The Material Composition And Tectonic Deformation Characteristics Of Buqingshan Tectonic Mélange

The Buqingshan tectonic mélange, which was formed in the process of the long-term northward subduction of the Tethys oceanic lithosphere plate during early Paleozoic-late Paleozoic, played an important role in the tectonic mélange of the southern margin of the East Kunlun. On the basis of structure and lithology double geological mapping with a large scale from Delisitan to Gerizhuotuo in the Buqingshan tectonic mélange. This article mainly to analyze the material composition, structure and tectonic setting of Buqingshan tectonic mélange in detail and divide the deformation sequence. At the same time, we explored the process in place of Buqingshan tectonic mélange. Some understanding and progress are proposed as follows.1.We identify seven different rock blocks and two related matrix of the tectonic mélange in Buqingshan area. Rock blocks mainly includes Delisitan ophiolite, Haerguole ophiolite, Delisitan granodiorite, Gerizhuotuo dacite and tuff, combination of limestone and basalt and Maerzheng Formation, matrix mainly includes chlorite schist and feldspar-quartz mylonite.2.There are three different tectonic settings of the Maerzheng Formation from south to north of the tectonic mélange.(1)The flysch sedimentary combination of strong deformation has the characteristics of accretionary wedge;(2)The turbidite and calcareous sandstone in the middle of tectonic mélange has the characteristics of forearc basin;(3)The calcareous sandstone and bioclastic limestone closely together with limestone of Suweimenke Formation has the characteristics of littoral facies sedimentary.3.The tectonic mélange has a characteristic of different rock blocks surrounding with strong deformation matrix, it present a characteristics of " net and knot framework ".4.The Buqingshan tectonic mélange has the characteristics of multi-stages tectonic movements, based on the study of geometry and kinematics between matrix and rock blocks of the tectonic mélange, a 4-phase deformation was recognized.(1)The first stage is regional penetrative mylonite foliation and deep ductile shearing deformation, it is probably reflects that the regional penetrative foliation may formed in a deeper level of the subduction zone at late of early Paleozoic;(2)The second stage is southward imbricate thrust fault with a series of overturned fold. The fold is nearly E-W trending, which reflects nearly N-S trending extrusion movement. This period of tectonic deformation is mainly formed by the subduction and accretion stage of oceanic crust.(3)The third stage is strong deformation of left strike-slip shear zone beside different rocks. Drag fold, kink structure and small plunging vertical fold can be seen beside the shear zone and the phenomenon such as boudinage and structural lenticular body can be seen in left strike-slip shear zone, this period is mainly due to the oblique collision during the Indo-Chinese epoch;(4)The fourth stage is thrust-nappe structure at the shallow crust, it is performanced in the thrust nappe of Suweimenke Formation limestone. Limestone nappe covers the early deformation in this area and reflect the characteristics of intracontinental adjustment.5. The Buqingshan tectonic mélange experienced a complex process in place and multiphase tectonic activity, its emplacement mechanism mainly is accretion-adhesion type. Through at least two times process in place, collisional strike slip and late superimposed reformation, finally the Buqingshan tectonic mélange created the present structure framework.