长江中下游庐江-枞阳火山岩矿集区深部结构与成矿作用
Deep structure and ore formation within Lujiang-Zongyang volcanic ore concentrated area in Middle to Lower Reaches of Yangtze River.
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摘要: 为探测长江中下游成矿带庐江-枞阳白垩纪火山岩盆地和铁、硫矿集区深部构造和地壳结构,探讨成矿深部控制条件,作者完成了穿越火山岩盆地的深反射地震剖面(150km,记录30s)和罗河铁矿区浅层高分辨反射地震剖面(20km),以及平行剖面的大地电磁、高精度重磁剖面,揭示了矿集区全地壳精细结构和电磁结构,同时开展区域构造测量和火山岩年代学研究,获得了新的认识。证实"耳状"的庐-枞火山岩盆地是一个沿北东向罗河断裂向东侧发育的非对称火山盆地,排除了另一半被断在西侧红层之下的判断;罗河断裂是一条切穿MOHO的深断裂,倾向南东,是引导地幔流体和岩浆上涌和喷发的通道,在中地壳形成岩浆房(反射亮斑);鉴别出多层界面,火山岩-侏罗系厚度约4~5km(其中火山岩厚度约3km),三叠系-震旦系变形层底界深度大致18~20km,变质基底组成中下地壳,MOHO平缓向北西倾,深度33~31km;追踪郯-庐断裂带的深部产状,陡立延伸到MOHO,宽约10km。从而揭示了早白垩系(132~127Ma)庐-枞火山岩矿集区深部过程与成矿、控矿作用。Abstract: To explore the crustal-depth structures in a volcanic depression, iron and sulfur ore concentrated area, and study deep process ore-formation within Lujiang-Zongyang area, along the metallogenic belt of Middle-Lower Reaches of Yangtze River during Cretaceous, the deep-probe project was carried. 150km long deep reflection seismic profile (recorded 30 seconds) across volcanic depression, 20km shallow high resolution reflection seismic profile in Luohe larger iron deposit (20km), magnetotelluric profiles, high resolution gravity and magnetic profiles parallel to the seismic profile were finished since 2006~2009, and the images of whose crustal fine structure and electromagnetic structures were revealed, simultaneously the regional tectonic analysis and volcanic rocks chronology were obtained. The all of new evidences indicated that Lu-Zong volcanic depression and iron deposits was controlled by a deep fault, NE-SW tending Luohe fault, which cut through crust to MOHO and the half-round sharp ("ear-sharp") depression was an asymmetric volcanic eruption along Luohe fault expending from west to east, excluded the hypothesis that another half buried in west of Luohe fault under red bed basin. The Luohe fault is considered as the tectonic channel linking from surface to mantle resulting in the upwelling and eruption of deep fluid, and magma chambers in mid-crust along bi-later of this channel can distinguished form "light spots" of the reflectors. The multi-layer borders were identified through the volcanic depression, the depth of Cretaceous volcanic rocks and Jurassic sedimentary strata is 4~5km (the depth of volcanic rocks is ca.3km), the depth of sequence of deformated layers from Sinian to Triassic is ca.18~20km, and the middle-lower crust consists of metamorphic basements.The MOHO has gentle north-west dipping and ca.33~31km depth. Tan-Lu fault, a larger left slip displacement fault, extended to MOHO with steep dipping, the width is ca.10km. Thereby, the deep process and mechanics of the mineralization within Lu-Zong volcanic depression during Early Cretaceous (132~127Ma) were revealed.
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