摘要
右江盆地三叠纪槽盆相浊流沉积岩系遭受过区域极低级变质作用。依据地质观察和伊利石结晶度、绿泥石－云母堆垛集合体、标志性粘土矿物及白云母（伊利石）ｂ０参数测定资料，阐述了泥质岩石的成岩变质作用经浅层（近）变质作用到浅变质作用的转换特征。变质温度区间为１５０—３５０℃，低压类型，具高地温梯度（４０—４３℃／ｋｍ）。变质级及亚带总体与地层时代及岩层在地层柱中的位置有耦合关系，而与区域变形强度无关。最后指出区域极低级变质作用是印支－燕山构造旋回早期及区域变形前的地质事件，属于地壳伸展构造背景下右江边缘型盆地内部的埋藏型变质作用。
The Youjiang River Mesozoic Basin (YRMB) is located in the vicinity of junctural zone between the Tethyan and near Pacific tectonic realms, in which thick turbidity current deposits are widely distributed and have a complicated deformation style and history. Geological observations and microtextural evidence show that the Triassic basin facies deposits underwent a regional very low grade metamorphism. Illite crystallinity ( B (001) ) measurements on a regional scale establish metamorphic framework for the tectonic belt which is subdiveded into five subzones, including the lower diagenetic zone, upper diagenetic zone, lower anchizone, upper anchizone and epizone. The illite crystallinity values for the subzone boundary are 0.500, 0.400,0.300 and 0.215° Δ2 θ , Cu Kα, respectively. Metamorphic p T conditions were determined by a combination of illite crystallinity, b 0 parameters, chlorite mica stacks and index clay minerals. The results indicate that the metamorphic temperatures range from 150℃ to 350℃ and the metamorphism is of a low pressure type characterized by high geothermal gradients(about 40—43℃/km) or high heat flow in the Youjiang River Basin. In general, variations in metamorphic grade in the Triassic strata can be correlated largely with the stratigraphic age or position in the stratigraphic column and there do not appear to have a consistent relationship between degree of deformation or cleavage in intensity and the grade of metamorphism. In addition, the regional deformation resulted in modification of chlorite meca stacks during cleavage development in the mudstone. It is shown that the very low grade metamorphic event represents an early feature in the Indorsinian Yanshanian tectonic cycle and the pre regional deformation, indicating a sedimentary burial depth related metamorphism developed in the Youjiang River Mesozoic continental marginal type basin under an extensional tectonic setting.
出处
《地质科学》
CAS
CSCD
北大核心
1998年第4期395-405,共11页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
国家自然科学基金
关键词
岩层
变质作用
地球动力学
三叠纪
右江盆地
Very low grade metamorphism, Illite crystallinity, Chlorite mica stack, Geodynamics, Youjiang River Basin
