冈底斯带扎雪石英二长斑岩体的地质特征及构造环境

The geology and tectonic setting of the Zaxoi beschtauite massifs in the Gangdise zone, Xizang

关键词:  冈底斯带  扎雪  石英二长斑岩体  始新世  构造环境

Key words:  Gangdise belt  Zaxoi  beschtauite  Eocene  tectonic setting

摘要:

扎雪石英二长斑岩体分布于冈底斯岩浆弧带的中段,侵入于前奥陶系松多岩群和石炭-二叠系来姑组中,并被帕那组火山岩呈火山沉积不整合覆盖,其黑云母K-Ar年龄值为54.42Ma,时代为始新世。岩石学和岩石化学特征:w(SiO₂)=67.04%~69.75%、w(Al₂O₃)=14.85%~16.75%、w(TiO₂)=045%~0.53%、w(K₂O+Na₂O)=9.64%~10.28%、w(K₂O/Na₂O)=1.8~1.97,表明扎雪石英二长斑岩体为酸性钾玄质浅成侵入岩。它与冈底斯带上广泛发育的林子宗群年波组火山同时异相,形成于印度板块和欧亚板块后碰撞阶段,成为大洋俯冲体制向大陆碰撞体制转换的岩石记录。

Abstract:

The Zaxoi beschtauite massifs occur in the central part of the Gangdise magmatic belt, and intruded into the pre-Ordovician Songduo Group Complex and Carboniferous-Permian Laigu Formation overlain unconformably by the Pana Formation volcanic rocks. The biotite in the beschtauite may be traced back to the Eocene, with a K-Ar age of 54.42 Ma. w(SiO₂)=67.04%-69.75%, w(Al₂O₃)=14.85%-16.75%, w(TiO₂)=0.45%-0.53%, w(K₂O+Na₂O)=9.64%-10.28%, w(K₂O/Na₂O)=1.8-1.97. The above-mentioned values indicate that the Zaxoi beschtauite massifs should be assigned to the acidic shonshonitic hypabyssal intrusive rocks. These massifs originated from post-collision stages of the Indian plate and Eurasian plate are believed to be coeval and allophased with the widespread volcanic rocks of the Linzizong Formation also in the Gangdise belt and recorded the transition from the oceanic subduction regimes to the continental collision regimes.