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Objective The Qinghai-Tibet Plateau is one of the most seismically active regions along the Mediterranean-Himalayan seismic belt. Understanding the earthquake-controlling effect of the active tectonic system in this region is crucial for analyzing regional strong earthquake hazards. Methods We analyzed earthquake activity with MW≥6.0 since 1990 and their tectonic mechanism around the Tibetan Plateau, focusing on the continental collision-extrusion tectonic system. Results The results show that the system plays a significant role in governing regional strong earthquake activity. Specifically, MW≥6.5 earthquakes primarily occur along the main boundary fault zone of this tectonic system, exhibiting a relatively regular spatio-temporal migration process. Moreover, the multi-layered extrusion-rotation active tectonic system in the eastern Tibetan Plateau constitutes the primary earthquake-controlling structure of the strong earthquake process since 1990, followed by the thrust faults of the Himalayan foreland. Therefore, the extrusion tectonic system of the Qinghai-Tibet Plateau should be the focus for the trend analysis of the strong earthquake activity in the future, especially the most active secondary extrusion tectonic units such as the Bayan Har block. Comparative analysis of strong earthquake activities in and around the Anatolian plate reveals similar continental collision-extrusion tectonic systems and earthquake-controlling effects in this area, indicating that this tectonic system is a typical earthquake-controlling structure in the intracontinental orogenic belt. Conclusion Further comprehensive analysis suggests that the active tectonic system can significantly control regional strong earthquake activity. Firstly, most of the strong earthquake events occur in the main boundary fault zone of the fault block in the tectonic system. Secondly, the strong earthquake events along different structural zones in the tectonic system often have linkage effects or mutual triggering relationships, and the complex or particular structural sites are often where double earthquakes or earthquake swarm activities easily occur. Thirdly, when a certain structural unit or tectonic zone in the tectonic system is in an active stage, strong earthquake clustering phenomena occur. Significance A thorough understanding of the coordinated deformation relationships between major active faults in the tectonic system, the segmented rupture behavior of strong earthquake activity in active fault zones, and the characteristics of "long period, quasi-periodicity and clustering" of strong earthquake recurrence in situ on active faults will assist in more accurately assessing the future seismic hazard of active fault zones when analyzing the future trend of strong earthquake activity based on the active tectonic system.

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Copyright of Journal of Geomechanics is the property of Journal of Geomechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper depicts the distribution of the Wushenqi paleo-uplift in the Ordos Basin by using the latest drilling and seismic data, and analyzes the tectonic evolution of the paleo-uplift with the support of Bischke curve and balanced section. The compressional Wushenqi paleo-uplift which developed in the Early Caledonian orogeny (Huaiyuan orogeny) is approximately a ellipse extending in S-N direction. Its long axis is about 194 km and short axis is about 55–94 km in nearly W-E direction. The denudation thickness and area of the Cambrian in the core are 170–196 m and 11 298 kmbrespectively. It was mainly formed during the Huaiyuan orogeny according to the chronostratigraphic framework. It was in the embryonic stage in the Middle–Late Cambrian, denuded after developed obviously at the end of Late Cambrian. The paleo-uplift of the 3rd member of the Ordovician Majiagou Formation was reactivated and reduced in area. In the sedimentary period of the Ma4 Member–pre-Carboniferous, the paleo-uplift experienced non-uniform uplift and denudation. It entered the stable period of burial and preservation in the Carboniferous and later period. The Wushenqi paleo-uplift was formed on the weak area of the basement and tectonic belts, into an compressional structure with irregular morphology, under the control of the non-coaxial compression in the south and north and the stress transmitted by the uplift in the basin. The Wushenqi paleo-uplift has a controlling effect on the sedimentary reservoirs and hydrocarbon accumulation.

Based on well horizon calibration, the typical seismic profiles in southwestern Tarim Basin were interpreted systematically, regional geological sections were established, and the regional denudation thickness of each tectonic period was restored. On this basis, the plane morphology maps of ancient structures of the Cambrian pre-salt dolomites in different periods were compiled, and the spatial distribution, development, evolution and migration of paleo-uplift in the late Early Paleozoic were analyzed. In the late Early Paleozoic, there existed a unified regional paleo-uplift widely distributed in southwestern Tarim Basin, which is called the southwestern Tarim plaeo-uplift. The “Tarim SW paleo-uplift” and “Hetian paleo-uplift” proposed in previous literatures are not independent, but the result of the spatio-temporal migration and evolution of the southwestern Tarim paleo-uplift identified in this paper. The southwestern Tarim paleo-uplift emerged at the end of Middle Ordovician, and took its initial shape with increased amplitude in the Late Ordovician. During the Silurian, the southwestern Tarim paleo-uplift rose steadily and expanded rapidly to the east, incorporating Pishan—Hetian and other areas, with the structural high locating in the Pishan—Hetian area. During the Devonian, the southwestern Tarim paleo-uplift began to shrink gradually, to a limited range in the Pishan—Hetian area in the southern part of the basin. During the Carboniferous, the southwestern Tarim paleo-uplift became an underwater uplift, that is, the paleo-uplift gradually died out. The southwestern Tarim paleo-uplift belongs to the forebulge of the southwestern Tarim foreland basin in the late Early Paleozoic, and its formation and evolution are related to the early Paleozoic orogeny of the West Kunlun orogenic belt in the south of the Tarim Basin. The migration of the southwestern Tarim paleo-uplift from the northwestern part of the southwestern Tarim Basin to the Pishan—Hetian area indicates the early Paleozoic orogenic process of the West Kunlun orogenic belt, which started in the western section at the end of Middle Ordovician and extended from west to east in a “scissor” style. The migration and evolution of the southwestern Tarim paleo-uplift controlled the development of unconformities at the end of Middle Ordovician, the end of Late Ordovician, and the end of Middle Devonian, and the spatial distribution of dissolved fracture-cave reservoirs in weathered crust below the unconformities in the southwest of Tarim Basin. The migration of the structural high of the southwestern Tarim paleo-uplift also played an important role in controlling the development of dissolved fracture-cave reservoirs in weathered crust.

Copyright of World Nuclear Geoscience is the property of World Nuclear Geoscience Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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Rockfall in limestone mines is a common geohazard in the Changdu area of eastern Tibet and one of the leading geo-safety issues that mining enterprises and railway projects are faced with. We carried out a detailed geohazard survey using the methods of general geology, structural geology, and geohazard geology. We found the rockfall development pattern, characterized rock mass structural planes, discussed the collapse's mechanism, and established its failure mode. The results show that rockfall sites in the study area show a linear spreading along the fold and thrust zone. Five groups of steep-dip structural planes have developed in the rock body, including the longitudinal joint (S1), the transverse joint (S2), the X-type conjugate shear joints (S3 and S4), and the interlayer shear joint (S5). Paired with regional folds and hedging faults, these structural planes cut the rock mass into broken blocks. The collapses are the product of coupled internal and external dynamic geological processes. The sedimentary foundation of the rockfalls in the Qamdo area is the limestone from the upper Triassic Bolila Formation (T3b) formed in the intracontinental rift basin. The strongly folded orogeny triggered by the Cenozoic (Cz) India-Eurasia collision laid down the tectonic framework in the region, which is the essential condition for rockfall development. The strong Neotectonic movement since the Quaternary (Q), frequent hot and humid climate alternations with abundant rainfall since the Late Pleistocene (Q3), everyday human activities, and other internal and external dynamic coupling effects are the main triggering factors of the rockfall disaster. Three failure modes of rockfall are identified, namely toppling, falling, and sliding. The research results have specific guiding significance for rockfall prevention and control in the karst area and the railway construction in the Sichuan-Tibet area.

The northern South China Sea continental margin is the key or critical segment of the Ocean-Continent Connection Zone (OCCZ) of the Great South China Block, the junction between the Tethyan and the (Paleo-) Pacific dynamic systems, and the interaction area between the Indian Ocean and the Pacific Ocean. However, due to the low-degree geophysical exploration in the past, the regional tectonic background, processes and mechanism of the transition between the Tethyan and the Pacific tectonic domains are unclear. Based on the latest large number of seismic profiles, we focus on the Cenozoic basin structure in the continental margin of the northern South China Sea and try to reveal the Mesozoic basement structures of the northern South China Sea continental margin, with the aim of exploring the pre-Cenozoic tectonic evolution and the Cenozoic opening, spreading, ridge fossil and closure of the South China Sea oceanic basin, so as to serve the accurate oil and gas exploration in this area at the same time. The seismic interpretation of the Pearl River Mouth Basin and the field structural investigation of the South China continental margin show that the OCCZ of the South China Block has experienced three processes: Mesozoic Indosinian collisional orogeny, Early Yanshanian accretionary orogeny and Late Yanshanian transpressive orogeny. During the Cenozoic era, it experienced the dispersive extension into basins under the control of NW-SE-directed normal extension in the early stage, the dextral pull-apart into basins under the control of NE-NNE-trending strike-slip faults in the middle stage, and the sinistral pull-apart into basins under the control of NW-WNW strike-slip faults in the late stage. In general, the transition process from the Tethyan to the Pacific tectonic systems can be subdivided into four stages: the transition from the Paleo-Tethyan to the Neo-Tethyan tectonic systems, the transition from the Neo-Tethyan to the Paleo-Pacific tectonic systems, the transition from the Neo-Tethyan to the Pacific tectonic systems, and the transition from the Paleo-Pacific to the Pacific tectonic systems. The tectonic transition of the East Asian OCCZ reflects the long-term mechanism of the Earth plate dynamic system driving the plate superconvergence in East Asia, in particular of the importance of the deep or submarine “Triple Poles”, the Southeast Asian U-shape subduction system, the Pacific LLSVP and the African LLSVP. More importantly, the Southeast Asian U-shape subduction system is also one of the important dynamic engines of the Earth plate motion.

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The Transantarctic Mountains across the central Antarctic continent are the Ross orogenic belt formed by westward subduction of the Paleo-Pacific underneath the East Gondwana active continent margin in the early Paleozoic. The sedimentary, deformation and metamorphism, and granitic magmatic intrusion in this stage represent the process of the Ross Orogeny. Due to the significant difference in age among the three elements mentioned above, there is no precise time defined on the Ross Orogeny. In this paper, detrital zircon U-Pb dating of gravel and sand samples from moraines and coastal sediments in the Inexpressible Island of Northern Victoria Land was carried out. The ages of four samples with different gravel diameters range from 2443 to 323 Ma and are mainly concentrated between 530~450 Ma, with a peak age of~485 Ma. Most of the zircons show oscillatory zoning in CL images and have Th/U ratios great than 0.1 (mainly>0.4), with REE characteristics indicating a magmatic origin. Therefore, these ages reflect the timing of magmatic activity in the provenance of the loose sediment samples. The age composition of detrital zircons is consistent with the age of magmatic intrusion, intracontinental deformation and depositional stratigraphy in the surrounding areas, suggesting that the magmatic activity in the Northern Victoria Land and its surrounding areas might have lasted up to 450 Ma in the intracontinental deformation stage, which may represent the end time of the Ross Orogeny. These results provide a new constraint for the tectonic evolution of the Ross Orogeny on the Gondwana continental margin.

The discriminant indexes, petrogenesis and tectonic significance of unfractionated A-type granites have been widely recognized, while there has not been a universal consensus on the discriminant criterion of highly fractionated A-type granites. LA-ICP-MS zircon U-Pb dating shows that Dajin granites form at Early Paleozoic(～440 Ma), and have high Rb contents(>400×10-6), Rb/Sr and Rb/Ba values, and relatively low Zr/Hf values, illustrating that they are highly fractionated. According to the high zircon saturation temperature(819 ℃-863 ℃), and high Ga/Al(2.6-3.1), Zr+Nb+Ce+Y contents and the evolution trend of specific geochemical indexes, Dajin granites are comprehensively determined as highly fractionated A-type granites. Combining with geochemical and Nd-Hf isotopic compositions, it is suggested that Dajin granites are mostly likely generated by partial melting of the mafic lower crustal rocks, and experienced high degree fractional crystallization and contamination of a samall amount of the wall rock materials. As consequence to post-orogenic lithospheric delamination, the forming time of Dajin A-type granites represent the timing of geodynamic transition of Kwangsian orogeny from orogenic compression to post-orogenic extension in the northeastern Guangxi. [ABSTRACT FROM AUTHOR]

The super-large Kalqiar fluorite deposit was discovered recently in Altyn Tagh area of Xinjiang. The deposit is located at Azhong micro-massif in central Altyn Tagh orogeny. The ore bodies are distributed along the contact zone of Middle Ordovician monzogranite and metamorphic complexes, and controlled by ductile shear zone and fractur e structure. The main ore type is fluorite calcite veins. The mineral composition is mainly calcite and fluorite with a small amount of quartz and K-feldspar. The source of ore-forming materials and genesis of the deposit are unclear. The geological characteristics of fluorite deposit were systemly summarized, and the vertical zoning of ore vein, ore fabric, and REE compositions of ores and surrounding rocks were detailed studied. The results show that the chondrite-normalized REE patterns of fluorite calcite veins display right-dipping, the Eu has obvious negative anomaly ( 0. 33-0. 44), and Ce abnormality is not obvious (1.02-1.07); the chondrite-normalized REE patterns of fluorite calcite veins are basically consistent with those of metamorphic complexes and monzogranites. It is suggested that the ore-forming materials are derived from Palaeoproterozoic metamorphic complexes and Middle Ordovician monzogranites. Finally, the ore-forming model of the superlarge Kalqiar fluorite deposit is established. [ABSTRACT FROM AUTHOR]

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Hatu pluton in the southern margin of West Junggar invades into Early-Middle Devonian marine volcanic-sedimentary strata. The lithology of Hatu pluton is mainly composed of monzonitic granite, syenite granite and a small amount of alkali feldspar granite, which is an ideal object to study the tectonic setting of Late Carboniferous in West Junggar. The granites in Hatu pluton have high SiO2(72.06%-76.53%), Na2O+K2O(7.80%-8.57%)and Al2O3(12.55%-14.06%)contents, low CaO(0.20%-1.58%)and MgO(0.07%-0.42%)contents, with A/CNK(1.06-1.15)and A/NK(1.15-1.36)showing the characteristics of weakly peraluminous-strongly peraluminous granite. The granites have high total contents of REE((88.14-139.53)×10-6)and ratios of LREE/HREE((La/Yb)N is 3.04-6.50), and the chondrite-normalized REE pattern exhibits a typical right-dip “V” shape with a strong negative Eu anomaly, indicating that some plagioclases may be retained as a residue in the source area or there is the separation and crystallization of plagioclases. Meanwhile, the granites display significant enrichments of large ion lithophile elements(Rb, Th, U, K and Pb), relative enrichments of Zr and Hf, and depletions in Ba and Nb, especially Sr, Ti and P. The above characteristics demonstrate that Hatu pluton is a typical weakly peraluminous-strongly peraluminous A2-type granite. Combined with diagrams of major and trace elements, Hatu pluton in West Junggar is formed in a post-orogenic extension setting, and the petrogenesis is related to the juvenile crust that comprised both oceanic crust and island arc, which results from partial melting and fractionation under low pressure condition. [ABSTRACT FROM AUTHOR]

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The deformation feature and dynamic processes of the lithosphere in the southeastern margin of Qinghai-Tibet Plateau are significantly different from the principal part of the plateau, where forward collision is taking as the main form. The deformation patterns of the lithosphere in southeastern margin of Qinghai-Tibet Plateau are mainly characterized by lateral slip on the shallow crust, and accompanied by a series of deep processes to be revealed. Undoubtedly, the exploration and study of lithospheric structure in the southeastern margin of Qinghai-Tibet Plateau are indispensable to understand the deep dynamic process and collisional orogeny of Qinghai-Tibet Plateau. It is crucial to reveal the three-dimensional structure of the lithosphere and deep dynamic background of metallogenic zone associated with the deep process of lateral collision deformation for the integrity of the theoretical framework of continental collision orogeny and mineralization. The research results and basic knowledge of crust-upper mantle structure detection in the southeastern margin of Qinghai-Tibet Plateau are systematically sorted out, the recent progress and new understanding of deep structural seismic exploration in the southeastern margin of Qinghai-Tibet Plateau and its adjacent areas during recent decades are emphatically introduced, mainly in natural seismic imaging, artificial seismic profile and deep dynamics of the crust-upper mantle structure, which can be used as a reference for researchers interested in geosciences of Qinghai-Tibet Plateau. [ABSTRACT FROM AUTHOR]