利用深地震测深数据重建青藏高原侧向碰撞成矿带地壳结构

Due to the strong mineralization within different tectonic evolution episodes and environments, many kinds of metal and non-metal mineral resources are widely distributed around the Tibet plateau lateral collision belt, where is located around the Sanjiang area. Nowadays for the strategic demands of “Deep Resource Exploration and Mining” , there are some typical problems about the huge gold and polymetallic mineralization in this lateral collision belt need to be clarified, such as: 1) What’s there deep background and geodynamic process related with the mineralization? Does there exist low velocity zones within the crust corresponding to the surface cenozoic mineral resources or not? And is there a crust-mantle transition zone connected to the low velocity layer in the upper mantle? 2) What’s the coupling relationship between the typical ore concentration area with the crustal structure of Emeishan Large Igneous Province? 3) the contact relationship among the Songpan-Ganzi fold system, the Sanjiang fold system and the Yangtze block? In the past days it is difficult to know the crustal feature beneath this lateral collision belt in Yunnan province due to the lack of Deep Seismic Sounding (DSS) profile traverse the typical ore concentration areas and also because of the limitation of just one component seismic data. Therefore in order to disclose the crustal low-velocity-zones, the crust-mantle transition zone and other deep structures related to the mineralization beneath the lateral collision metallogenic belt, this project aims to reconstruct the P-wave, S-wave velocity and Poisson ratio structure of the crust layer by layer based on the 3-components seismic data acquired in December 2016 on the 410 km-long DSS profile that across the Jinding and Beiya ore concentration areas. Hence this research will bring new scientific information to promote the metallogenic theory of this Tibet plateau lateral collision belt.

位于青藏高原东南缘三江地区及其邻域的青藏高原侧向碰撞带在构造演化的不同阶段均发育丰富的成矿作用,广泛分布多种金属、非金属矿产。国家“深地资源勘查开采”的巨大战略需求促使人们面临一系列与该地区巨量金及多金属成矿相关的重要科学问题，如成矿作用的深部背景和动力学过程如何、地壳内是否存在与新生代矿产资源关联的低速区、下地壳是否存在与上地幔低速通道相连的壳幔过渡带及松潘甘孜块体、扬子地块和三江褶皱带的拼贴关系等。以往由于缺乏横穿金顶、北衙等典型矿集区的测深剖面，及受制于单分量地震资料，人们难以了解侧向碰撞带典型矿集区下方的地壳结构特征。本课题拟基于2016年12月采集的跨金顶和北衙矿集区410公里长剖面的三分量深地震测深资料，联合P波和S波走时数据逐层反演地壳纵横波速度及泊松比，揭示与成矿作用密切相关的地壳低速区及壳幔过渡带等深部结构，为完善青藏高原侧向碰撞带成矿理论提供深部科学依据。

青藏高原东南缘侧向碰撞成矿带广泛分布多种矿产资源。本项目基于该区主动源和被动源地震资料研究该区地壳结构，探讨该区新生代成矿作用的深部背景和动力学过程。首先利用410km长营盘-盘龙测深剖面采集的主动源地震数据，在通过震相分析获取纵波和横波震相数据基础上，通过走时反演构建了该剖面纵波速度、横波速度及纵横波速度比模型，其结果揭示出金顶铅锌矿和北衙金矿区附近的浅表高速体、北衙金矿及六苴铜矿下方显著的上地幔高速体，及扬子克拉通内上地壳底部明显的低速异常条带等图像特征。推测浅表高低速异常接触带附近由于较强的区域应力作用利于裂隙发育，深部含矿岩浆沿裂隙向上运输至浅部地壳，及高温热液对浅部地壳含矿岩石的交代可能是该区新生代以来成矿的重要机制。其次基于240km长绿春-马关短周期密集台阵采集的被动源地震数据，开展接收函数、H-K扫描及背景噪声成像研究，其结果发现哀牢山隆起下方地壳存在2条显著倾斜界面、地壳平均波速比明显偏高、Moho面转换波能量显著偏弱,且剖面浅部地壳存在一系列高速和低速异常体。推测以上结构特征可能暗示新生代以来红河断裂及哀牢山地区壳幔物质和热交换活跃，并引起地壳掀斜式抬升、剧烈造山和地表火山活动；幔源岩浆沿红河断裂底侵上涌，壳内岩石部分熔融、流体发育及局部铁镁质组分含量偏高，是哀牢山南段哈播、铜厂、大坪等金矿新生代发育成矿的深部原因。