Journal of Asian Earth Sciences最新文献

Three color variations of grey members (including grey and banded juvenile clasts) were observed in the 52 ka ignimbrite deposits of Maninjau caldera, Indonesia; namely dark grey (DGM), pale grey (PGM), and light grey (LGM). All grey members were phenocryst-rich ( 24, 20, and 31 % for DGM, PGM, and LGM, respectively) and comprise plagioclase, pyroxene, amphibole, biotite, and oxides as the main phenocryst phases; however, apatite is exclusively present in DGM. Plagioclase with unzoned and coarsely sieved texture was observed in all grey members, while finely sieved and oscillatory zoned textures were exclusive in LGM. Notably, DGM is characterized by the highest MgO value among all grey members, followed by PGM and LGM (∼0.72, 0.46, and 0.34 wt% MgO under ∼74.0 wt% SiO₂, respectively). Based on the amphibole geothermobarometer and plagioclase hygrometer, we found that all grey magmas were stored at a relatively similar range of pressure and water content, but DGM yields a higher apparent temperature than those of PGM and LGM. Such distinctive petrography and chemical characteristics, coupled with different temperature conditions strongly suggest that each grey member originated from different magma bodies, which were stored below the most voluminous white magma (the source of white pumice). The sudden decompression of the white magma via overpressure causes destabilization to the smaller grey magmatic bodies, allowing them to rise and erupt as grey and banded pumices during the final eruption stage. Our results enrich the evidence of the formation of multiple magma reservoirs in large-silicic magmatic systems, which might be a common behavior before large eruptions. Moreover, our detailed glass compositions for each juvenile type may be useful for further regional tephrochronology studies.

The Pamir Plateau, NW prolongation of the Tibetan Plateau, experienced late Cenozoic thrusting and extensional shearing/faulting and mainly receives moisture from the mid-latitude Westerlies. Thus, this region provides a natural laboratory to study how tectonic activity and climate impact topography. In this study, we extracted geomorphic indices from digital elevation model data, including local relief, normalized channel steepness index (k_sn), river longitudinal and χ profiles, as well as cross-valley profiles, to reveal the topographic variations across the Pamir Plateau, and to analyze the effects of tectonic activity and climate on its topography. Because the upper reaches of the Panj, Ghez, and Tashkurgan river catchments, and the Karakul Lake endorheic catchment are located in extremely low precipitation regions and dominantly result from late Cenozoic crustal extension, they generally have low local relief and k_sn values, gentle gradients on the χ-elevation plots, and wide valleys, especially along the intermontane basins. By contrast, the lower reaches of the Panj, Ghez, and Tashkurgan catchments generally have high local relief and k_sn values, steep gradients on the χ-elevation plots, and narrow V-shaped, deeply-incised valleys. For the lower reaches of the Panj catchment in the western Pamir, this difference is due to relatively high precipitation from the Westerlies, but for those of the Ghez and Tashkurgan catchments in the eastern Pamir, although they receive low precipitation, they cross the footwall of the Kongur Shan normal fault, along which tectonic uplift rates are particularly high. During the past ∼ 25 Ma, the drainage divide between the Panj catchment and the Ghez and Tashkurgan catchments migrated eastwards from the Pamir Plateau interior to its present location along the eastern Pamir Range, driven by high precipitation and erosion to the west.

The concentration of atmospheric CO₂ increased rapidly during the last deglaciation due to CO₂ outgassing from oceans. However, records of deglacial surface seawater pCO_2-sw are sparse, hindering our understanding of the process and mechanism of air-sea CO₂ exchange and its influence on glacial-interglacial climate change. Here we reconstructed surface seawater pCO_2-sw for the last deglacial period using carbon isotope composition (δ¹³C) of giant diatom (Ethmodiscus rex) frustules from deep-sea sedimentary core collected in the Philippine Sea, western Pacific. Results showed that air-sea CO₂ was fluctuating in the western Pacific during the last deglaciation. The gradients of air-sea CO₂ are dominated by monsoon and biological productivity. The enhanced East Asian winter Monsoon and shallow thermocline during late Heinrich Stadial 1 maintained equilibrium in the air-sea CO₂ exchange balance. During the Bølling period, enhanced East Asian Summer Monsoon has been observed to accelerate the dissolution of eolian-dust and promoted the growth of Ethmodiscus rex, which has been linked to increased primary productivity and, consequently, the uptake of atmospheric CO₂ in the western Pacific. During the Allerød period, continued enhancement of EASM allowed the Philippine Sea to act as a weak CO₂ source releasing CO₂ to the atmosphere. During the Younger Dryas period, as the EASM weaken and the EAWM strengthen, ΔpCO_2(sw-atm) decreased. Our findings highlight the tropical ocean’s role in deglacial air-sea CO₂ exchange and provide insights into the monsoonal and biological drivers of the processes.

The nature of the crustal deformation of the northeastern margin of the Tibetan Plateau is vital for elucidating the expansion mechanism of the plateau. We installed 21 continuous GNSS stations and obtained a horizontal velocity field with high spatial resolution. We also acquired a line-of-sight(LOS) velocity field with Sentinel-1 images covering the study area from 2014 to 2022. A multi-scale spherical wavelet method was employed to unify the reference frames of GNSS and InSAR data. After unifying the reference frame, the two data types achieve high consistency. Combining GNSS and InSAR velocities yielded the three-dimensional interseismic velocity field in the northeastern margin of the Tibetan Plateau. Furthermore, we analyzed the crustal deformation characteristics based on the three-dimensional deformation field. The crustal deformation exhibits a pronounced northeastward shift relative to the Ordos block, whereas the interior of the Ordos block remains remarkably stationary, behaving as a rigid unit. The Liupanshan fault is primarily characterized by uplift, devoid of any notable horizontal deformation across the fault. The left-lateral strike-slip mainly characterizes the Haiyuan fault.. The maximum east–west deformation velocity on the southern side of the fault is approximately 3.9 mm/yr, decreasing to about 1.0 mm/yr at the eastern end of the fault. The western segment of the West Qinling fault exhibits a minor east–west motion. Our result provides essential data for further study of the crustal deformation patterns.