Citation: | CHENG Zhaoxun, WANG Yan, QIAN Cheng, YANG Xiaoping, LI Zhonghui, LIU Hongwei, XIAO Lin. The discovery of the Paleoproterozoic metamorphic rocks in Ulanhot, Inner Mongolia, and its geological significance[J]. Geological Bulletin of China, 2018, 37(9): 1599-1606. |
A set of amphibolite schist, diopside tremolite schist and amphibolite gneiss supracrustal rock assemblage was newly discovered in Dongbaiyinwusu area. The rocks have generally experienced high greenschist facies and low amphibolite facies metamorphism and the multiple tectonic transformation of plagioclase in later stage. The hornblende schist protolith comprised basic volcanic rocks, whose zircon crystal, cathodoluminescence, back scattering image and high Th/U ratio characteristics suggest magmatic zircon. By using zircon U-Pb dating LA-ICP-MS technology, the authors obtained the isotopic age of 1864.1±7.3Ma, suggesting Paleoproterozoic and representing magma formation age, which constrains the formation age of supracrustal rocks and proves the existence of Precambrian crystalline basement in Ulanhot area. A comparison with the Paleoproterozoic magmatic zircon ages of southern Songnen massif shows that the west margin of Songnen massif can extend to the Ulanhot area.
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Geological schematic map of the study area
Measured section of eastern Proterozoic epidermal rocks in Ulanhot, Inner Mongolia
Macrophotograph of plagioclase amphibole schist and plagioclase amphibole gneiss
Fold deformation of the middle vein of metamorphic rock series
Diagram of F-TiO2
Diagram of ((al+fm)-(c+alk))-Si
Diagram of(al-alk)-c
Field features and microphotograph
CL images of zircons in PM028B101
PM028B101 age concordent diagram of zircon in plagioclase amphibole schist