Southeastern Tibetan Research Articles

Enhancing Geological Understanding and Identifying Gold Anomalies in the Ailaoshan Orogen

AbstractThe Ailaoshan Orogen in the southeastern Tibet Plateau, situated between the Yangtze and Simao blocks, underwent a complex structural, magmatic, and metamorphic evolution resulting in different tectonic subzones with varying structural lineaments and elemental concentrations. These elements can conceal or reduce anomalies due to the mutual effect between different anomaly areas. Dividing the whole zone into subzones based on tectonic settings, ore cluster areas, or sample catchment basins (Scb), geochemical and structural anomalies associated with gold (Au) mineralization have been identified utilizing mean plus twice standard deviations (Mean + 2STD), factor analysis (FA), concentration‐area (C‐A) modeling of stream sediment geochemical data, and lineament density in both the Ailaoshan Orogen and the individual subzones. The FA in the divided 98 Scbs with 6 Scbs containing Au deposits can roughly ascertain unknown rock types, identify specific element associations of known rocks and discern the porphyry or skarn‐type Au mineralization. Compared with methods of Mean + 2STD and C‐A model of data in the whole orogen, which mistake the anomalies as background or act the background as anomalies, the combined methods of FA and C‐A in the separate subzones or Scbs works well in regional metallogenic potential analysis. Mapping of lineament densities with a 10‐km circle diameter is not suitable to locate Au deposits because of the delineated large areas of medium‐high lineament density. In contrast, the use of circle diameters of 1.3 km or 1.7 km in the ore cluster scale delineates areas with a higher concentration of lineament density, consistent with the locations of known Au deposits. By analyzing the map of faults and Au anomalies, two potential prospecting targets, Scbs 1 and 63 with a sandstone as a potential host rock for Au, have been identified in the Ailaoshan Orogen. The use of combined methods in the divided subzones proved to be more effective in improving geological understanding and identifying mineralization anomalies associated with Au, rather than analyzing the entire large area.

A mysterious treasure originated from Africa: evolutionary history of the endangered spoon-winged lacewings (Neuroptera: Nemopteridae: Nemopterinae) from China

Abstract The spoon-winged lacewings (Neuroptera: Nemopteridae: Nemopterinae) are a group of charismatic insects with morphological and biological specializations. Among the known 105 species of Nemopterinae worldwide, only one species, namely Nemopistha sinica Yang, 1986, is recorded from East Asia. However, the morphology, taxonomic status, and evolutionary history of this rare species are poorly known. Here, we present a systematic revision of the Chinese Nemopterinae and establish a new genus, Sinonemoptera, that comprises Sinonemoptera sinica (Yang, 1986) comb. nov. from western Yunnan and a new species, Sinonemoptera tibetana sp. nov., from southeastern Tibet. Based on the phylogeny of Nemopterinae combining morphological and molecular evidence, Nemopterinae are divided into two major clades by the length of the adult abdomen, and Sinonemoptera gen. nov. together with some Afrotropical genera constitute a monophyletic lineage characterized by a long abdomen. Our results suggest a Late Cretaceous African origin and three Tertiary transcontinental dispersals in shaping the global distribution of Nemopterinae. Our ecological niche modelling demonstrates the specific requirement for warm and dry habitats in nemopterines and highlights the urgent need for protection of the savannah-like habitat along the Nujiang valley for the Chinese Nemopterinae.

Mineralogical and magnetic variations of periglacial loess in SE Tibet reveal mid-Pleistocene expansion of Tibetan glacial activity

The formation and evolution of the cryosphere on the Tibetan Plateau is of great significance in understanding the Earth's carbon and climatic system. Periglacial loess deposits in southeastern Tibet offer a means to constrain this history as they contain critical information on glacial grinding and frost shattering processes in high-altitude mountain regions through time, which yield lithogenic fractions of largely loess silts and sands. Based on combined analyses of lithogenic magnetic properties and mineralogical composition, here we find that increasing high mountain production and supply of fresh detrital components since the mid-Pleistocene climate transition (MPT, 1.2–0.7 Ma) led to a substantial increase of the lithogenic susceptibility and decrease in chemical weathering intensity of periglacial loess in southeastern Tibet. The agreement of these findings with similar results from eolian loess on the northern margins of the Tibetan Plateau suggests a plateau-wide glacier expansion during the MPT. Enhanced glacial erosion and freeze-thaw activities occurred in the high-altitude mountain regions of the plateau during the MPT, thereby providing vast amounts of fresh detritus for the formation of loess deposits. High and constant values of lithogenic magnetic parameters in the loess deposits after 0.7–0.6 Ma further indicate that the Middle Pleistocene is a critical period for the establishment of modern-like glacial and periglacial landforms on the Tibetan Plateau. Our results further suggest that enhanced Quaternary glaciation in SE Tibet occurred earlier than in the north, which we attribute to climate cooling combined with regional seasonal snowline lowering. As such, a close relationship exists between global climate changes, development of pan-Tibetan glaciations, and large-scale dust emission.

Petrogenesis and Tectonic Implications of the Oligocene Dalongtan Shoshonitic Syenite Porphyry in Central Yunnan, Southeastern Tibetan Plateau: Constraints from Geochronology, Geochemistry and Sr-Nd-Hf Isotopes

Shoshonitic rocks are widely distributed in post-collisional settings and provide key information on deep geodynamic mechanisms and magmatic evolution. In this paper, we present petrographic, zircon U-Pb age-related, trace elemental, Hf isotopic, bulk-rock elemental, and Sr-Nd isotopic data of the Dalongtan shoshonitic syenite porphyries (DSSPs) in central Yunnan, southeastern Tibet. The DSSPs formed at 33.2 ± 0.3 Ma in a post-collisional setting. They define linear trends on Harker diagrams, and they display similar trace element patterns and enriched bulk-rock Sr-Nd isotopes [(87Sr/86Sr)i = 0.70964–0.70968, εNd(t) = −12.9 to −12.7] and zircon Hf isotopes (εHf(t) = −15.7 to −13.1) to the coeval mantle-derived potassic mafic rocks. This suggests that the DSSPs were fractionated from the lithospheric mantle-derived mafic magmas. The DSSPs, along with the coeval felsic and mafic magmatic rocks (37.2–32.3 Ma), exhibit a planar distribution on the SE Tibet and predate the left-lateral shearing of the Ailaoshan–Red River shear zone (ARSZ) (32–22 Ma), suggesting that there are no genetic relationships between them. The DSSPs have geochemical characteristics similar to those of A-type granites, with high total alkalinity (10.39–11.17 wt.%), HFSE concentrations (Zr + Nb + Ce + Y = 890.2–1054.3 ppm), Ga/Al ratios (10,000 × Ga/Al = 2.95–3.46), whole-rock zircon saturation temperatures (906–947 °C), and oxygen fugacity (ΔFMQ = +3.30–+4.65), indicating that they are products of the high-temperature melting of the lithosphere as a result of asthenosphere upwelling in extensional settings. Based on our data and regional observations, it is proposed that the generation of the DSSPs may be linked to the convective thinning of the thickened lithospheric mantle following the India–Asia collision.

Geochemical Characteristics of Thermal Springs and Insights Into the Intersection Between the Xiaojiang Fault and the Red River Fault, Southeastern Tibet Plateau

AbstractDuring the ongoing uplift and expansion of the southeastern margin of the Tibetan Plateau, the front edge of the Sichuan‐Yunnan rhombic block (SYB) has experienced intense tectonic activity and frequent seismicity. In this study, the fluid geochemistry in the primary active faults at the front edge of the SYB was investigated, with the aim of understanding the tectonic activity and intersection relationship between the Xiaojiang fault (XJF) and the Red River fault (RRF). Thermal spring water and gases exhibit a coupled spatial distribution relationship; relatively high ion concentrations and 3He/4He ratios (Rc/Ra ratios of 0.21 to 0.62Ra) are observed along the RRF, Qujiang fault (QJF), and Shiping‐Jianshui fault (SJF). Multidisciplinary research results have indicated that mantle‐derived intrusion has been detected in the crust beneath the QJF and SJF. The current tectonic activity in the front edge of the SYB remains intense, with compressive stresses shifting toward the western side of the XJF and accumulating on the QJF and SJF. This has led to the development of fractures, enhancing the water–rock interaction and deep‐derived gas degassing along the faults. The unmixing characteristics of fluids at the intersection area of these two faults suggest the absence of conduits for fluid migration between the faults. Owing to the lower gas 3He/4He ratios, lower shear strain rates, stable reservoir temperature field, and extremely low historical seismicity in the Indo‐Chinese block, it is speculated that the current movement of the XJF may not cut through the RRF and continue southward.

Cenozoic crustal thickness variations and surface uplift in the southeastern Tibetan Plateau: Insights from detrital zircon trace elements in the Gongga Shan region

The timing and mechanism of uplift in the southeastern Tibet Plateau have long been subjects of debate. The Gongga Shan region, positioned at the convergence of the Songpan-Ganzi, Chuandian, and Yangtze blocks, serves as a crucial vantage point for unraveling the evolutionary history of the southeastern Tibet Plateau. Nevertheless, the uplift history of the Gongga Shan region remains shrouded in uncertainty. By employing multivariate trace element ratios and reconstructing crustal thickness using zircon Eu/Eu*, our research has unveiled distinct periods of crustal thickening and thinning events. Within the time span of ∼240–160 Ma, a discernible thickening trend emerged from ∼35 to ∼45 km between ∼240 and ∼ 215 Ma, followed by a relatively stable phase from ∼215 to ∼170 Ma, and subsequently a decline from ∼170 to ∼160 Ma, reducing the thickness from ∼45 to ∼30 km. In the period from ∼55 to ∼5 Ma, an initial increase in thickness occurred from ∼30 to ∼60 km between ∼55 and ∼ 30 Ma, succeeded by an overall thinning from ∼60 to ∼35 km between ∼30 and ∼ 10 Ma. Moreover, based on our reconstructed crustal thickness data, we have traced the paleo-elevation changes in the Gongga Shan region from the Cenozoic to the present, revealing a fluctuation from ∼0.5 to ∼4.5 km. We attribute the Triassic-Jurassic crustal thickening and subsequent thinning to the Triassic orogeny and post-collision extension following the closure of the Paleo-Tethys Ocean. Our findings further suggest that during the Eocene-Oligocene period, the Gongga Shan region experienced significant crustal thickening and surface uplift, indicative of intense compression. This phenomenon likely resulted from the northeast-directed compression of the Indian-Eurasian plate, causing substantial crustal shortening and thickening in specific areas of the southeastern Tibet Plateau, leading to rapid surface uplift. Subsequently, during the Oligocene-Miocene, the detachment and subsidence of the lithospheric mantle triggered rapid crustal thinning in the Gongga Shan region. This phase was accompanied by relatively stable and slight surface uplift, signifying a shift in the plateau uplift mode of the southeastern Tibet Plateau from compression to lateral extrusion.

Present‐day Upper‐crustal Strain Rate Field in Southeastern Tibet and its Geodynamic Implications: Constraints from GPS Measurements with ABIC Method

AbstractThe Earth's surface kinematics and deformation are fundamental to understanding crustal evolution. An effective research approach is to estimate regional motion field and deformation fields based on modern geodetic networks. If the discrete observed velocity field is obtained, the velocity related fields, such as dilatation rate and maximum shear strain rate, can be estimated by applying varied mathematical approaches. This study applied Akaike's Bayesian Information Criterion (ABIC) method to calculate strain rate fields constrained by GPS observations in the southeast Tibetan Plateau. Comparison with results derived from other three methods revealed that our ABIC‐derived strain rate fields were more precise. The maximum shear strain rate highlighted the Xianshuihe–Xiaojiang fault system as the main boundary for the outward migration of material in southeastern Tibet, indicating rotation of eastern Tibet material around the eastern Himalaya rather than whole extrusion along a fixed channel. Additionally, distinct dilatation rate patterns in the northeast and southwest regions of the fault system were observed. The northeast region, represented by the Longmenshan area, exhibited negative dilatational anomalies; while the southwest region, represented by the Jinsha River area north of 29°N, displayed positive dilatational anomalies. This indicates compression in the former and extension in the latter. Combined with deep geophysical observations, we believe that the upper and lower crusts of the Jinsha River area north of 29°N are in an entire expanding state, probably caused by the escape‐drag effect of material. The presence of a large, low‐viscosity region south of 29°N may not enable the entire escape of the crust, but instead result in a differential escape of the lower crust faster than the upper crust.

A Critical Appraisal of the Sensitivity of Detrital Zircon U–Pb Provenance Data to Constrain Drainage Network Evolution in Southeast Tibet

AbstractProvenance tools, particularly detrital zircon U–Pb analysis, have been widely employed to test drainage network evolution in southeast Tibet and its linkage with the growth of the Tibetan Plateau. Numerous provenance studies have been conducted on the sediments in the paleo‐Yangtze and paleo‐Red River drainage basins. Nevertheless, it is still hotly debated as to whether a “Mississippi” (dendritic) pattern Greater paleo‐Red River, originating from southeast Tibet and draining to the South China Sea, existed in the early Cenozoic, and was subsequently captured by the paleo‐lower Yangtze due to uplift of southeastern Tibet. In this study, in addition to presenting new data from the Gonjo and Jianchuan basins along which the Greater paleo‐Red River is proposed to have flowed, we compiled all the published detrital zircon U–Pb data from the paleo‐upper Yangtze and paleo‐Red River drainage basins from Triassic and younger rocks. Our large database of detrital zircon U–Pb analyses shows that the different terranes in the paleo‐upper Yangtze and paleo‐Red River drainage basins have similar zircon U–Pb signatures since the Late Triassic closure of the Paleo‐Tethys Ocean. Therefore, most of the sediments in the Cenozoic sedimentary basins in southeast Tibet could have been either deposited by long‐distance transport in large rivers from southeast Tibet or recycled from local bedrock. Given the potential importance of sedimentary recycling that we have demonstrated, this poses challenges to the use of detrital zircon U–Pb analyses to determine paleodrainage in this region. We therefore further explored the previously relatively limited use of Sr–Nd isotopes on mudstones and detrital mica 40Ar/39Ar ages, with new analyses from the Gonjo and Jianchuan Basins, to determine if these techniques were better suited to reconstruct paleodrainage evolution. Whilst these techniques do show some promise, more analyses and strategic sampling are required to obtain a full understanding of the extent of their potential utility. Overall, our integrated provenance study indicates that the available data are not sufficiently conclusive to support or refute the Greater paleo‐Red River capture model.

Elevation-Dependent Natural Regeneration of Abies georgei var. smithii Forest in Southeastern Tibet

The comprehensive impacts of biotic and abiotic factors on the natural regeneration of Abies georgei var. smithii (Abies) forests in Tibet are not thoroughly understood. To address this gap, our study focused on the regeneration densities of Abies seedlings, saplings, and small trees across 21 plots (each 20 m × 20 m) along an elevation gradient from 3730 m to 4330 m in the Sygera Mountains of Southeastern Tibet. We meticulously measured a suite of 11 variables that describe stand structures and ecological conditions. Through analyses using Spearman’s correlation analysis, hierarchical partitioning, and multiple linear regression, we identified key ecological drivers for successful Abies regeneration. Our results highlighted a peak in the abundance of seedlings, saplings, and small trees at an elevation of 3930 m. As the elevation rose from 3730 m to 4330 m, we observed an initial increase followed by a decrease in canopy cover (canopy), mother tree density (MotherT), 1000-seed weight (SeedW), litter thickness (LitterT), moss cover (MossC), moss thickness (MossT), soil moisture (SM), and soil bulk density, while mean annual temperature and soil depth to permafrost consistently decreased. The critical ecological drivers for Abies natural regeneration were identified as follows: MossT was pivotal for seedling density; canopy and MossC were influential for sapling density, and MotherT was the main factor affecting the density of small trees. This study suggests that a high density of mother trees and a thick and highly covered layer of moss are conducive to the natural regeneration of Abies in the Sygera Mountains. Understanding the current status of regeneration is vital for informing conservation and management strategies for Abies forests in Tibet.

Elevational distribution patterns and drivers factors of fungal community diversity at different soil depths in the Abies georgei var. smithii forests on Sygera Mountains, southeastern Tibet, China.

Soil fungal communities play a crucial role in maintaining the ecological functions of alpine forest soil ecosystems. However, it is currently unclear how the distribution patterns of fungal communities in different soil layers of alpine forests will change along the elevational gradients. Therefore, Illumina MiSeq sequencing technology was employed to investigate fungal communities in three soil layers (0-10, 10-20, and 20-30 cm) along an elevational gradient (3500 m to 4300 m) at Sygera Mountains, located in Bayi District, Nyingchi City, Tibet. The results indicated that: 1) Soil depth had a greater impact on fungal diversity than elevation, demonstrating a significant reduction in fungal diversity with increased soil depth but showing no significant difference with elevation changes in all soil layers. Within the 0-10 cm soil layer, both Basidiomycota and Ascomycota co-dominate the microbial community. However, as the soil depth increases to 10-20 and 20-30 cm soil layers, the Basidiomycota predominantly dominates. 2) Deterministic processes were dominant in the assembly mechanism of the 0-10 cm fungal community and remained unchanged with increasing elevation. By contrast, the assembly mechanisms of the 10-20 and 20-30 cm fungal communities shifted from deterministic to stochastic processes as elevation increased. 3) The network complexity of the 0-10 cm fungal community gradually increased with elevation, while that of the 10-20 and 20-30 cm fungal communities exhibited a decreasing trend. Compared to the 0-10 cm soil layer, more changes in the relative abundance of fungal biomarkers occurred in the 10-20 and 20-30 cm soil layers, indicating that the fungal communities at these depths are more sensitive to climate changes. Among the key factors driving these alterations, soil temperature and moisture soil water content stood out as pivotal in shaping the assembly mechanisms and network complexity of fungal communities. This study contributes to the understanding of soil fungal community patterns and drivers along elevational gradients in alpine ecosystems and provides important scientific evidence for predicting the functional responses of soil microbial ecosystems in alpine forests.

The evolution of glacial lake and glaciers and their potential impact on glacial debris flow activity in the Palong Zangbu catchment in Southeastern Tibet

Due to warm and humid air currents of the Indian Ocean and the southwest monsoon, the Palong Zangbo catchment in southeastern Tibet has developed oceanic glaciers in the valley, and the activity of glacial debris flows has been gradually intensified under neotectonic activity, frequent earthquakes, climate change, and extreme rainfall. In this paper, the topographic and morphological data of the debris flow basin, the dynamic evolution characteristics of glaciers and glacial lakes were analyzed by using multisource long-term series of remote sensing images. Simultaneously, the distribution of moraines and landslide sources were extracted based on satellite image. In addition, climate change in the study area was analysed using temperature and rainfall data from the last 40 years, revealing that the average temperature in the study area from May to October presented a fluctuating tendency as a whole, especially after 2013, when the temperature gradually increased. As these temperature changes led to continuous melting of the glaciers in the study area, the glacier area decreased from 8,300 km2 in 1988–4,584 km2 in 2019, which decreased nearly 45%. However, the number and area of glacial lakes in the study area gradually increased under a power-law trend, which further led to a significant increase on the possibility of glacial lake rupture in the study area. Due to the joint effects of earthquakes, glacier melting and glacial lake collapse, the debris flows in the study area were well developed, and a total of 122 debris flows were found with varying channel lengths, areas and material sources. Importantly, the characteristics of the glaciers, glacial lakes and climate change in the study area have indicated that the glaciers have retreated, the number of glacial lakes has increased, and the risk of debris flow in this basin will increase in the future. Therefore, it is necessary to strengthen monitoring and early warnings on floods due to glacial lake collapses and debris flows in the study area to improve the risk management of debris flows and floods and the prevention and mitigation of disasters.

Enhanced glacial lake activity threatens numerous communities and infrastructure in the Third Pole

Glacial lake outburst floods (GLOFs) are among the most severe cryospheric hazards in the Third Pole, encompassing the Tibetan Plateau and surrounding Himalayas, Hindu Kush, and Tianshan Mountains. Recent studies on glacial lake changes and GLOF characteristics and risks in this region have shown scattered and insufficiently detailed features. Here, we conduct an appraisal of the GLOF risks by combining high-resolution satellite images, case-by-case high-precision GLOF modeling, and detailed downstream exposure data. The glacial lake changes from 2018 to 2022 in the region were primarily driven by the accelerated expansion of proglacial lakes. The GLOF frequency has exhibited a significant increasing trend since 1980, with intensified activity in Southeastern Tibet and the China-Nepal border area over the past decade. Approximately 6,353 km2 of land could be at risk from potential GLOFs, posing threats to 55,808 buildings, 105 hydropower projects, 194 km2 of farmland, 5,005 km of roads, and 4,038 bridges. This study directly responds to the need for local disaster prevention and mitigation strategies, highlighting the urgent requirement of reducing GLOF threats in the Third Pole and the importance of regional cooperation.

Petrogenesis of the Late Eocene to Early Oligocene Yao'an Shoshonitic Complex, Southeastern Tibet: Partial Melting of an Ancient Continental Lithospheric Mantle beneath the Yangtze Block

AbstractCenozoic potassic–ultrapotassic igneous rocks are widespread in the southeastern Tibetan Plateau. Their petrogenesis and magmatic processes remain subject to debate in spite of numerous publications. Almost all of the Cenozoic extrusive and intrusive rocks in the Yao'an area, western Yunnan Province, SW China, are geochemically shoshonitic, collectively termed here the Yao'an Shoshonitic Complex (YSC). The YSC is located in the (south) easternmost part of the ENE–WSW‐trending, ∼550 km‐long and ∼250 km‐wide Cenozoic magmatic zone; the latter separates the orthogonal and oblique collision belts of the India–Eurasia collision orogen. Previously published geochronological and thermochronological data revealed that the rocks of the YSC were emplaced over a short timespan of 34–32 Ma. This and our new data suggest that the primary magma of the YSC likely was formed by partial melting of ancient continental lithospheric mantle beneath the Yangtze Block. This part of the continental lithospheric mantle had likely not been modified by any oceanic subduction. Fractionation crystallization of an Mg‐ and Ca‐bearing mineral and Ti‐Fe oxides during the magmatic evolution probably account for the variable lithologies of the YSC.

The late Eocene rise of SE Tibet formed an Asian ‘Mediterranean’ climate

Southeastern (SE) Tibet forms the transition zone between the high interior Tibetan Plateau and the lowlands of southwest China. So understanding the elevation history of SE Tibet, a biodiversity hotspot, enlightens our understanding of the interactions between tectonics, monsoon dynamics and biodiversity. Here we reconstruct the uplift history of the Markam Basin, SE Tibet, during the middle−late Eocene based on U − Pb dating, plant fossil assemblages, and stable and clumped isotope analyses. Our results suggest that the floor of the Markam Basin was at an elevation of 2.6 ± 0.9 km between 42 Ma and 39 Ma, where the mean annual air temperature (MAAT) was 13.2 ± 2.4 °C. The basin then rose rapidly to 3.8 (+0.6/−0.8) km before 36 Ma. Integrated with existing paleoelevation data, we propose that the high plateau boundary (∼3.0 km) of SE Tibet formed during the late Eocene. Numerical climate modeling with realistic paleo-landscapes shows that with the rise of SE Tibet, a Mediterranean-like climate developed in the region characterized by bi-modal precipitation with two wet seasons in boreal spring and autumn. The high topographic relief of SE Tibet, coupled with this distinctive Mediterranean-like climate system, helped develop the high biodiversity of the Hengduan Mountains.

Upper crustal structure across the Xiaojiang fault system revealed by ambient noise tomography from a dense short-period array

The Central Yunnan block (CYB) plays a key role in accommodating the crustal tectonic deformation of the southeastern Tibet, but its exact mechanism is poorly understood. Here we obtained a fine S-wave velocity structure of the upper crust across the Xiaojiang fault system in CYB, using the ambient noise tomography with a linear dense short-period array. The result shows a strong S-wave velocity variation along the profile, which is consistent with geomorphology and hypocenters occurred in this area. The velocity variations along the profile correspond well to the major faults seen on the surface and are consistent with the transition from surface erosion, to ductile basement and to rigid basement in the greater depth. Combining the upper crustal structure from our image with the location of hypocenters, we propose that most faults of Xiaojiang fault system cut through the upper crust steeply and control the tectonic deformation of the upper crust in the CYB.

New records of the white-cheeked macaque provide range extension for the endangered primate in Gaoligong Mountains.

White-cheeked macaque Macaca leucogenys is a recently described primate species discovered by camera-trap surveys in the Medog region in 2015. The species was thought to be narrowly distributed in southeastern Tibet. However, knowledge on the distribution and conservation of the species is quite limited. Based on a systematic camera-trapping survey, we report the occurrence of the species in the Gaoligong Mountains, over 350km southeast of the nearest known population. We recorded 3025 photographs of white-cheeked macaques representing 481 independent records from 59 camera-trap stations with total trapping efforts of 18,437 camera days. Notably, part of the newly discovered locations of the white-cheeked macaque are outside of nature reserves without any formal protection and management. Our survey also confirms the occurrence of ten primate species in the Gaoligong Mountains, accounting for 35.7% of China's primates, including the Skywalker hoolock gibbon Hoolock tianxing and the Myanmar snub-nosed monkey Rhinopithecus strykeri etc. These findings reveal a new distribution record for the white-cheeked macaque and further highlight the conservation values of Gaoligong Mountains for globally threatened primate species. We also provide a preliminary report on the daily activity patterns of this endangered species, which enriches the bio-ecological data of the poorly studied species. We believe the report has significant implications for understanding the ecology of the species and improving conservation planning.

Petrogenesis of the Eocene Highly Fractionated Granite Porphyry with REE Tetrad Effect: An Example from Western Yunnan, Southeastern Tibetan Plateau

Highly fractionated granites are widely distributed in the crust and provide unique windows into magmatic evolution. This study reports petrography, zircon U–Pb ages, trace elemental, and Hf isotopic, as well as whole-rock elemental and Nd isotopic data of highly fractionated granite porphyries from the Shiguanshan area in western Yunnan, southeastern Tibet. The granite porphyries were formed at 34.0 ± 0.3 Ma in a post-collisional setting. They are strongly peraluminous (A/CNK = 1.95–2.80), have high SiO2 content (SiO2 = 78.16–79.13 wt.%) and zircon saturation temperatures (803–829 °C, average 819 °C), and low MgO, with pronounced enrichment in Pb, U, Th, and Rb, and depletion in Ti, Eu, P, Sr, and Ba, and belong to highly fractionated A-type granites. These rocks define linear trends on Harker diagrams and display similar enriched whole-rock Nd isotopic (εNd(t) = −12.8 to −12.3) and zircon Hf isotopic (εHf(t) = −10.4 to −8.8) compositions compared to the published data of coeval mantle-derived syenite porphyries, which can be attributed to fractional crystallization processes. A quantitative model suggests that the Shiguanshan granite porphyries likely formed through the fractionation process of a mineral assemblage consisting of plagioclase, K-feldspar, biotite, and amphibole (in a ratio of 40:30:25:5), with fractionation degrees of 50%–55%. The magmatic textures and zircons, decoupling between the REE tetrad effect and fractionation of twin-elements, along with the modeling result of Rayleigh fractionation, suggest that the REE tetrad effect in the Shiguanshan granite porphyries may be caused by fractionation of accessory minerals. Our data, along with regional observations, propose that the generation of these granite porphyries is possibly related to lithospheric removal following the Indo–Asia collision.

Variations, controls and predictions of soil saturated hydraulic conductivity under different land use types in the alpine region of Tibet, China

Understanding the variations and controls of soil saturated hydraulic conductivity (Ks) under different land use types in the alpine region of Tibet is fundamental for predicting Ks in high-altitude regions where sample points are difficult to obtain and is important for establishing the regional soil hydrological model. In this study, soils samples under farmland, forestland, and grassland were collected from an east-west transect in southeastern Tibet, China. Basic soil properties and Ks were measured to analyze the influencing factors of Ks under different land use types and to establish suitable pedotransfer functions (PTFs) for predicting Ks in the alpine region. The average value of Ks followed the decreasing order of grassland (2.33 cm h−1) > farmland (2.12 cm h−1) > forestland (1.59 cm h−1). Ks of grassland (0.25–9.19 cm h−1) decreased gradually with increasing soil depth. Ks of farmland (0.11–8.82 cm h−1) increased initially and then decreased with increasing soil depth, whereas Ks of forestland (0.12–4.46 cm h−1) exhibited the opposite trend. There were significant differences in the main controlling factors of Ks under different land use types. In farmland, soil bulk density (BD), non-capillary porosity (Pn), clay and gravel content (GC) were the main drivers of Ks (P < 0.05). The dominant influencing factors of Ks in forestland were BD and total porosity (Pt) (P < 0.05), while Pn and GC were the main factors controlling Ks in grassland (P < 0.05). Compared with the multiple linear stepwise regression models and published PTFs, the BP neural network transfer model had better prediction accuracy for Ks in the alpine region. Our results not only provide hydraulic parameters for regional hydrological modeling and but also lay a foundation to construct Ks prediction models for other alpine regions in the world.

Receiver Function Adjoint Tomography for Three‐Dimensional High‐Resolution Seismic Array Imaging: Methodology and Applications in Southeastern Tibet

AbstractA new technique for P‐wave receiver function (PRF) inversion, within the framework of wave equation‐based adjoint tomography and referred to as receiver function adjoint tomography (RFAT), has been developed to obtain models of Vp, Vs, and density. This innovative technique fits the synthetic PRFs with observed PRFs and can better image the lateral variations of Vs from the crust to the uppermost mantle than traditional 1‐D PRF inversion. We utilized RFAT to perform high‐resolution imaging beneath a dense seismic array in Southeastern Tibet, revealing low‐velocity zones extending from the uppermost mantle to the crust, as well as an eastward dipping Moho under the Red River Fault (RRF). Our inversion results provide direct evidence for the existence of a distinct asthenospheric upwelling channel beneath the RRF, and further highlight the effectiveness of RFAT for accurately imaging subsurface structures.

Coexisting High-Al and High-Cr Chromitites in the Dingqing Ophiolite (SE Tibet): Inferences to Compositional Heterogeneity in the Tethyan Upper Mantle

The Dingqing ophiolite represents a significant allochthonous ophiolite nappe in the eastern segment of the Bangong–Nujiang suture zone in southeastern Tibet. The microanalytical data of associated podiform chromitites classify them into two distinct varieties: high-Al and high-Cr. The coexistence of both high-Cr and high-Al chromitites in the Dingqing ophiolite suggests a complex or multistage evolutionary history of the host rocks. New petrological and geochemical analyses are used herein to unravel the interrelationships between the chromitite ores and host rocks and assess the mechanism of formation. The Dingqing ophiolitic nappe is made up mainly of harzburgite, dunite, and less abundant pyroxenite and gabbro. Several small lens-shaped bodies of chromitite ore are mostly confined to the harzburgite rocks, with ore textures varying from massive to sparsely disseminated chromite. In addition to magnesiochromite, the orebodies contain minor amounts of olivine, amphibole, and serpentine. The textural relationships provide compelling evidence of plastic deformation and partial melting of the associated peridotites. Detailed examination of the Cr-spinel grains reveals a wide range of composition, spanning from high-Al (Cr# = 3.18–59.5) to high-Cr (Cr# 60.3–87.32). The abundances of the platinum-group element (PGE) in chromitites are significantly variable (93 to 274 ppb). Formation of the Dingqing peridotites most likely took place in a mid-ocean ridge (MOR) setting, and subsequent modifications by supra-subduction zone (SSZ) melts resulted in heterogenous or mixed geochemical characteristics of these rocks. Chemistry of the spinel–olivine–clinopyroxene assemblage demonstrates multiple stages of partial melting of the source mantle rocks, including an early phase of restricted partial melting (~20%–30%) and a later phase of extensive partial melting (&gt;40%). The formation of the high-Al chromitite type was associated with the early phase (constrained melting), whereas extensive partial melting in the late stages likely led to the accumulation of high-Cr podiform chromitite bodies.