Search Results (5)

The Yutian region at the southwestern termination of the Altyn Tagh Fault has experienced four moderate-to-strong earthquakes since 2008, providing an opportunity to investigate fault interactions within a transtensional tectonic setting. In this study, we derive the coseismic deformation and slip model of the 2020 Mw 6.3 Yutian earthquake using ascending and descending Sentinel-1 InSAR data. The deformation field exhibits a characteristic subsidence–uplift pattern consistent with normal faulting, and the preferred slip model indicates a north–south-striking fault with slip concentrated at depths of 6–9 km. To place this event in a broader tectonic context, we incorporate published slip models for the 2008 and 2014 earthquakes together with a simplified finite-fault model for the 2012 event to construct a unified four-event source framework. Static Coulomb stress calculations reveal complex interactions among the four earthquakes. Localized positive loading from the 2012 event partially counteracts the negative $\Delta CFS$ imposed by the 2008 and 2014 earthquakes, reshaping the stress field rather than simply promoting or inhibiting failure. The cumulative stress evolution shows persistent unclamping and repeated shear-stress reversals, indicating that the 2020 earthquake resulted from long-term extensional loading superimposed on multi-stage coseismic stress redistribution. These results demonstrate that multi-event stress analysis provides a more reliable framework for assessing seismic hazards in regions with complex local stress fields. 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

Asymmetric deformation has been observed along the Altyn Tagh Fault (ATF), the northern boundary of the Tibetan Plateau. Several mechanisms have been proposed to explain this asymmetry, including contrasts in crustal strength, lower crust/upper mantle rheology, deep fault dislocation shifts, and dipping fault geometry; however, the real scenario remains debated. This study utilizes a time series Interferometric Synthetic Aperture Radar (InSAR) technique to investigate spatially variable asymmetries across the western section of the ATF (83–89°E). We generated a high-resolution three-dimensional (3D) crustal velocity field from Sentinel-1 data for the northwestern Tibetan Plateau (~82–92°E; 33–40°N). Our results confirm that pronounced greater deformations within the Tibetan Plateau occur only along the westernmost section of the ATF (83–85.5°E). We propose this asymmetry is primarily driven by a splay fault system within a transition zone, bounded by the ATF in the north and the Margai Caka Fault (MCF)–Kunlun Fault (KLF) in the south, which accommodates an east–west extension in the central Tibetan Plateau while transferring sinistral shear to the KLF. The concentrated strain observed along the ATF and MCF–KLF lends more support to a block-style eastward extrusion model, rather than a continuously deforming model, for Tibetan crustal kinematics. Full article

The Kaladawan iron deposit is located in the North Altyn Tagh and exhibits occurrences of iron ore bodies at the contact zone between Ordovician magmatic rocks (basalts, rhyolite, and granodiorite) and marble. However, controversy persists regarding the genetic classification and metallogenic mechanism of this deposit. Through a field investigation, single mineral in situ geochemical analysis, whole-rock geochemical analysis, and Fe isotope determination, the following conclusions are made: (1) Ti-(Ni/Cr) and (V/Ti)-Fe diagrams indicate that the magnetite from all studied rocks underwent hydrothermal metasomatism, while (Ni/(Cr + Mn))-(Ti + V) and (Ca + Al + Mn)-(Ti + V) diagrams suggest a skarn origin for these magnetites. Therefore, it can be inferred that the Kaladawan iron deposit is skarn-type. (2) The iron ore exhibits similar rare-earth-element characteristics to the altered basalt. Additionally, the altered basalts (δ⁵⁶Fe = 0.024~0.100‰) are more enriched in light Fe isotopes than the unaltered basalts (δ⁵⁶Fe = 0.129~0.197‰) at the same location, indicating that the ore-forming materials of the Kaladawan iron ore are mainly derived from basaltic rocks. (3) According to the law of mass conservation and the intermediate Fe isotopic composition of the iron ore between the granodiorite and basalt, the hydrothermal fluid for the formation of iron ores was inferred to be derived from the late intrusive granodiorite. Full article

The origin of granitic rocks from the South Qilian orogenic belt is of great significance for understanding the continental tectonic framework of Western China. Currently, scholars have different opinions on the tectonic evolution of the South Qilian. Huashigou granite, which exhibits multiple intrusive episodes, is a suitable example for studying the tectonic evolution of the South Qilian. New zircon U–Pb ages and the whole-rock elemental and Sr–Nd–Hf–O isotopic compositions of Huashigou granitic rocks are presented here to investigate their petrogenesis and discuss the tectonic implications for the evolution of the South Qilian orogenic belt. LA-ICP-MS zircon U–Pb dating yielded crystallization ages of 368.7 ± 3.5 Ma, 261.5 ± 0.63 Ma, and 262.2 ± 1.4 Ma for granodiorites from the Hua1 pluton, quartz diorites from the Hua2 pluton, and porphyritic tonalites from the Hua4 pluton, respectively. Late Devonian granodiorites from the Hua1 pluton belonged to the metaluminous calc-alkaline series and were characterized by an enrichment in LREEs, a depletion in HREEs, negative Eu anomalies, and Sr/Y ratios of 9.17 to 11.67. They showed (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.712356 to 0.71195, ε_Nd(t) values of −6.56 to −6.14, and an ε_Hf(t) value of −2.06. Middle Permian granitic rocks mainly consisted of quartz diorites and porphyritic tonalites, which are part of the metaluminous tholeiitic series and weakly peraluminous tholeiitic series, respectively. Quartz diorites from the Hua2 pluton were characterized by an enrichment in LREEs, depletions in HREEs and HESEs, weak negative Eu anomalies, and Sr/Y ratios of 13.25 to 14.79. They showed (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.705905 to 0.705971, ε_Nd(t) values of +0.78 to +0.82, and a δ¹⁸O_V-SMOW value of 12.4‰. Porphyritic tonalites of the Hua4 pluton were characterized by an enrichment in LREEs, depletions in HREEs and HESEs, weak negative Eu anomalies, and Sr/Y ratios of 9.22 to 12.74. They showed (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.719528, ε_Nd(t) values of −8.57, and a δ¹⁸O_V-SMOW value of 11.8‰. We can conclude that Late Devonian granodiorites were derived from the partial melting of enriched and shallow-depth crustal materials, whereas Middle Permian granitic rocks were formed by the delamination of a thickened lower crust after the closure of the Paleo-Tethys Ocean, which caused the underplating of mantle-derived basaltic magma, inducing the partial melting of the lower crust at different depths. Our results show that there were at least two important stages of compressional and extensional tectonic switches in the South Qilian orogenic belt during the Late Paleozoic Era, and the evolution of Altyn Tagh–Qilian–North Qaidam had evident stages. Full article