大兴安岭中部地区的岩石圈精细结构及地壳生长方式的构造数值模拟研究

The Great Xing'an Range is located on the eastern part of the Xing'an-Mongolia orogenic zone between the Siberia Block and the North China Block, a region with strong superposition of the subduction and sealing of the Paleozoic Paleoasian Ocean, the collision between the blocks and the post-collision extension. The formation and evolution of the Eurasia was reflected by the strong accretion and reconstruction of the continental crust since Phanerozoic. The lithosphere structure of the Great Xing'an Range contains the influence of the different tectonic domains in different stages, which is the key region to research and solve the tectonic evolution of the Northeast Asia and the Central Asian Orogenic Belt. The abundant deposits were discovered in this region with relation to the Mesozoic magmatism. Investigation the lithosphere structure and using Numerical modeling to simulate the crustal growth, could not only be meaningful to unravel the regional tectonic evolution, but also be helpful to understand the deep background of the depositing, and to explore the ore prospecting targets. We propose to combine the deep seismic reflection data, the wide-angel reflection/refraction data and magnetotelluric sounding data to reveal the detailed lithosphere structure of the Great Xing'an Range, then construct the crustal model based on the new data and previous probing data to numerical simulate the relationship between the Xing'an and Songnen blocks. Afterwards, we will discuss the crustal growth model of the Great Xing'an Range, and try to figure out the relationship between the mineralization and the magmatic or fluid activities.

大兴安岭位于兴蒙造山带东段，夹持于西伯利亚板块和华北板块之间，经历了古亚洲洋俯冲闭合、陆陆汇聚以及碰撞后伸展等地质过程，系统的保存了欧亚大陆形成与演化的信息。其岩石圈结构和地壳变形记录了不同时期、不同构造域的地质影响，是研究和解决东北亚乃至中亚造山带地质演化历史的关键部位。由于其复杂的地质演化过程，大兴安岭地区蕴育了丰富的矿产资源，多数与中生代岩浆活动关系密切。系统揭示其岩石圈精细结构以及运用构造数值模拟其地壳生长方式，不仅具有重要的基础地质科学意义，而且对于更好的理解成矿作用的深部背景，流体与成矿作用的关系，探索有利的成矿靶区具有重要的经济和社会效益。本项目拟针对这一关键地区，以进行反射、折射地震和大地电磁资料的特别处理，以揭示岩石圈精细结构，并通过构造数值模拟兴安与松嫩地块间的相互作用，探讨大兴安岭的地壳生长方式，以及大兴安岭岩浆作用与成矿作用间的关系。

大兴安岭地区位于兴蒙造山带东段，位于华北板块与西伯利亚板块之间的碰撞拼贴过程及其夹持区域。该区域经历了古亚洲洋构造域和中生代西太平洋构造域的叠加影响，绝大部分地壳是在古生代期间固结形成的，以相对年轻的物质组成、镶嵌叠覆的地质结构、漫长复杂的地质历史和巨大的资源潜力为特征，是人类认识大陆形成演化、重建地球地质历史的天然实验室，也是中国主要的矿产资源基地，发育铅锌, 铜和钼等矿产，广泛分布着中生代的花岗岩和火山岩。项目通过对深地震反射、地震宽角反射与折射和大地电磁资料等综合地球物理工作的联合解译，揭示了大兴安岭中部的岩石圈精细结构，并探讨了大兴安岭的地壳生长方式，认为大兴安岭的岩石圈地幔和下地壳经受了底侵作用，壳内发生了部分熔融，性岩浆（岩墙和岩席）留在了地壳底部，而长英质的岩浆则向上侵入并到达地表，部分随后被剥蚀掉。这些代表侵入岩浆的透明反射区截穿了壳内的其它反射，代表了他们侵入于两个地块碰撞后。大兴安岭的岩石圈可能被底侵作用所断，可能同蒙古-鄂霍茨克洋的向东俯冲有关。这种特征同在中亚造山带的中段的特征十分相似，我们因而推测后碰撞的底侵作用在中亚造山带的中东段应该普遍存在。同时，壳内叠置的反射体也表明了在中新生代大兴安岭垂向生长之前，大兴安岭的隆升也可能由于晚泥盆世-石炭纪松嫩地块和兴安地块之间的碰撞拼合而引起的地壳缩短有关。