期刊
PRECAMBRIAN RESEARCH
卷 332, 期 -, 页码 -出版社
ELSEVIER
DOI: 10.1016/j.precamres.2019.105397
关键词
Central Asian Orogenic Belt; Neoproterozoic; Zircon dating; Sm-Nd isotope systematics; High-temperature granulite; Granitoid magmatism
资金
- Russian Science Foundation [14-27-00058]
- Russian Foundation for Basic Research (RFBR)
- Ministry of Science and Technology (MoST) of Taiwan [19-55-52001]
- RFBR [17-05-00357]
Within the Chu-Kendyktas Precambrian terrane located in Southern Kazakhstan (in the western part of the Central Asian Orogenic Belt), medium- and high-grade metamorphic formations have been identified and attributed to the Aydaly and Shukyr Complexes. The Aydaly Complex is predominantly composed of orthogneisses with a Neoproterozoic protolith age of 790 Ma and subordinate high-temperature granulites comprising a succession of amphibolites, amphibole-rich granulites, mesocratic granulites, and melanocratic (clinopyroxene-rich) and leucocratic (melt-rich) granulites, which were evidently formed at moderate pressures of 6-9 kbar and high temperatures, increasing from 700 to 900 degrees C or more. The clinopyroxene-rich granulites of the Aydaly Complex contain detrital zircon grains of mainly Palaeoproterozoic (1790-2058 Ma) and, to a more limited extent, Neoarchean (similar to 2500 Ma) ages, with preserved magmatic zoning and indicating a sedimentary origin of the protolith via mafic greywackes that were subsequently metamorphosed to amphibolites. The age estimates of the leucocratic melt-rich granulites, which form veins or layers within the clinopyroxene-rich melanosome, correspond to the range 770-790 Ma and define the Neoproterozoic stage of magmatism and granulite metamorphism. Hence, the deposition of the sedimentary protolith for the Aydaly Complex granulites and its subsequent emplacement at mid-crustal levels occurred from the middle Palaeoproterozoic (similar to 1800 Ma) to the late Tonian (similar to 770-790 Ma). In turn, the Shukyr Complex consists of garnet-biotite schists, which are characterised by a significantly lower grade of metamorphism compared to the Aydaly Complex, at around T similar to 600 degrees C. The garnet-biotite schists are thought to represent moderate-temperature hornfels, located at the contact between the protolith (shales) and the Early Palaeozoic Ulken massif granitoids. The deposition of the Shukyr Complex protolith occurred during the Ediacaran-Cambrian, as a result of the erosion of mainly Mesoproterozoic (1000 Ma), and to a lesser extent Palaeoproterozoic (2460 Ma), rocks. The Sm-Nd whole-rock isotopic compositions suggest that the formation of the protoliths of the Aydaly and Shukyr Complexes was related to the reworking of Palaeoproterozoic continental crust.
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