Late carboniferous-middle permian granitoids in south Mongolia: implications for post-subduction processes in southern central asian orogenic belt

ABSTRACT

Late Carboniferous to Permian granitoids in South Mongolia records the processes from collision to post-orogenic extension for the southern Central Asian Orogenic Belt (CAOB). Systematic geochemical (major, trace elements, and Sr-Nd-Hf isotope) and geochronological (zircon U-Pb age) analyses on granitoids provide constraints on the post-subduction processes of the CAOB in South Mongolia. Based on these results, the South Mongolia Granitoids (SMG) can be subdivided into three groups: (1) Late Carboniferous (319–307 Ma) unfractionated I-type granitoids (SMG I) with adakite-like high Sr (310–1260 ppm) and low Y (6–20 ppm) contents, and high Sr/Y (20–150) ratios; (2) Late Carboniferous to Early Permian (316–279 Ma) highly fractionated I-type granitoids (SMG II) that are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE) and show strongly negative Ba, Nb, Ta, Sr, P and Ti anomalies and positive K and Th anomalies; (3) Middle Permian (post-279 Ma) A-type granitoids (SMG III) with SiO2 (59–61 wt %), high Al2O3 (18–19 wt %) contents, and high total alkalis concentrations (Na2O+K2O = 9.5–10.1 wt %). The SMG I and II were most probably derived from partial melting of juvenile lower crustal rocks of basaltic composition, likely produced by magmatic underplating. In contrast, SMG III may have been formed by the mixing of mantle- and crustal-derived magmas sources. Additionally, SMG II and III record significant assimilation and fractional crystallization processes. The Late Carboniferous to Permian (319–279 Ma) SMG likely reflect that South Mongolia evolved from initial collision to orogenesis, and finally into an intraplate setting.

KEYWORDS:

• Post-subduction magmatism
• adakite-like granitoids
• i- and A-type granitoids
• underplating basic intrusion
• south Mongolia
• central Asian Orogenic Belt

Acknowledgments

This study was financially supported by Strategic Priority Research Program of Chinese Academy of Sciences [Grant No. XDB 41000000], the Chinese Academy of Sciences [Grant No.: GJHZ1805], the National Natural Science Foundation of China [Grant Nos.: 41702217 and 41772230], the Ministry of Science and Technology of China [Grant No.: 2012FY120100] and the Chinese Scholarship Council. Prof. Q.L. Li and Y.H. Yang, at the Institute of Geology and Geophysics, Chinese Academy of Sciences, are thanked for their assistance during age dating. We thank Ms. D. Oyun and PhD Maik at the Mongolian University of Sciences and Technology for their supports during the field investigations in Mongolia.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by the the Ministry of Science and Technology of China [2012FY120100]; the Chinese Scholarship Council ; the Chinese Academy of Sciences [GJHZ1805]; the National Natural Science Foundation of China [41702217,41772230]; Strategic Priority Research Program of Chinese Academy of Sciences [XDB 41000000].