南部拉萨地块晚白垩世花岗岩类年代学与地球化学

发布时间：2018-01-13 05:20

  本文关键词：南部拉萨地块晚白垩世花岗岩类年代学与地球化学　出处：《中国地质大学(北京)》2017年博士论文　论文类型：学位论文

  更多相关文章： 青藏高原 拉萨地块 晚白垩世 埃达克岩 岩石成因

【摘要】：南部拉萨地块中生代岩浆岩大面积分布,对其成因与源区信息及构造环境、地球动力学背景的探讨还需进一步进行。本文报道了拉萨地块南缘克曲-松卡一带侵入于叶巴组火山岩中的中-酸性侵入岩的锆石U-Pb年代学、锆石Hf同位素及全岩地球化学,并结合南部拉萨地块已有成果,探讨了中生代至新生代以来,南部拉萨地块花岗岩类岩石成因和区域岩浆-构造演化。锆石U-Pb年龄结果显示,本文中酸性侵入岩的侵入年代为晚白垩世(90.3~98.7Ma)。锆石Hf同位素方面,εHf(t)为较大正值(+9.4~+15.7),变化范围不大,显示亏损源区的地球化学特征。TDM=135~380Ma,TDMC=150~557Ma,地幔模式年龄和地壳模式年龄较年轻。全岩Sr-Nd同位素给出类似结果,εNd(t)=+3.6~+4.3,Nd同位素地幔模式年龄属新元古代-早古生代阶段(476~728Ma),为新生地壳的源区特征。克曲-松卡地区的花岗岩类总体富碱、富钾,属于高钾钙碱性-钾玄质岩石系列。A/CNK=0.66~1.03,属于偏铝质-弱过铝质岩石。岩石镁含量偏低,Mg O=0.25~3.82%(Mg#=24.33~40.68)。微量元素方面,富集轻稀土元素、亏损重稀土元素,轻重稀土分异不强([La/Yb]N=8.0~25.6)。δEu=0.57~1.10,多数样品显示轻微Eu负异常,少数为Eu正异常。岩石富集大离子亲石元素(LILE)而亏损高场强元素(HFSE)。本文晚白垩世花岗岩类岩石主要来源于新特提斯大洋板片俯冲消减过程中,新生镁铁质地壳的部分熔融,中部拉萨地块基底物质混入极少。与此形成对比的是,南部拉萨东段与西段的花岗岩类,则有更为富集的同位素特征和更为古老的地幔、地壳模式年龄,显示明显的古老地壳物质混入特征。晚白垩世侵入岩具有埃达克质岩石亲缘性,新特提斯洋大洋地壳部分熔融来源的埃达克岩以早白垩时期的马门安山岩和南部拉萨地块东段晚白垩世紫苏花岗岩为代表;而本文拉萨地块南缘晚白垩世埃达克质岩石及始新世以来的,在南部拉萨地块广泛出露的埃达克岩及含矿的埃达克质斑岩,则来源于在新特提斯洋俯冲背景下,增厚下地壳的部分熔融。
[Abstract]:The Mesozoic magmatic rocks in the southern Lhasa block are widely distributed, and the origin, source information and tectonic environment are discussed. This paper reports the zircon U-Pb geochronology of the intermediate-acid intrusive rocks in the volcanic rocks of the Yeba formation in the southern margin of the Lhasa massif. Zircon HF isotopes and whole-rock geochemistry, combined with the results of the Lhasa block in the south, have been discussed from Mesozoic to Cenozoic. Genesis and regional magmatic tectonic evolution of granitic rocks in the Lhasa block, southern China. Zircon U-Pb age shows. The intrusive age of the intermediate-acid intrusive rocks in this paper is the late Cretaceous (90.3n) 98.7 Ma.The zircon HF isotopes, 蔚 Hfct), are relatively positive (9.4 ~ 15.7). The range of variation is not large, indicating that the geochemical characteristics of the source area of Changzhangyuan... TDM 135T ~ (38) Ma ~ (38) TDMCN ~ (150) ~ (557) Ma. The mantle model age and the crustal model age are younger. The Sr-Nd isotopes of the whole rock show similar results, 蔚 Ndt0 = 3.6 ~ 4.3. The ND isotopic mantle model age belongs to Neoproterozoic to early Paleozoic stage, which is the source of the new crust. The granitoids in Kechu-Songka area are rich in alkali and potassium. It belongs to the high-potassium calc-alkaline-potash rock series. A / CNK = 0.661.03, belongs to the metaluminum-weak peraluminous rock, and its magnesium content is on the low side. MgO 0.25 ~ 3.82% mg #Li 24.33 ~ 40.68%. In respect of trace elements, they are enriched in light rare earth elements, depleted in heavy rare earth elements, and have little difference between light and heavy rare earth elements (P < 0.05). [La/Yb > 8. 0 ~ 25. 6. 未 EU 0. 57 ~ 1. 10, and most of the samples show slight negative EU anomalies. A few are EU positive anomalies. The rocks are enriched with large ion lithophile elements (LILE) and are depleted of high field strength elements (HFSEs). The late Cretaceous granitic rocks in this paper are mainly derived from the subduction process of the new Tethys oceanic plate. In contrast, the granitoids of the eastern and western Lhasa sections in the south of Lhasa, by contrast, are partially melted in the newly formed magnesia-ferric crust, and the basement material of the Lhasa block in the central part of the region is very little. There are more enriched isotopic characteristics and older mantle, crustal model ages, indicating obvious characteristics of the mixing of ancient crustal materials. The late Cretaceous intrusive rocks are related to adakian rocks. The early Cretaceous Maman andesite and the late Cretaceous Perilla granites in the eastern Lhasa block are the representative of the adakite which originated from the partial melting of the oceanic crust of the NeoTethys Ocean. However, the late Cretaceous adakitic rocks in the southern margin of the Lhasa massif and the adakite widely exposed in the southern Lhasa block and the mineral-bearing adakitic porphyry originated from the new Tethys subduction background. Thickening the partial melting of the lower crust.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P597.3;P588.121
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本文编号：1417644