摘要
本区太古界的麻粒岩系和孔兹岩系经历两次变质作用;第一次结束于2400Ma左右,其PTt轨迹为顺时针,早期为角闪岩相,T=600～650℃,P>0.60～0.80GPa,接着近等压增温,峰期为麻粒岩相,T≈850℃,P=0.8～1.0GPa,相应深度30km左右,冷却阶段压力变化不大,这种轨迹仍代表陆壳因碰撞而增厚的造山带;第二次发生于1800～2000Ma,PTt轨迹亦为顺时针,但早期增温同时减压,峰期T≈770℃,P=0.60GPa,接着近等热减压,压力降至0.4GPa左右,然后大幅度降温,这种轨迹可能形成于晚期地壳松弛性拉张和减薄环境下。
The Arcbean metamorphic complex in Jining district of Nei Mongol is composed of granulite series and khondalite series. They experienced two metamorphic events at c. 2500 Ma and 1800～2000 Ma respectively. Their PTt paths were deduced on the basis of petrographic evidence and P-T estimates from geothermobarometers.
The first metamorphism occurred over the whole area. Its PTt path is clockwise, and characterized by an amphibolite-facies pre-peak stage at T=600～650℃ and P>0.6～0.8 GPa, and a granulite-facies peak stage at temperature about 850℃ and pressure 0.8～1.0GPa. This PTt path suggests a tectonic environment similar to a collision orogenic belt with double crust due to tectonic thickening of the sequence and also to possible obduction of the neighbouring terrane. However, the decompression process was not apparent in cooling stage of this metamorphism.
The second metamorphism was only superimposed on most part of the khondalite series. Its PTt path is also clockwise, but is characterized by increasing temperatare with decreasing pressure at the beginning period and succeeded by a near isothermal decompression process. The drop of temperature is more apparent relatively to pressure in its cooling stage. This PTt path may be related tectonically to the waning extension of the crust by the end of early Proterozoic.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
1991年第4期1-12,共12页
Acta Petrologica Sinica
基金
国家自然科学基金48970102
关键词
麻粒岩
岩相
变质作用
PTT轨迹
Jining district of Nei Mongol
Archean granulite-facies terrane
Metamorphic PTt path
Tectonic environment
