冈底斯岩浆弧中段古近纪“双峰式”火山岩的地质特征及其构造意义

The geology and tectonic implications for the Paleogene bimodal volcanic rocks in the middle part of the Gangdise magmatic arc, southern Xizang

关键词:  “双峰式”火山岩  地球化学  构造环境  古近纪  冈底斯岩浆弧

Key words:  “bimodal” volcanic rocks  geochemistry  tectonic setting  Paleogene  Gangdise magmatic arc

摘要:

冈底斯岩浆弧中段的西藏措勤县中卢古地区古近纪火山岩十分发育,岩石类型以基性端元和酸性端元火山岩为主,中性火山岩十分少见。基性火山岩相对富集不容元素及REE,其源区所处构造部位较深,为受地壳物质混杂的过渡型幔源区;酸性火山岩则为地壳物质重熔的产物,形成的构造环境为岛弧夭折期的初始裂谷。

Abstract:

The Paleogene volcanic rocks crop out over a wide area of the Zhonglugu region, Coqen, southern Xizang. The rock types are dominated by the basic and acidic volcanic rocks with a small amunt of median volcanic rocks, and may be assigned to the bimodal volcanic rocks. The basic volcanic rocks are relatively enriched in the incompatible elements and REE. The principal sources of detritus lay to the deep-seated crustal matter-contaminated transitional mantle levels. The acidic volcanic rocks resulted from the remelting of the crustal material in the tectonic setting of incipient rifts during the collapse of island arcs. The recognition of the bimodal volcanic rocks is of important geological implications for the improvement of the knowledge on the formation and development of the Gangdise magmatic arc, southern Xizang.