- journal_title：Geological Society of America Bulletin
- Contributor：Guang Zhu ; Cheng-Long Xie ; Wen Chen ; Bi-Wei Xiang ; Zhao-Qi Hu
- Publisher：Geological Society of America
- Date：2010-
- Format：text/html
- Language：en
- Identifier：10.1130/B30028.1
- journal_abbrev：Geological Society of America Bulletin
- issn：0016-7606
- volume：122
- issue：3-4
- firstpage：506
- section：STRUCTURAL GEOLOGY
We conducted structural and geochronological studies on the Hongzhen metamorphic core complex in the eastern Yangtze craton. The hanging wall of the Hongzhen metamorphic core complex consists of Neoproterozoic to Permian unmetamorphosed strata, which were folded during NW-SE shortening in the Middle Triassic, and Cretaceous terrestrial basins. The exposed Paleoproterozoic Dongling Complex in the footwall is widely overprinted by a detachment ductile shear zone, which has consistent SW-plunging mineral elongation lineations and top-to-the-SW shear indicators. Analysis of the mesostructures, microstructures, and quartz C-axis fabrics indicates that they formed within a low-angled, SW-dipping, extensional shear zone at midcrustal levels. Four muscovite grains separated from mylonites within the shear zone yielded 40Ar/39Ar plateau ages ranging from 128.5 ± 1.0 Ma to 126.1 ± 1.1 Ma. They are interpreted as cooling ages of the shear zone associated with the Hongzhen metamorphic core complex. We propose that the Hongzhen metamorphic core complex was initiated as a midcrustal, low-angle extensional shear zone with top-to-the-SW shear sense at ca. 145 Ma, and the shear zone was then warped and uplifted by the emplacement of the Hongzhen granite at 122 Ma. Brittle normal faulting and basin rifting in the hanging wall also developed during the formation of the Hongzhen metamorphic core complex, but these processes continued until the Late Cretaceous. This study of the Hongzhen metamorphic core complex demonstrates that the eastern Yangtze craton was also involved in the Early Cretaceous extension widely occurring in the eastern China continent. A NE-SW extensional direction during the Early Cretaceous is indicated by the Hongzhen metamorphic core complex.