【作者】 李金冬；

【导师】 翟裕生；

【作者基本信息】 中国地质大学（北京） ， 矿物学、岩石学、矿床学， 2005， 博士

【摘要】 湘东南地区位于扬子陆块与华南陆块的接合地带,属南岭东西向构造-岩浆-成矿带中段北部,区内中生代花岗岩与有色金属矿产非常发育。本文对湘东南地区中生代花岗岩进行了系统的年代学、地质学、岩石学、岩石地球化学等研究,结合构造、盆地沉积及火山岩等其它地质要素特征,对湘东南地区中生代构造-岩浆-成矿动力学过程进行了深入分析。获得以下主要展和认识: 1、首次对湘东南地区中生代花岗岩形成的3 个主要阶段的时限进行了较精确的厘定和总结:第一阶段印支期时限约为233～210Ma,第二阶段燕山早期时限约为174～135Ma,第三阶段燕山晚期,时限约为130～85Ma,即白垩纪。2、研究确定湘东南地区中生代花岗岩存在两种主要成因类型,即壳源型与壳幔混源型。印支期花岗岩为典型壳源型,是中地壳和下地壳重熔的产物。燕山期花岗岩主要为壳幔混源型。3、中生代不同阶段花岗岩形成的构造环境有别。印支期花岗岩形成于陆内同造山构造环境,且于主俯冲汇聚的峰期之后挤压松弛条件下侵位;燕山早期花岗岩形成于后造山伸展构造环境;燕山晚期花岗岩形成于陆内裂谷环境。4、研究表明区域构造格架和岩石圈结构主要控制了中生代花岗岩浆活动。印支后期,茶-郴断裂以东的隆起区由于俯冲板片的叠置与横向收缩,地壳厚度大,加厚熔融机制使中地壳结晶片岩、片麻岩熔融,形成酸性程度高的花岗质岩浆;断裂以西的拗陷区增厚幅度较小,下地壳基性岩熔融而形成偏基性岩浆。燕山早期,隆起区以及拗陷区内的局部隆起地带,可能由于具有厚的地壳与地幔岩石圈,岩石圈发生大规模拆沉,导致中地壳结晶片岩大量熔融,从而形成酸性程度高的规模较大的中深成岩体;拗陷区陆壳和地幔岩石圈较薄,壳幔作用及其引起的热扰动作用较弱,中地壳结晶片岩小规模熔融产生的岩浆,分别沿断裂上侵于近地表而形成酸性的花岗斑岩和石英斑岩、偏中性的花岗闪长斑岩小岩体。5、提出并论证了区内印支期花岗岩矿化弱,而燕山早期花岗岩矿化强的原因,认为可能主要是由于构造体制不同所致。前者形成于区域挤压构造体制,不发育开放的断裂与裂隙系统,不利于成矿。后者则形成于区域后造山的拉张构造环境,断裂与裂隙系统高度开放,有利于成矿流体的运移、物质交换与矿质沉淀。6、提出了湘东南地区燕山早期成矿差异性和成矿专属性的主要深层原因是更多还原

【Abstract】 As a northern part of the middle segment of the Nanling EW-trending tectonic-magmatic-metallogenic belt, Southeast Hunan Province is situated at the junction of Yangtze Block and South China Block. There occur a great number of the Mesozoic granites associated with abundant metallic mineral resources. A chronological, geological, petrological, petrochemical and isotopic geochemical study on the Mesozoic granites combined with a comprehensive research on the other geological records such as structures, basin sediments and volcanic rocks has been carried out, which provides some new insight into the Mesozoic dynamic process of tectonism-magmatism-metallogeny in Southeast Hunan Province. The following are the major progresses and inclusions. 1. The formation time of the Mesozoic granites in Southeast Hunan Province is defined for the first time to be in the range of 233～210 Ma in the Indosinian, 174～135 Ma in the Early Yanshanian, and 130～85 Ma in the Late Yanshanian. 2. The Mesozoic granites occurred in Southeast Hunan Province can be divided into two genetic types. The first type is a crust-derived type represented by the Indosinian granites, and the other is a crust-and mantle-derived type predominated by the Yanshanian granites. 3. The tectonic settings for formation of the Mesozoic granites of different stages are different. The Indosinain granites were formed in an intracontinental syn-orogenic environment, the Early Yanshanian granites in a post-orogenic extensional environment, and the Late Yanshanian granites in an intraplate rifting environment. 4. The regional structure framework and the lithospheric structure play an important role in controlling the Mesozoic granitic magmatic activities. In the late Indosinian, intensive thickening caused by superposition of subducting slabs with transverse shortening in the upwelling region to the east of the Chaling-Chenzhou fault resulted in the partial melting of crystalline schist and gneiss in the middle crust to form granitic magma with high acidity. In contrast, slight thickening in the down-warping region to the west of the fault led to the partial melting of basic rocks in the lower crust to form sub-basic magma. In the Early Yanshanian, large scale delamination of the lithosphere possibly owing to occurrence of the thicker crust and mantle in the Yanlin-Ruchen upwelling region and the local upwelling places of the Hengyang-Guiyang down-warping region was responsible for the partial melting of crystalline schist in the middle crust to form bigger plutons with high acidity. In contrast, the magma produced by partial melting of crystalline schist in the middle crust on a smaller scale caused by weak interaction of crust with mantle and its thermal disturb in the down-warping region with thinner lithosphere mixed with mantle-derived magma and moved along faults up to shallow level of crust to form small bodies of granite porphyry, quartz porphyry, and granodiorite. 5. Different tectonic regimes are responsible for the existence of difference in possibility of mineralization between the Indosinian and Early Yanshanian granites. The transformation of the regional tectonic regime from Indosinian compression to Early Yanshanian post-orogenic extension led to the less development of open fault and fracture systems in the Indosinian granites associated with weak mineralization, but development of open fault and fracture systems in the Early Yanshanian granites associated with strong mineralization. 6. A new consideration is brought forward that the special tectonic setting is the major cause for occurrence of metallogenic difference and specialization in Early Yanshanian in Southeast Hunan Province. In the upwelling region to the east of the Chaling-Chenzhou fault and the local upwelling places of the down-warping region to the west of the Chaling-Chenzhou fault, partial melting of plenty of schist in the middle crust followed by crystallization and fractionation of magmas in a large-scale magma chamber resulted in the formation of larger monzogranite and alkali granite plutons and enrichment of incompatible elements such as W and Sn, etc. to form W-Sn-polymetallic deposits. In the down-warping region to the west of the Chaling-Chenzhou fault, magma produced by partial melting of crystalline schist in the middle crust on a smaller scale mixed with mantle-derived magma rich in compatibe elements such as Pb, Zn, Cu and Au to form small bodies of granite porphyry, quartz porphyry, and granodiorite associated with responding ore deposits.更多还原