Early Paleozoic Ocean Plate Stratigraphy of the Beishan Orogenic Zone, NW China: Implications for Regional Tectonic Evolution

The Beishan orogenic zone is a key area to understand evolution of the Central Asian Orogenic Belt that is an accretionary factory well-enough preserved in the Paleozoic. In early Paleozoic, the tectonic mélange zone containing the coherent unit and mélange unit is triggered by the complicated accretionary process of the Beishan area. The early Paleozoic tectonic evolution of the Beishan orogenic zone is investigated in this study using sedimentology and stratigraphic correlations of the lowe Paleozoic deposits. From the Cambrian to the middle Ordovician, this region was characterized by geographically extensive, flat-bedded siliceous mudstone, indicating the existence of a large ocean basin. The oceanic plate entered the convergence phase in terms of the Wilson Circle during the Middle Ordovician, when numerous magmatic arcs formed along two opposite sides of the ocean. The magmatic arcs became the widest during the Silurian, suggesting that the Hongliuhe-Niujuanzi-Xichangjing Ocean(HNX;a southern branch of the Paleo Asian Ocean) was reduced to a small residual ocean in the central Beishan region by that time, and probably lasted till the Carboniferous or later by newly published data.

Relation between structural evolution of the Longmenshan orogenic zone and sedimentation of its foreland basin

In order to determine the area for oil and gas exploration in China’s north Sichuan basin,we have divided the time during which the Longmenshan foreland basin was formed into five periods,based on the sedimentary response relationship of the foreland basin to structural evolution: 1) a late Triassic Noric period;2) an early-Middle Jurassic period;3) a late Jurassic to early Cretaceous period;4) a late Cretaceous to Paleogene-Neogene period and 5) the Quaternary period. As well,we analyzed the sedimentary environment and lithologic features of every basin-forming period. The results show that there are several favorable source-reservoir-cap assemblages in our study area,making it a major region for future oil and gas exploration in China’s northern Sichuan basin.

Ray equation migration of wide-angle reflections in Dabie orogenic zone

ay equation migration of wide-angle reflections in 2-D medium is one kind of Kirchhoff prestack depth migration method. Based on ray theory, this method can be used extensively in 2-D inhomogeneous medium, and shows its advantage in wide-angle reflection study. After calculating ray fields, we can get the wave fields of sources and receivers by interpolation, and the intensity (or amplitude) AP corresponding to the depth point P at travel-time tP=tSP+tPR can be found in seismograms. Ray equation migration is completed by transforming AP according to the specific relation, migrating it to the depth point, then calculating the ray fields of lots of sources and receivers in the same way and finally stacking the outcomes. Numerical calculation has yielded satisfactory results. Data processing of the Zhuangmu-Yuexi-Huangmei-Zhanggongdu profile passing through the Dabie orogenic zone provides a structural form of M-discontinuity along the profile. The result shows that the high pressure metamorphic rock zone of South Dabie rock mass is related to the uplifting of M-discontinuity here. 'Mountain root' exists under North Dabie rock mass, which conforms with gravity isostasy theory. The Xiaotian-Mozitan fault is a suture zone as a result of the collision of North China plate with Yangtze plate, and extends through M-discontinuity. The abyssal fault near Liu'an is the extended eastern section of the Luonan-Minggang fault, which is also confirmed here.

Tectonites in the Shear Zone Array of the Tongbai-Dabie Orogenic Belt

A series of tectonites were formed in the shear zone array of the Tongbai--Dabie Orogenic Belt, including mylonites, blastomylonites, semi--plastic mylonites and foliated cataclasitesas a result of multiple strain localization, strain softening and deformation partitioning.

Petrological Study on the Ductile Shear Zones in the Core of the Eastern Qinling Orogenic Belt in Western Henan

A series of ductile shear zones of the overthrust and strike-slip-types and related ductile shear metamorphicrocks, including tectonic melange and mylonites. were formed in the core of the Qinling orogenic belt in thecourse of the Caledonian-Indosinian ductilc and brittle-ductile reworking. The study on their petrography. va-riations in composition and conditions of formation is conducive to revealing the metamorphism-deformationhistory of the core of the Qinling orogenic belt and further to understanding the dynamic mechanism of its evo-lution.

New U-Pb Geochronological Constraints on Formation and Evolution of the Susong Complex Zone in the Dabie Orogen

Objective The Susong complex zone（SCZ）is a relatively lowgrade metamorphic unit mostly with an epidoteamphibolite facies,located in the southernmost part of the Dabie orogen.However,its rock compositions,ages,

Intracontinental Orogenic Igneous Rocks and Orogenic Processes in Qinghai-Xizang-Himalaya

Based on the discussion on the intracontinental orogenic igneous rocks formed after India-Asia collision (40 or 45 Ma),the intracontinental orogenic processes of Qinghai-Xizang (Tibet )-Himalaya are traced . Muscovite/two mica granite is considered as a petrological record of intracontinental subduction. Volcanic rocks of shoshonite series are believed to be the products of the orogenic and outside cratonic lithosphere convergence . The intracontinental orogenic igneous rocks are developed only on the margins of the orogenic belt. The pairing phe nomenon of the igneous rock zones is regarded as one of the best signs to recognize the special range of orogenic belt . The stage of magmatic activity is a representation and indicator of orogenic episode . Three pairs of the igneous events in Oligocene , Miocene and Pleistocene and their space distribution indicate three corresponding orogenic episodes and the horizontal expansion across the orogenic belt , respectively . On the northern and southern margins of the orogenic belt are always developed the volcanic eruption of the shoshonite series and the muscovite two mica granite intrusion ,indicating the different nature of the margins .In the former case the colder crust and hotter mantle . as well as the double crust resulted from the horizontal shortening are developed , and in the latter case the hotter crust and colder mantle , the double crust by the overlapping of two crusts are formed . During the Pleistocene orogenic episode the interior of the orogenic belt , i. e. the Gandise - Qiangtang might be going to the stage of the orogenic collapse . and the compressional orogeny might occur only at both the mar gins . The orogenic processes mentioned above show that beneath the Qinghai - Xizang (Tibet ) Himalaya,the deeper mantle has been always undergoing a descending convergence , rather than the simple orogeny resulted from the underthrusting of the India continent only . The dynamic forces that results in rapid uplift of the plateau since Pleistocene come from the buoyances caused by the compressional stress and mountain root at the margins and by the lithosphere delamination and mountain root in the interior .

Ore-forming Conditions and Prospecting in the West Kunlun Area,Xinjiang, China

The West Kunlun ore-forming belt is located between the northwestern Qinghai-Tibet Plateau and southwestern Tarim Basin. It situated between the Paleo-Asian Tectonic Domain and Tethyan Tectonic Domain. It is an important component of the giant tectonic belt in central China (the Kunlun-Qilian-Qinling Tectonic Belt or the Central Orogenic Belt). Many known ore-forming belts such as the Kunlun-Qilian Qinling ore-forming zone, Sanjiang (or Three river) ore-forming zone, Central Asian ore-forming zone, etc. pass through the West Kunlun area. Three ore-forming zones and seven ore-forming subzones were classified, and eighteen mineralization areas were marked. It is indicated that the West Kunlun area is one of the most favorable region for finding out large and superlarge ore deposits.