Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5784864 | Precambrian Research | 2017 | 50 Pages |
Abstract
Four metamorphic mineral assemblages, formed at different metamorphic stages, are identified in pelitic granulites exposed in the Jidong terrane, east Hebei Province, North China Craton (NCC). Prograde mineral assemblages (M1) are represented by biotite, plagioclase, quartz, and ilmenite, preserved as mineral inclusions within garnet porphyroblasts. Peak mineral assemblages (M2), which are represented by the garnet cores, rutile, pseudomorphs of sillimanite after kyanite, and some matrix minerals, formed at P-T conditions of â¼12-13 kbar/820-850 °C. Post-peak mineral assemblages (M3), which consist of the inner rims of garnets and some matrix minerals, formed at P-T conditions of â¼11 kbar/850 °C. The final retrograde mineral assemblages (M4) are mainly represented by matrix biotite without rutile exsolution, and minor matrix plagioclase with relatively high anorthite content. High-resolution secondary ion mass spectrometry (SIMS) UâPb dating of metamorphic zircons demonstrates that the pelitic granulites possibly reached the peak metamorphic stage at â¼2.5 Ga. Younger metamorphic ages (2.41-2.45 Ga) possibly represent the cooling ages of the granulites. Accordingly, the pelitic granulites exposed in the Jidong terrane record clockwise P-T-t paths with sequential isothermal decompression (ITD) and isobaric cooling (IBC) segments, likely caused by a subduction-collision event during the late Neoarchean to early Palaeoproterozoic in the eastern NCC.
Keywords
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geochemistry and Petrology
Authors
Jun-Sheng Lu, Ming-Guo Zhai, Lin-Sheng Lu, Lei Zhao,