This study presents the petrology, geochronology, and geochemistry of two Carboniferous granites in the Jalaid Banner area, middle Great Xing' an Range, NE China, with the aim of resolving their petrogenesis and tectonic background, and the history of accretionary orogenesis. The monzogranite intrusions were formed during the Early Carboniferous (334Ma) and Late Carboniferous (316Ma). The Early Carboniferous monzogranite has high SiO2 and Al2O3 contents, and yields aluminum saturation index (ASI) values of > 1. 1 , indicating a strongly peraluminous S-type granite. It shows low Rb/Ba and Rb/Sr ratios that indicate a clay-poor source (e. g. , greywacke) provided the bulk of the material to the primitive magma. The compositional fields of experimental melts derived from dehydration melting of various bulk compositions show that the magmatic source was derived mainly from the partial melting of metasedimentary rocks. This monzogranite yields strongly positive epsilon(Hf) (t) values and young two-stage (t(DM2)) Hf model ages of 1048Ma to 637Ma, indicating that the primitive magma formed from partial melting of relatively young lower-crust material. A small number of negative epsilon(Hf) (t) values and relatively old two-stage (t(DM2)) Hf model ages (1863 similar to 1268 Ma) indicate a minor component of Precambrian crustal material in the primitive magma. Zircon saturation temperatures correspond to magmatic crystallization temperatures of 850 similar to 800 degrees C. The Late Carboniferous monzogranite shows enrichment in light rare earth elements and large ion lithophile elements (e. g. , Rb, Ba, U, and K) , depletion in heavy rare earth elements, and has the geochemical features of unfractionated I-type granite. The primary magma was derived from partial melting of metabasalt rocks in the middle to lower crust at pressures above those of the garnet stability field (<10kb). The positive epsilon(Hf) (t) values (2. 1 similar to 8. 9) and young two-stage (t(DM2)) Hf model ages (1094 similar to 701Ma) imply a contribution by younger lower-crust materials to the formation of the primitive magma. Mineral fractionation is inferred to have been relatively weak during the evolution of the magma, and the partial melting that produced the primitive magma occurred under H2O-unsaturated conditions. The Early Carboniferous monzogranite formed in a post-collisional tectonic setting, indicating that the collision between Xing' an and Songnen blocks began prior to the middle Early Carboniferous (ca. 334Ma). The formation of the Late Carboniferous monzogranite was closely related to a post-collisional event that involved the tectonic rearrangement of accreted blocks during a period of waning compressional stress. This led to the final stabilization of the collision-related orogenic belt comprising the Xing' an and Songnen blocks, which typically occurs during the later post-collisional stage after early syn-collisional thrusting and folding. The eastern segment of the Central Asian Orogenic Belt records remarkable crustal accretion events during the Neo-proterozoic to Cambrian and the Late Paleozoic. Crustal accretion occurs via both horizontal and vertical accretion. In the present case, a two-stage model of continental growth is proposed, whereby mantle-derived mafic or ultramafic magmas intruded the lower crust to form the basic basaltic rocks, followed by the melting of these basaltic rocks to form the felsic rocks that intruded the upper crust. Break-off of the pre-subduction lithosphere or delamination of the lower crust led to the upwelling of asthenospheric-mantle-derived material that played an important role in orogenic accretion, as it provided heat for partial melting and contributed to continental accretion.
