藏北新生代火山作用的时空演化与高原隆升

Spatial—Temporal Evolution of Cenozoic Volcanism and Uplifting in North Tibet

本文通过对藏北新生代火山岩的岩石化学和同位素年龄资料的综合分析,系统确定了火山岩的岩石系列组合及其生成时序。根据岩石系列的时空演化规律将藏北新生代火山活动划分为3个构造—岩浆亚旋回,火山活动自南向北依次形成羌塘(44～24 Ma)、中昆仑—可可西里(19～7 Ma)、西昆仑—玉门(约5 Ma以来)3条火山岩亚带。各岩带分别以高钾钙碱性或钾玄岩系列构成火山活动的主体,以碱性钾质火山活动而结束。构造—火山旋回与高原脉动隆升具有明显的耦合性,旋回间歇期与高原夷平期相对应。笔者认为这一火山作用规律是高原每次脉动隆升过程中,构造性质由挤压、增厚,向伸展滑移转化的结果,火山作用旋回受岩石圈水平挤压、增厚和深部地幔热物质沿构造薄弱带挤压上升两种作用的相互消长所制约。

Following the collision of the Indian plate with the Eurasia Continent at 45 Ma,the Cenozoic volcanic activities of North Tibet show three tectonic-magmatic subcycles. Three corresponding volcanic subzones were formed,from South to North,they are the Qiangtang(44～24 Ma) , Kunlun—Hohxil(19～7 Ma) and west Kunlun—Yumen (5 Ma) volcanic subzones. Each subcycle began with volcanic activities of high-K alkali-calcic or shosernite seires, ended with alkali potassic volcanic activities and the appearance of plateau planation surfaces. The evolument of volcanic series is closely related transformation from the pulasting compression , thickening to extension and slippery of the lithosphere in both time and space.