【作者】 谢建成；

【导师】 常印佛； 杨晓勇；

【作者基本信息】 中国科学技术大学 ， 地球化学， 2008， 博士

【摘要】 安徽铜陵地区是我国著名的长江中下游铜-金-铁-硫成矿带的一个重要的成矿区,是我国乃至世界夕卡岩成矿模式的一个典型地区,备受中外地质学家重视。铜陵地区岩浆岩与成矿关系密切,一直以来也是地质学家研究的重点内容。虽然前人在岩浆岩研究方面取得了丰硕的成果,但仍存争议之处:一是侵入岩成因及其所处的大地构造背景;二为本区侵入岩年代学。在前人工作基础上,本论文针对铜陵地区急需解决的关键问题,分别对本区三类与成矿密切相关的侵入岩组合,即辉石闪长（二长）岩、石英闪长（二长）岩和花岗闪长岩组合岩石进行岩石学、矿物学、元素-同位素地球化学和LA-ICP-MS锆石年代学研究以及首次对本区矿石中黄铁矿进行了精确Re-Os同位素定年研究,初步获得以下成果:1.铜陵地区侵入岩岩石学和矿物学特征反映岩浆混合作用可能是本区花岗岩类岩石形成的主要作用。2.铜陵地区侵入岩和矿床流体包裹体特征表明成矿流体主要来源于岩浆热液。降温、减压和沸腾作用可能是导致流体中巨量铜金元素沉淀的主要因素。3.铜陵地区侵入岩岩石系列主要为碱性和亚碱性系列,高钾钙碱性系列和橄榄安粗岩系列。其某些地球化学特征和Adakite岩的地球化学特征一致。4.含矿侵入岩元素-同位素地球化学特征显示其不是单一岩浆演化而是至少两个端元成分混合而成;幔源岩浆和壳源岩浆的混合,可能有来自古太平洋板块俯冲带来的混入端元是其特征的形成机制。5.高质量锆石U-Pb同位素²⁰⁶pb/²³⁸U加权平均年龄结果表明铜陵地区中酸性侵入岩的成岩序列为花岗闪长岩→辉石（二长）闪长岩→石英（二长）闪长岩。对比前人发表高精度的同位素年龄（Ar-Ar法,单颗粒锆石U-Pb法）,我们认为铜陵地区岩体侵入后有个快速抬升/快速冷却的过程。6.铜陵地区主要表现出两次集中的岩浆侵入事件和两次成矿事件。一次岩浆侵入时间为138～140Ma,这次显著的岩浆侵入事件对应了本区大规模的一次与高Ce异常流体密切相关的铜金成矿事件;另一次侵入时间在130～132 Ma,与庐枞和宁芜盆地的火山岩及浅成侵入岩的年龄相一致（约127～131Ma）,但在本区没有成矿事件。考查庐枞地区存在中一大型斑岩铜矿床（如沙溪）,因此本区深部是否存类似斑岩型铜矿床（化）,是一个值得深入探讨的课题。另一次可能与低Ce异常流体密切相关的铁硫成矿事件（约126Ma,新桥）,这次成矿事件与长江中下游地区120～126 Ma岩浆活动属于同一时代。7.岩石地球化学和同位素地球化学特征十分清晰地表明:本区燕山期火成岩形成于与古太平洋板块俯冲密切相关的大陆边缘岩浆弧的内陆一侧。我们认为,俯冲作用导致板片洋壳部分释放的超临界流体,受其影响地幔楔熔融形成富集S等挥发份和Cu、Au等成矿元素的母岩浆,为铜陵地区提供了成矿物质来源,其与地壳物质的混合释放出含Cu,Au的热液,最终形成铜陵地区目前矿床分布格局。更多还原

【Abstract】 The Tongling region of Anhui Province is an important ore district of the famous Lower and Middle Yangtze River Cu-Au-Fe-S metallogenic belt in China, and also a good example of skarn deposits in China. Many researchers have documented that the metal deposits are closely related to the Mesozoic intrusive rocks in the region. Although plentiful and substantial results in the magmatic rocks have been obtained, many questions remain unsolved, the crucial one is the genesis of intrusive rocks and tectonic setting, the key problem is chronology of these intrusive rocks.In this study, mineralogy, petrology, element and isotopic geochemistry, LA-1CP-MS zircon chronology of three-type Mesozoic intrusives （i.e., pyroxene diorite-monzonite, quartz diorite-monzonite and granodiorite assemblies related with ore-forming） were systematically investigated in the Tongling region, respectively. We also firstly obtained Re-Os precise dating of pyrite in Xinqiao ore deposit. The results are as follows:1. The mixing of magmas was likely the main function of granitoid crystallization, on the basis of petrology and mineralogy characteristics of the intrusive rocks.2. Evidences from fluid inclusion characteristics of the intrusive rocks and ore deposits manifest that ore-forming fluids of the Cu-Au deposits are mostly magmatic in origin. The processes of cooling down, decompress and boiling possibly led to enrichments of large amounts of copper and gold during rock-fluid interaction.3. The ore-bearing intrusive rocks are mainly alkaline and sub-alkaline series, high-K calc-alkaline series and shoshonitic series. Some geochemical characteristics are consistent to that of adakite.4. The ore-bearing intrusive rocks aren’t single but magma mixture of more than two compositional end-members, i.e., the mixing of mantle-derived and crust-derived magmas, the possible end-member derived from subduction of West Pacific plate. This is possibly the distinguished features of the rock-forming mechanism in the Tongling region.5. The results of high precise zircon U-Pb isotopic ages present the orders of intrusions in Tongling region: granodiorite→pyroxene diorite-pyroxene monzodiorite→quartz diorite-quartz monzodiorite. The zircon U-Pb ages are also identical to other Ar-Ar, Rb-Sr isotopic ages within errors, manifesting the intrusive rocks experienced fast cooling during and/or immediately after crystallization.6. Laser ablation ICP-MS zircon U-Pb dating yielded two groups of ages （c.a. 130-132 Ma and 138-140 Ma） for the intrusive rocks, which are the most important magmatic rocks in Tongling area related to Cu-Au deposits. Combined the high-precision zircon U-Pb datings and pyrite Re-Os age for Xinqiao ore deposit with zircon trace element measurements, the one ore-forming event with high Ce abnormality （molybdenite Re-Os age of 138-140Ma） was closely related to copper and gold ore deposit, another probably ore-forming event with low Ce abnormality （about 126 Ma） closely related to iron and sulfur ore deposits in the Tongling region.7. The results of petrochemistry and Sr-Nd-Pb isotopes clearly indicate that West Pacific subduction was the dominant factor controlled Mesozoic ore-forming intermediate intrusive rocks in Tongling, which is the major tectonic event in eastern China in the Early Cretaceous. The geochemical characteristics of these intrusives were likely formed in magmatic arc in land edge. The subducted slab released high fO₂ aqueous supercritical fluid, melting of the mantle wedge formed mother magmas enriched volatilizations （S and so on） and ore-forming elements （Cu, Au and so on）. The mixing of the mother magmas and the crustal matters released Cu, Au-bearing epithermal. These ore metal-bearing epithermal ultimately formed ore deposits in the Tongling region.更多还原