【作者】 马立成；

【导师】 董树文；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2009， 博士

【摘要】 长江中下游地区庐江-枞阳(以下简列为庐-枞)陆相火山岩盆地形成于中生代晚期,是长江中下游多金属成矿带中著名的铁、铜矿集区之一。通过庐-枞矿集区典型矿床的成矿规律,野外构造变形形迹的几何学、运动学、动力学特征的系统测量及中生代古应力场的反演,结合穿越庐-枞矿集区的高分辨率反射地震剖面、大地电磁测深剖面、重磁异常剖面和地质剖面的综合解释,特别是深部主要构造界面特征的研究,建立了庐-枞矿集区深部构造作用与浅表成矿响应的过程。庐-枞盆地中生代可识别出的构造变形及古应力场恢复,该区主要经历了两次构造运动和三期构造变形,即:(1)中三叠世-中侏罗世(240-180Ma)近南北向挤压,为印支运动的产物,它是华北板块与扬子板块碰撞后的大别山前陆缩短带变形应力场:(2)晚侏罗世-早白垩世早期(170-140Ma)北西-南东向挤压,是燕山运动主幕陆内多向挤压造山阶段的构造反映,后期由于郯-庐断裂左行走滑导致逆时针旋转改造了印支期的构造形迹方向;(3)早白垩世中期(140-110Ma)北北西-南南东向拉伸,为燕山陆内造山的后效大陆伸展期,庐-枞地区内多旋回的火山喷发和多期次的岩浆侵入活动从深部带来了巨量的成矿物质,形成了庐-枞铁、铜矿集区。区域上及庐-枞盆地内年代学统计说明,该矿集区形成时代为135-130Ma;铁矿成矿层位主要在龙门院组、砖桥组、双庙组,浮山组成矿信息微弱。区内反射地震特征、电性差异及重、磁异常剖面综合解释表明:(1)庐—枞火山岩盆地深部MOHO面深度范围在9.6～11sTWT,深度约33—30km,相差3km以上,由大别造山带至沿江构造带MOHO面逐渐变浅,成小角度北西倾,在郯庐断裂带和罗河断裂两处有错断。反射地震剖面显示郯庐断裂带的宽度8～10km,深部产状陡立,断面边界北西倾;火山岩盆地西北缘的罗河断裂,深部南东倾,切穿MOHO,控制早白垩世火山岩分布产出,浅部北西倾,为后期的正断层,控制上白垩统红层界线;(2)郯庐断裂、罗河断裂等NNE-NE断裂系统是庐—枞盆地的控制构造;盆地北缘的庐江—黄姑闸断裂,可能是盆地北缘铁矿、铅锌矿的主控矿断裂;火山岩盆地之下,上地壳发育多组弧形强反射,推测可能为岩瘤,说明火山岩盆地之下假设的约800km~2侵入岩体是存在的;火山岩盆地深部3～4.2sTWT存在构造分界面,可能是浅部盖层和基底之间的滑脱面,该结构面在MT电性剖面中为低阻带,与地震剖面中反射波谱特征相互印证;5～7sTWT弧形强反射界面,深度15～20km,可能是中、上地壳的分界,或深部岩浆房顶面或底等。(3)庐—枞火山岩只分布在罗河断裂以东呈“耳状”,反射地震剖面、重磁异常和MT测深剖面上均能明显反映火山岩与其它沉积地层之间界线,其中火山岩的厚度约2～3km;而罗河断裂西侧红盆之下不存在另一半“耳”状的火山岩盆地。(4)反射地震剖面显示向南东倾斜的罗河断裂在深部切穿了MOHO,错断约3km,东侧抬升,沿断裂两侧中下地壳间的强反射被切断呈不连续弧形产出,表明罗河断裂是庐—枞火山岩盆地深部地幔流体运移及岩浆上涌的通道,庐—枞火山岩龙门院旋回、砖桥旋回和双庙旋回的喷发以裂隙式为主,向东不对称喷发,而浮山旋回以中心式喷发为主。庐—枞矿集区形成于晚侏罗世东亚汇聚的构造背景,170-140Ma前后太平洋板块斜向俯冲到欧亚板块之下,地壳增厚,中国东部高原形成,并导致NNE向郯-庐断裂带左行走滑及罗河断裂形成,出现造山型埃达克岩系;140Ma前后中国东部由挤压转为伸展,岩石圈拆沉减薄,郯庐断裂带沟通了地壳和地幔通道,减压作用降低了地幔岩石的熔点,富集地幔部分熔融,沿罗河断裂上涌在中下地壳界面形成岩浆房,幔源岩浆与地壳岩石发生作用,形成埃达克质-碱质岩浆并喷发、侵入,从深部带来巨量的成矿物质,浅表富集后形成庐-枞铁、硫、铜矿集区(135-130Ma)。对应早白垩纪中期NNW-SSE伸展应力场,NE向罗河断裂及其次级断裂和火山活动裂隙系统,直接控制了火山岩盆地西缘罗河铁矿、大包庄铁矿、泥河铁矿、杨山铁矿以及盆地内部的钟山、小岭硫铁矿等。盆地北部和东部的火山岩和侏罗系砂岩之间的不整合面也是良好的成矿赋存空间,盆地北缘龙桥铁矿、马鞭山铁矿和岳山铅锌矿处于不整合接触面和断裂交汇部位上。更多还原

【Abstract】 The Lujiang-Zongyang(Lu-Zong for short) continental volcanic basin,one of the famous iron and copper ore concentrated areas in polymetallic metallogenic belt in the Middle to Lower Reaches of Yangtze River,formed during the Late Mesozoic.Through the research on metallogenic rules of typical deposits,systemic measurements of geometry,kinematics and dynamics of tectonic deformation symbols in the field,and the inversion of Mesozoic paleo-stress fields,combined with the comprehensive interpretation of main structural interfaces and structural assemblages in the deep on high resolution reflection seismic profiles,magnetotelluric sounding profiles,gravity and magnetic anomaly profiles,and geological cross sections across the Lu-Zong basin,the coupling processes of deep tectonism and near-surface metallogenic responses are established in the Lu-Zong ore concentrated area successfully.Based on the identification of the Mesozoic structural deformations and the recovery of the Mesozoic paleo-stress fields in Lu-Zong area,it is concluded that the Lu-Zong basin has suffered from two periods of tectonic movements and three stages of paleo-stress fields:(1) approximately N-S compression from Middle Triassic to Middle Jurassic(240～180 Ma) during Indosinian movement,represented by the stress field in Dabieshan foreland belt forming after the collision between North China and Yangtze plates;(2) The NW-SE compression from Late Jurassic to Early Cretaceous(170～140 Ma) during the main episode of Yanshan movement,which is the tectonic response of multi-direction compressive orogeny.Then,the structural direction was changed for the sinistral strike-slip of Tanlu fault;(3) the NNW-SSE continental extension(equal NEE-SWW compression) during middle Early Cretaceous(140～110Ma),which is the after effect of the Yanshan intracontinental orogeny. According to the geochronological statistics in Lu-Zong region and the Middle to Lower Reaches of Yangtze River,it is suggested that Lu-Zong ore concentrated area formed due to the huge magnitude of metallogenic materials brought from the deep through multi-cycle volcanic eruptions and multi-phase intrusions in 135～130 Ma,with the forming of iron ore-bearing strata of Longmenyuan,Zhuanqiao and Shuangmiao formations,and weak metallogenic information in Fushan formation. The comprehensive interpretation of seismic reflection characteristics,electric differences, gravity and magnetic anomaly shows that:(1) The MOHO interface occurs at ca.9.6～11 s TWT in the seismic profiles across the Lu-Zong volcanic basin,with the depth range of ca.33～30 kin and 3 km difference in depth.The MOHO interface,dipping in northwest with small angle,becomes shallower gradually from Dabie orogenic belt to Changjiang structural belt.The MOHO was truncated to be imbricate by the Tanlu fault belt and Luohe fault for two times.The seismic profiles show that the Tanlu fault belt has a width of ca.8～10 kin,dipping steeply in north-west.The Luohe fault,located at the northwestern margin of the Luzong basin,is dipping in southeast and cut through the MOHO in the deep, controlling the distribution of volcanic rocks in Early Cretaceous.The Luohe fault becomes to be a normal fault in the later period and dips in northwest in the shallow,controlling the distribution of the Upper Cretaceous red beds;(2) The NNE to NE striking Tanlu fault system,including Tanlu and Luohe faults etc,is considered to be the basin-controlling structure;the Lujiang-Huangguzha fault,located in the north side of the basin,may be the ore-controlling fault of Longqiao iron deposit and Yueshan lead-zinc deposit.The sedimentary characteristics in the shallow and some intrusive bodies under the sedimentary layers in the Changjiang tectonic belt are significant on the seismic profile.The multi-group arc-shaped strong reflection in the upper crust could be plutonic bodies under the volcanic basin,indicating the hypothesis of huge intrusive body with 800 km~2 could be right.The structural interface with ca.3～4.2 s TWT on the seismic profile,with depth of ca.6～8 km,and the lower resistance belt displayed on magnetotelluric sounding profile,may be the detachment surface between the shallow cover and the basement.The other structural surface with ca.5～7 s TWT and depth of ca.18～20 km on the seismic profile,may be the interface between the Middle and the Upper Crust,could be either the top or the bottom of magma chamber;(3) The volcanic rocks,with the thickness of ca.2～3 km,distribute only to the east of the Luohe fault with an ear-sharp,evidently identified by the seismic,gravity and magnetic anomaly, and magnetoteUuric sounding profiles.There is not another half of the ear-sharp basin under the red basin to the west of the Luohe fault;(4) The SE-dipping Luohe fault cut through the MOHO interface with a displacement of ca.3 km in the deep.The MOHO interface uplifted at the east side of the Luohe fault.The discontinuous arc-shaped strong reflections truncated by the Luohe fault in the Middle and Lower Crust shown on the seismic profile,suggest that the Luohe fault was the channel of mantle fluid migration and magma upwelling in the deep of the Lu-Zong volcanic basin.The volcanic rocks of Longmenyuan,Zhuanqiao and Shuangmiao cycles are mainly belonging to the eastward asymmetric fissure-type eruptions,though those of Fushan cycle are belonging to the central-type eruption.The Lu-Zong ore concentrated area formed in the tectonic setting of East Asia multi-direction convergent tectonic system in the Late Jurassic(ca.170～140 Ma),when the Pacific Plate subducted obliquely underneath the Eurasian Plate,the East China Plateau formed due to crustal thickening,the Tanlu sinistral strike-slip fault and the Luohe fault formed simultaneously,and the orogenic adacite series occurred.At ca.135～130 Ma,the tectonic regime transformed from compression to extension in eastern China,when the lithosphere delamination and thinning occurred,the melting point of mantle rocks decreased for the extension and decompression of the Tanlu fault zone,the enrichment mantle suffered partial melting and upwelling along the Luohe fault,the magma chambers formed at the interface of the Middle-Lower Crust,the mantle-derived magma interacted with crustal rocks,the adakite-alkaline magma formed and erupted or intruded, and the Lu-Zong Fe-S-Cu ore concentrated area formed due to the enrichment of huge metallogenic material brought from the deep through the Tan-Lu and Luohe faulting.Corresponding to the NNW-SSE extensional stress field during middle Early Cretaceous,the NW striking Luohe fault and its secondly faults and the cracks of volcanic apparatus controlled the formation and distribution of the Luohe,Dabaozhuang,Nihe,and Yangshan iron deposits at the western margin of the Lu-Zong volcanic basin and Zhongshan and Xiaoling pyrite deposits etc insider the basin.The unconformity between the Cretaceous volcanic rocks and the Jurassic sandstone is also the favorable metallogenic space in the northern and eastern parts of the basin. The Longqiao and Mabianshan iron deposits and Yueshan lead-zinc deposit formed in the unconformity and located at the intersections of the faults.更多还原