Late Paleozoic Sedimentary Basin and Tectonic Evolution in Southwestern Tianshan Mountains, Xinjiang
|School||Chengdu University of Technology|
|Keywords||Southwest Tianshan Late Paleozoic Qul Group Figure You Kee Group Show Licorice Lake Group Yeyungou Group Sedimentary characteristics Ophiolite Volcanic Rock characteristics Petrochemistry REE Trace Isotope South Tianshan ocean Sedimentary basin Tectonic evolution|
Tianshan in the hinterland of the Eurasian continent, is a complex structure of the mountain, Composed by a series of near east-west mountain ranges and basin, valley Holding on Many Mountains,and is one of the most complex orogenic belt in the world .Southwestern Tianshan orogenic belt is one of the most complex geological structures areas in the whole Tianshan orogenic belt, conserving the important information of the Asian continent evolution, and it’s valuable is that it completely saved the information of the region’s Paleozoic oceanic crust evolution and development. Among them, Late Paleozoic tectonic evolution of southwestern Tianshan is the most important and most complex events in the process of formation and the Tianshan orogenic belt evolution. Currently because different research methods adopted by academics, research focus and testing of analytical tools focus on different, We are many differences between understanding of sedimentary basins and tectonic evolution of Southwestern Tianshan in the region. Studying the evolvement of late paleozoic era tectono-magmatic and sedimentary response in Southwestern Tianshan mountains, not only can promote the study of Southwestern Tianshan Late Paleozoic tectonic evolution and development of the Tianshan orogenic belt evolution, also has great guidance significance for mineral exploration in this place.Upper Devonian - Lower Carboniferous strata extensively developed in the southwestern Tianshan area.It is the major sedimentary geological body of southwestern Tianshan region, Formed by ku-le-hu group ((D3-C1) k), tu-you-ke-a-xiu Group (C1t), gan-cao-hu Group (C1g) and ye-yun-gou Group (C1yy).Ku-le-hu group((D3-C1)k)is a slope-Deep-sea sedimentary facies deposit, it is divided into turbidite intrafacies and deep sea basin silica rock、argillaceous siltstoue intrafacies,development of carbonate turbidite,Pyroclastic turbidites,deep-sea radiolarian chert(Manganese layer folders)and radiolarian tuff.There are a large number of Late Devonian - Early Carboniferous radiolarians in the siliceous rocks。Siliceous rocks by the group characteristics and structure of macro-structure, trace elements, rare earth elements and other studies have shown that,siliceous rocks is product of the continental margin environment, part of the role of the release of volcanic SiO2 adding into it。Ku-le-hu group was formed in the basin, an extensional environment,As the tensile by a big margin, ocean crust has been pulled a large number of developmental basic volcanic rocks, mafic volcanic rocks developed a clear pillow-like structure.Tu-you-ke-a-xiu group (C1t) is the new study in rock stratigraphic units of this paper,the first group developed a large number of inter-sedimentary carbonate rocks which with major lithologic mafic volcanic rocks and volcanic rocks.In accordance with its combination of rock, sedimentary structures, sequence features and characteristics of rare-earth trace elements analysis, mafic volcanic rocks of oceanic island volcanic rocks; the second paragraph of the construction of a set of flysch, shows the characteristics of turbidite sedimentary rocks, Ce negative anomaly,sedimentary environment in the deeper water to restore the environment or the sedimentary environment is relatively distant from the continental environment; The third lithologic composition of the siliceous rocks high field,development of a large number of radiolarian fossils in siliceous rocks, siliceous rocks and limestone of the disappearance of a large number of emergence indicating that they reached a deep-sea basin depth of the carbonate compensation depth (CCD) below, led to siliceous sediments and other ocean sediments deposited mainly,has Ce positive anomalies features,indicates that away from the continental sedimentary environment during this period is relatively close, ocean basin with a deep-sea basins due to the characteristics of compensation.Gancaohu Group deposition of shallow continental shelf and the continental shelf edge of sedimentary basins, rocks are mainly of a combination of a small amount of carbonate clastic rock folder, intermediate-mafic volcanic rocks, ultramafic volcanic breccia lava, its carbonate rocks of tidal energy with low-energy band→shallow platform facies transition zone→platform marginal shoal relative to the product of environmental sedimentology.By Southwestern Tianshan Late Devonian - Early Carboniferous Stratigraphic analysis can draw such a conclusion, in the period between Late Devonian and Carboniferous, late Paleozoic South Tianshan oceanic basin changed, such as extended continental crust, new oceanic crust, expansion of ocean basin, and the formation of Late Paleozoic South Tianshan oceanic limited basin.Ophiolite suite of Late Paleozoic South Tianshan limited in the southern slopes of Hal Hill - Hora Hill along with north and south. The north branch of Ophiolite suite belt along with the kul lake, the southern slope of Ke Ke Tie Ke Da Ban, the southern slope of Tie li Mai Tida Ban. The south Branch of Ophiolite suite belt along with the Mei Si Bu La Ke, Al-teng Coles River, Man Da Le Ke, Kara Guo Le, Du Ku Highway 965km ,Se Ri Ke Ya Yi La Ke. The basic rocks TFe, MgO average content of Ophiolite close to the average MORB,K-rich. Most of trace elements ranging from ocean island basalts (OIB) and mid-ocean ridge basalt (MORB), close to mid-ocean ridge basalt, but has the character of transition by the mid-ocean ridge basalt transitional to oceanic island basalts. Loss of rock light rare earth and heavy rare earth rich and rare-earth distribution curve of right-wing which characteristics similar to N-type mid-ocean ridge basalt. Macro-composition of the rock, and volcanic rocks accompanied the deposition of mainly pelagic chert, radiolarian chert. According to radiolarian siliceous rocks in the identification and 40Ar/39Ar dating results, the ophiolite may be the geological age identified as D2-C1.Comparison of Late Paleozoic volcanic rocks in southwestern Tianshan Development, volcanic rocks are mainly distributed in the next Devonian, Lower Carboniferous and Lower Permian. Lower Devonian volcanic rocks occur in the Al-teng Coles Group and Apa DELCAM group.Al-teng Caicos Formation volcanic rocks are mainly basalt.Its trace elements and REE characteristics indicate the environment of mid-ocean ridge basalt.Apa DELCAM Group volcanic rocks in both calc-alkaline series and tholeiitic series features, formed in the active continental margin back-arc basin expansion. Lower Carboniferous volcanic rocks occur in the diagram show You Kee Group. It’s lithology mainly basalt and pillow-like structure.It’s K, Zr, Sm strong losses and significant enrichment of light rare earth and heavy rare-earth loss.Its rare earth basalt distribution curve curve shape similar to volcano oceanic island alkaline of Hawaii Kohala. Comprehensive determine the volcanic rocks should be formed in the oceanic island (seamounts) environment. Occurrence of Permian volcanic rocks Tikanlike formation for small groups, mainly in acidic volcanic rocks, trace the performance of K, Zr, Sm losses, the overall characteristics and A-type granites are similar significant enrichment of light rare earth and heavy rare-earth loss. Rare-earth distribution curve showed a right-wing single-oblique curve and Eu also showed a strong loss. It is formed in the intraplate environment, in relation to the intracontinental orogeny.Late Paleozoic tectonic evolution of Southwestern Tianshan is an important segment, and inherited the early Paleozoic tectonic evolution of southwestern Tianshan background. Integrated Southwestern Tianshan Late Paleozoic sedimentary rocks, volcanic rocks, ophiolites features were analyzed.South Tian shan ocean didn’t closure during the collision in the early Paleozoic subduction.Oceanic basin going through an expansion in the Late Devonian to Carboniferous. In the late Paleozoic, Southwest Tianshan and tectonic evolution of sedimentary basins through the following three stages: 1, Late Paleozoic South Tianshan oceanic basin of the expansion phase, which began in the Late Devonian, at least extend to the Early Carboniferous; 2, Late Paleozoic South Tianshan Ocean subduction collision and oceanic basin closure stage, the Late Paleozoic South Tianshan ocean subduction-collision orogeny may end at the end of the Late Carboniferous, the Tarim plate and the central Tianshan micro-Yili micro-plate end-bridging, welding, the original split Xinjiang ancient Craton again, stitching together to form a unified land mass, and the formation of residual basin; 3, Collision period intraplate evolution stage, the two bridging plate collision, due to thermal relaxation effects occurring tensile, triggering a granitic magma activity.It’s characterized by wide distribution and free from the boundaries of tectonic units.There was a series of basic intrusive rock.