摘要
地质背景我国云南到东南亚地区存在一条呈南北延伸的巨型花岗岩岩基带,大致沿东经100°—120°。该带与东南亚锡矿带在成因上有密切联系。其北端始自云南西部的临沧复式岩基(LC GB,图1),经泰国北部的中带花岗岩,向南延至马来西亚半岛的西部花岗岩带,断续延伸逾2400km。此花岗岩带在构造位置上与海西—印支期的东南亚大陆微板块碰撞缝合线非常吻合。李春昱等把该缝合线命名为澜沧江碰撞带(图1)。碰撞带以西以南的地块称羌塘-唐古拉-保山微板块,其古生界的生物群和沉积环境具有罔瓦纳亲缘性;碰撞带以东以北的地块为扬子板块或广义的华南板块,具华夏亲缘性。两个大陆相撞时间在北段稍早。
The Linchang Composite Granite Batholith (LCGB) of west Yunnan is an important constituent of the collision--related granite belt of a Permian--Triassic suture zone in this area. It consists of Pinhejie granite in the north and Linchang granie (LG) in the south, which are connected with each other at depth. The Pinhejie granite is NNW trending, 70 km long, 3--9 km wide and 450 km2 in area. Its eastern part is Pinhejie gneissic granite (PGG), with a Rb-Sr isotopic age of 309±27 Ma and an initial Sr ratio of 0.7153±3. Its western part is Pinhejie massive granite (PMG), with a Rb-Sr isotopic age of 294±6 Ma and an initial Sr ratio of 0.7205±3. The LG is an extremely large batholith, with a total length of 370 km, a width of 18--36 km and a total area of some 10000 km^2. The Rb-Sr age of LG is 275±59 Ma, with an initial Sr ratio of 0.7240±19. A combinated Rb-Sr isochron line for LG and PMG could be obtained with an age of 292±15 Ma and an initial Sr ratio of 0.7216±7. These data show that emplacement of LCGB took place approximately in the range from 292 to 275 Ma, i. e. in the Permian period. The modelling composition of source materials for LG is equivalent to a mixture consisting of 80% upper crustal Sr plus 20% lower crustal Sr. It suggests that the collision--related LCGB is a typical peraluminous S type granite in genesis.
出处
《云南地质》
1989年第3期189-204,共16页
Yunnan Geology
