Relationship of the Tarim Craton to the Central Asian Orogenic Belt: insights from Devonian intrusions in the northern margin of Tarim Craton, China

The boundary and relation of the Tarim Craton to the Central Asian Orogenic Belt (CAOB) and its role in the formation history of the CAOB remain controversial. This article presents ages and Hf-in-zircon isotopic and geochemical results for gabbroic, dioritic, and granitic plutons from the northern margin of Tarim Craton (NMTC), and discusses their petrogenesis and tectonic regimes as well as the boundary between the CAOB and the Tarim Craton. These plutons yield zircon ages of 424–385 Ma. In the Quruqtagh zone south of the Xinger Fault, the gabbroic pluton shows enrichment in LREEs and LILEs, depletion in HFSEs and positive εHf(t) values (+4.0 to +11.4), suggesting that parental magmas of gabbros were likely derived by partial melting of a depleted mantle wedge previously metasomatized by slab-derived aqueous fluids. In the Hulashan Zone north of the Xinger Fault, the studied rocks include one dioritic pluton and three granitic plutons. The geochemical characteristics and petrogenesis of the dioritic pluton are similar to those of the studied gabbroic with positive εHf(t) values (+3.0 to +9.4). The three granitic plutons display relative depletion in HFSEs and enrichment in LILEs. Their variable εHf(t) values range from −2.1 to +8.9, with TDM2 ages of 858–1503 Ma, suggesting complex crustal sources with different proportions of juvenile and ancient materials. This article confirms and evidences an Andean-style active continental margin of the Tarim Craton due to southward subduction of the South Tianshan Ocean. Furthermore, our Hf isotopic data, together with regional data from the literature, show that the Hulashan zone to the north to the Xinger Fault has younger continental materials in deep than these of NMTC south of the fault, and is similar to microcontinental fragments in the CAOB. This suggests that the Xinger fault may be the boundary between the Tarim Craton and Tianshan orogen.