Igneous Records of Mongolia–Okhotsk Ocean Subduction: Evidence from Granitoids in the Greater Khingan Mountains

Large-scale Mesozoic granitoids are exposed in the Greater Khingan Mountains. Their relationship with Mongolia–Okhotsk and Paleo-Pacific Ocean is still under discussion a matter of debate. In this study, field observations were made total 18 vicinity Heihe–Baishilazi area northern part Mountains sampled for petrological, geochronological, geochemical research. addition, to complement 90 granitic samples from Xinghua, Dajinshan, Yili, Chabaqi, Sankuanggou areas compiled order reveal rock assemblages, magma sources, then inquire into tectonic background. Zircon LA–ICP–MS U–Pb dating indicates that two Heihe formed Early Jurassic period (194.2 ± 1.4 Ma 183.1 1.3 Ma), εHf(t) values TDM2 zircons mainly +5.8 +10.7 528 834 Ma, respectively, large variation range. The intrusive rocks (108 total) belonging T1T2G1G2 assemblage contained tonalites (T1), trondhjemites (T2), granodiorites (G1), granites (G2). These presented as subalkaline series plot alkali versus SiO2 (TAS diagram), medium-K calc-alkaline high-K on K2O diagram, metaluminous peraluminous characteristics an A/CNK A/NK diagram. shown MA (magnesium andesite) LMA (lower (or non) magnesium MgO which can be further divided higher-pressure TTG subtype (corresponding high-SiO2 adakite (HSA)) lower-pressure typical suprasubduction zone rocks). enriched light rare earth elements (LREEs) ion lithophile (LILEs) depleted heavy (HREEs) high-field-strength (HFSEs), corroborating environment. Regional correlations well indicate subduction environment during Jurassic; primary had presumably originated melting young hot oceanic crust eclogite amphibolite facies conditions. According spatial assemblages (T1T2G1 G1G2 G2), we speculate northeastern Heihe, Baishilazi, Xinghua westward Dajinshan adjacent ocean outer zone, whereas southwestward Sankuanggou, Chabaqi continent, forming inner zone. distribution sites zones southward subduction. Therefore, propose direct connection Ocean.