东昆仑希望沟中二叠世辉长岩Sr-Nd-Lu-Hf同位素特征及其地质意义

东昆仑东段希望沟-哈陇休玛一带有多处镁铁-超镁铁质岩的出露,针对希望沟地区中二叠世辉长岩3块样品进行的全岩Sr-Nd同位素及锆石Lu-Hf同位素测试,结果表明:希望沟辉长岩87Sr/86Sr为0.707 445~0.707 676,(87Sr/86Sr)i值为0.707 045~0.707 297,高于现代深海拉斑玄武岩(0.702 0~0.703 5),143 Nd/144 Nd的初始计算值为0.512 476~0.512 543,εNd(t)值为-2.65^-1.34,Nd(t)值受蚀变影响较小,基本反映了其源区洋岛玄武岩的同位素特征;176 Lu/177 Hf在0.000 592~0.001 860间,εHf(t)在2.27~5.46间,一阶段Hf模式年龄为691Ma^816Ma,平均为758Ma,表明岩浆源区主要来源于亏损地幔并有少量壳源物质(如洋壳沉积物)的加入。结合区域构造演化特征,认为希望沟辉长岩源区主要为洋岛玄武岩,是东昆仑地区阿尼玛卿古特提斯洋向北俯冲的结果。

Sr-Nd-Lu-Hf ISOTOPIC CHARACTERISTICS AND GEOLOGICAL SIGNIFICANCE OF THE MIDDLE PERMIAN GABBRO IN XIWANGGOU AREA,EAST KUNLUN

Sr-Nd and zircon Lu-Hf isotopes of the middle Permian gabbro in Xiwanggou- Halongxiuma area,east section of East Kunlun,are analyzed.The results show that the 87Sr/86Sr is 0.707~0.707 676,(87Sr/86Sr)ivalue is 0.707 045~0.707 297,the initial 143 Nd/144 Nd calculated value is 0.512 476~0.512 543,and the value ofεNd(t)is-2.65^-1.34.Nd(t)value is hardly affected by the alteration and basically reflects the isotopic characteristics of the oceanic island basalt in the source area.176Lu/177 Hf is in the range of 0.000 592~0.001 860,and the ratio ofεHf(t)is from 2.27to 5.46.The first stage Hf mode age varied from 691Ma^816Ma,with an average of 758Ma,indicating that the magma source is mainly derived from the depleted mantle with the addition of crustal source material(such as oceanic crust sediments).On the basis of the regional tectonic evolution characteristics,it is considered that the source area of Xiwanggou gabbro is mainly the oceanic island basalt,resulted from the northward subduction of Animaqing Paleotethys Oceans in the east Kunlunshan area.