Search Results (7)

The Longshou Shan area is located on the northeastern margin of the Tibetan Plateau in northwest China. The study area is located where the sinistral Altyn Tagh and Haiyuan Faults overlap and the Qilian Shan thrust fault systems in the northeastern Kunlun–Qaidam Block converge. This region experiences frequent seismic events, including large-magnitude earthquakes, which are significant indicators of ongoing tectonic deformation and stress accumulation in the Earth’s crust. The seismicity of Longshou Shan is not only a consequence of its tectonic setting but also a key factor in understanding the seismic hazard posed to the surrounding areas. The tectonic activity within the Longshou Shan region of NW China is a focus of our geomorphological research due to its significance in understanding the complex interactions between tectonic forces and surface processes. Situated on the northeastern edge of the Tibetan Plateau and along the eastward trace of the Altyn Tagh Fault, Longshou Shan is crucial for investigating the plateau’s northward expansion. This study leverages ALOS-based digital elevation models (DEMs) and geomorphic indices to evaluate the tectonic activity in the area, employing various indices such as mountain front sinuosity, valley floor width-to-height ratio, hypsometric curves, asymmetry factors, basin shape indices, and channel steepness index to provide a comprehensive tectonomorphological analysis. Our results indicate intense tectonic activity on both sides of Longshou Shan, making it a highly hazardous seismic area. We also highlight the importance of thrust faults and related crustal shortening in the formation and expansion of the plateau. Full article

Under a warming–humidifying climate, precipitation patterns on the Qinghai–Tibet Plateau have significantly shifted due to a water imbalance in its solid–liquid structure. Using monthly precipitation data (1961–2023), we analyzed the spatial distribution and dynamics of 200 mm and 400 mm isohyets through climate propensity rates and centroid center migration. The results show: (1) precipitation increased significantly (4.17 mm/decade), decreasing spatially from southeast to northwest. Regionally, it increased in areas like the southern Qinghai Plateau region, but declined in the southern Himalayas and central–southern Altyn−Tagh Mountains. (2) The 200 mm line migrated northward in southern Qiangtang, shrank around Qaidam Basin, with an overall northeastward shift; the 400 mm line moved westward in eastern Qiangtang and Hehuang Valley, northward in southern Qinghai, trending northwest. (3) From 1961 to 1990 and 1991 to 2023, the 200 mm isohyet’s centroid shifted 49 km north and 17 km east, while the 400 mm isohyet moved 22 km north and 19 km west. (4) Vertically, the 200 mm isohyet ascended by 7.11 m/decade, while the 400 mm line rose more slowly (2.61 m/decade). These changes indicate a significant shift in precipitation distribution, impacting regional hydrological processes. Full article

In arid regions, climatic fluctuations significantly affect vegetation structure and function. Sun-induced chlorophyll fluorescence (SIF) can quantify certain physiological parameters of vegetation but has limitations in characterizing responses to climate change. This study analyzed the spatiotemporal differences in response to climate change across various ecological regions and vegetation types from 2000 to 2020 in Xinjiang. According to China’s ecological zoning, R1 (Altai Mountains-Western Junggar Mountains forest-steppe) and R5 (Pamir-Kunlun Mountains-Altyn Tagh high-altitude desert grasslands) represent two ecological extremes, while R2–R4 span desert and forest-steppe ecosystems. We employed the standardized precipitation evapotranspiration index (SPEI) at different timescales to represent drought intensity and frequency in conjunction with global OCO-2 SIF products (GOSIF) and the normalized difference vegetation index (NDVI) to assess vegetation growth conditions. The results show that (1) between 2000 and 2020, the overall drought severity in Xinjiang exhibited a slight deterioration, particularly in northern regions (R1 and R2), with a gradual transition from short-term to long-term drought conditions. The R4 and R5 ecological regions in southern Xinjiang also displayed a slight deterioration trend; however, R5 remained relatively stable on the SPEI24 timescale. (2) The NDVI and SIF values across Xinjiang exhibited an upward trend. However, in densely vegetated areas (R1–R3), both NDVI and SIF declined, with a more pronounced decrease in SIF observed in natural forests. (3) Vegetation in northern Xinjiang showed a significantly stronger response to climate change than that in southern Xinjiang, with physiological parameters (SIF) being more sensitive than structural parameters (NDVI). The R1, R2, and R3 ecological regions were primarily influenced by long-term climate change, whereas the R4 and R5 regions were more affected by short-term climate change. Natural grasslands showed a significantly stronger response than forests, particularly in areas with lower vegetation cover that are more structurally impacted. This study provides an important scientific basis for ecological management and climate adaptation in Xinjiang, emphasizing the need for differentiated strategies across ecological regions to support sustainable development. Full article

The recently discovered Mida nephrite deposit, located in the East Kunlun Mountains, Qiemo County, Xinjiang, Northwest China, contains new types of white and greenish white nephrite formed by limestone replacement, which shows microstructures, macroscopic features and country rocks typologies that are quite different from those of the other deposits along the Kunlun–Altyn Tagh Mountains. The gemological and mineralogical characteristics of Mida nephrite are presented here. These nephrites show an ivory white color and a porcelain-like appearance, with semitranslucent-to-opaque transparency and a porcelain-to-greasy luster. Petrographic study, electron probe microanalysis (EPMA) data and scanning electron microscopy (SEM) images have indicated that the nephrite is composed of tremolite, accompanied by minor quartz, calcite and diopside. Tremolite aggregates have shown different textures, like flaky, granular, fibrous–felted, bundle, radial and metasomatic relict textures. Quartz has appeared in granular or disseminated form, dispersed in the tremolite matrix. Calcite has shown a metasomatic relict texture in the white nephrite samples. Diopside has shown euhedral grains, with some distributed with a certain geometric appearance. Based on our observations, it is suggested that the quartz in the nephrite originated from Si-rich hydrothermal fluids. We propose that the substantial size difference of mineral grains, together with uncompacted grains with inter-particle pores, are the main reasons for the internal reflection and refraction under transmitted light, which allow less transmitted light to pass through the nephrite body and generate the appearance of a semitranslucent-to-opaque transparency, ivory white color and porcelain luster. Our study has unveiled that the Mida nephrite is not typical of the two known types (D-type: dolomite-related; S-type: serpentinite-related) and is overlapped by quartz grains dispersed throughout the less compact tremolite matrix. These observations would help set it apart from the majority of nephrite jades found in the Kunlun Mountains region and provide valuable insights for enhancing comprehension of the diversity of the nephrite deposits. Full article

The tectonic evolution of the Altyn Tagh Fault (ATF) remains controversial during the Tertiary. Qaidam Basin is the largest and highest plateau inland basin inside the Tibet Plateau. Sediments in the basin provide sedimentary records of the evolution history of its surrounding orogens, such as the ATF, located on the northwest margin of the Qaidam Basin. Comprehensive analyses of sandstone petrography, heavy mineral assemblages, and mineral geochemistry were adopted to effectively indicate the tectonic evolution history of ATF. The result indicates that the sediments in a wide range of the northwestern Qaidam Basin (e.g., the Xichagou section, the Yueyashan section) were derived from the Altyn Mountains. The increasing immaturity of sediments, increased denudation, and sedimentation processes from the early-middle Miocene to the Pliocene can be explained by the active tectonic setting of the ATF. During the early Miocene (ca. 22 Ma), there was an abrupt change in the heavy mineral composition of sediments in the northwestern Qaidam Basin. This change may be attributed to the large-scale slip motion along the ATF. Therefore, ~22 Ma is the key transforming period of the ATF system. On the foundation of the above, we suggest a two-stage evolution model of the ATF during the Tertiary: (1) From the late Eocene to the Oligocene, the tectonic setting of the ATF was relatively calm; (2) During the early Miocene period, the ATF underwent large-scale tectonic activation. It is likely to be a strike-slip tectonic activity, accompanied by an uplift of the Altyn Mountains. The active tectonic setting of the ATF was sustained after the Miocene. Full article

Using provenance analysis to build an accurate source-to-sink relationship is the key to infer mountain building scenarios around the Qaidam Basin, and also important to understanding the uplift and expansion of the Tibetan Plateau. However, some conflicting provenance inferences are caused by different interpretations for the prevalent existence of the late Paleozoic to early Mesozoic age group in detrital zircon U‒Pb age spectra of the Paleogene strata at the northern Qaidam Basin, and these need to be resolved. In this article, an integrated study of sediment distribution, heavy mineral assemblages, and detrital zircon U‒Pb geochronology is carried out to analyze provenance of the Paleogene strata at the northern Qaidam Basin. The decreasing trends of the net sand to gross thickness ratios and conglomerate percentages away from the Qilian Mountains and Altyn Tagh range to basin interior clearly support they are the provenance areas. Sedimentation of materials from the Altyn Tagh range is spatially confined to a small area in front of the mountains. A large sandy body with a uniform distribution of detrital zircon ages (containing a lot of the late Paleozoic to early Mesozoic zircon ages) and heavy mineral assemblages in the Xiaganchaigou Formation is supplied by the Qilian Mountains. Full article

The historic Yinggelike nephrite jade deposit in the Altyn Tagh Mountains (Xinjiang, NW China) is renowned for its gem-quality nephrite with its characteristic light-yellow to greenish-yellow hue. Despite the extraordinary gemological quality and commercial significance of the Yinggelike nephrite, little work has been done on this nephrite deposit, due to its geographic remoteness and inaccessibility. This contribution presents the first systematic mineralogical and geochemical studies on the Yinggelike nephrite deposit. Electron probe microanalysis, X-ray fluorescence (XRF) spectrometry, inductively coupled plasma mass spectrometry (ICP-MS) and isotope ratio mass spectrometry were used to measure the mineralogy, bulk-rock chemistry and stable (O and H) isotopes characteristics of samples from Yinggelike. Field investigation shows that the Yinggelike nephrite orebody occurs in the dolomitic marble near the intruding granitoids. Petrographic studies and EMPA data indicate that the nephrite is mainly composed of fine-grained tremolite, with accessory pargasite, diopside, epidote, allanite, prehnite, andesine, titanite, zircon, and calcite. Geochemical studies show that all nephrite samples have low bulk-rock Fe/(Fe + Mg) values (0.02–0.05), as well as low Cr (0.81–34.68 ppm), Co (1.10–2.91 ppm), and Ni (0.52–20.15 ppm) contents. Chondrite-normalized REE patterns of most samples exhibit strong to moderate negative Eu anomalies (0.04–0.67), moderate LREE enrichments, nearly flat HREE patterns, and low ΣREE contents (2.16–11.25 ppm). The nephrite samples have δ¹⁸O and δD values of 5.3 to 7.4‰ and –74.9 to –86.7‰, respectively. The mineralogy, bulk-rock chemistry, and O–H isotope characteristics are consistent with the dolomite-related nephrite classification. Based on mineral paragenetic relationships, three possible mineral crystallization stages are recognized: (1) diopside formed by prograde metasomatism; (2) nephrite jade formed by retrograde metasomatism and replacement of Stage I anhydrous minerals; (3) hydrothermal alteration after the nephrite formation. Features of transition metal contents indicate that the color of the Yinggelike nephrite is likely to be controlled by the Fe²⁺, Fe³⁺, and Mn. Yellowish color is related to Mn and especially Fe³⁺, while greenish color is related to Fe²⁺. Our new mineralogical and geochemical results on the Yinggelike nephrite provide better constraints on the formation of other nephrite deposits in the Altyn Tagh Mountains, and can facilitate future nephrite prospecting and research in the region. Full article