资溪—光泽杂岩体年代学，地球化学及成因：对华南内陆印支期岩浆活动形成构造背景的制约

发布时间：2018-05-06 21:16

本文选题：花岗岩 + 辉长岩　；参考：《中国科学院研究生院(广州地球化学研究所)》2015年硕士论文

【摘要】：华南三叠纪花岗岩分布广泛,尤其是武夷山到湘中雪峰山的华南内陆地区。本文选择江西与福建交界的资溪-光泽杂岩体,通过系统的LA-ICP-MS锆石U-Pb定年分析,获得资溪花岗岩体的年龄为231.7-238.0Ma;而光泽中-基性岩体的SHRIMP锆石U-Pb年龄为220.1-231.7 Ma。资溪花岗岩地球化学特征显示出:(1)具有高Si O2,高K2O,弱过铝质(ACNK=1.00-1.11)的特征,属于高钾钙碱性系列;(2)微量元素和稀土元素上,亏损Ba,Sr,Nb,Ta,Ce,和Ti,并出现Eu(δEu=0.35-0.47)的负异常;Th,U,Nd,La,Pb的富集,轻重稀土分异明显(La/Yb)N=28.8,(Sm/Yb)N=4.4;(3)初始Sr比值高(Isr=0.7068-0.711 3),εNd(t)低(εNd(t)= 11.94~ 7.66)反映它们来自于地壳源区,并有少量基性岩/年轻物质的加入。光泽辉长岩地球化学特征显示出:(1)Si O2=51~59%,具有比资溪花岗岩低的K2O,Na2O和Al2O3含量,较高的Mg O,Mn O,Ti O2,Fe2O3和P2O5含量,属于高钾钙碱性-钾玄岩系列;(2)微量元素和稀土元素上表现出与资溪花岗岩相似的特征,但是比资溪花岗岩具有更高的大离子亲石元素和高场强元素(Ba,Ti,Sr)和更弱的Eu负异常(δEu=0.50~0.69);(3)具有比资溪花岗岩高的初始Sr比值(ISr=0.71096~0.71169),低的εNd(t)(εNd(t)=-10.08~-9.16),表明光泽辉长岩来自于富集岩石圈地幔源区。光泽辉长岩微量元素特征上显示出经历过俯冲流体交代作用的岛弧特征(如亏损Nb-Ta,高Th,富集LILEs),很可能与古太平洋板块向华南板块水平俯冲有关。此外,结合收集的华南内陆地区已有的印支期岩浆岩的年龄资料,观察其年龄在SE-NW和SW-NE向的时空变化情况,发现华南内陆印支期岩浆岩年龄分布具有从东南沿海到北西内陆地区呈逐渐变年轻的趋势,而在大致沿武夷山走向的南西到北东方向上呈宽阔的近水平的线性分布趋势。我们的研究认为,大约260Ma的印支期沿海岩浆弧消失约20Ma之后,~240Ma在距离海沟大约400~500km的整个武夷山地区几乎同时出现,是水平俯冲造成的华南内陆新生岩浆弧形成,类似于新生代北美拉拉米造山和墨西哥中部的水平俯冲情况。由于加厚的中下地壳温度较高,少量水平俯冲前端脱水形成的地幔岩浆侵入中、下地壳,带来的热很容易造成中、下地壳物质发生部分熔融,形成北武夷,乃至整个武夷山地区大量的印支期花岗质岩浆岩。
[Abstract]:The Triassic granites in South China are widely distributed, especially in the inland areas of South China from Wuyi Mountain to Xuefeng Mountain in Central Hunan. In this paper, the Zixi lustre complex at the junction of Jiangxi and Fujian is selected. By systematic LA-ICP-MS zircon U-Pb dating, the age of Zixi granitic body is 231.7-238.0 Ma, while the SHRIMP zircon U-Pb age of lustrous meso-basic rock body is 220.1-231.7 Ma. The geochemical characteristics of Zixi granites show that they have the characteristics of high Sio _ 2, high K _ 2O and weak peraluminous ACNK _ (1.00-1.11). They belong to the high-potassium calc-alkaline series (~ (2) trace elements and rare earth elements. The difference between light and heavy rare earth elements is obvious (La / Yb ~ (28. 8) / Sm- / Yb ~ (4 / 4) N ~ (3) the initial Sr ratio is high (Isr = 0.7068-0.711 ~ (3), 蔚 Ndt _ (t) is low (蔚 Ndndt ~ (?) = ~ (11.94) ~ (7.66), which indicates that they are from the crustal source region and have a small amount of basic rock / young material added. The geochemical characteristics of lustrous gabbro show that the content of K _ 2O-Na _ 2O and Al2O3 is lower than that of Zixi granite, and the content of Fe _ 2O _ 3 and P2O5 is higher than that of Zixi granite. The trace elements and rare earth elements are similar to those of Zixi granite. However, compared with Zixi granites, they have higher large ion lithophile elements and high field strength elements, such as Baan Tiao Sr) and weaker EU negative anomalies (未 EU ~ (0.50) ~ (0.69) with a higher initial Sr ratio than the Zixi granites, and a lower 蔚 -Ndtt ~ (-10.08) ~ (-9.16), which indicates that the lustrous gabbro originated from the enriched lithospheric mantle source area. The trace element characteristics of the lustrous gabbro show that the island arc features experienced subduction fluid metasomatism (such as depleted Nb-Ta, high Thh, enriched Lile Esn), which may be related to the paleo-Pacific plate subduction to the South China plate level. In addition, based on the collected age data of Indosinian magmatic rocks in inland South China, the temporal and spatial variations of their ages in the direction of SE-NW and SW-NE are observed. It is found that the age distribution of the Indosinian magmatic rocks in South China shows a trend of gradually becoming younger from the southeast coast to the north west inland area, and a broad near level linear distribution trend in the direction of the south west to the north east roughly along the Wuyi Mountain strike. Our study suggests that about 240 Ma after the disappearance of the Indosinian coastal magmatic arc about 260Ma occurred almost simultaneously in the entire Wuyishan area, about 400~500km from the trench, resulting from horizontal subduction of the inland Cenozoic magma in southern China. Similar to the Cenozoic Lalami orogenic and central Mexico horizontal subduction. Due to the thickening of the middle and lower crust temperature, a small amount of horizontal subduction front end dehydration of the mantle magma intrusion, the lower crust, the heat is easy to cause partial melting of the lower crust material, resulting in the north Wuyi. The Indosinian granitic magma in Wuyishan area.
【学位授予单位】：中国科学院研究生院(广州地球化学研究所)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P597.3;P542

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