大别山北缘深部结构的高精度重磁电震解析

大别山北缘位于大别造山带与华北陆块会聚地带,其深部精细结构还存在一些争议问题.根据近年来在研究区域内采集的地球物理数据,通过OMEGA、OASIS和FUGRO-LCT等多个重磁电震软件处理,获得了深部信息丰富的多种地球物理属性图像.本文从中选取了2条平行的电法和地震剖面,辅以高精度重磁数据,揭示了大别山北缘深部地质结构总体呈现华北陆块南向俯冲、北淮阳构造带向北逆冲的特征,并可清楚地识别大别山北缘造山带、肥南山前坳陷带和肥北斜坡带.其特征分别如下:①大别山北缘造山带,地震反射杂乱,电性高阻大于2000Ωm,以磨子潭-晓天断裂为界分为北大别杂岩带和北淮阳构造带,主要由大别群、卢镇关杂岩和佛子岭群组成,沿舒城-信阳断裂逆冲于中、下侏罗统之上,浅部发育北倾的金寨-龙门冲滑覆断裂.②肥南山前坳陷带,上部为中、新生界,呈现中低阻特征,地震反射界面清楚,断面波明显;下部为华北型前中生界沉积岩(上部可能残存古生界),电性特征为低阻(5~50 Ωm),地震反射较连续,内部反射弱.以六安断裂为界分为舒城凹陷和肥中断裂带,其北侧边界为肥中断裂.③肥北斜坡带,上部主要为侏罗系,呈现中低阻、水平层状地震反射特征;下部主要为霍邱群,电性为高阻,地震反射杂乱;中间为华北型前中生界沉积岩,向北逐渐减薄、直至缺失.上述认识将为华北陆块南向俯冲、南北板块碰撞缝合线和油气资源勘查等研究提供深部地质约束.

The fine deep structure of the northern margin of the Dabie Orogenic Beltfrom gravity-magnetic-electrical-seismic combination survey

There are still some controversial problems about the fine deep structure of North Huaiyang Tectonic Belt,which lies in the convergence area of Dabie Orogen and North China Block.In this paper,based on two parallel electrical and seismic profiles and high resolution gravity-magnetic data,the deep geological structure of North Huaiyang Tectonic Belt was revealed.The general feature was the southward subduction of North China Block and the northward thrust of North Huaiyang Tectonic Belt,and the North Margin of Dabie Orogen,Feinan Piedmont Depression Belt,and Feibei slope zone were clearly distinguished.(1) North Margin of Dabie Orogen Belt: the seismic reflection was not clear;the electrical characteristic was high resistivity larger than 2000 Ωm.It can be divided into North Dabie complex zone and North Huaiyang Tectonic Belt by the Mozitan-Xiaotian Fault.The North margin of Dabie Orogen Belt mainly consisted of Dabie Group,Luzhenguan complex zone,and Foziling Group,thrusting on Middle-Lower Jurassic Series along the Shucheng-Xinyang Fault.In the shallow,there was the north dipping Jinzhai-Longmen thrust-slip fault.(2) Feinan Piedmont Depression Belt: the upper part was Mesozoic-Cenozoic;the electrical characteristic was middle-low resistivity;the seismic reflection was clear.The lower part was North China type Pre Mesozoic(there may be the Paleozoic remaining in the upper part),the electrical characteristic was low resistivity(5~50 Ωm),the seismic reflection was continuous and weak reflection in the interior.It can be divided into Shucheng Depression and Feizhong Fault by the Liu′an Fault,the north boundary was Feizhong Fault.(3) Feibei Slope zone: the upper part was Jurassic,the electrical characteristic was middle-low resistivity;the seismic reflection showed as horizontally layered.The lower part mostly was Huoqiu Group;the electrical characteristic was high resistivity;the seismic reflection was not clear.The middle was North China type Pre Mesozoic,gradually thinning toward north till disappear.All of the above revealed deep structure will provide the deep geological constraints for the studying of southward thrust of North China Block,the suture zone position of the North-South Block collision and oil and gas exploration,etc.