摘要
豫西横穿秦岭造山带的以反射地震为主的综合地球物理探测,发现秦岭现今北界存在华北地块南部自北向南向秦岭的巨型陆内俯冲带,深达Moho面以下,与之相伴而生,在中上地壳发育自南向北的逆冲推覆构造带,千公里东西向延伸,主要发生于晚白垩世100Ma±,成为秦岭与华北地块间中新生代重要陆内构造。它是秦岭造山带岩石圈现今三维结构的基本要素和组成部分。秦岭造山带岩石圈现今结构具有流变学分层的“立交桥”式三维结构框架模型。显然它们具有统一的动力学背景,是秦岭造山带现今处于印度—青藏、太平洋和欧亚板块的西伯利亚地块等三大构造动力学体系复合部位,导致其从深部地幔动力学的最新调整到上部地壳响应所发生的壳慢等圈层相互作用的综合产物,可能是大陆长期保存、演化的主要途径与形式之一,具有重要的大陆动力学意义,对中国大陆构造、灾害、环境研究也具重要意义。
The northern boundary of the Qinling orogen is demonstrated by many pieces of evidence to be a huge intracontinental subduction zone where the southern North China Block underthrust beneath the Qinling from north to south and extended down below the Moho.This intracontinental subduction zone is well revealed by seismic reflection profiles across the eastern Qinling in western Henan province.North directed thrust systems were developed in the middle and upper crust in association with the subduction zone,extending over 1000 km along their tectonic strike from Baoji eastward to Tanlu fault and probably connecting with the thrust system on the northern edge of the Qinling orogen to the west.The intracontinental subduction zone formed during the Cretaceous and then controlled the Mesozoic Cenozoic tectonic evolution of the region between North China Block and the Qinling. Present three dimensional lithospheric framework of the Qinling can be described as a flyover type structure with three rheologically different layers,as revealed by geological,geochemical and geophysical studies.The upper layer,from 0 20 km,is actually a zone with brittle,viscoelastic and ductile deformation,and featured by antecedent E W striking lineament.The middle layer from 20 80 km is a zone typfied by flat rheological layering,including the Moho.The lower layer below the depth of 60 80 km is in adjusting upper mantle and characterized by N S striking geophysical anomaly zones.The N S striking strutures in lower layer,resulted from active adjustment of upper mantle materials,pass upwards to the antecedent E W striking lineaments in the upper layer through a middle flat rheological zone,showing a crosscutting relationship of structures in upper and lower tectonic layers of the Qinling lithosphere,so called flyover type 3 D framework. As its northern boundary,this intracontinental subduction zone is a basic component of present lithospheric framework of the Qinling orogen.It formed in the same dynamic regime as other Mesozoic Cenozoic structures.Active deep mantle dynamic processes in the Qinling region are controlled by the interacting between three adjacent major plates,i.e.,north moving Indian plate,west subducted Pacific plate and south moving Siberian plate.The mantle activation exerted strong influence on the upper crust,resulting in rapid vertical uplift,lateral accretion,and modification of old structures.The present flyover type 3 D framework of the Qinling is built up by joint action of tectonic processes of different crust lithospheric layers and represents one type of orogenic structures preserved through long term geological evolution.