摘要
青藏高原是我国岩浆岩最发育的地区之一,出露着从元古宇到新生代各个地质时期多种类型的火山岩与侵入岩,面积达30万km2左右,占全区面积的10%以上。这些岩浆岩在青藏大陆动力学研究中有着重要的作用,既是探测深部的"探针"和"窗口",又是构造演化的记录,并形成重要的构造-岩浆-成矿带。本文拟通过岩浆作用和岩浆岩来研究青藏高原演化的一些科学问题。(1)印度-亚洲大陆碰撞时限:印度-亚洲大陆碰撞时限是青藏高原形成演化中一个非常重要的基础问题,也是国际上争论的一个热点,到目前为止,分歧仍然很大,从主张早于70Ma到34Ma都有。本文根据来自我国西藏南部延伸1500km以上的主碰撞带的综合证据提出,印度-亚洲大陆碰撞开始的时间为70/65Ma,完成的时间在40Ma左右,这个时期称为同碰撞期,40Ma之后转入后碰撞期。(2)同碰撞阶段的壳-幔交换—底侵与岩浆混合作用:南冈底斯带同碰撞花岗岩中有着丰富的岩浆底侵作用与岩浆混合作用证据。这两种作用,通过岩浆作用实现壳-幔间物质和能量的交换,是重要的大陆地壳生长方式。(3)青藏巨厚地壳的成因:双倍于正常厚度的巨厚地壳,是青藏高原最显著的特点之一,世界瞩目。通过对同碰撞与后碰撞火成岩的研究提出"两类地壳、两种机制"的认识,即新生地壳与再生地壳;构造挤压增厚机制与地幔物质注入增厚机制。(4)青藏岩石圈的组成、结构与演化:高原岩石圈地幔存在三种地球化学端元,存在三种岩石圈结构类型,已在青藏高原多处发现地幔与下地壳岩石的地表露头及火成岩所携带的深源岩石包体。(5)青藏高原深部物质的可能流动:青藏高原新生代碰撞-后碰撞火成活动有规律的时空迁移,以及深部地球物理探测。
The Tibetan Plateau is one of the regions in China where igneous rocks are very widely developed.Various types of volcanic and plutonic rocks are distributed over 300,000 km 2 in area and take 10%area of the entire Plateau.These igneous rocks and carried deep-seated nodules play important roles in understanding geodynamic evolution of the Tibetan Plateau,as either lithoprobes/windows or tectonic records,and are closely related to mineralization as well.This paper discusses some important scientific topics via studying igneous rocks.（1） The timing of Indo-Asia collision：This is a very important scientific problem.There is,however,a wide range of discrepancy about the timing of initiation of the collision（from earlier than 70 Ma,to even later than 34 Ma） .According to multiple lines of evidences from the 1500 km-extending main collision zone in southern Tibet,we deduced a conclusion that Indo-Asia collision likely started from 65/70 Ma and completed in c.40 Ma（syn-collisional stage） ,and then transformed into post-collisional stage after 40 Ma.（2） Underplating and magma mixing,an event of mantle-crust interaction during syn-collisional stage：There are abundant evidences for underplating and magma mixing in southern Gangdese.Animportant process of continental growth and evolution took place in the Tibetan Plateau.（3） The origin of formation of extremely thick crust of the Tibetan Plateau：A deduction of＂Two types of crust and two types of mechanism＂is suggested based on the studies of collisional and post-collisional igneous rocks.There are two types of crust,juvenile crust and recycled crust,in the Plateau.Crustal thickening of the Plateau was caused by two types of mechanism,i.e.,both structural compression and input of mantle materials via magmatism.（4） The composition,structure and evolution of the lithosphere of the Tibetan Plateau：There are three geochemical reservoirs in the lithospheric mantle,and three types of lithospheric structure underneath the Tibetan Plateau.Nodules and outcrops of mantle/lower crust-seated rocks are found in several locations of the Plateau.（5） Possible lateral flow of lower crust and upper mantle：Migration of collisional and post-collisional volcanism with time shows a highly distinctive pattern,which can be interpreted to reflect lateral flow of the lower crust and asthenospheric mantle induced by the approach and ensuing collision of relatively thick（India and Eurasia） continental plates.
出处
《高校地质学报》
CAS
CSCD
北大核心
2011年第3期351-367,共17页
Geological Journal of China Universities
关键词
青藏高原
岩浆作用
岩浆岩
大陆碰撞
壳幔交换
地壳生长
岩石圈
横向流动
Tibetan Plateau
magmatism
igneous rocks
continental collision
mantle-crust interaction
crust growth
lithosphere
lateral flow
