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羌塘中部各拉丹冬二长花岗岩体同位素地质年代学和地球化学研究

Isotope Geochronology and Geochemical Characteristics of Geladandong Monzonitic Granite in Centeral Qiangtang

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【作者】 白云山李莉牛志军姚华舟段其发

【Author】 BAI Yunshan LI Li NIU Zhijun YAO Huazhou DUAN Qifa Yichang Institute of Geology and Mineral Resources, Yichang,Hubei, 443003

【机构】 宜昌地质矿产研究所宜昌地质矿产研究所 湖北宜昌443003湖北宜昌

【摘要】 羌塘中部各拉丹冬岩体主要由二长花岗岩组成,其单颗粒锆石U-Pb年龄为40±3Ma,Rb-Sr等时线年龄为47±0·4Ma,斜长石、角闪石、黑云母K-Ar年龄分别为37·1Ma、48Ma和45·8Ma,形成于始新世。岩石富碱高,高钾(K2O>Na2O),属高钾钙碱性系列。微量元素以富集LREE、LILE(Th、U等),相对亏损HFSE为特征,(87Sr/86Sr)i为0·70701~0·70724,εNd(t)为-6·0~-4·1,δ18O值为8·18‰~9·01‰,构造背景为火山弧花岗岩。55Ma以来,印度板块与欧亚板块碰撞,大范围抬升,青藏高原在经历近南北向挤压缩短的过程中,可能在羌塘地体上产生了平行于主压应力方向的张性构造,导致了各拉丹冬花岗岩体侵位。应为青藏高原隆升在北羌塘陆块所表现的构造热事件之一。

【Abstract】 The Geladandong intrusive body mainly consists of monzonitic granite, with the single zircon UPb age being 40±3 Ma, the RbSr isochron age of the rock being 47±0.4 Ma, and the KAr ages of plagioclase, hornblende and biotite being 37.1 Ma, 45.8 Ma, 48 Ma, respectively. The rock body was formed in Eocene. The rocks have high content of alkali and potash (K2O>Na2O), belonging to highpotash calcalkalic series. The trace elements are characterized by enrichment of LREE, LILE (Th, U) and depletion of HFSE. The 87 Sr/ 86 Sr ratios, the ε Nd (t)ratios and the δ 18 O values range from 0.70701 to 0.70724, -6.0 to -4.1, and 8.18‰ to 9.01‰, respectively. These data prove that the tectonic setting is volcanic island arc granite. The collision of the Indian plate with the Eurasian plate led to the largescale uplift from 55 Ma. During the nearly SNtrending compression and shortening, QinghaiTibet plateau probably produced a tensile structure parallel to the main stress in Qiangtang terrane, leading to the emplacement of Geladandong granite. This is one of the hot tectonic events produced in northern Qiangtang terrane by the uplift of QinghaiTibet plateau.

【基金】 国土资源部国土资源大调查项目(编号:200013000135)资助。
  • 【文献出处】 地球学报 ,Acta Geoscientica Sinica , 编辑部邮箱 ,2006年03期
  • 【分类号】P597
  • 【被引频次】9
  • 【下载频次】186
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