喜马拉雅造山带加里东期构造作用:以马拉山-吉隆构造带为例

Himalaya in the Caledonia time: A record from the Malashan-Gyirong area,southern Tibet

青藏高原是由复合地体和复合造山拼贴体组成,是新元古代以来长期活动、多期造山及新生代最后隆升的基础上形成的高原。最近在马拉山-吉隆构造带中厘定出形成于445～431Ma的碎屑锆石,包括岩浆成因和变质成因,以及447Ma的变质事件,比已有关于安第斯型造山作用的认识晚30～60Myr。主量、微量和同位素特征显示志留纪片麻岩具有和奥陶纪花岗岩一致的地球化学特征,属于同一套岩石。综合已有现象推断出：喜马拉雅地区古生代构造事件持续时间更长,微陆块与冈瓦纳大陆北缘的碰撞作用可能发生在志留纪,引发奥陶纪的岩浆岩发生变质作用,以及志留纪的岩浆活动,这些热事件属于加里东期构造作用。

The Tibet Plateau consists of complex terrain and orogen,have experienced multi-periods of orogentic events since Neo-Proterozoic and finally rise at Cenozoic. In the Malashan-Gyirong area,there are 445 ～ 431 Ma detrital zircons,magmatic and metamorphic origin,as well as 447 Ma metamorphism,which are younger 30 ～ 60 Myr than the reported Andean-type orogeny along the margin of the Gondwana. The characteristics of whole-rock major and trace element as well as isotope indicate that the Silurian granitic gneiss have similar geochemical composition as the Ordovician granite. Combined with previous studies,it is deduced that the collision between those microcontinents or terranes and the north margin of the eastern Gondwana occurred at Silurian,and trigged the metamorphism of the Ordovician granites and the Ordovician magmatism,which are the Caledonia tectonic event.