摘要
通常认为青藏高原的钾质-超钾质火山岩的形成多与地幔有着紧密的联系,然而最近对青藏高原的一些钾质-超钾质火山岩的研究显示一些钾质火山岩也可以起源于下地壳。青藏高原西南部查孜地区中新世火山岩是形成于13～11Ma左右的一套钾质-超钾质岩石,根据岩石化学组成将其分为中基性火山岩组、中性火山岩组和流纹质火山岩。其中中基性火山岩组可能源于一个富含金云母的富集地幔源区;中性火山岩组可能是富钾的镁铁质下地壳部分熔融的产物;流纹质火山岩可能是拉萨地块在中新世时期的伸展构造运动而导致中上地壳因减压而发生部分熔融的产物。结合查孜地区及其邻近火山岩的年龄、化学组成以及岩浆组合,初步认为查孜地区火山岩可能与高原在中新世发生伸展活动而产生的南北向地堑系统有关。
It is generally believed that potassic and ultrapotassic volcanic rocks in Qinghai-Xizang （Tibetan） plateau plateau are closely related to a mantle source, but recent studies show that some potassic rocks in Qinghai-Xizang may also come from the lower crust. The Miocene volcanic rocks distributed in Caze area, south-western Qinghai-Xizang plateau are potassic to ultrapotassic volcanic suite. They may be divided into three the intermediate-basic subgroup, the intermediate subgroup and the K-rich rhyolites on th geochemical compositions. Volcanic rocks of the subgroups, i.e., e basis of their intermediate-basic subgroup were probably derived from a phlogopite-bearing enriched upper mantle source. Volcanic rocks of the intermediate subgroup have some compositional features similar to an adakitic melt, implying that they were probably generated by partial melting of the relative K-rich marie lower ernst beneath the Lhasa block. However, the K-rich rhyolites were probably derived from the middle-upper crust by decompression-melting caused by extension during Miocene in the southern Qinghai-Xizang plateau. Based on the study of geochronology, chemical composition, regional tectonics and magmatic association in the Caz6 area and adjacent volcanic rocks, it is suggested that the formation of Caze volcanic rocks be correlated to the N-S striking grabens produced by extension during Miocene in the southern Qinghai-Xizang plateau.
出处
《地球化学》
CAS
CSCD
北大核心
2007年第5期437-447,共11页
Geochimica
基金
国家重点基础研究发展计划项目(2002CB412602)
中国科学院知识创新工程重要方向项目(KZCX3-SW-143
KZCX3-SW-122)
国家杰出青年基金(40425003)
关键词
南北向地堑
钾质-超钾质岩
流纹质岩
中新世
查孜
青藏高原
N-S striking graben
potassic-uhrapotassic volcanic rocks
rhyolite
Miocene
Caze area
Qinghai Xizang plateau
