Journal of Asian Earth Sciences最新文献

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.

This study investigates the seismic behavior and deformation characteristics in the outer-arc region off the Nicobar trench using stress inversion and teleseismic finite-fault modeling. The spatial and depth-wise variations in stress field in this region indicate variations in post-seismic deformation scenarios along the arc. The lateral shear, similar to the north Wharton basin, is the major deformational field in the Nicobar segment, favoring earthquake faulting along ∼ESE or ∼NNE nodal planes here. Shallow oblique-normal faulting and deeper oblique-reverse regimes are observed in the Nias region. These observations suggest that the plate bending effects directly influence the ongoing tectonics in the Nias region. Moreover, variations in the stress fields across the arc could be indicative of an uncoupled plate interface. Our finite-fault modeling analysis indicates dominant ∼ESE-WNW fault plane orientations for selected events from this region. This suggests the possibility of faulting within similarly oriented active shear structures within the northern Wharton Basin, contrasting the prevailing ∼N-S faulting pattern in that area. Besides, the centroid depths of most of these earthquakes are typically within the 600°C isotherm. However, the seismic slip may extend deeper by rupturing the crust, occasionally reaching upper mantle depths.

We study attenuation of seismic waves in the source area of Palghar swarm in western part of India. The intrinsic and scattering loss are separated using the Wennerberg method in the assumption of co-located source and receiver. The coda-normalization and single back-scattering model of coda wave generation are used for determining Q factors describing attenuation for body (Q_P and Q_S) and coda (Q_C) wave, respectively. The data set includes 1419 high-quality earthquakes (1.5 < M_L<4.7) during intense swarm from 2019 to 2022 recorded by six stations in the Palghar region. Analysis is performed at five central frequencies 1.5, 3, 6, 12, and 24 Hz for varying lapse time windows of 5 to 40 s. The frequency-dependent P- and S-wave attenuations are expressed as ${Q_P=\left(8.7\pm 1\right)f}^{\left(0.85\pm 0.01\right)}$ and ${Q_S=\left(28.4\pm 0.4\right)f}^{\left(0.87\pm 0.004\right)}$, respectively in 1.5–24 Hz. The spatially averaged frequency-dependent coda Q_C(f) relations are ${Q_C=\left(26.9\pm 13\right)f}^{\left(0.93\pm 0.04\right)}$ and ${Q_C=\left(138.8\pm 41\right)f}^{\left(1.08\pm 0.05\right)}$ for 5 and 40 s, respectively. The S-waves attenuate faster than the coda waves in 1.5–24 Hz. The Q_P/Q_S ratio is greater than unity in the analysed frequencies. Intrinsic attenuation dominates the scattering attenuation in the whole frequency range. Dominant intrinsic absorption with its strong frequency dependence requires the presence of fluids in the shallow crust, as shown from other geophysical methods in the Palghar swarm area. Attenuation mechanisms are found to be similar for other swarm areas worldwide. The attenuation results could be useful while finding the earthquake source parameters to correct the path in the modelling for accurately estimating source scaling relations of swarm-related earthquakes.

The Indian Ocean lithosphere is a complex assemblage of large igneous provinces, seamounts, plateaus and ridges of different loading ages and tectono-thermal evolution. As a proxy for the strength of tectonic plates, effective elastic thickness (T_e) illustrates the relationship between surface deformation and lithospheric rheology of the diverse provinces in response to long-term tectonic processes. Mapping the spatial variations in lithospheric rheology can aid in understanding the detailed tectono-thermal history of the Indian Ocean. In this paper, we perform an assessment of the spatial variation of T_e for the Indian Ocean from the inversion of the real free-air admittance between free-air gravity anomalies and bathymetry corrected for the effect of density variations within sediments using a continuous wavelet spectral analysis. Incorporating the effect of sediments substantially reduces T_e estimates and better corresponds with the tectonic units in the study region. The results show low overall T_e over the Indian Ocean attributed to magmatism and temperature during a multistage opening process. We further demonstrate that temperature controls the strength of warm and young oceanic lithosphere, evidenced by the positive correlation between T_e and geothermal proxies. Finally, moderately low T_e values at the Southwest Indian Ridge suggest a relatively cold ultraslow lithosphere with sparse magmatism compared to typical mid-ocean ridges.

To constrain the incipient Pacific-type orogeny and tectonic processes in the Early Paleozoic proto-East Asian continental margin, the Motai–Matsugadaira–Yamagami (MMY) metamorphic rocks in the South Kitakami belt, northeast Japan were investigated. They are divided into two different types: amphibolite-facies rocks associated with serpentinite and blueschist-facies rocks associated with pelitic and psammitic schists. Three geochemical groups are identified from the MMY metamorphic rocks. Groups 1 and 2 resemble geochemical characteristics of mid-ocean ridge basalt and continental arc rocks, respectively. Group 3 exhibits considerable depletion of highly incompatible elements, which is caused by the high degree of partial melting of a hot mantle plume. The zircon U–Pb ages of Group 1 indicate that the protoliths experienced amphibolite-facies metamorphism soon after their formation in the Early Ordovician. Group 2 exhibits a coeval zircon U–Pb age with Group 1. The age distribution of detrital zircons in the MMY psammitic schists shows a peak of 500–400 Ma, the presence of Archean to Neoproterozoic zircons, and the youngest Late Devonian zircon. The following model is proposed for the tectonic evolution of the proto-East Asian continental margin: (1) the formation of an arc in the eastern margin of the South China craton in the Cambrian to Ordovician; (2) the subduction of a spreading axis and an oceanic plateau at the same time as the continental arc formation; (3) the consumption and subduction of arc materials by tectonic erosion; and (4) the formation of the Carboniferous accretionary complex and high-pressure metamorphic rocks under steady oceanic plate subduction. The proposed tectonic evolution model may also be applicable to equivalent Early Paleozoic rocks in southwest Japan.