The Volcanic Activity Characteristics And Tectonic Evolution Of Rift From Carboniferous To Early Permian In The Southeast Of Heishanling, Xinjiang Beishan

Beishan tectonic belt is located in the northeastern margin of Tarim plate. It is gripped between Kuruktag and Dunhuang block and it is extended from the Tarim oldland. According to the temporal and spatial characteristics of their activities, it can be divided into North and South two zones: North zone with activities for the early Paleozoic, late Paleozoic southern belt. The most study area is located in the southern belt, the Carboniferous - Early Permian happened strong volcanic and magmatic activity, forming a large number of volcanic rocks, a systematic analysis to these volcanic rocks of various features can reveal tectonic evolution of the history in this area, and also can reveal the relationship to the Tianshan Mountains, a huge complex and the Central Asian orogenic Belt. This paper discussed the change of the stratigraphic units from Carboniferous to Early Permian in the southeast of Heishanling area, and then focused on the petrology of volcanic rocks, rock chemistry and geochemistry. The main understanding of:1. The Upper Carboniferous strata division of the study area is re-determined. In the both sides of the Maotoushan Fault area, from north to south on both sides followed by exposed stone the Shibanshan Formation (C₂sb), the Shengliquan Formation (C₂sl) and the Ganquan Formation (C₂g), then based on the characteristics of the original sedimentary structures zoned the Shengliquan Formation paragraph C of Upper Carboniferous (paragraph green tuff, layers containing a large number of auriferous quartz veins) and it is closely related to volcanic activity, it should be classified into the Ganquan Formation, and the true meaning of the Shengliquan Formation is a quiet period of semi-deep sea - the construction of deep-sea flysch facies.2. The fossils such as Schubertella sp., Fusulinella cf.vozhgalensis Aljutovella sp., Aljutovella isvarica, Staffella sp., Ozawainella sp. and Eofusulina ?sp. has been discovered in limestore, which located in the Maotoushan area, of the upper Ganquan Formation. These fossil activity era was in the end of Late Late Carboniferous. Accordingly, the era of the Ganquan Formation has been determined to the Late Late Carboniferous.3. Through the deposition of construction and regional comparative analysis of the study area has found that it had experienced the initial Early Carboniferous rift, as early as the Late Carboniferous - sustained medium-term extension, the end of the Late Carboniferous contraction and the extrusion of the early Permian under the context of the contraction. In the period of the Shibanshan Formation, Beishan rift stretched from west to east, and then in the period of the Shengliquan Formation the stretching of Beishan rift was continue towards east. In the Late Carboniferous period of the Ganquan Formation, the rift was healing from west to east.4. The Ganquan Formation of the Upper Carboniferous and the Hongliuhe Formation of the Lower Permian volcanic rocks will be discussed as a keystone. A more comprehensive exposition of the rock occurrence, the rock composition, petrology, petrochemistry, petrology and geochemistry, etc. characteristics have be given, through the above-mentioned studies have shown: The Ganquan Formation extrusion of volcanic rocks is the production under the context of contraction, from the deposition construction and the same period of the intrusion of rock chemistry and geochemical characteristics also confirmed the front judge, the convergent of Beishan rift occurred in the end of the Late Carboniferous.The volcanic rocks distributed in the Yantan fracture ( formerly designated as the Ganquan Formation), in this study, through the the rock occurrence, the characteristics of the rock composition and reliable U-Pb isotope SHRIMP dating results will be re-determined for the Early Permian and classified as the Hongliuhe Formation.At the same time, the Early Permian period of volcanic activity in the period of the Hongliuhe Formation should be considered as a successive and evolutive stage from the Late Carboniferous volcanic activity. The extension of the Hongliuhe Formation happened under the context of the constriction, and it is also a short-term counter-productive. Contacting occurred at the end of the Late Carboniferous contraction extrusion event, this cleavage event is likely to be from the belt thickening lithosphere delamination and led to partial melting of mantle that caused by an increase.5. The volcanic activity of study area significantly controlled by deep fault, from the Carboniferous to Early Permian volcanic activity center migrated from north to south, as early as the Carboniferous period of the study area are relatively in the quiet volcanic basin; the Late Carboniferous volcanic activity centre moved to the area of Maotoushan, volcanic activities is eruption of central type; In the study area of Early Permian exist north and south zone of volcanic activity, the North zone cracked overflow eruption, while the south zone is eruption of central type.6. Based on a typical fossil data, regional stratigraphic correlation, as well as more accurate information SHRIMP dating for the volcanic activity during this period to establish a more accurate time scale. On this basis the study area will be the Late Paleozoic Carboniferous - Permian intracontinental rift evolution is divided into stages of development: Early Carboniferous rift edge of the initial rift phase; Late Carboniferous early and middle period of quiet activities in Rift Valley; Late Carboniferous period starting the end of RiftValley contraction; Early Permian rift extrusion period of the inheritance and development ofcontraction.