长江源区新生代火山岩的年代学研究

长江源区的火山岩包含了青藏高原北部新生代火山岩形成及演化的全部信息，其年代学研究对查明青藏高原北部新生代火山活动时空演化具有重要意义。通过K—Ar同位素年代学研究，将长江源区新生代的火山活动划分为3期：第Ⅰ期(40．1-35．1Ma)火山喷发较弱，形成小范围分布的细粒安粗岩和斑状粗面岩；第Ⅱ期(26．5～17．6Ma)火山喷溢最为强烈，形成大面积厚层黑色气孔状安粗岩；第Ⅲ期(5．5-4．61Ma)由潜火山作用形成球粒状、斑状粗面岩岩丘。长江源区3个期次的火山喷发与青藏高原北部火山活动的阶段性相对应。长江源区新生代火山岩的演化特征为：从早到晚，岩石系列由高钾钙碱性系列→钾玄岩系列演化；岩性由安粗岩→粗面岩演化。

Chronology of Cenozoic volcanic rocks in the source region of the Yangtze River

Volcanic rocks in the source region of the Yangtze River contain all the information of the formation and evolution of Cenozoic volcanic rocks in northern Tibet, and its chronological research has important significance for the understanding of the temporal-spatial evolution of Cenozoic volcanic activities in northern Tibet. Based on K-Ar isotope chronological research,Cenozoic volcanism in the source region of the Yangtze River is divided into three phases. In the first phase (40.1-35.1 Ma) volcanism was weak, forming fine-grained latite and porphyritic trachyte of limited distribution. In the second phase (26.5-17.6 Ma), volcanic eruption was strongest,forming extensive thick-bedded, black,vesicular latite. In the the third phase (5.5-4.61 Ma), volcanic mounds of spherulitic-porphyritic trachyte were produced by subvolcanism.The three phases of volcanic eruption in the source region of the Yangtze River correspond with the phases of volcanic activities in northern Tibet. From early to late, the Cenozoic volcanic rocks in the source region of the Yangtze River evolved from high-potassium calc-alkaline series to shoshonite series and from latite to trachyte.