胶北地体地壳增生与再循环及巨量金来源

发布时间：2018-07-12 15:50

本文选题：胶北地体 + 锆石U-Pb年代学　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：中生代以来,华北克拉通东部发生了大规模的岩石圈减薄以及陆内变形与岩浆活动,并伴随金属成矿作用,尤其在胶北发生了金的大规模聚集,而区域金成矿作用与地壳增生及再循环密切相关。为此,论文通过对晚侏罗世玲珑黑云母花岗岩和早白垩世郭家岭花岗闪长岩中继承锆石U-Pb年代学和Hf同位素及地球化学组成分析,厘定区域岩浆-热事件和地壳演化历史,探讨古老物质再循环过程和金的可能来源,获得以下主要认识:(1)郭家岭花岗闪长岩相对玲珑黑云母花岗岩缺失新元古代-早侏罗世继承锆石,这段时间的继承锆石主要来自扬子板块。造成这种差异可能为晚侏罗世俯冲的扬子板块构造板底垫托在胶北地体下造成,而后受热扰动发生侵蚀作用发生部分熔融,花岗质熔体被抽取密度增大,而后由于重力不稳定发生拆沉作用,块体沉入岩石圈地幔,早白垩世拆沉的扬子板块未为郭家岭花岗闪长岩提供物质。(2)胶北地体前寒武纪经历了3.2Ga、~2.9Ga、2.8-2.7Ga、2.5Ga、2.2-1.8Ga岩浆活动,其中活动最为强烈的时间为~2.5Ga和2.2Ga。~3.2Ga为古太古代陆核形成阶段,~2.9Ga、2.8-2.7Ga主要为地壳增生阶段,~2.5Ga主要为地壳重熔改造,存在少量新生地壳。2.2Ga-1.8Ga为地壳的重熔改造。从古元古代到中生代则主要表现为老地壳的重熔再造,古老基底发生多次再循环。另外胶北地体经历了三期主要的变质作用,时间为~2.5Ga、1.9~1.8Ga和250~200Ma。~2.5Ga的变质事件和同时期岩浆活动可能与地幔柱导致的底侵作用有关。1.9~1.8Ga的变质事件与造山运动有关,另从沉积建造、岩浆活动及变质作用的特征,发现胶北与辽吉地区具有相似性,表明胶北地体应是辽吉地块向南延伸的一部分,250~200Ma与晚三叠世华北板块和扬子板块发生的碰撞事件及之后超高压变质岩的折返有关。(3)多期俯冲-碰撞事件为胶北地区形成陆下富集岩石圈地幔提供了条件,而富集岩石圈地幔低程度部分熔融可产生富金熔体,而由于俯冲的太平洋板块脱水提供氧化环境,有利于金从富金熔体中释放;且胶北老基底发生重熔改造后,其中的金发生活化可进一步提供成矿物质。因此才造成在如此小范围内形成如此众多的金矿床。
[Abstract]:Since the Mesozoic, large-scale lithospheric thinning, intracontinental deformation and magmatic activity have occurred in the eastern part of the North China Craton, accompanied by metallization, especially in Jiaobei. The regional gold mineralization is closely related to crustal accretion and recirculation. Therefore, based on the analysis of zircon U-Pb chronology and HF isotopic and geochemical composition of inherited zircon from Linglong biotite granite and early Cretaceous Guojialing granodiorite of late Jurassic, the paper determines the history of regional magmatic and thermal events and crustal evolution. The recirculation process of ancient materials and the possible sources of gold are discussed. The main results are as follows: (1) the granodiorite of Guojialing is relatively Linglong biotite granite without inherited zircon from Neoproterozoic to early Jurassic. This period of inherited zircon mainly comes from the Yangtze plate. The difference may be caused by the subduction of the Yangtze plate in the late Jurassic under the Jiaobei terrane, and then the erosion occurs by thermal disturbance, and the densities of granitic melts are increased. Then, due to gravity instability, the block sank into the lithospheric mantle, and the Yangtze plate did not provide material for the Guojialing granodiorite. (2) the Precambrian magmatic activity of 3.2GaGA-2.8-2.7GA-2.5Ga2.2-1.8Ga was experienced in the Jiaobei area, and the Yangtze plate did not provide material for the Guojialing granodiorite. The most active time is 2.5Ga and 2.2Ga.3.2Ga is the PaleoArchean continental nucleation stage, 2.9Ga 2.8-2.7Ga is the crustal accretion stage and 2.5Ga is mainly crustal remelting transformation, and there is a small amount of newly formed crust. 2.2Ga-1.8Ga is crustal remelting transformation. From Paleoproterozoic to Mesozoic, the remelting of the old crust and recirculation of the ancient basement occurred. In addition, the Jiaobei terrane experienced three major metamorphic events, the metamorphic events of 2.5Ga1.9- 1.8Ga and 250Ga-200Ma.2.5Ga and magmatic activities of the same period may be related to the mantle plume induced underplating. The metamorphic events of 1.9and 1.8Ga are related to the orogenic movement, and from the sedimentary formations, the metamorphic events may be related to the mantle plume, and the metamorphic events of 1.9and 1.8Ga are related to the orogenic movement. The characteristics of magmatic activity and metamorphism show that there are similarities between Jiaobei and Liaoji areas. It is suggested that the Jiaobei terrane is a part of the Liaoji block extending southward with the collision events of the North China plate and the Yangtze plate in the late Triassic and the exhumation of the ultrahigh pressure metamorphic rocks. (3) the multi-stage subduction-collision event is the Jiaobei area. The formation of the subcontinental enriched lithospheric mantle provides the conditions for the formation of the subcontinental lithospheric mantle. The low-degree partial melting of the enriched lithospheric mantle can produce gold-rich melts, and since the subducted Pacific plate dehydration provides the oxidizing environment, it is advantageous for the gold to be released from the gold-rich melts, and after the remelting of the old basement in Jiaobei, One of the blond hair life can provide further mineral formation. As a result, so many gold deposits were formed in such a small range.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P618.51;P548

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