Geochemistry of ~2.5 Ga granitoids at the northern margin of the Yinshan Block: implications for the crustal evolution of the North China Craton

Abstract

In order to further constrain the crustal development and tectonic evolution of the North China Craton (NCC) during late Neoarchean to early Paleoproterozoic, we performed petrological and geochemical analyses on forty-six granitoid samples from the northern margin of the craton at Siziwangqi in central Inner Mongolia. The granitoids commonly consist of a tonalite-trondhjemite-granodiorite (TTG) suite and alkali feldspar (rich in potassium) granites. The geochemistry and isotopic characteristics suggest that they formed in a subduction-related arc setting. An Andean-type magmatic arc model is proposed to explain several unique geochemical features of the Siziwangqi granitoids, notably that the rocks are metaluminous to peraluminous and belong to the calc-alkaline (TTG) and subalkaline to alkaline (alkali feldspar granite) series. The TTG granitoids are characterized by light LREE enrichment, a weak positive Eu anomaly, and flat heavy HREE profiles. The alkali granite is also enriched in the LREE but has a strong positive chondrite-normalized Eu anomaly and displays weak HREE enrichment. Petrogenetic studies reveal that most samples are of I-type granitoids. The data further suggest that the subduction-induced magmatism and slab rollback processes may have triggered reworking of both juvenile arc crust and minor older continental crust material along the north margin of Yinshan Block, leading to the formation of granitoids from S- to I-type in the study area. Overall, the NCC experienced a tectonic regime that changed from compressional to extensional during the early Paleoproterozoic at ∼2.4 Ga, after the ca. 2.5 Ga cratonization event.