【作者】 李鹏春；

【导师】 陈广浩； 牛贺才；

【作者基本信息】 中国科学院研究生院（广州地球化学研究所） ， 构造地质学， 2006， 博士

【摘要】 湘东北地区位于扬子与华夏板块的交接部位江南造山带的中段,不仅具有独特的地质构造特点,而且以强烈的花岗岩岩浆作用及大规模金多金属成矿作用而著称。论文对该区显生宙加里东期、印支期和燕山期主要花岗岩体进行了详细系统的构造地质学、岩石学、元素地球化学和Sr-Nd-Pb同位素地球化学研究,并结合元古宙变质基底的研究,探讨了花岗岩源区、成因机制、深部动力学过程及构造岩浆演化等问题。 本区元古宙基底由中元古代冷家溪群和新元古代板溪群两套浅变质岩系组成。它们具有岩石地球化学相似性,其源区物质以长英质岩石为主,中等化学风化程度,原岩沉积于活动大陆边缘构造背景。 加里东期花岗岩主要由板杉铺岩体、宏夏桥岩体以及张坊岩体组成,岩性以黑云母花岗闪长岩为主,主要造岩矿物由钾长石、斜长石、黑云母、石英、角闪石等组成。具高SiO₂、Al₂O₃、K₂O、Sr和低Y、Yb含量,高Mg#和Sr/Y、La/Yb比值。REE表现为轻稀土显著富集的右倾型,富集大离子亲石元素（Cs、Rb、Ba、Th、U等）,亏损高场强元素（Nb、Ta、Ti等）,Eu极弱负异常（Eu/Eu^*=0.75～0.91）,类似于埃达克岩特征。可能是板块俯冲引起的玄武岩浆底侵,使下地壳发生部分熔融,并与其进行物质交换所形成的。 印支期花岗岩在本区出露很少,岩性主要为中细粒黑（二）云母花岗闪长岩,主要矿物由斜长石、钾长石、石英和黑云母组成。具高K低Na和Mg特征,属于高钾钙碱性系列。Sr含量高,Y和Yb含量低,因而有高Sr/Y和La/Yb比值。富集大离子亲石元素（Cs、Rb、Ba等）,亏损高场强元素（Nb、Ta等）,Eu弱负异常,REE发生了明显分馏。本文认为其可能是加厚的陆壳（>50 km）底部下地壳基性岩部分熔融的产物,热可能主要来自地幔（热）流的上升。 湘东北燕山期岩浆活动最为强烈,以燕山早期花岗岩分布最为广泛,主要由幕阜山、连云山、金井、望湘、蕉溪岭、龙王排等岩体组成。岩性以二云母二长花岗岩为主,主要矿物成分为石英、斜长石、钾长石、黑云母和白云母等。更多还原

【Abstract】 The northeastern Hunan Province, which connects the Yangtze and Cathaysian blocks, located in the central section of the Jiangnan Orogen, not only has idiographic tectonic characteristics, but also is famous for intensive granitic magmatism and extensive gold ploymetallic ore formation. In this paper, the auther has detailedly and systemically researched the characteristics such as tectonics, geology, petrochemistry and Sr-Nd-Pb isotopic geochemistry of Caledonian, Indosinian and Yanshanian granitoids, and contrasted it to Meso- and Neo- Proterozoic meta-sedimentary rocks, then discussed the scientific problems such as sources, mechanisms of genesis, deep dynamic processes and tectono-magmatism evolutions.The Proterozoic basement is composed of meta-sedimentary rocks of the Mesoproterozoic Lengjiaxi and Neoproterozoic Banxi Groups, which have similar petrochemical characteristics. We suggest that the felsic component rocks were dominant in the source area which has undergone middling chemical weathering. These sedimentary rocks were deposited in active continental margins.The Caledonian granitoids are mostly composed by Banshanpu, Hongxiaqiao and Zhangfang granitic bodies. And their main minerals are orthoclase, plagioclase, biotite, quartz and hornblende,etc. They have high Sr content and low Y and Yb contents, therefore possessing high Sr/Y and La/Yb ratios. They are enriched in large ion lithopile elements（LIFE） such as Cs, Ba and Th, and depleted in high field strength elements（HFSE） such as Nb, Ta and Ti. Those compositional characteristics, similar to those of adakite suggest that the granitoids, related to subduction, were most likely derived from lower crustal partial melting, which caused by basaltic magma underplating caused by subduction and interacted to some extent with basaltic magma material.The Indosinian granitoids in southeastern Hunan Province are geochemically similar to adakite, with characteristics of high Al₂O₃ and Sr contents and La/Y and Sr/Y ratios, low Y and Yb concentrations, very weak negative Eu anomalies, enrichment in large ion lithopile elements（LIFE） such as Cs, Ba and Th and depletion in high field strength elements（HFSE） such as Nb and Ta. We believe that they are likely resulted from partial melting of thickened lower crust, hot mantle liquids probably provide the heat energy.There are intensive magmatism in Yanshanian epoch in northeastern Hunan Province. Based on geochemical characteristics, the Yanshanian granitoids can be divided into two types: a high-Sr and low-Y （adakite-like） and a low-Sr and low-Y.The former has high SiO₂, Al₂O₃, Na₂O, Sr concentrations, but low K₂O,Y and Yb concentrations, therefore possessing high La/Yb and Sr/Y ratios. They enriched in LILE and depleted in HFSE, with very weak negative Eu anomalies. These geochemical features are similar to those of adakites. But the Sr-Nd compositions are different from those of adakite generated by slab-melting, and its Pb compositions are similar to those of adakites from assimilation and fractional crystallization （AFC） processes involving a basaltic magma. The high-Sr and low- Y type rock may be derived from partial melting of thickened lower crust, followed contamination of crustal intermediate-rock.The latter, on the one hand, is different from the former by its low Sr content and obviously negative Eu anomaly;on the other hand, is similar to adakite by its low Y and HREE contents. Its Sr-Nd-Pb and other major and trace elements compositions are similar to those of high-Sr and low-Sr type. Therefore, it is suggested that the low-Sr and low-Y type, is also generated by partial melting of relatively thick lower crust, which closely related to the basaltic magma underplating.The tectono-magmatism in northeastern Hunan Province might be a consequence of interaction between the Yangtze and Cathaysian plates and deep lithospheric processes. Phanerozoic tectono-magmatism evolution experienced subduction of the south China sea, continental-continental collision which thickened crust, extension-cracking and introcontinental rifted orogen, and finally, resulted in "basin-range" type tectonic landforms, large-scale granitic generation and extensive gold ploymetallic ore formation.更多还原