西藏冈底斯地块中新生代中酸性侵入岩特征与构造环境

冈底斯地块上的中新生代中酸性岩浆活动，是北部班公湖一怒江和南部雅鲁藏布两个特提斯演化及其后的陆内汇聚碰撞造山和后造山伸展等大地构造事件的完整记录。地块上的中酸性岩浆活动可划分为三个带，其中北部岩带岩浆岩形成于燕山期，其类型从早期的Ⅰ型到中期的过渡型再演化为晚期的S型，分别形成于板块俯冲-缝合-碰撞等构造条件下，是北部班公湖一怒江特提斯演化的集中反映。中部和南部岩浆岩带则集中体现了南部雅鲁藏布特提斯时空演化的完整经历，其中，南部岩带岩体以燕山晚期为主，喜山早期次之，成因及形成环境与特提斯洋壳向北俯7中作用密切相关(燕山晚期)，同时俯冲结束后的同碰撞条件下的岩浆活动在该岩带内也有明显的反映(喜山早期)；中部岩带岩体以喜山早期为主，燕山晚期次之，岩体大部分为同碰撞环境下岩浆活动的产物，它表征了随着洋壳板块向北俯冲程度的加深和强度的加剧，岩浆活动中心在不断向北迁移，并最终缝合碰撞的过程。因此，该岩带内岩浆岩主要形成于俯冲的晚阶段及缝合后的同碰撞条件下。喜山晚期的小斑岩体实际上广泛出露于整个冈底斯地块上，它反映的是该区在经历了碰撞造山后发生的陆内伸展的构造过程。

CHARACTERISTICS OF INTERMEDIATE TO ACIDIC MAGMATISM OF MESOZOIC TO CENOZOIC ON GANDISE MASSIF, TIBET

Intermediate to acidic magma activities of Mesozoic to Cenozoic on Gandise Massif completely recorded those tectonic events including Tethys evolvement and the succeeding intracontinental convergence and collision orogeny and post orogeny spreading in Bangonghu-nujiang in the north and Yaluzangbu in the south. The intermediate to acidic movements on the massif can be classified into three belts in which the magmatic rocks in north belt were formed in Yanshanian age and the rock types evolved from type I in the earlier stage to transition type in the middle stage and type S in the late stage. They were formed under structure conditions of plate subduction-suture-collision respectively, and ypically reflect the Bangonghu-Nujiang Techys evolvement in north. The magmatite belts in center and south reflect the whole time and space evolvement of Tethys in southern Yaluzangbu in which the rocks in south belt are mainly formed in late Yanshanian period and less in early Yanshanian period. Their origins and forming environments are closely associated with the subduction of Tethys oceanic plate towards north (late Yanshanian period) while the magmatic movement in collision condition after subduction in the rock belt is also obvious (early Himalayan period); the rocks in center belt were mainly formed in earlier Himalayan period and less in late Yanshanian period and most of the rocks are origin in magmatic activities in collision environment. It is indicated that the center of magmatic movement were moved to north continuously and finally sutured with the subduction of oceanic plate towards north becoming fiercely and intensified. Therefore magmatic rocks in the rock zone mainly formed at syn-collision stage in late subduction period or after stylolitization. Extensive occurrence of small porphyry bodies of late Himalayan on Gandise Maffis reflects that this area was subjected an intracontinental spreading tectonic process after collision orogeny.