西藏及腾冲地区晚新生代火山作用的构造背景

Tectonic Settings of Late Cenozoic Volcanism in Tibet and Tengchong Area,China

青藏高原新生代以来发生全球瞩目的块体挤出、构造隆升的同时,也形成了60～40 Ma、30～15 Ma及小于5 Ma的火山活动,这些火山活动出现在板块俯冲、碰撞、及碰撞后持续南北向深层挤压的不同构造背景之下,后者以钾玄岩为主。发生于4～0.01 Ma期间的腾冲地区高钾钙碱性玄武岩、玄武安山质火山活动(分为4～0.9 Ma,0.8～0.1 Ma,小于0.1 Ma三期)为印度板块持续向北挤入导致的其东侧右行走滑形成的剪切—拉张的构造背景下形成的,岩浆活动的深部为先存的大陆边缘环境。火山活动与缅甸弧的俯冲作用、密支那—曼德勒缝合带的活动无关。

Contemporaneously with the geological block escaping and tectonic uplifting developed in the Tibetan Plateau in the Cenozoic, volcanism took place during 60～40 Ma, 30～15 Ma and later than 5 Ma (Middle Pliocene—Late Pleistocene). The three-stage volcanism belongs to different tectonic settings, such as subduction of the plate, collision of the continental plates and continued N-S-compression and injection beneath the crust during the post-collision, respectively. The volcanic rocks of the third stage are mainly shoshonite series. The volcanism with high-K calc-alkaline basalt and basaltic-andesite series during 4 Ma to 0. 01 Ma in the Tengchong area was controlled by the tectonic setting of right-hand shear-extension that resulted from the continued northward injection of the Indian plate into Eurasian plate. The magma was from the existed orogenic belt of the continental margin on the southeastern side of the Tibetan plateau. The volcanism is not related with the subduction of the Burma or the activation of the Myitkyina-Mandalay suture.