期刊
GEOLOGICAL MAGAZINE
卷 160, 期 8, 页码 1624-1648出版社
CAMBRIDGE UNIV PRESS
DOI: 10.1017/S0016756823000626
关键词
Central Asian Orogenic Belt; high-pressure metamorphism; Precambrian; early Palaeozoic; continental crust; zircon dating; phase diagram modelling; Palaeo-Asian Ocean
This study investigates the high-pressure metamorphism of the Precambrian continental crust in Kazakhstan and Kyrgyzstan, indicating deep-seated metamorphism and evolutionary processes under restrictive conditions. The age distribution of zircons reveals the sources and metamorphic timing of these rocks.
In this study, we investigated the high-pressure (HP) metamorphism of the Precambrian continental crust exposed in the Zheltau terrane in South Kazakhstan (Koyandy complex) and the Chu-Kendyktas terrane in the North Tien Shan of Kyrgyzstan (Aktyuz, Kemin and Kokdzhon complexes) within the SW part of the Central Asian Orogenic Belt. HP quartz-feldspar lithologies of the Koyandy complex consist of migmatized kyanite-bearing garnet-mica paragneisses, garnet-kyanite paragneisses and their derivatives associated with eclogites. Paragneisses demonstrate prograde evolution involving mica dehydration melting and producing magnesium-rich garnet, kyanite and K-feldspar at the near-peak to retrograde stages at pressures of 15-18.5 kbar and temperatures of 800-870(degrees)C. The widespread growth of micas in these rocks reflects lower stages of retrogression at P = 10-12 kbar and T = 720-770(degrees)C. The age distributions of the cores of detrital zircon grains from the paragneisses indicate a predominance of Neoproterozoic and minor occurrence of Mesoproterozoic and Palaeoproterozoic sources of their protoliths. The ages of similar to 487-485 Ma obtained from the zircon rims of the paragneisses reflect the timing of their HP metamorphic re-equilibration. These age clusters are consistent with the age estimates obtained from the rims of zircons in the eclogite-bearing garnet gneisses of the adjacent Aktyuz complex in the North Tien Shan. The P-T paths and zircon ages obtained from the high-grade quartz-feldspar gneisses of the Zheltau and Chu-Kendyktas terranes are thus interpreted to indicate involvement of the crustal material derived from the Precambrian basement (magmatic zircons aged ca. 844 Ma) and its Ediacaran-Cambrian sedimentary cover (detrital zircons with maxima at 1 Ga and 800-600 Ma) in the latest Cambrian subduction processes induced by the closure of the oceanic basins assigned to the Palaeo-Asian Ocean.
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