Mesoarchean to Paleoproterozoic crustal evolution of the Taihua Complex in the southern North China Craton

Abstract

The Taihua Complex is exposed mostly in the central-western part along the southern margin of the North China Craton (NCC). In this study, field geological, geochemical, LA-ICP-MS zircon U-Pb age dating and Lu-Hf isotopic analysis are applied to the orthorgneisses, felsic leucosomes, and granites of the Taihua Complex, in order to provide constraints on its crustal evolution from the Mesoarchean to Paleoproterozoic (ca. 2.9–1.8 Ga). The ca. 2.90–2.73 Ga magmatism was an important episode of contemporaneous crustal growth and crustal reworking. Among them, the ca. 2.90 Ga granodioritic enclaves have features similar to those of the Archean sanukitoids, and were generated by the direct partial melting of peridotitic mantle wedge in the subduction processes, representing the early continental nucleus. The ca. 2.84 Ga high Mg# TTGs were derived from the partial melting of subducted oceanic crust after interaction with mantle wedge, whereas the ca. 2.82–2.77 Ga low Mg# TTGs were originated from the partial melting of underplated basaltic crust, pointing to a series of continuous arc magmatic activities. The formation of the ca. 2.75–2.73 Ga crust-derived granites and felsic leucosomes in association with the contemporaneous metamorphism indicate the presence of a crustal anatexis, which probably was the result of an important magmatic underplating event. The magmatism between 2.9 Ga and 2.73 Ga indicates that the increased crust-mantle interaction and crustal differentiation stimulated the crust in the Taihua Complex to become more matural. The ca. 2.57–2.43 Ga magmatism represents another prominent magmatism in the Taihua Complex. The TTG gneisses and dioritic gneisses aged at ca. 2.57–2.50 Ga were derived from partial melting of the hydrated basalts under eclogite to garnet amphibolite facies conditions with interaction between initial melts and mantle wedge, indicating that incessant subduction led to the amalgamation of micro-blocks. The intrusion of granitic rocks, felsic leucosomes, TTG-like gneisses accompanied by metamorphism during ca. 2.50–2.43 Ga indicate that a dominant crustal anatexis event occurred in association with the cratonic stabilization processes. The ca. 2.36–2.24 Ga magmatism was also characterized by reworking of the basement rocks, which are represented by the intrusion of calc-alkaline monzogneisses, A-type granitic gneisses and mafic dykes. This scenario was coeval with the formation of volcanic-sedimentary sequences, indicating the presence of an extension event in the Taihua Complex. The ca. 1.96–1.85 Ga tectono-thermal event represented the last phase of compressional deformation and consequent metamorphism, leading to reworking of the pre-existed basement rocks. This event formed a WNW-ESE trending metamorphic belt that extends over 1000 km along the southern margin of the NCC and was well concordant with the world-wide orogeny associated with the amalgamation of Nuna supercontinent. Subsequently, widespread A-type granites, mafic dykes and volcanic rocks aged of ca. 1.84–1.74 Ga formed, marking the final consolidation of the crystalline basement at the Taihua Complex. Since then, the southern NCC became stable and entered into the stage of development of platform.