长江中下游宁芜火山岩盆地深部结构特征——来自反射地震的认识  

Deep structure of Ningwu volcanic basin in the Middle and Lower Reaches of Yangtze River: Insights from reflection seismic data

作　　者：梁锋[1] 吕庆田[1] 严加永[1] 刘振东[1] 

机构地区：[1]中国地质科学院矿产资源研究所,国土资源部成矿作用和资源评价重点实验室,北京100037

出　　处：《岩石学报》2014年第4期941-956,共16页Acta Petrologica Sinica

基　　金：国家"深部探测技术与实验研究"专项课题(SinoProbe-03-02);国家自然科学基金重点项目(40930418)联合资助

摘　　要：宁芜火山岩盆地是长江中下游成矿带的重要组成部分,盆地内广泛产出玢岩型铁矿床。为探讨宁芜火山岩盆地深部结构,作者完成了三条穿越宁芜火山岩盆地的深反射地震剖面。三条剖面的长度不一,NW01剖面长度42km,NW02长56.3km,NW03长27.1km。三条剖面的排列长度都为720道,采样间隔2ms,记录长度16s。因为本文的主要研究对象是宁芜火山岩盆地上地壳的结构特征,因此只用了总记录长度的前4s数据。通过本次研究揭示了宁芜矿集区的上地壳精细结构、岩浆和断裂系统的空间展布形态。不仅验证了以往对盆地的部分认识,而且给出了新的认识。(1)发现了直接控制盆地火山-岩浆活动的南东和北西边界断裂并非人们经常认为的两大基底深断裂:方山-南陵断裂和长江断裂带,而是北西向F1和南东向F2断裂;(2)宁芜火山岩盆地以马鞍山-薛津断裂为界向北北东方向滑脱,造成了盆地南西高北东低的隆凹构造格局;(3)阐明了就位于盆地下方的为火山-岩浆活动提供补给和热源的岩浆房的空间展布特征;(4)清晰地厘定了盆地内的断裂系统,其中最主要的断裂是隐伏于宁芜火山岩盆地深部的控制深部岩浆活动的盆中基底断裂(BCF),控制着深部岩浆岩的空间展布格局并对宁芜火山岩盆地的地层和断裂系统有强烈地改造作用。本文的发现为宁芜火山岩盆地深部结构认识、成矿预测及成矿动力学分析提供了可借鉴的证据。Ningwu volcanic basin is an important part of the Middle-Lower Reaches of Yangtze metallogenic belt, which has been famous for porphyry-type iron deposit. To explore and discuss its deep structures and the process of geodynamic, three seismic reflection profiles crossing the Ningwu volcanic basin were completed in a number of key areas in Ningwu volcanic basin. They vary in length, NW01 is about 42km long, NW02 56. 3kin, NW03 27. lkm. Channel numbers are all 720. Sample interval is 2ms. Time length of record is 16s. Seismic reflection data of 4s are cut out to analysize structure characteristic under Ningwu volcanic basin. According to the interpretation results which, combined with other studies, provide new insight into the varied tectonic, fine structure of the upper crust, spatial distribution patterns of magma and fauh systems are revealed. In addition, the lower layered reflectivity characteristics and Moho discontinuity imaged along the seismic profiles reveals that underplating and delamination occurs under the lower lithosphere under the Ningwu volcanic basin during approximately Mesozoic. Reflective upper crust can be related to geological structures at the surface; the thin-skinned tectonics implied has yet to be reconciled with the block tectonics of the crust. The Moho reflection has highly variable characteristics as imaged within transects and among different transects. Crustal and Moho reflectivity is caused by a wide range of features, including fault/shear zones, lithologic contacts, compositional layering. The work not only vertifies previous understandings to the basin, but present new understanding results. （ 1 ） NE and SW boundary faults of the basin are discoveried, which are not traditionally so-called Yangtze fault （NW） and Fangshan-Nanling fault （SE）, but FI （NW dipping） and F2 （SE dipping） fault, controlling the volcanic rock distribution of the Ning-Wu volcanic basin. （2） Maanshan-Xuejin fault is a key one which control spatial structure of SW-NE of the basin. T

关 键 词：矿集区 深部勘探 断裂系统 构造演化 莫霍面 长江断裂带 

分 类 号：P541[天文地球—构造地质学] P631[天文地球—地质学]