Research On The Crustal Structure And Metallogenic Background Of The Northern Himalayan Metallogenic Belt From Deep Seismic Reflection Profiles

The Northern Himalayan Metallogenic Belt(NHMB),also refered to as the Tethys Himalayan Metallogenic Belt(THMB),is an important component of the global Tethys-Himalayan metallogenic domain.It is of great significance to the study of the deep structure and metallogenic process of the collisional orogenic system of the Himalayas-Tibet that understanding the deep controlling factors of large metallogenic belts from a macro scale,and that figuring out the deep crustal structure of large metallogenic belts and finally understand the geodynamic background of large-scale deep mineralization.This study mainly uses deep seismic reflection profiles to research the crustal structure and metallogenic background of the NHMB.The study area is located at nearby 92°E in south Tibet.The deep seismic reflection profile strart from about25 km north of the main detachment fault of the Southern Tibet Detachment System(STDS),and then passing northward in turn through the Zhaxikang ore concentration area,the Yarlhashampo dome,across the InduYarlung suture zone(IYS),and end in the Gangdise magma belt.The profile is consist of 660 shot-garhter records with the total length of 160 km.The seismic data was acquired in two years with two segments.This study spliced and processed deep seismic reflection data through revised prcocessig flow based on the regular processing.Besides,this paper explores the workflow of obtaining fine structure from shallow to deep crust based on deep reflection data,using information such as first arrival,reflectiion and surface waves.After interpreation,deep seismic reflection profile was obtained that revealed the fine crustal structure of the NHMB..The main insights and conclusions obtained are as follows:(1)The method of obtaining fine structures from shallow to deep based on deep seismic reflection data is explored : non-raytracing tomography refraction static correction and robust surface-consistent deconvolution technology can improve the image quality of reflected data,the method of amplitude recovery based on relative amplitude retention is a key step to response the relative change of the reflection coefficient of the crust,the inverted near surface shear wave velocity structure from surface wave in shot-garher can effectively supplement the shallow information of the structure.(2)The significantly different reflection characteristics between the two sides of the IYS shows that IYS is the material boundary of the two continental crusts.According to different reflection characteristics,the crust of the NHMB can be divided into upper-middle-lower crust bounded by the STDS and the Main Himalayan Thrust(MHT).The upper crust is characterized by variable dip angles of the reflection events,the middle crust is multiple north dipping duplex,and the lower crust is weak reflection.(3)The STDS is a ductile shear zone and detachment zone with a certain thickness in the crust.The dome structures,faults,folds,etc.observed on the surface are located on top of it.The STDS is a key factor to control of mineralization in the NHMB.