长江中下游成矿带及邻区地壳结构——MASH成矿过程的P波接收函数成像证据?  

Crustal Structures Beneath the Mid-lower Yangtze Metallogenic Belt and Its Adjacent Regions in Eastern China-Evidences from P-wave Receiver Function Imaging for a MASH Metallization Process?

作　　者：史大年[1] 吕庆田[1] 徐文艺[1] 严加永[1] 赵金花[1] 董树文[2] 常印佛 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037 [2]中国地质科学院,北京100037 [3]安徽省地调院,合肥230001

出　　处：《地质学报》2012年第3期389-399,共11页Acta Geologica Sinica

基　　金：国土资源部深部探测技术与实验研究专项-深部矿产资源立体探测技术及实验研究项目-长江中下游成矿带地壳结构与深部过程探测实验课题(课题编号SinoProbe-03-02;行业基金项目编号201011047);国家自然科学基金(编号40930418)共同资助的成果

摘　　要：利用长江中下游成矿带多学科深部探测剖面于2009年11月至2011年3月间采集的天然地震数据,通过天然地震接收函数成像等分析研究,得到了研究区地壳和上地幔结构的清晰图像。接收函数成像结果显示研究区内Moho面深度存在着明显的起伏变化,在长江中下游成矿带(指剖面穿过的长江中下游成矿带宁芜矿集区,下同)下方存在着"幔隆构造"。在剖面东南端(即扬子克拉通北缘),Moho面相对稳定,深度约为30km;在茅山和江南断裂附近,Moho面存在上下起伏现象;在剖面中部或宁芜矿集区下方,Moho面存在明显隆起,深度只有28km;在郯庐断裂带下方,Moho面明显加深,深度达到36km;进一步向北到华北地台南缘,Moho面深度逐渐恢复到了32km左右的平均深度水平。其次,我们在接收函数成像结果中发现,长江中下游成矿带与其周边下地壳结构存在着明显的差异,成矿带的下地壳具有显著的地震波方位各向异性。扬子克拉通北缘的下地壳呈高速的近水平状结构,地震波各向异性特征不明显;与此相比,长江中下游成矿带的下地壳虽然也呈近水平状结构特征,但是,对于沿成矿带走向方向传播的地震波,其下地壳具有高速特征,而对于垂直于成矿带走向方向上传播的地震波,其下地壳却又表现为低速特征,这意味着成矿带的下地壳存在着平行于成矿带走向(即近北东—南西)方向的地震波各向异性,我们解释其是下地壳熔融并沿成矿带走向水平流动导致矿物晶体定向排列的结果。最后,在郯庐断裂以西的华北地台南缘观测到一条从上地壳延伸到中下地壳的南南东向倾斜的转换震相,我们推测它可能是合肥盆地内地壳伸展构造的反映。此外,我们发现接收函数成像结果中观测到的"幔隆构造"与远震P波层析成像结果在成矿带下方150km深度上显示的上地幔低速异常(江国明等,另文发表)存在着良好的对应�Using the passive-source seismic data collected during November 2009 to March 2011 from a multidisciplinary transect in the mid-lower Yangtze metallogenic belt,we perfomed studies of receiver function imaging and others,and achieved seismic images of the crust and upper mantle structures in the study region with great clearance.First,the receiver function images show the Moho depth varies significantly along the profile in the study region,and a ＂mantle uplift＂ is seen just beneath the Yangtze metallogenic belt（to be more precisely,refers to the Nanjing-Wuhu ore district of the Yangtze metallogenic belt in all this paper）.In the southeast section of the profile,the Moho topography is relatively stable with depths about 30 km beneath the northern margin of Yangtze craton;it is shown rugged up in the vicinity of the Jiangnan fault and the Maoshan fault;the Moho is shown uplift apparently to a depth of only about 28km beneath the centre part of the cross-section or the Nanjing-Wuhu ore district;it is seen deepened up to a depth of about 36 km below the Tan-Lu fault zone;the Moho depth is shown gradually restored to the average depth in the study region or about 32 km to further north beneath the southern margin of North China block.Secondly,we found the lower crust of the Yangtze metallogenic belt is different from that of its surrounding area in the structures from the receiver function results.The lower crust of the Yangtze metallogenic belt is seen apparently seismic azimuthal anisotropic.The lower crust of the northern margin of Yangtze craton is seen in a nearly layered structure of high velocity but lacks significant seismic anisotropy;Contrastly,the lower crust beneath the Yangtze metallogenic belt is,though in a sub-horizontal layered structure,seen to be of high velocity for seismic waves propagated approximately along the strike of the metallogenic belt,and to be of low velocity for waves propagated approximately normal to the strike,which implies that the lower crust of the metallogenic belt posse

关 键 词：长江中下游成矿带 天然地震探测 接收函数成像 地壳结构 成矿作用 

分 类 号：P618.41[天文地球—矿床学]