东昆仑得尔龙地区华力西期花岗岩地质地球化学特征及构造环境分析

Analysis on Geological and Geochemical Characteristics and Tectonic Environment of the Variscan Deerlong Granite in East of Kunlun Mountains

摘要:

东昆仑得尔龙地区花岗岩体侵位于二叠纪—三叠纪早期，岩石类型为黑云母花岗闪长岩、黑云母二长花岗岩、二云母二长花岗岩。早期次的黑云母花岗闪长岩中含有暗色的镁铁质矿物包体。SiO2含量为65.04%~73.47%，全碱含量为5.29%~8.52%，K2O/Na2O平均值为0.70，Al2O3平均为14.79%；亏损高场强元素Ta，Nb；∑REE平均为142.9×106，轻稀土元素相对富集，（La/Yb）N平均为17.15，δEu平均为0.71，表现为弱亏损。研究表明得尔龙地区花岗岩属次铝过铝（高钾）钙碱性S型花岗岩，形成于后造山环境；岩浆源区的物质是多源的，主要为地壳物质的重熔，其次为幔源岩浆的底侵。

Abstract:

The emplacement of Deerlong granite in east of Kunlun mountains intruded in Permian period to the early Triassic period. The types of granite include biotite granodiorite, biotite monzonitic granite and two mica monzonitic granite. There are mafic xenoliths in biotite granodiorite of the early period time. As showed by geochemical analyses: the content of SiO2 is 65.04%~73.47%, the content of total alkali is 5.29%~8.52%, average value of K2O/Na2O is 0.70, and average content of Al2O3 is14.79%. The Deerlong granite has a lower content of HFSE such as Nb and Ta, and a normal total REE concentration(142.9g/g). Chondritenormalized REE patterns show a remarkable enrichment in LREE (La/Yb)N=17.15. Eu values (0.71) indicates that the primitive magma was basic and enriched in plagioclase most likely. In general, geochemical and isotopic analyses indicate that the Deerlong granite is metaluminous or peraluminous, calcalkaline (some are high K) Stype granite. Its primitive magma could be mainly sourced from melting of the crust, and is most likely to have been contaminated by the mantle in the early stage of magmatism evolution.