A ca.2.1 Ga Andean-type margin built on metasomatized lithosphere in the northern Yangtze craton, China: Evidence from high-Mg basalts and andesites

We report for the first time the presence of a suite of Paleoproterozoic (2.12 Ga) metamorphosed high-Mg basalts and andesites in the Huangling dome, northern Yangtze craton, China, which provide new insights into crustal growth processes in the craton during the Paleoproterozoic era. The high-Mg basalts and andesites are mineralogically and texturally amphibolites and quartz-bearing amphibolites, respectively, and occur as deformed layers within the metasedimentary rocks of the Shuiyuesi Group in the northern Huangling dome. We present new field and petrographic observations, zircon U-Pb ages, in situ zircon Hf isotope and whole-rock major and trace element and Nd isotope data, to assess the petrogenetic origin and geodynamic setting of these high-Mg rocks. The igneous zircons from the andesites yield a weighted age of ca. 2.12 Ga that is interpreted to be the formation age of the magmatic protolith. The basalts are characterized by moderate SiO2 (49 wt.%), low TiO2 (0.63-0.65 wt.%), high MgO (13.7-14.6 wt.%) and high Mg-numbers (58-59). The andesites have 53-60 wt.% SiO2, 0.45-0.50 wt.% TiO2 and 6.6-9.5 wt.% MgO contents, yielding high Mg-numbers (63-76). Both the basalts and andesites are enriched in LILE and LREE, but depleted in Nb, Ta, and HREE. Zircons in the andesites have epsilon(Hf)(t) values between -0.2 and +3.3 and corresponding Hf isotopic model age (T-DM1) of 2.4 Ga, reflecting various degrees of crustal input. They have negative epsilon(Nd)(t) values, ranging from -4.4 to -2.7. Geochemical characteristics of the basalts and andesites indicate that they are equivalent to high-Mg basalts and andesites, respectively, occurring in Phanerozoic suprasubduction zones. The Nd and Hf isotope compositions of the high-Mg rocks suggest that they were derived from partial melting of subarc lithospheric mantle above a subducting oceanic slab. The formation age and general geochemical characteristics of the high-Mg rocks reveal the presence of a Paleoproterozoic (2.1-2.2 Ga) Andean-type continental margin developed on metasomatized litho spheric mantle in the northern Huangling dome. The geochemical and geochronological data presented in this study provide important insights into Paleoproterozoic evolution of the Yangtze craton. (C) 2017 Elsevier B.V. All rights reserved.