Journal of Asian Earth Sciences最新文献

The northern South China Sea (SCS) experienced a significant transition from a lacustrine to marine environment in the Paleogene, and its deep-water basin of Zhu-II Depression is in particular extensively studied due to its richness in oil and gas resources. However, limited number of boreholes in the deep-water area has long constrained a better understanding on the provenance of the Paleogene strata and the associated sediment transport processes. In this study, detrital zircon U-Pb ages and three-dimensional (3D) seismic-reflection data were systematically employed to investigate the “source-to-sink” pathways and interplay of longitudinal and transverse sediment dispersal. Our results indicate that the Zhu-II Depression sediments of the northern SCS were predominantly derived from the surrounding nearby paleo-uplifts in the early and middle Eocene. A significant provenance shift took place in the late Eocene, when the local paleo-uplift source was replaced by a distant source from the western SCS. Sediments were transported from west to east by the “Kontum-Ying-Qiong River” as a longitudinal dispersal. In the Oligocene, the “Kontum-Ying-Qiong River” delivered large amounts of sediments from Central Vietnam to the eastern part of the northern SCS. Meanwhile, the Pearl River gradually evolved through regional tectonic processes and influenced the deep-water area of Zhu-II Depression as a transverse dispersal. Sediments from both “Kontum-Ying-Qiong” and Pearl Rivers converged and deposited as deep-water deltas in the Zhu-II Depression. This dual provenance system in the northern SCS deep-water area was featured by the interplay between longitudinal and transverse sediment dispersal. It was largely controlled by the tectonic-palaeogeographic pattern inherited from the Mesozoic arc system.

This study examines the evolution characteristics of shale pores in the Late Permian Longtan Formation located in the Lower Yangtze region of South China. The complete process of thermal evolution of the samples was achieved through thermal simulation experiments while identifying qualitatively the pore types and their development characteristics using field emission-scanning electron microscope (FE-SEM). Quantitative analysis of pore size distribution was conducted through mercury intrusion capillary pressure (MICP), nitrogen (N₂) and carbon dioxide (CO₂) adsorption experiments. The paper comprehensively analyzed the pore evolution characteristics and controlling factors of shale in the study area, with an analysis of diagenetic differences. Findings reveal that during the pore evolution process, both morphology and pore size are influenced by thermal maturity. The pore volume is dominated by mesopores and macropores, while the specific surface area is mainly dominated by mesopores and micropores. Thermal evolution promotes the formation of micropores and mesopores but hinders the development of macropores. Moreover, clay minerals transformation and mineral dissolution make certain contributions to the development of micropores. The diagenesis in the study area is controlled primarily by the pyrolysis of organic matter. Pyrite and clay minerals are the first to dissolve, followed by calcite and quartz. Five stages of evolution characterization have been identified from low-mature stage (R_o = 0.88 %) to overmature stage (R_o = 3.35 %) in combination with diagenesis. The development of pore structure and its influencing factors vary across different stages. The influencing factors mainly include hydrocarbon generation from organic matter, compaction, mineral transformation, and dissolution. The process of hydrocarbon generation in organic matter occurs throughout the entire pore evolution process, resulting in the development of numerous micropores and mesopores. Compaction primarily impacts pore development during the early diagenetic stage, causing a substantial transition of primary mineral pores from macropores to mesopores. Mineral transformation and dissolution take place during and after the middle diagenetic stage. The former governs the development of mesopore-sized clay interlayer pores, while the latter primarily generates micropores.

The South Yellow Sea Basin is the largest sedimentary basin in the Yellow Sea. The Gunsan Basin in the central eastern part of the Northern South Yellow Sea Basin comprises the Western, Central, and Eastern Subbasins. The Eastern Subbasin marks the eastern margin of the South Yellow Sea Basin. Interpretation of multi-channel seismic profiles and balanced cross-section restoration of depth-converted seismic profiles reveal the structural characteristics and evolution of the Eastern Subbasin. The subbasin comprises three groups of faults: NW-SE, NE-SW, and NNE-SSW trending faults. The subsidence pattern of the subbasin, derived from the cross-section restoration analysis, indicates five distinguished evolution phases: (i) rapid subsidence in the Late Cretaceous, (ii) slow subsidence from the Paleocene to the Eocene, (iii) accelerated subsidence in the Oligocene, (iv) alternation of the uplift and subsidence in the Early Miocene, and (v) gradual subsidence since the Middle Miocene. The main and moderate subsidence can be explained by the combination of extension in the SE and NE-SW directions that formed double duplex structures. We suggest that the NW oblique subduction of the Pacific Plate under the NE Asia margin induced both extension toward the trench and dextral strike-slip parallel to the margin. The extension toward the trench caused SE transtension in a local pull-apart setting, whereas the dextral strike-slip parallel to the margin caused NE-SW extension, inducing more significant subsidence. The combined processes resulted in the progressive development of nested duplex structures. The evolution of the Eastern Subbasin is not compatible with previously suggested models for the western part of the South Yellow Sea Basin including foreland basin formation and transtension induced by branch faults of the Tan-Lu Fault.

Alkaline lake is one of the most productive ecosystems on Earth, commonly characterized by massive organic matter accumulation. However, the primary biological precursors of organic matters and the controls on their accumulation in the ancient alkaline lakes remain poorly understood. Here we use petrology and organic geochemistry analysis of the Upper Paleozoic Fengcheng Formation of the Halaalate area in the Junggar Basin, NW China, to study the biological diversity and controls of water salinity on primary productivity in the ancient alkaline lakes. Two depocenters have been identified in the Halaalate area: a proximal depocenter close to the boundary mountains and a distal depocenter far away from source areas. The results show that water salinity was much larger for the first and second members of Fengcheng Formation (FC1 and FC2) compared to the third member (FC3), and the distal depocenter had more saline lake water than the proximal depocenter. Abundant primary producers have been identified to be flourishing in the low-salinity alkaline lakes, such as cyanobacteria, dinoflagellates and green algae, whereas only a special haloalkaliphilic green alga can survive in the hypersaline alkaline lakes. Therefore, the low-salinity alkaline lakes are characterized by a higher primary productivity and can deposit mudstones containing richer organic matters compared to the high-salinity ones. This study suggests that water salinity is the major factor controlling the biomass and biodiversity of ancient alkaline lakes and mudstones deposited in the low-salinity alkaline lakes are more promising for oil exploration.

An M_W 7.4 earthquake struck Maduo County, Qinghai, China on 22 May 2021. To better understand the seismogenic structure of this region, we collect local earthquake arrival time data at the MAD station in the China Earthquake Networks Center observational bulletins during 1 June to 20 September 2021, and manually pick P and S wave arrival times from high-quality seismograms recorded at 34 recently deployed MaduoArray portable seismic stations. Using these arrival times, we relocate the Maduo earthquake sequence using earthquake association, absolute location and relative location methods. Our results show that the 2021 Maduo earthquake sequence occurred along the Kunlun Mountain Pass-Jiangcuo fault zone in the NWW-SEE direction and the aftershocks are located on both sides of the mainshock, showing characteristics of bilateral rupture. Vertical cross-sections of the aftershock distribution illustrate a nearly vertical shape of the seismogenic fault that tilts toward the northeast and southwest in different sections, reflecting a complex geometry of the fault plane. There is a horsetail bifurcation phenomenon at the eastern end of the fault zone. A sparse area of aftershocks appears at about 30 km east of the mainshock epicenter, which may be associated with a uniform fault friction and sufficient release of rupture energy caused by super-shear rupture of the mainshock. Taking into account many geophysical results including seismic tomography and magnetotelluric soundings, we speculate that the occurrence of the Maduo earthquake could be affected by crustal fluids in the fault zone. The fluids may ascend from the lower crustal flow beneath northeastern Tibet.

Rodingite, a metasomatic rock type related to the serpentinisation of ultramafic rocks, occurs as dykes or lenses in serpentinite of the ophiolitic mélange. The formation age, protolith and metamorphic context of the rodingites are crucial for evaluating the hydrothermal activity of the ancient ocean floor and the tectonic history of the ophiolite. This study presents particular research on metamorphic petrology, geochemistry and zircon U–Pb chronology of rodingites and their associated mafic–ultramafic rocks in the Baixingtu ophiolite, the middle segment of the Erenhot-Hegenshan ophiolite belt (EHOB), southeastern Central Asian Orogenic Belt. The mean metamorphic ages of rodingites are 345.8 ± 3.8 Ma, 339.9 ± 4.8 Ma, and 344.5 ± 9.2 Ma. According to the chlorite thermometer, the final mineral assemblages of rodingites formed at temperatures ranging from 114.99 °C to 351.10 °C. The high oxygen fugacity of nascent clinopyroxenes and the negative anomaly of Ce in adjacent serpentinites (δCe = 0.34–0.77) prove that rodingitisation occurs in shallow oceanic crust by the reaction of seawater with ultramafic rocks to produce Ca-rich fluids. Accordingly, the Baixingtu ophiolite was produced by an ocean floor metamorphism, whose rodingitisation occurred shortly after the formation of the oceanic crust. Combined with other ophiolite data from the EHOB, the Hegenshan Ocean was constantly generating new oceanic crust in the Early Carboniferous.

The objective of this study is to systematically document the depositional architecture and evolution of the carbonate platform margin in the Lower Cambrian Xiaoerblak Formation of the northwestern Tarim Basin. This study uses the following approaches: (1) seismic reflector identification; (2) lithofacies and paleoenvironmental interpretation based on Paleozoic outcrops; and (3) thin section examination. Identification of seismic reflectors and determination of lithofacies associations in Paleozoic outcrops reveal two phases of architectural evolution of the Xiaoerblak Formation platform margin. Phase 1 corresponds to the Lower Xiaoerblak Formation, characterized by discontinuous to semicontinuous moderate- to high-amplitude reflectors, revealing a uniform, gentle ramp platform margin thinning toward the basin. The dolomudstone and laminate lithofacies associations in the outcrops show a middle-ramp low-energy depositional environment. Phase 2 corresponds to the Upper Xiaoerblak Formation. The seismic stratigraphic units display upwardly convex irregular reflectors, indicating the development of a rimmed carbonate platform margin system. The lithofacies associations reveal reef-shoal interbedding, suggesting a high-energy marginal marine environment. The tectonic and paleomorphic evolution of the Tarim Basin, along with Paleozoic outcrop features, suggest that paleomorphic inheritance from the Neoproterozoic created a homogeneous, broad, low-angle shelf. This, combined with the continuous sea-level fall in the early Cambrian and the tropical environment, provided an ideal depositional environment for carbonate platform development in the Xiaoerblak Formation.

This study aims to constrain the paleolatitude of the southern margin of the Lhasa terrane during the late Paleocene and refine the constraints on intracontinental shortening within Asia resulting from the India–Asia collision. An integrated paleomagnetic and petrographic study was conducted on the upper Paleocene Jialazi Formation in the Xigaze forearc basin, southern Tibet. The limestone in the Jialazi Formation was demonstrated to reliably preserve primary remanence. Combined with previously published data, the tilt-corrected mean direction was Ds = 166.6° and Is = -38.2° with α₉₅ = 4.1 (n = 118), corresponding to a paleomagnetic pole at 75.3°N, 323.4°E, with an A₉₅ of 3.7°. Consequently, the paleolatitude of the Xigaze forearc basin from 56–59 Ma was estimated at ∼ 21.5°N for the reference point at 29.8°N, 84.9°E. Compared with data from the western Lhasa terrane, the Xigaze forearc basin and the Linzhou Basin, these findings suggest that the southern margin of the Lhasa terrane had an east–west orientation during the Late Cretaceous–early Eocene. A comparison with the apparent polar wander paths for Asia indicates that the intracontinental shortening between the Lhasa terrane and stable Asian interior has been 890 ± 470 km since the late Paleocene.

International Ocean Discovery Program (IODP) Expedition 350 drilled Site U1437 in a submarine volcano-bounded basin situated in the modern Izu-Bonin rear-arc, NW Pacific Ocean. Subaqueous volcaniclastic sediments and rocks with a maximum deposition age of 15.4 ± 0.8 Ma were recovered from 0 to 1,806.5 m below seafloor (mbsf). In order to document post-depositional processes in such geological setting, we describe variations in bulk and clay mineralogy over the entire volcaniclastic succession. Four alteration stages (1, 2, 3 and 4) were identified through the occurrence and development of diagenetic background mineral assemblages (smectite ± Na-Ca zeolites ± illite) that were further superimposed by hydrothermal alteration. Stages 1 and 2 are characterized by diagenetic reactions linked with low fluid/rock interactions that enabled glass devitrification and subsequent lithification under burial conditions. Stages 3 and 4 are characterized by moderate to pervasive alteration processes that are well developed in coarser-grained rocks, and that may be induced by thermal pulses associated with fluid inputs. Below 1,460 mbsf, infilling and replacement textures overprinted the background alteration and can be directly linked with the development of two hydrothermal mineral assemblages: (i) ordered C/S (chlorite-smectite mixed-layers) ± chlorite ± albite, and (ii) calcite ± chalcedony ± anhydrite ± laumontite. Both assemblages evidence relatively low-temperature (up to 225 °C) hydrothermal activity that affected subaqueous volcaniclastic rocks at Site U1437. These assemblages are comparable with propylitc alteration facies present in ore-bearing hydrothermal systems. The preferential development of alteration mineral assemblages in high-permeability, coarse-grained lithofacies, reflects the significant influence of the physical properties of volcaniclastic rocks with depth on chemical kinetics, in comparison with those imposed by the local geothermal gradient.

Deciphering the interactions between tectonic and exhumation processes in the Tanggula Mountains (central-northern Tibetan Plateau) can provide insights into the processes of the Tibetan plateau uplift and its geomorphic evolution. In this study, we present new detrital apatite fission track (AFT) data from Cenozoic sediments of the Tuotuohe Basin (northeastern part of the Qiangtang terrane) and its periphery (including the Tanggula Mountains), with the aim to reconstruct the cooling history of the Tanggula Mountains during the Cretaceous and the Cenozoic era. Our results show that the provenance of detrital material evolved in the Tuotuohe Basin and highlight that previously deposited sediments were recycled into the Tuotuohe Basin at ∼ 27.5 Ma. The data further outline that the Tanggula Mountains and the Tuotuohe Basin experienced three major phases of tectonic uplift and exhumation: 122–106, 65–54, and 44–35 Ma. These exhumation-induced cooling phases might be related with three phases of primary tectonic activity, i.e., the collision between the Qiangtang and Lhasa terranes (central part of the Tibetan Plateau) that started during the Early Cretaceous, the collision of the Indian and Eurasian plates in the Early Cenozoic and finally, the “hard collision (the Indian and Eurasian continents)” that occurred during the Early Eocene–Oligocene.