滇西无量山地区的构造变形和变质作用

Deformation and metamorphism of Wuliangshan area,western Yunnan

无量山构造带位于滇西兰坪一思茅盆地中段西侧北北西一南南东走向的复背斜。在复背斜中部发育北北西一南南东向的左旋走滑韧性剪切带。中部剪切带变质作用达绿帘角闪岩相的蓝晶石带高于绿片岩相黑云母带的围岩。用共生的黑云母一石榴石温压计计算得到中部剪切变质带西缘变质温度为600℃-650cc，压力为5．6kba；东缘温度为550℃-600℃，压力为5kba左右。结合同构造期石榴石变斑晶的环带成分和多硅白云母b。值的分析，首次在滇西提出该剪切变质带是进变质的，以不均一的、非连续的变质作用为主要特征，与区域变质作用不同。无量山中部韧性剪切变质带的进变质作用与剪切带中岩石的变形强度有关。岩石变形愈强，变形能就愈大，随之转化成的热量就愈大，该热能参与到岩石变质作用中，提高了岩石的变质程度。这一思路有可能成为研究变形与变质作用的一条有效途径。

The Wuliangshan metamorphic belt is a striking NNW-SSE anticlinorium,with both limbs limited by faults. In the middle part of the anticlinorium,there is a striking NNW-SSE sinistral ductile shear zone. The metamorphic grade of the middle shear zone reaches to kyanite zone of epidote amphibolite facies,which is obviously higher than the biotite zone of greenschist facies in the surrounding rocks. Using the biotite-garnet thermobarometry, the P-T conditions are yielded at 600 ℃- 650 ℃and 5.6 kbar at the western edge, as 550 ℃ - 600 ℃ and 5 kbar at the eastern edge,respectively. It is first advanced in Western Yunnan that this shear zone is a progressive metamorphic zone according to the compositional zone of contemporaneous garnet and the b0 value of phengites. The metamorphism of the shear zone has the characteristics of inhomogeneity and uncontinuative isograde,which is different from the regional metamorphism of homogeneity and isograde. The theory of deformation energy is first used to discuss the mechanism of the shear-metamorphic zone in this paper. The metamorphism of the ductile shear zone in Wuliangshan area has a relation with the deformation of the rocks,namely the stronger the formation, the higher the metamorphic grade. This is reduced to the heat, transformed from the deformation energy and then causing higher-grade metamorphism with the strengthening of the formation.