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作为TTG质岩石的一个重要组成部分,一般认为奥长花岗质岩石是基性岩部分熔融的产物,但在很多TTG片麻岩地体中,如在冀东麻粒岩相区的奥长花岗岩呈较小的岩脉、侵入体,或者呈英云闪长质片麻岩中的浅色体产出,显示近原地熔融成因.本文以冀东地区英云闪长质片麻岩样品J13为基础,并结合锆石定年研究,探讨该区奥长花岗质岩石的成因,模拟在不同压力(0.7、1.0和2.0GPa)下发生的变质熔融反应以及熔体的常量、微量元素成分特征.结果表明,英云闪长质片麻岩在石榴二辉麻粒岩相条件下,如0.9~1.1GPa/800~850℃,发生角闪石脱水熔融,熔融程度为5~10wt.%,残余物中石榴石含量为5~10wt.%时,产生的熔体的成分与冀东奥长花岗质岩石有很大的相似性,如La/Yb值高,Yb含量低等,但模拟熔体的常量元素成分相对高K2O、低CaO、Mg~#偏低,表明冀东奥长花岗岩脉体和浅色体可能包含了部分残余矿物并受到结晶分异的影响.锆石定年结果表明,研究区英云闪长质片麻岩原岩结晶年龄为(2518±12)Ma,变质年龄为(2505±19)Ma,奥长花岗质岩脉的结晶年龄为(2506±6)Ma,二者之间存在密切成因联系.
As an important part of TTG rocks, it is generally accepted that the dolomitic granites are the product of partial melting of basic rocks. However, in many TTG gneisses, such as the magmatic granulite in the eastern Hebei granulite facies Showing small dikes, intrusions, or light-colored bodies in the Ying-dioritic gneisses, indicating near-in-situ melting. In this paper, the Jiyun diorite samples of Jiyun diorite J13 Based on the zircon dating, the origin of the granodiorites in the area is discussed to simulate the metamorphic melting reactions at different pressures (0.7, 1.0 and 2.0 GPa), as well as the melt constants and trace element compositions The results show that the amphiboleitic gneisses are dehydrated and melted by amphibole in the garnet two galenic facies, such as 0.9 ~ 1.1GPa / 800 ~ 850 ℃, the melting degree is 5 ~ 10wt.%, When the content of garnet in the residue is 5 ~ 10wt.%, The composition of the melt produced has great similarities with the Jidiao granite rocks, such as high La / Yb value and low Yb content, but the simulation The relatively high K2O, low CaO and Mg ~ # components of the melt show that the veins and light bodies of Jidongian granodiorite may contain some residual The results show that the age of the original rocks of the Yingyan dioritic gneisses in the study area is (2518 ± 12) Ma, metamorphic age is (2505 ± 19) Ma, The crystallization age of the Gang dikes is (2506 ± 6) Ma, and there is a close genetic relationship between them.