Mixed crystalline basement of Junggar basin revealed by wide-angle seismic evidence

Junmeng Zhao,Zongjin Ma,Yingcai Zheng,Yong Song,Bhupati Neupane,Hongbing Liu,Xiaojun Wang,Xinfa Chen,Wenjiao Xiao,I P Strelchenko,Baoli Bian,Xiankang Zhang,Qiang Xu,Heng Zhang

doi:10.21285/2686-9993-2021-44-1-8-29

Abstract

A wide-angle seismic reflection / refraction survey along a ~ 600 km long transect through the Junggar basin from Emin to Qitai allows to receive several images near N-S trending blind faults, which are located at the lower part of the upper crust, the middle crust and the lower crust within the basin and cut up the Moho. These faults, with high seismic velocity and without obvious dislocation, are considered as “extensional faults” formed by north-south compression and east-west extension. These deeply rooted faults provide channels via which basic to ultra-basic materials from upper mantle migrate into the crust and mix up with the crustal material causing thin thickness, high seismic velocity, high density and high magnetic intensity after cooling in the crust of the basin.

Highlights

A wide-angle seismic reflection / refraction survey along a ~ 600 km long transect through the Junggar basin from Emin to Qitai allows to receive several images near N-S trending blind faults, which are located at the lower part of the upper crust, the middle crust and the lower crust within the basin and cut up the Moho
Based on the 1:200000 Bouguer gravity anomaly map of Xinjiang (Fig. 7), there are two gravity gradient zones in the northern and southern margins of the Junggar basin, which clearly delineate the shape of the basin
Based on the Bouguer anomaly and aero-magnetic anomaly maps (1:200,000 scale), the 2D P wave velocity structure, and the faults investigated at the surface of the transect from Emil to Qitai, we constructed a model for the density structure

Summary

Velocity structure of the crust and upper most mantle

Under the condition of 2D lateral inhomogeneous medium, we conducted ray tracing and constructed theoretical seismograms for each shot point with an improved SEIS83 program [22], which are presented in Fig. 4, and obtained the 2D velocity structure (Fig. 5, b). Based on the 1:200000 Bouguer gravity anomaly map of Xinjiang (Fig. 7), there are two gravity gradient zones in the northern and southern margins of the Junggar basin, which clearly delineate the shape of the basin. This is in agreement with the landscape and geological framework. Based on the Bouguer anomaly and aero-magnetic anomaly maps (1:200,000 scale), the 2D P wave velocity structure, and the faults investigated at the surface of the transect from Emil to Qitai, we constructed a model for the density structure. The 2D density structure (Fig. 8, a) and magnetic intensity structure (Fig. 8, b) were obtained according to the Syn-Source theory and through joint inversion of gravity with geomagnetism and constrained by gravitational and geomagnetic anomalies along the profile (Fig. 7) [24]

Inference on the rock properties of the Junggar basin

Rock Granite

Список литературы