conjugated strike-slip faults; therefore, the distribution of LVZs in the crust of the plateau may be an important factor to the formation and distribution of the extensional structures. ...
... Recent high-resolution crustal velocity models have proved the existence of weak zones in the middle to lower crust and some spatial relationships between the crustal weak zones and the N-S-trending structures (rifts and mountain ranges; Unsworth et al., 2005;Dong et al., 2016;Liang et al., 2016;Nie et al., 2020). These weak zones are generally considered to be the results of crustal anatexis (Rosenberg and Handy, 2005) and can promote crustal flow and deformation (Wang et al., 2010(Wang et al., , 2012Jamieson et al., 2011;Cao and Neubaur, 2016;Dong et al., 2016;Bischoff and Flesch, 2018;Pang et al., 2018;Zhang et al., 2022). Therefore, the N-S-trending structures may have a genetic connection to deep-seated tectonothermal processes, and the Cenozoic granites may be key geologic records to unmask their genesis. ...
... The initial topographic rise could have led to the development of gravitationally induced pressure gradients, which could have caused high rates of lateral (orogen-parallel) flow within the middle-to lower-crustal weak zone Bischoff and Flesch, 2018). This would have initiated localized ductile extension at deep crustal levels but subsequent brittle normal faults at shallow structural levels ( Fig. 7; Pang et al., 2018;Bischoff and Flesch, 2018). Progressive India-Asia convergence during the Miocene further facilitated N-S compression and perpendicular extension (Kapp and Guynn, 2004;Styron et al., 2011). ...
Large-scale N-S shortening induced by India-Asia convergence caused the formation of numerous E-W−trending mountain ranges in Tibet. However, the mechanism(s) of formation of N-S−trending mountain ranges remains elusive. We report on a felsic magmatic belt located along the N-S−trending Yardoi-Kongbugang mountain ranges on the flank of the Cona rift in the eastern Tethyan Himalaya. Zircon and monazite geochronology and whole-rock geochemistry revealed three epochs of middle- to lower-crustal anatexis beneath the Cona rift at ca. 47−42 Ma, 35−34 Ma, and 24−14 Ma. The mid-Eocene and early Oligocene granitoids show adakitic signatures indicating continuous crustal thickening, while the formation of Miocene leucogranites and N-S−trending dacitic dikes was related to ductile crustal extension. Silicic melts were exposed along the whole rift since the early Oligocene, suggesting that the early Oligocene could be regarded as a transitional epoch from tectonic compression to orogen-parallel extension. Widespread mid-Eocene and Miocene magmatism in the Himalaya, together with coeval metamorphic anatexis, represents two phases of crustal weakening. The weakened crustal zones under continued India-Asia convergence may have favored uplift and subsequent lateral flow of the weak zones, which initiated E-W extension. Finally, significant upwelling of the weak zones evolved into magma extrusion and formed the N-S−trending mountain ranges. This study provides new insights into the mechanisms of surface uplift and E-W extension and challenges the common view of initiation of E-W extension in southern Tibet not earlier than the early Miocene.
... The east-west extensions of the Tibetan Plateau have formed a series of north-south rifts in southern Tibet since the Cenozoic (Armijo et al., 1986;Tapponnier et al., 2001;Hou et al., 2006;Zhang et al., 2007;Xu et al., 2006;Yin, 2006;Zhang., 2007aZhang et al., 2012;Xue et al., 2021). A high-conductivity and lowvelocity layer, which is interpreted as a partial melting layer in the middle and lower crust, is widely distributed under these northsouth trending rifts (Unsworth et al., 2004(Unsworth et al., , 2005Nabelek et al., 2009;Jin et al., 2010;Xie et al., 2017;Liang et al., 2018;Pang et al., 2018;Xue et al., 2021). Over time, some of these melts migrated upwards in the CR through the rock boundaries and weak zones (Hill et al., 2015). ...
A series of extensional structures, including the southern Tibet detachment system (STDS), the north-south trending rifts (NSTR), and the northern Himalayan gneiss dome (NHGD), developed from the collision and compression between the Indian and Eurasian plates. These tectonic movements were accompanied by magmatism and polymetallic mineralization. Cuona Rift (CR) is located on the STDS next to the Yalaxiangbo Dome (YD) and passes through the Zhegucuo-longzi fault (ZLF), the Lhozhag fault (LZF), the Rongbu-Gudui fault (RGF), the Cuonadong dome (CD), and the YD. The study area contains numerous metal deposits, such as rare metal ore, lead zinc ore, gold deposits, and two geothermal fields, i.e., the Cuona geothermal field (CGF) and the Gudui geothermal field (GGF). Current research on the geological structures from the STDS to the YD is mainly based on magnetotelluric and natural seismic imaging. These surveys have a low resolution, making it impossible to image the shallow crust in detail. This study obtained about a 112 km S-wave velocity profile from the STDS to the YD using the multichannel surface wave imaging method. The profile results indicated that the average thickness of the sedimentary layer from the STDS to the YD is 400–500 m, while it is more than 800 m at certain fault zones. The CD is connected to the high-velocity body below the Zhaxikang ore concentration area (ZOCA) and may have the same provenance. The thermal conductivity reveals that the CGF, the GGF, and the ZOCA have high values and a more intense thermal radiation capacity. This drives the migration and circulation of the thermal fluids in the CGF and the GGF, causing them to continuously transmit heat to the shallow surface along the fault system. The migration of the thermal fluids extracts useful elements from the geological bodies through which it flows. When these elements mix with the atmospheric infiltration water, it precipitates to form the Zhaxikang hydrothermal superimposed transformation type lead-zinc polymetallic deposit.
... As the continent-continent collision, a variety of tectonically and seismically active faulting zones are formed in different regions of Tibetan Plateau, with NW-SE and NE-SW trending conjugate strike-slip faults in central Tibet and N-S normal faulting systems in southern Tibet (Pang et al., 2018), and these rifts always suggest generally east-west extension of the Tibet (Molnar and Tapponnier, 1978). However, the mechanism of these extensional structures is still unclear. ...
... Under the condition of bidirectional (N-S compression and E-W extension) lithospheric deformation, Frontiers in Earth Science frontiersin.org the widely distributed mid-lower crustal weak zones resulting from dehydrate melting or wet melting play a crucial role in the formation of the N-S trending rifts (Pang et al., 2018). Eastward crustal flow occurred due to the pressure difference in the westeast direction (Clark and Royden, 2000), which could create a west-east basal shear on the Tibetan crust that facilitates surface rifting. ...
The well-known N-S-trending fault in the Yangbajing area plays a crucial role in the tectonic evolution of the Tibetan Plateau. Previous researches on a few E-W geophysical profiles suggested that the eastern shear at the base of the upper crust and/or lithosphere deformation brought on by asthenosphere upwelling are the major causes of the Yadong-Gulu rift’s creation. Here we propose a 3-D electrical resistivity model derived from the magnetotelluric (MT) array data spanning the Yadong-Gulu rift (YGR), and the distribution of temperature and melt fraction is estimated by the experimental calibrated relationships bridging electrical conductivity and temperature/melt fraction. The result reveals that the Indian slab subducted steeply in the east of the Yadong-Gulu rift, while Indian slab may have delaminated with a flat subduction angle in the west. The temperature distribution shows that the upper mantle of the northern Lhasa terrane is hotter than that of the southern Lhasa terrane. This is likely the result of mantle upwelling caused by either the subduction of the Indian slab or thickened Tibetan lithosphere delamination. Moreover, the strength of the mid-lower crust is so low that it may meet the conditions of the local crust flow in the west-east direction. The local crustal flow and the pulling force from the upwelling asthenosphere jointly contributed to the formation of the Yadong-Gulu rift. These main factors exist in different stages of the evolution of the Yadong-Gulu rift.
... In southern Tibet, the low-velocity and high-conductivity mid-lower crustal zones reveal widely distributed weak crustal zones (Dong et al., 2020;Hetényi et al., 2011;Huang et al., 2020;Wang et al., 2017;Wei et al., 2001). It has been noted that weak crustal zones could facilitate the formation of N-S rifts in southern Tibet (Bischoff & Flesch, 2018;Pang et al., 2018). However, recent geophysical observations showed that not all rifts in southern Tibet are accompanied by prominent low-velocity crustal zones underneath, such as the Yadong-Gulu rift (YGR) (Huang et al., 2020). ...
... For the rifts developing in the thickened crust with slow extensional rate, such as a series of N-S rifts in southern Tibet, by considering the joint effects of slow boundary extensional rate, a weak mid-crustal layer and asthenospheric upwelling, our 2D numerical models simulate the evolution of multiple rifts developing within the upper crust and throughout the whole thickened crust. The 2D numerical results confirm the key role of the low-density and low-viscosity mid-crustal layer in initiating rifts in the upper crust, consistent with the previous 3D model results constrained by bidirectional deformation (Pang et al., 2018). Our numerical results reveal that the weak mid-crustal layer imposes considerable extensional stress and thermally weakens the overlying upper crust, thereby promoting fast formation of upper crustal rifts. ...
Plain Language Summary
The Tibetan Plateau is one of the most spectacular orogenic belts on the Earth and is characterized by thickened crust and a series of rifts parallel to the collisional direction in the southern part. Systematic research on the formation mechanisms of these rifts can help us to comprehensively understand the dynamic processes during the sustained growth of Tibetan Plateau. To distinguish the preliminary driving forces of rifting, numerical geodynamic modeling was implemented to evaluate and justify several hotly debated hypotheses based on geophysical observations and geochemical constraints. Our 2D numerical modeling simulated the evolution of multiple rifts under the premise that the model configurations are comparable to the lithospheric structure determined via recent seismology imaging across a series of rifts in the study region. Moreover, comparative numerical simulations reveal distinct effects of the weak mid‐crustal layer and small‐scale mantle plume on promoting different types of rifts. Our simplified 2D model provides useful implications for the mechanism of hybrid passive‐active rifting processes in southern Tibet.
... As a consequence, rifting can develop in the upper crust (e.g., Yari Rift, Longgar Rift, Nyma-Tingri Rift, Xainza-Dinggye Rift, Yadong-Gulu Rift, and Riduo-Cuona Rift) (Figure 9). This concept has been illustrated with a 3-D thermal-mechanical numerical model from Pang et al. (2018). Furthermore, the low-viscosity and high-melt-fraction zones not only exist beneath one rift, but exist between at least two N-S rifts, which further indicates that there may be weak coupling between east-west extensional crustal tectonics and lithospheric deformation. ...
The tectonic dynamics of the Lhasa‐Gangdese terrane, southern Tibet, are still unclear and open questions persist regarding the structure, physical properties, and rheology of the lithosphere. A three‐dimensional electrical resistivity model was generated beneath the Lhasa terrane, 79°−94°E and 28°–33°N, an area of ∼1,500 by ∼600 km, using data from 537 magnetotelluric measurements. To overcome computational challenges, we present an approach in which multiple high‐resolution models from overlapping subregions are combined by means of an error‐weighted averaging scheme to construct a continuous electrical resistivity model. Based on the electrical structure, the rheology of the mid‐lower crust was investigated by constraining the melt fraction, in order to explore controls on dynamic mechanisms from a whole‐system perspective. The models shed light on the vertical and lateral migration of crustal materials, magma transportation, and continental deformation in the Lhasa terrane. The model shows resistive features in the south that may represent the Indian plate, and conductive features above this that may represent the migration of materials beneath the Lhasa terrane, both of which vary substantially along the Indus‐Yarlung Zangbo suture. In the mid‐lower crust, conductive features (with a likely corresponding decrease of the effective viscosity) may be related to underplating, magma reservoirs, mineralization sources, and vertical motion of buoyant materials. A weakened mid‐lower crust has consequences for surface deformation and may have contributed to the formation of (north‐south) rift zones. Furthermore, the inhomogeneous distribution of weakened areas in the mid‐lower crust has implications for the local lateral migration of materials.
... However, owing to the sparsity of GPS sites, comprehensively and quantitatively determining the fault activity using GPS data is difficult. Many scholars have used numerical simulation method based on GPS velocity data to study dynamic problems in southern Tibet (Liu and Yang 2003;Ye and Wang 2004;Wang et al. 2006;Xu and Zhao, 2009;Pang et al. 2018), such as the extensional state uplift and formation mechanisms. These studies, which are largely based on three-dimensional rheological models, emphasize the influence of the rheological layering structure of the lower crust on the surface crustal deformation, but rarely consider the influence of faults. ...
The moderate-strong (M ≥ 5, since 1976; or M ≥ 6.5, overall) earthquakes of the north to south trending (NS-trending) faults and their vicinity in the southern Qinghai–Tibet Plateau exhibit prominent spatial concentration distribution characteristics. However, research on the southern Tibet faults is limited. Hence, this study used a two-dimensional viscoelastic finite element model to simulate crustal movement in southern Tibet based on 1991–2015 GPS velocity data. The current deformation field, tectonic stress field, fault slip, and stress accumulation rates distribution were obtained to analyze the relationship between fault activity and earthquake distribution. The results revealed that the simultaneous effected by of the NE-trending compression and uneven EW-trending tension on the study area. Crustal deformation exhibited simultaneous NS-trending compression and EW-trending stretching. The EW- and NWW-trending faults and the NS-trending faults differed in their mechanical properties and movement modes. The NS faults were primarily subjected to extensional stress with normal motion. The remarkable heterogeneity of the fault segments influenced the distribution of moderate-strong earthquakes and types of earthquake ruptures. The concentrated distribution of moderate-strong earthquakes on the NS-trending normal fault and its vicinity depended largely on the high slip rate, strong tensile stress, and geometric strike of the fault segment. This study aids in understanding the heterogeneity in normal fault activity in southern Tibet and is the basis for seismic hazard assessment.
... The lithospheric-scale rifting means that the "initiation" of regional extension could be manifested by a series of related processes, such as the ductile deformation at middle-lower-crust levels, rapid exhumation of footwall rocks of normal faults at the upper to middle-crustal level, and surface depressions accompanied by basin formation. Rifting may propagate very quickly from the lower-crustal level to the earth surface (Liao & Gerya, 2014;Pang et al., 2018). Therefore, we argue that although these processes happen at different structural levels, all of them are actually related to the initiation of rifting and could be used to constrain its timing (e.g., Cooper et al., 2015;Lee et al., 2011;Styron et al., 2011 and references therein). ...
A key issue in the Cenozoic evolution of the Tibetan plateau is the geodynamic drivers for north‐trending rifting in southern Tibet. Recent studies have demonstrated an eastward propagation pattern for rift initiation, but the along‐strike variations remain poorly resolved. Two models that predict different north‐south rift kinematics include northward underthrusting or southward tearing of the Indian lithospheric slab, predicting a northward or southward propagation trend of individual rifts along strike, respectively. The Yadong‐Gulu rift (YGR) is an ideal case to investigate this issue due to its long strike length (∼500 km) and location above proposed slab‐tear structures. Here, we compile constraints on both rift initiation and acceleration, and report new apatite fission track and (U‐Th)/He thermochronological data along the southern segment of YGR. Our main findings are as follows. First, the rifts west of the YGR initiated simultaneously along strike, which we suggest is at odds with predictions of either slab‐tear or slab‐underthrusting models. However, most of these rifts show a northward younging pattern in rift acceleration, which may be governed by low‐angle Indian slab underthrusting released by slab tearing. Second, the initiation timing of the Yadong rift is constrained at ∼13–11 Ma. Combined with published constraints along strike, we demonstrate a clear northward propagation in rift initiation along the YGR. This kinematic pattern may be affected by its orientation of the most oblique northeast‐trending among all rift systems or the outward expansion of the Himalayan arc.
