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6883882 
Journal Article 
Carboniferous mantle-derived felsic intrusion in the Chinese Altai, NW China: Implications for geodynamic change of the accretionary orogenic belt 
Cai, K; Sun, Min; Yuan, C; Xiao, W; Zhao, G; Long, X; Wu, F 
2012 
Yes 
Gondwana Research
ISSN: 1342-937X 
ELSEVIER 
AMSTERDAM 
22 
2 
681-698 
English 
WOS:000307602000025 
This paper reports whole-rock Sr-Nd and zircon U-Pb and Hf isotopic compositions, as well as major and trace element data, for the granodiorites and their mafic microgranular enclaves (MMEs) in the Tuokesalei area, northwestern Chinese Altai. The granodiorites are characterized by peraluminous compositions (A/CNK = 1.01-1.45), with relatively high SiO2 (64.4 to 70.9 wt.%) and low MgO (0.75 to 1.97 wt.%) contents. These rocks possess low total rare earth element (REE) contents (67-187 ppm) with weakly negative Eu anomalies and mantle-like whole-rock Nd-Sr isotopic compositions (epsilon(Nd)(t) = +2.5 to +4.5; (Sr-87/Sr-86)(i) = 0.7038 to 0.7048) and zircon epsilon(Hf)(t) values (+ 5.93 to + 12.9). The MMEs contain abundant magmatic amphiboles and needle-like apatites, have low SiO2 (51.7 to 54.3 wt.%) and high MgO (2.86 to 3.75 wt.%) and REE contents (162-298 ppm), and are characterized by moderately negative Eu anomalies (Eu/Eu* = 0.40-0.60) and slightly depleted to enriched LREE ((La/Nd)(N) = 0.74-1.41) and flat HREE ((Gd/Yb)(N) = 1.16-139) patterns. The MMEs have whole-rock Nd-Sr isotopic compositions (epsilon(Nd)(t) = +2.6 to +2.7. (Sr-87/Sr-86)(i) = 0.7034-0.7050) similar to those of the host granodiorites. Their similarities in crystallization age, mineral assemblage and isotopic composition document that the MMEs may represent an early crystallized phase, which was broken into pieces and brought to the shallow level during the host magma ascent and emplacement. Their precursor magmas were probably derived from an oceanic lithospheric mantle, which was characterized by pronounced Nd-Ta depletions. Mineral compositions of MMEs suggest that amphibole was a major early fractional mineral, which effectively differentiated the mantle-derived basaltic liquids to silica-rich melts. Zircon U-Pb dating yielded an age of 313 +/- 5 Ma for the host granodiorites and 313 +/- 13 Ma for their MMEs. The geochemical data of this study records an important episode of magmatism in an environment transitional from a subduction-related regime to a post-tectonic extension. Results of this study suggest that the accretionary orogenic process did not completely terminate until the Late Carboniferous to Permian in this region. (C) 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. 
Granodiorite; MME; Accretionary orogenic belt; Geochemistry; Geochronology; Chinese Altai; CAOB