Abstract The nearly E-W-trending Aqqikkudug-Weiya zone, more than 1000 km long and about 30 km wide, is an important segment in the Central Asian tectonic framework. It is distributed along the northern margin of the ...Abstract The nearly E-W-trending Aqqikkudug-Weiya zone, more than 1000 km long and about 30 km wide, is an important segment in the Central Asian tectonic framework. It is distributed along the northern margin of the Central Tianshan belt in Xinjiang, NW China and is composed of mylonitized Early Palaeozoic greywacke, volcanic rocks, ophiolitic blocks as a mélange complex, HP/LT-type bleuschist blocks and mylonitized Neoproterozoic schist, gneiss and orthogneiss. Nearly vertical mylonitic foliation and sub-horizontal stretching lineation define its strike-slip feature; various kinematic indicators, such as asymmetric folds, non-coaxial asymmetric macro- to micro-structures and C-axis fabrics of quartz grains of mylonites, suggest that it is a dextral strike-slip ductile shear zone oriented in a nearly E-W direction characterized by “flower” strusture with thrusting or extruding across the zone toward the two sides and upright folds with gently plunging hinges. The Aqqikkudug-Weiya zone experienced at least two stages of ductile shear tectonic evolution: Early Palaeozoic north vergent thrusting ductile shear and Late Carboniferous-Early Permian strike-slip deformation. The strike-slip ductile shear likely took place during Late Palaeozoic time, dated at 269±5 Ma by the40Ar/39Ar analysis on neo-muscovites. The strike-slip deformation was followed by the Hercynian violent S-type granitic magmatism. Geodynamical analysis suggests that the large-scale dextral strike-slip ductile shearing is likely the result of intracontinental adjustment deformation after the collision of the Siberian continental plate towards the northern margin of the Tarim continental plate during the Late Carboniferous. The Himalayan tectonism locally deformed the zone, marked by final uplift, brittle layer-slip and step-type thrust faults, transcurrent faults and E-W-elongated Mesozoic-Cenozoic basins.展开更多
Meso\| and microstructural characteristics of cataclastic fault rocks developed in the Xialu chert are described. The Xialu chert represents pelagic and deep marine sediments (Middle Jurassic—Lower Cretaceous), and o...Meso\| and microstructural characteristics of cataclastic fault rocks developed in the Xialu chert are described. The Xialu chert represents pelagic and deep marine sediments (Middle Jurassic—Lower Cretaceous), and occupies the southern marginal part of the E—W trending Yarlung Zangbo suture zone. The apparent total thickness of siliceous deposits exceeds 1km. The current study is concentrated along the two measured sections, Xialu\|E and Xialu\|W. The Xialu\|E section is composed mainly of red chert associated with reddish purple siliceous mudstone and greenish gray mudstone. The beds steeply dip north or south. The 45m section studied is divided into three units (chert unit, chert\|siliceous mudstone unit, and melange unit from north to south). They are in fault contact with each other. In the southern half of the chert unit and the northernmost of the chert\|siliceous mudstone unit, a 15m thick cohesive cataclasite zone can be defined. The cataclasites are composed of chert fragments in a fine grained matrix, and deformed with jigsaw puzzle structures. The chert\|siliceous mudstone unit is made up of four slabs of chert\|siliceous mudstone sequence. Mesoscopic duplex zones in thickness from 1 to 3m are recognized at slab boundaries. Flat and ramp structure and associated P foliations, R1 shears, Y surfaces are developed. Shear spacing range from 1 to 10cm. The slip senses are dextral strike\|slip movement along these duplex zones. The cataclasite zone is cut by the duplex zone along the southern boundary.展开更多
The Xianshuihe fault zone is a seismo-genetic fault zone of left-lateral slip in Southwest China. Since 1725, a total of 59 Ms ≥ 5.0 earthquakes have occurred along this fault zone, including 18 Ms 6.0–6.9 and eight...The Xianshuihe fault zone is a seismo-genetic fault zone of left-lateral slip in Southwest China. Since 1725, a total of 59 Ms ≥ 5.0 earthquakes have occurred along this fault zone, including 18 Ms 6.0–6.9 and eight Ms ≥ 7.0 earthquakes. The seismic risk of the Xianshuihe fault zone is a large and realistic threat to the western Sichuan economic corridor. Based on previous studies, we carried out field geological survey and remote sensing interpretation in the fault zone. In addition, geophysical surveys, trenching and age-dating were conducted in the key parts to better understand the geometry, spatial distribution and activity of the fault zone. We infer to divide the fault zone into two parts： the northwest part and the southeast part, with total eight segments. Their Late Quaternary slip rates vary in a range of 11.5 mm/a –（3±1） mm/a. The seismic activities of the Xianshuihe fault zone are frequent and strong, periodical, and reoccurred. Combining the spatial and temporal distribution of the historical earthquakes, the seismic hazard of the Xianshuihe fault zone has been predicted by using the relationship between magnitude and frequency of earthquakes caused by different fault segments. The prediction results show that the segment between Daofu and Qianning has a possibility of Ms ≥ 7.0 earthquakes, while the segment between Shimian and Luding is likely to have earthquakes of about Ms 7.0. It is suggested to establish a GPS or In SAR-based real-time monitoring network of surface displacement to cover the Xianshuihe fault zone, and an early warning system of earthquakes and post seismic geohazards to cover the major residential areas.展开更多
The Garzê–Yushu strike-slip fault in central Tibet is the locus of strong earthquakes（M 〉 7）. The deformation and geometry of the co-seismic surface ruptures are reflected in the surface morphology of the fau...The Garzê–Yushu strike-slip fault in central Tibet is the locus of strong earthquakes（M 〉 7）. The deformation and geometry of the co-seismic surface ruptures are reflected in the surface morphology of the fault and depend on the structure of the upper crust as well as the pre-existing tectonics. Therefore, the most recent co-seismic surface ruptures along the Garzê–Yushu fault zone（Dangjiang segment） reveal the surface deformation of the central Tibetan Plateau. Remote sensing images and field investigations suggest a 85 km long surface rupture zone（striking NW-NWW）, less than 50 m wide, defined by discontinuous fault scarps, right-stepping en echelon tensional cracks and left-stepping mole tracks that point to a left-lateral strike-slip fault. The gullies that cross fault scarps record systematic left-lateral offsets of 1.8 m to 5.0 m owing to the most recent earthquake, with moment magnitude of about M 7.5, in the Dangjiang segment. Geological and geomorphological features suggest that the spatial distribution of the 1738 co-seismic surface rupture zone was controlled by the pre-existing active Garzê–Yushu fault zone（Dangjiang segment）. We confirm that the Garzê–Yushu fault zone, a boundary between the Bayan Har Block to the north and the Qiangtang Block to the south, accommodates the eastward extrusion of the Tibetan Plateau and generates strong earthquakes that release the strain energy owing to the relative motion between the Bayan Har and Qiangtang Blocks.展开更多
Specialists think tectonic mixtite zone in Lancang River, which lies in southern and eastern fringe of Qingzang plateau, is the suture line (or contact strip) between Gondwana Land and Yangtz block (Fan Chengjun, 1982...Specialists think tectonic mixtite zone in Lancang River, which lies in southern and eastern fringe of Qingzang plateau, is the suture line (or contact strip) between Gondwana Land and Yangtz block (Fan Chengjun, 1982; Liu Zhengqian, etc, 1991; Fang Runsen,1993).By regional geological study (Legend:1∶50000) in Tu’e, western Yunnan, the author think major fracture zone about 6\|8km from western Lancang River is fragile\|ductile shear zone between batholithic granite of Biluo snow mountain and Jurassic\|Cretaceous slight curdle strata. The zone is a very complicated tectonic mixtite zone (width:0.7\|6km; strike: SN\|direction). Study based on geometric structure, constitution, metamorphism, deformation and kinematic characteristics, the author sum up the following features about the complex deformation zone.(1) Tectonic mixtite zone is a very complicate blocks made up of curdle blocks and residual blocks of granite. Its’ geometric structure is a net\|shape structure composed of matrixes and chaotic blocks in plane and have two kinds of structure types (obduction schists in early diagenesis and heteroploytypes in late diagenesis) in section.展开更多
A set of pull\|apart basins were formed along the Weixi—Qiaohou right\|lateral slip shear zone of the western part of Honghe fault zone during the period from Miocene to Quaternary.A rock suite of alkaline basalt\|tr...A set of pull\|apart basins were formed along the Weixi—Qiaohou right\|lateral slip shear zone of the western part of Honghe fault zone during the period from Miocene to Quaternary.A rock suite of alkaline basalt\|trachyte\|leucite phonolite is distributed in the Pliocene basin developed in the middle and northern parts of the fault. The location of these rocks and the features of the basin indicate the close relationship between the rock suite and the strike\|slipping.. The sedimentological and chronological evidences prove that Dianxi plateau uplifted quickly in the Pliocene. We can get the information about the plutonic process of the uplift of the plateau from this alkaline rock association. There are mainly olivine\|pyroxene\|trachyandesite and biotite\|trachyte in the rock association. The rocks are often of porphyritic texture and block or semi\|directional flowage structure while the matrix is of trachytic or microcrystalline texture. The phanerocrysts are diopsidic augite, rimpylite, biotite and perthite (olivine sometimes can be seen). The matrix are made up of alkaline feldspar microcrystalline (30%～50%), short\|grained diopside (10%～15%), light\|colored volcanic glass (0～15%) and some magnetite, while feldspar microcrystalline in some rocks are arranged directionally. And there are sharp\|edged or round pyroxenite enclaves and hemicrystalline of short grained sinaite, biotite sinaite and felsic breccia in the trachyte, with good demarcation line. The pyroxenite enclaves in the trachyte are of different size, and the size of the biggest ones are 10cm or so with the characteristic of plastic yield flowing. Sinaite hemicrystalline may come from the older intrusions of Pliocene and Eocene epoch.展开更多
文摘Abstract The nearly E-W-trending Aqqikkudug-Weiya zone, more than 1000 km long and about 30 km wide, is an important segment in the Central Asian tectonic framework. It is distributed along the northern margin of the Central Tianshan belt in Xinjiang, NW China and is composed of mylonitized Early Palaeozoic greywacke, volcanic rocks, ophiolitic blocks as a mélange complex, HP/LT-type bleuschist blocks and mylonitized Neoproterozoic schist, gneiss and orthogneiss. Nearly vertical mylonitic foliation and sub-horizontal stretching lineation define its strike-slip feature; various kinematic indicators, such as asymmetric folds, non-coaxial asymmetric macro- to micro-structures and C-axis fabrics of quartz grains of mylonites, suggest that it is a dextral strike-slip ductile shear zone oriented in a nearly E-W direction characterized by “flower” strusture with thrusting or extruding across the zone toward the two sides and upright folds with gently plunging hinges. The Aqqikkudug-Weiya zone experienced at least two stages of ductile shear tectonic evolution: Early Palaeozoic north vergent thrusting ductile shear and Late Carboniferous-Early Permian strike-slip deformation. The strike-slip ductile shear likely took place during Late Palaeozoic time, dated at 269±5 Ma by the40Ar/39Ar analysis on neo-muscovites. The strike-slip deformation was followed by the Hercynian violent S-type granitic magmatism. Geodynamical analysis suggests that the large-scale dextral strike-slip ductile shearing is likely the result of intracontinental adjustment deformation after the collision of the Siberian continental plate towards the northern margin of the Tarim continental plate during the Late Carboniferous. The Himalayan tectonism locally deformed the zone, marked by final uplift, brittle layer-slip and step-type thrust faults, transcurrent faults and E-W-elongated Mesozoic-Cenozoic basins.
文摘Meso\| and microstructural characteristics of cataclastic fault rocks developed in the Xialu chert are described. The Xialu chert represents pelagic and deep marine sediments (Middle Jurassic—Lower Cretaceous), and occupies the southern marginal part of the E—W trending Yarlung Zangbo suture zone. The apparent total thickness of siliceous deposits exceeds 1km. The current study is concentrated along the two measured sections, Xialu\|E and Xialu\|W. The Xialu\|E section is composed mainly of red chert associated with reddish purple siliceous mudstone and greenish gray mudstone. The beds steeply dip north or south. The 45m section studied is divided into three units (chert unit, chert\|siliceous mudstone unit, and melange unit from north to south). They are in fault contact with each other. In the southern half of the chert unit and the northernmost of the chert\|siliceous mudstone unit, a 15m thick cohesive cataclasite zone can be defined. The cataclasites are composed of chert fragments in a fine grained matrix, and deformed with jigsaw puzzle structures. The chert\|siliceous mudstone unit is made up of four slabs of chert\|siliceous mudstone sequence. Mesoscopic duplex zones in thickness from 1 to 3m are recognized at slab boundaries. Flat and ramp structure and associated P foliations, R1 shears, Y surfaces are developed. Shear spacing range from 1 to 10cm. The slip senses are dextral strike\|slip movement along these duplex zones. The cataclasite zone is cut by the duplex zone along the southern boundary.
基金supported by the Special Project of Basic Work of Science and Technology(grant No.2011FY110100-2)the Project of China Geological Survey(grant No.1212010914025 and No.12120113038000)the Project of 12~(th) Five-Year National Sci-Tech Support Plan(grant No.2011BAK12B09)
文摘The Xianshuihe fault zone is a seismo-genetic fault zone of left-lateral slip in Southwest China. Since 1725, a total of 59 Ms ≥ 5.0 earthquakes have occurred along this fault zone, including 18 Ms 6.0–6.9 and eight Ms ≥ 7.0 earthquakes. The seismic risk of the Xianshuihe fault zone is a large and realistic threat to the western Sichuan economic corridor. Based on previous studies, we carried out field geological survey and remote sensing interpretation in the fault zone. In addition, geophysical surveys, trenching and age-dating were conducted in the key parts to better understand the geometry, spatial distribution and activity of the fault zone. We infer to divide the fault zone into two parts： the northwest part and the southeast part, with total eight segments. Their Late Quaternary slip rates vary in a range of 11.5 mm/a –（3±1） mm/a. The seismic activities of the Xianshuihe fault zone are frequent and strong, periodical, and reoccurred. Combining the spatial and temporal distribution of the historical earthquakes, the seismic hazard of the Xianshuihe fault zone has been predicted by using the relationship between magnitude and frequency of earthquakes caused by different fault segments. The prediction results show that the segment between Daofu and Qianning has a possibility of Ms ≥ 7.0 earthquakes, while the segment between Shimian and Luding is likely to have earthquakes of about Ms 7.0. It is suggested to establish a GPS or In SAR-based real-time monitoring network of surface displacement to cover the Xianshuihe fault zone, and an early warning system of earthquakes and post seismic geohazards to cover the major residential areas.
基金supported by the China Earthquake Administration Research Fund(Grant No.DZJ2016-18)the National Natural Science Foundation of China(Grant No.41602222)
文摘The Garzê–Yushu strike-slip fault in central Tibet is the locus of strong earthquakes（M 〉 7）. The deformation and geometry of the co-seismic surface ruptures are reflected in the surface morphology of the fault and depend on the structure of the upper crust as well as the pre-existing tectonics. Therefore, the most recent co-seismic surface ruptures along the Garzê–Yushu fault zone（Dangjiang segment） reveal the surface deformation of the central Tibetan Plateau. Remote sensing images and field investigations suggest a 85 km long surface rupture zone（striking NW-NWW）, less than 50 m wide, defined by discontinuous fault scarps, right-stepping en echelon tensional cracks and left-stepping mole tracks that point to a left-lateral strike-slip fault. The gullies that cross fault scarps record systematic left-lateral offsets of 1.8 m to 5.0 m owing to the most recent earthquake, with moment magnitude of about M 7.5, in the Dangjiang segment. Geological and geomorphological features suggest that the spatial distribution of the 1738 co-seismic surface rupture zone was controlled by the pre-existing active Garzê–Yushu fault zone（Dangjiang segment）. We confirm that the Garzê–Yushu fault zone, a boundary between the Bayan Har Block to the north and the Qiangtang Block to the south, accommodates the eastward extrusion of the Tibetan Plateau and generates strong earthquakes that release the strain energy owing to the relative motion between the Bayan Har and Qiangtang Blocks.
文摘Specialists think tectonic mixtite zone in Lancang River, which lies in southern and eastern fringe of Qingzang plateau, is the suture line (or contact strip) between Gondwana Land and Yangtz block (Fan Chengjun, 1982; Liu Zhengqian, etc, 1991; Fang Runsen,1993).By regional geological study (Legend:1∶50000) in Tu’e, western Yunnan, the author think major fracture zone about 6\|8km from western Lancang River is fragile\|ductile shear zone between batholithic granite of Biluo snow mountain and Jurassic\|Cretaceous slight curdle strata. The zone is a very complicated tectonic mixtite zone (width:0.7\|6km; strike: SN\|direction). Study based on geometric structure, constitution, metamorphism, deformation and kinematic characteristics, the author sum up the following features about the complex deformation zone.(1) Tectonic mixtite zone is a very complicate blocks made up of curdle blocks and residual blocks of granite. Its’ geometric structure is a net\|shape structure composed of matrixes and chaotic blocks in plane and have two kinds of structure types (obduction schists in early diagenesis and heteroploytypes in late diagenesis) in section.
文摘A set of pull\|apart basins were formed along the Weixi—Qiaohou right\|lateral slip shear zone of the western part of Honghe fault zone during the period from Miocene to Quaternary.A rock suite of alkaline basalt\|trachyte\|leucite phonolite is distributed in the Pliocene basin developed in the middle and northern parts of the fault. The location of these rocks and the features of the basin indicate the close relationship between the rock suite and the strike\|slipping.. The sedimentological and chronological evidences prove that Dianxi plateau uplifted quickly in the Pliocene. We can get the information about the plutonic process of the uplift of the plateau from this alkaline rock association. There are mainly olivine\|pyroxene\|trachyandesite and biotite\|trachyte in the rock association. The rocks are often of porphyritic texture and block or semi\|directional flowage structure while the matrix is of trachytic or microcrystalline texture. The phanerocrysts are diopsidic augite, rimpylite, biotite and perthite (olivine sometimes can be seen). The matrix are made up of alkaline feldspar microcrystalline (30%～50%), short\|grained diopside (10%～15%), light\|colored volcanic glass (0～15%) and some magnetite, while feldspar microcrystalline in some rocks are arranged directionally. And there are sharp\|edged or round pyroxenite enclaves and hemicrystalline of short grained sinaite, biotite sinaite and felsic breccia in the trachyte, with good demarcation line. The pyroxenite enclaves in the trachyte are of different size, and the size of the biggest ones are 10cm or so with the characteristic of plastic yield flowing. Sinaite hemicrystalline may come from the older intrusions of Pliocene and Eocene epoch.
