Upper Crustal Structure and Deformation of Lu-Zong Ore District: Constraints from Integrated Geophysical Data
In order to study the 3Dstructure of Lu-Zong ore-district,better understand the metallogenesis and provide in-depth information for deep mineral exploration,the author have finished five intersecting integrated geophysical profiles with total length of more than 300km.The survey methods include high resolution reflection seismic,magnetotelluric sounding(MT)and regional gravity.Some new discoveries were obtained regarding the upper crustal structure and deformation based on the integrated analysis of reflection seismic,MT,regional gravity and aeromagnetic data.In general,the Lu-Zong ore-district consist oftwo depression one uplift,e.g.,Qianshan-Kongcheng depression in the west and LujiangZongyang volcanic basin in the east,a uplift exist just in between.The north south structure shows a northward step-like uplift,two step-like faults are WNW-ESE trending Tangjiayuan-Zhuanqiao fault and Lujiang-Huangguzha-Tongling fault respectively.Lu-Zong volcanic basin presents a non-symmetrical shape with four inward dipping boundary faults.The northern and eastern boundary faults(BF2and LHTD)are deep faults,which control the development and evolution of the Lu-Zong volcanic basin.Tectonically, there are three WNW-ESE trending faults and six NE-SW trending faults cutting over the ore-district. From north to south,they are Lujiang-Huangguzha-Tongling detachement fault,Tangjiayuan-Zhuanqiao fault and Yijing-Taojiaxiang fault(BF3);from the west to the east,six faults are Tan-Lu,Chihe,LuoheQuekou,Zongyang-Huangtun,Taojiawan-Shijiawan and Along river fault.The formation and tectonic evolution of the ore-district was mainly affected by the Yanshanian intracontinental orogenic movement, and experienced the Middle~Late Jurassic contraction deformation due to the paleo-Pacific NW-trending subduction and Cretaceous extension deformation.Some other new findings regarding the nature of the faults were first obtained,e.g.,the Along river fault is a thrust fault in nature,Lujiang-HuangguzhaTongling fault is a SW-dipping detachement,the Tangjiayuan-Zhuangqiao fault is newly determined, which divide the Lu-Zong volcanic basin and Qianshan-Kongcheng depression into northern and southern parts.In the northeast of Lu-Zong ore-district,a NWW-SEE trending,probably the Early or Middle Jurassic basin was found from the seismic image with depth up to 5.0km,the author consider it to be the product of post-collision extension of Indosinian movement during the middle and early Late Triassic.