福建莆田地区晚中生代花岗岩年代学、地球化学及岩石成因

发布时间：2018-04-28 03:14

本文选题：花岗岩 + U-Pb定年　；参考：《中国地质大学(北京)》2016年硕士论文

【摘要】：华南东南沿海地区中生代花岗岩具有多期次,多成因的特点,该时期花岗岩岩石成因和构造背景一直存在较大争议,而且对于地处东南沿海的福建莆田地区花岗岩系统的研究较少。本文报道了莆田地区晚中生代花岗岩岩石学、锆石U-Pb年代学和锆石微量元素、锆石Hf同位素和全岩地球化学的研究结果,以期为深入探讨该地区的岩石成因、构造环境和地壳演化提供新资料。本文花岗岩样品主要采自于福建莆田地区的霞洋岩体、平海岩体和赤石岩体。岩石类型为钾长花岗岩、黑云母花岗岩、二长花岗岩、花岗斑岩和花岗闪长岩。LA-ICP-MS锆石U-Pb定年结果表明岩体侵位年龄为90Ma-122Ma,其中霞洋岩体为100~109Ma;平海岩体为122Ma;赤石岩体为90~119Ma;岩体为主体形成于早白垩世的花岗岩体。莆田地区白垩世花岗岩为不同分异程度的准铝-弱过铝、高钾钙碱性系列岩石。岩石具中等到较强程度的Eu负异常(δEu=0.11~0.85),轻稀土相对富集,重稀土相对亏损;富集Rb、K、Th、U、Pb,亏损Ba、Nb、Ta、Sr、P、Ti,成因类型属于不同分异程度的I型花岗岩。锆石Hf同位素总体为弱富集到弱亏损(εHf(t)=-4.2~+3.8),其中霞洋岩体为-4.2~-0.7;平海岩体-1.6~+0.6;赤石岩体为+0.3~+3.8。地壳模式年龄为中元古代和新元古代,较古老华夏古老地壳结晶基底明显年轻,暗示花岗岩源岩主要来自于古老下地壳的熔融并伴有幔源组分的加入。区域上看,与从内陆到沿海玄武质岩浆底侵作用越来越强的规律是吻合的。本文探讨了岩石成因类型。燕山晚期随着太平洋板块俯冲方式转变,俯冲后伴随着岩浆底侵作用使该地区地壳重熔,并混入了一定的幔源物质,构造环境的转变和岩浆分异演化等多种因素共同作用引发了莆田地区晚中生代花岗岩的形成。
[Abstract]:The Mesozoic granites in the southeast coastal area of South China have the characteristics of multi-stage and multi-genesis. During this period, the petrogenesis and tectonic setting of the granites have been controversial. Moreover, the study of granite system in Putian area, Fujian Province, which is located in southeast coast, is less. This paper reports the results of late Mesozoic granitic petrology, zircon U-Pb chronology, zircon trace elements, zircon HF isotopes and whole rock geochemistry in Putian area, with a view to further studying the petrogenesis of the area. The tectonic environment and crustal evolution provide new information. The granite samples in this paper are mainly collected from Xiayang, Pinghai and red rock bodies in Putian area, Fujian Province. The rock types are potassium feldspar granite, biotite granite, dicholomite granite, The U-Pb dating results of granitic porphyry and granodiorite. LA-ICP-MS zircon indicate that the emplacement age of the intrusive body is 90 Ma-122 Ma, of which the Xiayang rock body is 100 Ma, the Pinghai rock body is 122 Ma, the hematite body is 901 19 Ma, and the main body is the granitic body formed in the early Cretaceous. The Cretaceous granite in Putian area is a series of quasi-aluminum-weak peraluminous and high-potassium calc-alkaline rocks with different degrees. The rocks have negative EU anomalies of moderate to strong degree (未 EU ~ (2 +) 0.11C ~ (0.85), relatively enriched light rare earths, and relatively depleted heavy rare earths, and enriched RbPb, depleted Ba-Nb ~ (+) T _ (+) Sr ~ (+) P _ (+) Ti, and belong to I-type granites with different degrees of differentiation. The zircon HF isotopes are weakly enriched to weak depletion (蔚 Hfftnu -4.2 ~ 3.8g), in which the Xiayang rock body is -4.2 ~ -0.7; the Pinghai rock body is -1.6 ~ 0.6; and the red rock mass is 0.3 ~ 3.8. The crustal model ages are Mesoproterozoic and Neoproterozoic, which is obviously younger than that of the ancient Chinese crust, suggesting that the granitic source rocks are mainly derived from the melting of the ancient lower crust with the addition of mantle source components. Regionally, it is consistent with the increasing law of magmatic underplating from inland to coastal Black Tortoise. The petrogenetic types are discussed in this paper. In the late Yanshanian period, with the transformation of the subduction pattern of the Pacific plate, the crust of the area was remelted after the subduction with magmatic underthrust, and a certain amount of mantle material was mixed. The transformation of tectonic environment and magmatic differentiation and evolution caused the formation of late Mesozoic granites in Putian area.
【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】：2016
【分类号】：P597.3;P588.121

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