Monday, August 25, 2014

Evidence From China PaleoProterozoic Plate Tectonics did NOT Shutdown

Early Paleoproterozoic (2.45–2.20 Ga) magmatic activity during the period of global magmatic shutdown: Implications for the crustal evolution of the southern North China Craton


Diwu et al


A global database of zircon ages from both granitoids and detrital sediments shows an exceptionally and robust ages gap between 2.45 and 2.20 Ga. The early Paleoproterozoic magmatism dramatically decreased on the Earth, which was proposed to relate to the global plate tectonic shutdown. However, the available data indicate that 2.45–2.20 Ga magmatic rocks are widespread in the Taihua Complex during the quiet interval. The Taihua Complex is located in both the Lushan and Xiaoqinling areas along the southern segment North China Craton (NCC). The Complex is composed mainly of a gneiss series and the Khondalite-dominated supracrustal rock. The latter, occurs as a linear structural belt and was named the Khondalite Belt. The gneiss series in the Lushan area has an age of 2.85–2.72 Ga, whereas the Xiaoqinling region contains widespread tonalitic–trondhjemitic–granodioritic gneisses with ages of 2.45–2.20 Ga. Significant variation of Hf isotopes in zircons and whole-rock ɛNd(t) values suggest that these rocks were produced by variable mixing of a juvenile materials with older crust in an Andean-type continental margin arc or island arc setting. The depositional age of the sedimentary protoliths of the khondalite series can roughly constrained to between 2300 and 1970 Ma. It has been considered that they were deposited on a stable continental margin environment. The U–Pb dating of metamorphic zircons from the Taihua Complex suggest that the southern NCC underwent a polyphase tectonic evolution during the period 1.97–1.82 Ga, the peak metamorphism coeval with crustal thickening has occurred at ∼1.94 Ga.

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