右江盆地三叠系的极低级变质作用与变形构造——以天峨地区为例

右江盆地三叠纪槽盆相浊流沉积岩系广泛遭受过低级、极低级变质作用,变质变形构造发育,形成了具有规模呈带状展布的低变质强变形构造岩区带,劈理构造常密集发育构成劈理构造变形带.其中,强变形带剪切变形强烈,出现了明显塑性流变,构成碎屑岩质脆韧性剪切变形带.变质变形程度或级别与地层时代或岩层在地层柱中的位置相关,自下往上变质级别依次降低、变形强度递进增强.反映了区域低变质强变形作用是在"伸"、"缩"、"剪"构造机制背景下,以葡萄石-绿片岩相为特点,从区域埋藏型变质开始发生演变到剪切带内变质,不断向前递进发展变化的特征,是区域变质作用和强动力变质作用的复合变质作用.

Low Metamorphism and Deformation Tectonics of Triassic System in Youjiang Basin——Take Tian''e area as an example

The turbidite series of the Triassic geosyncline-basin facies suffer low,even very low metamorphism extensively in Youjiang Basin.The metamorphic and deformation tectonics develop and form a low metamorphism and strong deformation tectonic terrain,characterized of the belted tectonics.The cleavages often develop and constitute the tectonic deformation belt(with cleavages) in the terrain.Because of strong shear deformation in the belt,the plastic flow deformation appears clearly,and the brittle shear deformation belt with clasolite is constituted.The extent/grade of metamorphic-deformation depends on the geologic ages or the rock horizon in the lithostratigraphic column with the change from down to upper,the metamorphism decreases while the deformation increases in order.It demonstrates that the regional low metamorphism and strong deformation are formed under the tectonic mechanism setting characterized of "stretch","contract","shear",and are of prehnite-greenschist facies.In addition,the evolution of metamorphism from regional burial to inner shear belt reflects the characteristics of progressive development and the change of metamorphism,and the combination of the regional metamorphism with strong dynamometamorphism.