西藏班公湖—怒江结合带南缘革吉地区晚侏罗世流纹斑岩的成因——锆石U-Pb定年、地球化学和Hf同位素约束

发布时间：2018-06-15 06:08

本文选题：流纹斑岩 + 锆石U-Pb定年　；参考：《地球学报》2017年05期

【摘要】：西藏阿里地区革吉县乃不扎康巴流纹斑岩是班公湖—怒江成矿带南缘新发现的一套次火山岩,本文在地质调查和资料收集的基础上,开展了流纹斑岩锆石U-Pb定年和岩石地球化学和锆石Hf同位素特征研究。流纹斑岩具有高硅(SiO_2=73.93%~74.71%)、高Na_2O+K_2O含量(6.73%~7.30%),低TFe和Mg O含量等特征,属于弱过铝质高钾钙碱性系列且具有I型花岗岩地球化学特征;轻重稀土元素分馏明显,富集轻稀土元素,具有明显的负Eu异常,其LREE/HREE值为9.71~12.38,(La/Yb)N值为10.64~14.42,δEu=0.65~0.73;流纹斑岩相对亏损Nb、Ta、Ti等高场强元素,富集Rb、Th、U等大离子亲石元素,与典型活动陆源火山岩的微量元素特征类似;LA-ICP-MS锆石U-Pb定年结果表明乃不扎康巴流纹斑岩的形成时间为(151.6±1.2)Ma(MSWD=0.9),锆石εHf(t)值整体为负值( 9.4~2.6,平均为 3.1)且变化范围较大(可达11个ε单位)呈现出混合源区特征。Hf同位素数据和全岩锆石饱和温度(750~791℃)表明幔源物质在流纹斑岩形成过程中起到了重要作用。结合区域构造演化特征,认为该套流纹斑岩主要产于Slainajap洋的南向俯冲的背景之下,由幔源岩浆提供热量诱发古老拉萨下地壳发生部分熔融并与幔源岩浆发生混合形成初始母岩浆,之后经历一定程度的分离结晶作用形成。
[Abstract]:The Jiagi County, Jiagi County, Tibet, is a newly discovered subvolcanic rock in the southern margin of the Bangong Lake-Nujiang metallogenic belt. Based on the geological investigation and data collection, Zircon U-Pb dating, geochemistry and HF isotopic characteristics of zircon have been studied in this paper. The fluid-striped porphyry is characterized by high SiOShi (73.931), high Na2O K2O content (6.73K), low TFE and MgO contents, and belongs to the weak peraluminous high-potassium calc-alkaline series and has the geochemical characteristics of I-type granite. The fractionation of heavy and heavy rare earth elements is obvious, and it is rich in light rare earth elements, and is characterized by low TFE and MgO contents, and is characterized by the geochemical characteristics of I-type granites, and the fractionation of heavy and heavy rare earth elements is obvious, and it is rich in light rare earth elements. There are obvious negative EU anomalies with LREE / HREE value of 9.71 ~ 12.38% La- / YbN = 10.64 ~ 14.42, 未 EU ~ (0.65) ~ (0.73) = 0.73. The rhyolitic porphyry is relatively depleted of high field strength elements, such as NB ~ (+) ~ (-) ~ (1), and enriched in RbThU and other large ion lithophile elements, such as RbThU and other large ion lithophile elements. The trace element characteristics similar to those of typical active continental volcanic rocks are similar to those of LA-ICP-MS zircon U-Pb dating. The results show that the formation time of Neibukangba rhyolitic porphyry is 151.6 卤1.2 Ma-MSWD0. 9, and the zircon 蔚 Hftt is negative as a whole (9. 42.6, average is 3. 1), and the range of variation is large. The HF isotopic data and the zircon saturation temperature of the whole rock indicate that the mantle source material plays an important role in the formation of the rhyolitic porphyry. Combined with the characteristics of regional tectonic evolution, it is considered that this set of fluvial porphyry mainly occurred in the background of southward subduction of the Slainajap Ocean. Heat from mantle magma induces partial melting of the lower crust of ancient Lhasa and mixes with mantle magma to form initial mother magma and then to undergo a certain degree of separation and crystallization.
【作者单位】：中国地质大学(北京)地球科学与资源学院;中国地质科学院矿产资源研究所国土资源部成矿作用与资源评价重点实验室;成都理工大学地球科学学院;
【基金】：中国地质调查局二级项目(编号:DD20160026) 国家自然科学基金项目(编号:41403040)联合资助~~
【分类号】：P588.1;P597

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