Southern Tibet Research Articles

Subduction Evolution Controlled Himalayan Orogenesis: Implications from 3-D Subduction Modeling

Himalayan orogenesis remains enigmatic in terms of Tibetan Plateau geodynamics originating from the Cenozoic India–Eurasian continental collision. India underthrusts below Tibet to the Yarlung–Tsangpo suture, which has been identified as the northernmost boundary for underplating. However, the way in which the historical evolution of continental subduction induces plateau uplift and the way it controls the variation in uplift between outboard and inboard areas is still unclear. To interpret the evolutionary mechanisms involved in the Himalayan growth history, we constructed different 3-D dynamic models at important stages to address these questions related to the formation of the Himalayas on the basis of paleoenthalpy evidence encoded in fossil leaves from recently documented assemblages in southern Tibet. The results show that (1) the effect of crustal thickening was the predominant factor in the early evolution from the Paleocene to the early Eocene, which resulted in a moderate growth rate. (2) The consecutive slab break-off eastward from the western syntaxis and the associated slab rebound significantly accelerated orogenesis from the late Eocene to the Oligocene. The upwelling asthenospheric flow was a key control of increasing crustal buoyancy, which resulted in the fastest growth of the Himalayas during the early Miocene. (3) Thereafter, the gradually enhanced monsoon and surface erosion during accompanying the increasing mountain height resulted in a slowdown of the orogenic rate, which counterbalanced the buoyant force produced by asthenospheric flow driving continuous Himalayan growth.

Late Permian rift-related volcanic rocks from the Zhongba Terrane, Southern Tibet: implications for the opening of the Neotethys

ABSTRACT The questions of how and when the Neotethys Ocean opened are crucial for understanding the evolution of the Tethys Realm and the break-up of Gondwana. However, the evolution of the Neotethys remains controversial. Herein, we report the zircon U–Pb ages, whole-rock major as well as trace elements, and Sr–Nd isotopic data for the basaltic volcanic rocks from the Zhongba Terrane in the western Yalung–Zangbo Suture Zone. The results demonstrate that the Saga basalts were extruded during the Late Permian (257–258 Ma). All samples are characterized based on the low SiO2 content (44.03–50.33 wt%) and belong to the high-K calc-alkaline series. Furthermore, they exhibit light rare earth element enrichment ((La/Yb)N = 12.7–26.7); slightly positive Eu anomaly(Eu/Eu* = 1.01–1.14); prominent Nb and Ta positive anomalies; slightly negative Zr, Hf, and Ti anomalies and exhibit high ratios of Ta/Hf (0.93–1.21), Zr/Y (8.68–10.63), and Nb/Zr (0.39–0.45). The (87Sr/86Sr)i ratio varied from 0.7050 to 0.7063, with relatively constant and depleted εNd(t) values ranging from 0.52 to 1.08. The rocks were probably sourced from a low-degree partial melting of the asthenospheric mantle in a rift environment and had undergone the process of fractional crystallization. These characteristics indicate that the Saga basalts differ from the rift-related magmatic rocks produced by the Panjal Traps. Consequently, combined with the recently reported detailed fieldwork, the Zhongba Terrane disintegrated from the northern margin of Gondwana during the Late Permian, promoting the opening of the Neotethys Ocean, which is most likely caused by the northward subduction of the Paleotethys Ocean.

Sequential melting of deep crustal sources in a rift system: An example from the Southern Tibet

Sequential melting of deep crustal sources in a rift system: An example from the Southern Tibet

Structural and kinematic analysis of the Cuonadong dome, southern Tibet, China: Implications for middle-crust deformation

The Cuonadong Dome is located at the eastern part of the North Himalayan gneiss domes. Structural and kinematic analysis in the middle unit of the Cuonadong Dome provide significant new insights into the structural deformation of the middle crust in the Northern Himalaya. Field observations, microscopic kinematic and EBSD analyses, and deformation temperature estimates from the mid-crustal rocks of the Cuonadong Dome show high-strain D2 (top-to-N) kinematic fabrics with a downward-to-north progression from dominantly top-to-north shear in the garnet zone, to solely top-to-north shear in the kyanite/sillimanite zone. A combination of mineral assemblages, microstructures, and quartz crystal preferred orientation patterns indicates deformation temperatures associated with D2 kinematic fabrics increase with structural depth from ∼450 °C in garnet zone to > 630 °C in the kyanite/sillimanite zone. These values broadly overlap temperature range deduced from metamorphic petrography (450–630 °C). Microtextural relations indicate that peak metamorphism occurred post-D1 and pre-D2 deformation. Combined with the ∼1000-m-thick ductile deformation zone, the interpreted deformation temperatures yielded an average thermal field gradient of ∼ 180 °C/km over 1.05 km of structural thickness. Based on the geochronologic data, midcrustal D2 extensional deformation in the Cuonadong Dome initiated as early as early Oligocene (32 Ma) and ended during the middle Miocene (∼14 Ma). Comparative studies of D2 ductile deformation in midcrustal rocks from other North Himalayan gneiss domes and the South Tibetan Detachment System indicate that D2 shear zone in the Cuonadong Dome represent the northern part of the South Tibetan Detachment System, and highlight temporal and spatial variation in midcrustal D2 deformation patterns over the southern Tibet during the Himalayan orogeny.

Synotis nyalamensis (Asteraceae, Senecioneae), a new species from southern Xizang (Tibet), China

Synotis nyalamensis (Asteraceae, Senecioneae), a new species from Nyalam county in southern Xizang (Tibet), China, is described and illustrated. It is most closely similar to S. kunthiana, a species occurring in northwestern India, Nepal, and Pakistan, in having abaxially white-tomentose leaves and cylindric-campanulate capitula, but differs by having higher stature (45–60 vs. 20–40 cm), singular (vs. several) stems, caudate-acuminate (vs. acuminate) leaf tips, prominent (vs. obscure) nerves on abaxial side of leaves, and more disk florets (15–24 vs. 7–12).

Spatial Distribution of Soil Heavy Metals and Associated Environmental Risks near Major Roads in Southern Tibet, China.

Soil heavy metal pollution is becoming an increasingly serious environmental problem. This study was performed to investigate the contents of surface soil heavy metals (Cu, Zn, Pb, Cd) near six roads in the southern part of the Tibetan Plateau. Multivariate statistics, geoaccumulation index, potential ecological risk, and a human health assessment model were used to study the spatial pollution pattern and identify the main pollutants and regions of concern. The mean was ranked in the order Cd > Cu > Zn > Pb, with the average concentrations of Cd, Zn, and Cu exceeding their corresponding background levels 4.36-, 1.00-, and 1.8-fold, respectively. Soil Cd level was classified as posing a considerable potential risk near national highways and a high potential risk near non-national highways, whereas soil Cu, Zn, and Pb were associated with a low potential ecological risk for each class of roads. Furthermore, the non-carcinogenic risk due to soil heavy metals for each class of roads was within the acceptable risk level for three exposure pathways for both adults and children, but the carcinogenic risk attributable to soil Pb exceeded the threshold for children near highways G318, G562, and G219 and for adults near highway G318. Our work not only underscores the importance of assessing potential threats to ecological and human health due to soil heavy metal pollution on road surfaces but also provides quantitative guidance for remediation actions.

Future unbalanced-trends of grain supply and demand on the Tibetan Plateau

Forecasting the relation between grain supply and demand can help prevent potential food risk and realize sustainable agriculture development on the Tibetan Plateau (TP), which is an ecological security barrier for China. However, the patterns of future grain self-sufficiency at the county scale on the TP under different scenarios have been little analyzed. Using combining forecasts, production function, and scenario analysis, we evaluated the grain self-sufficiency ratios (SSRs) (i.e., the ratio of grain production to demand) of the staple, total, and balanced dietary grains on the TP at the county scale in 2030 and 2050. Our results showed that the staple grain on the TP will be sufficient with more than 150% SSR on average, but the supply will not meet the demands of both total grain (including staple and feed grain) and balanced dietary grain. Extreme disasters will increase the proportion of non-self-sufficient counties by 11%–16% compared with the base scenario, especially in southern Tibet. The positive effects of climate change will be low, but they can slow down the decline of SSRs in some counties in Sichuan Province and southern Tibet. In the future, the counties with better self-sufficiency will be mainly distributed in agricultural areas with high grain production, such as the Yarlung Zangbo River Basin in southern Tibet. Moreover, most counties in pastoral regions in the central TP and counties with greater population growth will not be self-sufficient. Our results provide important policy implications for agricultural layout and ecological security on the TP, such as the integrated development of agriculture and animal husbandry, increased concern about food risks in urban cities and agroecology, and the establishment of agricultural monitoring networks.

Co–Ni decoupling indicates fluid exsolution during the formation of podiform chromitites: Insights from the Luobusa ophiolite, southern Tibet

Podiform chromitites typically occur in harzburgites near the petrological Moho in ophiolite sections, and are petrologically and economically significant. Hydrous fluids may have an important role in the formation of podiform chromitites, although unambiguous evidence for the involvement of such fluids is rare. To examine whether hydrous fluids are involved in the formation of podiform chromitites, we measured the Ni, Co, Mn, and Zn contents of olivines and chromites in representative samples from the Luobusa ophiolite, southern Tibet, taking account of the different geochemical behaviors of these elements in melts and hydrous fluids. In the harzburgites, the olivine (Ol) has a limited compositional range (2605–2919 ppm Ni, 117–135 ppm Co, 736–1005 ppm Mn, and 28.9–35.7 ppm Zn), whereas the chromite (Chr) has a relatively variable composition (718–1239 ppm Ni, 364–493 ppm Co, 1314–2733 ppm Mn, and 1411–1900 ppm Zn). From the dunite lenses to the dunite envelopes, and to the chromitites, both olivine and chromite exhibit significant decreases in Co (Ol = 137 to 45 ppm; Chr = 542 to 168 ppm), Mn (Ol = 889 to 273 ppm; Chr = 2426 to 862 ppm), and Zn (Ol = 37.7 to 4.0 ppm; Chr = 1746 to 206 ppm) contents, and an increase in Ni contents (Ol = 3009 to 5946 ppm; Chr = 413 to 1462 ppm). These features cannot be fully explained by subsolidus re-equilibration, partial melting, fractional crystallization, and melt–rock reactions. Olivine relicts in chromite indicate the dissolution of pre-existing olivine in dunitic channels. The olivine dissolution may have been due to the water-rich nature of the parental melts of the chromitites. These observations and mass-balance calculations suggest that, during the formation of podiform chromitites, chromite crystallization was accompanied by olivine dissolution and exsolution of a hydrous fluid phase. This resulted in the preferential transfer of Ni into the melt and olivine relicts, and Co, Mn, and Zn into the fluid phase. As such, the chromite and olivine in the chromitites became Ni-rich and Co-, Mn-, and Zn-poor, which led to Ni–Co decoupling.

Along‐Strike Variation in the Initiation Timing of the North‐Trending Rifts in Southern Tibet as Revealed From the Yadong‐Gulu Rift

AbstractA 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.

Effect of Salinity in Alpine Lakes on the Southern Tibetan Plateau on Greenhouse Gas Diffusive Fluxes

AbstractInland waters play an important role in the global carbon cycle and are potential hotspots of greenhouse gas (GHG) production and emission. However, considerable uncertainty exists in GHG estimations from lakes on the Tibetan Plateau due, in part, to the lack of direct in situ observations and key predictor analyses. Considering that salinity is an important factor regulating lake GHGs, diffusive methane flux (FCH4) and carbon dioxide flux (FCO2) and concentrations of dissolved CH4 (dCH4) and CO2 (dCO2) were measured in 16 freshwater and brackish Tibetan lakes in Shigatse. The results demonstrated that FCH4 at the water–air interface in freshwater lakes (45.14 ± 58.86 μmol·m−2·s−1) was 15 times higher than that in brackish lakes (2.92 ± 3.85 μmol·m−2·s−1). There was a significant decrease in FCH4 from the littoral zone to the pelagic area in these lakes. The FCO2 in freshwater lakes (−0.18 ± 0.39 μmol·m−2·s−1) was significantly lower than that in brackish lakes (0.38 ± 0.22 μmol·m−2·s−1). Therefore, freshwater lakes were regarded as CO2 sinks, while brackish lakes were regarded as CO2 sources. According to the comprehensive CO2 equivalent diffusive fluxes (FCO2eq, 0.66 ± 0.97 μmol·m−2·s−1), the 16 lakes were a carbon source to the atmosphere during the sampling period. FCO2 enhancement could be compensated by the decrease in FCH4 at the water–air interface as a result of salinity gradients across lakes. Under the scenarios of climate warming and drying in southern Tibet from 2020 to 2035, lake FCO2eq tended to decrease in this area.

Early Jurassic Mafic Magmatism in the Eastern Tethyan Himalaya, Southern Tibet

Early Jurassic Mafic Magmatism in the Eastern Tethyan Himalaya, Southern Tibet

Grain size-dependent geochemical evidence reveals provenance and implications of aeolian sands, Dinggye region, southern Tibet

Grain size-dependent geochemical evidence reveals provenance and implications of aeolian sands, Dinggye region, southern Tibet

Subducting Indian Lithosphere Controls the Deep Carbon Emission in Lhasa Terrane, Southern Tibet

AbstractThe India‐Asia orogenic zone is considered to participate significantly in the Earth's geological carbon budget. However, the carbon cycling process at orogenic belts with ongoing continental subduction is poorly constrained. Here, new He‐C‐N systematics of hydrothermal gases in Lhasa terrane are reported to explore carbon cycling and the role of the subducting Indian slab. Except for samples where the CO2 content and C isotopic signature were modified by calcite precipitation, gas samples in Lhasa terrane display low 3He/4He ratios of 0.015–0.895 RA but with increasing mantle‐helium input from south to north. Our modeling results show that the continuous subduction of the Indian continental slab has caused high Th‐U contents and time‐integrated 4He production rates in the present mantle wedge beneath the Lhasa terrane. The N‐S helium isotopic trend can be interpreted as a northward‐decreasing mantle enrichment. Compared to volatiles showing crustal helium but mantle‐like δ13C ratios, mantle‐helium‐richer fluids display heavier δ13C ratios, higher CO2/3He and molar C/N values, indicating a substantial carbonate input. We propose that the heavier carbon isotopes are inherited from the carbonated‐enriched mantle (CEM) rather than the carbonate assimilation of the overlying continental crust. Combined with an eastward increase in dip angle of the Indian lithosphere, we suggest that the slab rollback has caused asthenosphere heat flow and consequent decarbonation in CEM beneath northern and eastern Lhasa terrane, leading to enhanced isotopically heavier carbon release. Our study highlights the controlling role of subducting Indian lithosphere on the regional distribution of volatiles in the Lhasa terrane.

Zircon U–Pb and sericite Ar–Ar geochronology, geochemistry and S–Pb–Hf isotopes of the Zebuxia Pb–Zn deposit, Tibet, southwestern China

The Zebuxia Pb–Zn deposit is located in southern Tibet and belongs to the western segment of the Northern Gangdese Metallogenic Belt. Based on the characters of deposit geology, geochronology, geochemistry, and S–Pb-Hf isotopes, the genesis and spatial–temporal evolution of the Pb–Zn mineralization in the Northern Gangdese Metallogenic Belt were elucidated. The results of sericite Ar-Ar dating yields an isochron age of 55.2 ± 0.8 Ma, accordant with the zircon U-Pb 54.9 ± 0.4 Ma age obtained from the biotite granite. The biotite granite is of high-K calc–alkaline and metaluminous with I-type affinity. The δ34S values of galena and pyrite range from + 1.3‰ to + 3.5‰ (mean = +2.4‰) and show magmatic origin. Pb isotopic results of galena and pyrite show the 206Pb/204Pb values are 18.611–18.666 (mean = 18.631), 207 Pb/ 204Pb values are 15.654–15.718 (mean = 15.678), 208Pb/204Pb values are 38.982–39.195 (mean = 39.064), representing the orogenic feature with upper crustal source mixed by mantle-derived materials. Based on the comprehensive analyses above, the Zebuxia Pb–Zn deposit belongs to structure–hydrothermal–filling type deposit. Combined with previous studies, we propose that the magmatic intensity determine the mineralization scale of the Pb–Zn deposits, while the nature of ore–related plutons constrain the source of mineralized fluids in the Northern Gangdese Metallogenic Belt. The investigation of the Zebuxia Pb–Zn deposit reveals the western section of the Northern Gangdese Metallogenic Belt has great prospecting potential as well.

Lithium isotope fractionation during magmatic differentiation and hydrothermal processes in post-collisional adakitic rocks

To investigate the behavior of Li isotopes during magmatic differentiation and the petrogenesis of Cu-bearing ore deposits, a suite of post-collisional adakitic rocks from Qulong region, southern Tibet, was studied. Their lithologies range from diorite through granodiorite to granite porphyry with the latter containing giant Cu deposits. Detailed evidence of field observation and geochemical signature suggest that these three sets of rocks were most likely formed by various degrees of partial melting and fractional crystallization from the same source. The dioritic enclave, granodiorite and granite porphyry have δ7Li values ranging from 0.2 to 8.2‰, 3.1 to 6.8‰, and 3.9 to 7.4‰, respectively. Most of these samples are overlapping in Li isotope composition, comparable to other granitoids worldwide, indicating insignificant Li isotope fractionation during partial melting and magma differentiation in adakite-like rocks. By contrast, their Li concentrations are mainly controlled by fractional crystallization as suggested from different modal mineralogy. This process does not lead to further enrichment of Cu although they have initial high concentrations (an average of ∼ 104 ppm). In comparison, granite porphyry has extremely high Cu contents (up to 2000 ppm) and their δ7Li values are positively correlated with Cu content, suggesting the involvement of magmatic fluids that most likely exsolved from deep magma chamber. Such fluids not only modified the Li isotopic compositions of granite porphyries, but also extracted metal elements from the highly evolved magma, eventually resulting in the Cu mineralization. Our work here provides new insight into the formation and evolution of the porphyry Cu-bearing deposit.

The genesis of Rare-alkali metal enrichment in the geothermal anomalies controlled by faults and magma along the northern Yadong-Gulu rift

Geothermal water from the hot springs in the Yadong-Gulu rift (YGR) of southern Tibet is extremely enriched in rare-alkali metal (RAM) elements; however, the mechanism of enrichment has long been debated. Much attention has been given to the deep melting magma of the YGR, but no direct evidence indicates whether and how it is connected to the RAM anomaly of hot springs. Determining the mechanism of RAM enrichment and its variations with the time and space of hot springs will contribute to the exploration of the hydrothermal metallogenic systems. This paper presents numerical hydrothermal numerical circulation models constrained by the geological data and the geophysical structure of the YGR. The results illustrate that the depths of boundary faults control the anomalous temperatures of hot springs. High-temperature springs (such as Yangbajing) could be induced by deep faults extending to the middle crust, whereas magma at a depth greater than 10 km has a limited effect on geothermal anomalies. Secondary faults define the extent of hydrothermal circulation and further determine the distribution of thermal anomalies across the rift. We simulate the enrichment and distribution of RAMs from a deep magma source. The pathways of RAMs from the source are consistent with hydrothermal circulation. RAM concentrations are lower in infiltrating groundwater and higher in ascending hot water. In general, deep faults control the hydrothermal circulation of geothermal groundwater. Deep faults and magma further constrain the distribution of RAM anomalies.

Reinvestigation of Devonian-Carboniferous palynostratigraphy in Yalai village, Nyalam County, southern Tibet, China

Reinvestigation of the Devonian-Carboniferous boundary sequence in Yalai village, Nyalam County, southern Tibet, enabled the recovery of well-preserved palynomorphs and conodonts in the Yali section. Based on quantitative analysis of the relative abundances of various palynomorphs, two palynological assemblages are recognized in the Famennian-Tournaisian boundary beds of the Yali section. In ascending order, they are the Retispora lepidophyta–Verrucosisporites irregularis (LI) assemblage and the Retispora lepidophyta–Vallatisporites vallatus (LV) assemblage. Both assemblages are tentatively correlated with the Famennian LN Biozone of Western Europe because of the appearance of Retispora lepidophyta and other index spores such as Vallatisporites verrucosus, Vallatisporites pusillites, Indotriradites explanatus, and Densosporites spitsbergensis in both palynological assemblages. The lower limestones of the Yali Formation yield biostratigraphic markers for the Devonian-Carboniferous boundary, including the conodont Siphonodella sulcata and Protognathodus kockeli, correlated with the VI Biozone from Western Europe and parts of Gondwana. The upper Lazhabu Member of the Yali Formation yielded Retispora lepidophyta, Vallatisporites vallatus, and Vallatisporites pusillites of the LV Biozone, indicating that some typical palynomorphs elements of the LN Biozone of Western Europe persisted into Tournaisian in southern Tibet.

Potential geographical distribution of Stipa purpurea across the Tibetan Plateau in China under climate change in the 21st century

Stipa purpurea ( S. purpurea ), a dominant herbage resource in alpine steppe, has an important impact on animal husbandry and the maintenance of natural environmental stability in the Tibetan Plateau (TP). As a hot spot of global warming, the TP has been greatly affected by climate change. Based on the MaxEnt model, we simulated the potential habitat changes of S. purpurea on the TP in the 21st century using 197 distribution records combined with current (2000–2018) and future (2021–2100) climate data. We also analyzed the critical factors influencing habitat distribution and driving habitat change. The results showed that the MaxEnt model performed well, with the area under the curve (AUC) value of training data and test data being 0.845 and 0.722, respectively. Annual precipitation, elevation, and annual average temperature were identified as the most critical environmental factors shaping the potential distribution of S. purpurea , and temperature was identified as the most critical factor driving S. purpurea habitat change. Under the current climate, the potential habitat area of S. purpurea was 55.15 × 10 4 km 2 , mainly distributed in the Eastern Qinghai-Qilian montane steppe, Southern Tibet montane shrub-steppe, and Ngari montane desert. By the end of the 21st century, the potential habitat area of S. purpurea showed an overall increasing trend, under two shared socio-economic pathways (SSP245 and SSP585) was 87.37 × 10 4 km 2 and 57.80 × 10 4 km 2 , respectively. A comparison of warming scenarios indicated that warming had a positive effect on the distribution of S. purpurea within a certain temperature range, but continued warming would limit distribution ranges. In response to climate warming in the 21st century, potential habitats of S. purpurea will shift northwestward and to higher altitudes. These results will provide a reference for implementing long-term conservation and management strategies on the TP and similar regions . • Species distribution modeling was used to predict the distribution of S. purpurea . • The “BioVars” package was used to calculate 19 bioclimatic variables. • Temperature contributed most to driving habitat redistribution of S. purpurea . • Warming had a positive effect on S. purpurea within a certain range. • Habitats of S. purpurea will shift northwestward and to higher altitudes.

Jurassic true polar wander recorded by the Lhasa terrane on its northward journey from Gondwana to Eurasia

Paleomagnetic data constrain paleogeographic motion of rocks relative to the Earth's spin axis, which is a sum of plate motion relative to the mantle and true polar wander. Discerning between these effects is challenging for studies aiming to reconstruct paleo-plate motions from deformed orogenic terranes. Here, we study the paleolatitudinal drift history of the Lhasa terrane of southern Tibet that migrated from the northern Gondwana to the southern Eurasian margin between late Triassic and early Cretaceous time. Previous work identified a 180 Ma near-equatorial Lhasa latitude and assumed near-constant paleolatitudinal drift. Large-scale true polar wander at this time, however, which has been argued for in previous work, requires highly variable Lhasa plate motion rates relative to Gondwana. Here, we test whether the alternative interpretation of constant plate motion rates provides a better prediction of paleomagnetic data. To this end, we present a new paleomagnetic pole from ∼155 Ma volcanics (here dated by U/Pb zircon) of the Lhasa terrane. Our pole comprises site mean directions from 46 lavas, passes a fold test, and is supported by an extensive rock magnetic and microscopic analysis that reveals no evidence of remagnetization. Our results give an average direction of D±ΔDx=337.1°±2.6°, I±ΔIx=−13.8°±4.9°, and a corresponding paleopole position at λp=45.3°N, φp=295.3°E with K=69.8 and A95=2.5°, predicting a similar near-equatorial, paleolatitude as at 180 Ma. This paleolatitudinal standstill is consistent with predicted paleolatitudes from global APWPs that account for Jurassic TPW and assume a constant Lhasa-Gondwana (India) oceanic spreading rate of ∼8 cm/a during the 215-130 Ma opening of the Neotethys and closure of the Mesotethys oceans. Contemporaneous arc magmatism on the Lhasa terrane was previously interpreted to indicate that the Lhasa terrane was located above a subduction zone during its northward journey to Tibet: our results show that if our reconstruction is accurate, then trench migration rates also must have been ∼8 cm/a. Our results are consistent with the range of rates of global long-lived trench migration that have been reconstructed in other studies, but they are much higher than measured in most modern systems. Our results more completely document the Lhasa terrane's separation from Gondwana and provide a straightforward methodology of using paleomagnetic data to test plate kinematic scenarios, overcoming the problem of the unknown effect of true polar wander on paleomagnetic data from deformed terranes.

Pronounced Changes in Thermal Signals Associated with the Madoi (China) M 7.3 Earthquake from Passive Microwave and Infrared Satellite Data

Thermal variations in surface and atmosphere observed from multiple satellites prior to strong earthquakes have been widely reported ever since seismic thermal anomalies were discovered three decades ago. These thermal changes are related to stress accumulation caused by the tectonic activities in the final stage of earthquake preparation. In the present paper, we focused on the thermal changes associated with the 2021 Madoi M 7.3 earthquake in China and analyzed the temporal and spatial evolution of the Index of Microwave Radiation Anomaly (IMRA) and the Index of Longwave Radiation Anomaly (ILRA) based on 8-year microwave brightness temperature (MWBT) and 14-year outgoing longwave radiation (OLR) data collected by satellites. We also explored their responses in different tectonic units (seismogenic fault zone and active tectonic block). Our results indicated that the enhanced IMRA was distributed along the seismogenic fault since mid-February and reappeared for a longer time and with stronger intensity in March and April 2021. The pronounced enhancement in the ILRA was observed within one month over Bayan Har tectonic and adjacent blocks. The higher ILRA over the tectonic blocks in the southern Tibet Plateau at the beginning of 2021 could be associated with the regional stress accumulation, as proven by the occurrences of two moderate earthquakes during this period.