Mantle magmatism, metamorphism and anatexis: evidence from geochemistry and zircon U–Pb-Hf isotopes of Paleoproterozoic S-type granites, Khondalite Belt of the North China Craton

Abstract

ABSTRACT S-type granites constitute an important component of the Paleoproterozoic Khondalite Belt in the North China Craton. Here we present results from petrography, geochemistry and isotope geochronology on the porphyritic garnet-bearing syenogranite and garnet-bearing monzogranite samples in the Jining-Liangcheng area. The geochemical characteristics of these samples indicate formation through partial anatexis of the khondalites, with heat and material input from mantle-derived magma. Geochemical similarities between the porphyritic garnet-bearing syenogranite, garnet-bearing monzogranite, and metapelitic gneiss suggest their broad affinity. Sensitive high-resolution ion microprobe zircon U–Pb dating revealed that the S-type granites formed at ca. 1.92–1.90 Ga and were subsequently metamorphosed at ca. 1.85 Ga. The ca. 1.92–1.91 Ga porphyritic garnet-bearing syenogranite shows zircon εHf(t) values of −1.94–+3.38 with two-stage Hf crustal model ages (TDM2) ages of ca. 2.42–2.59 Ga. The 1.91–1.90-Ga garnet-bearing monzogranites show zircon εHf(t) values ranging from −4.36 to +0.38, with TDM2 ranging from ca. 2.57 to ca. 2.82 Ga. The geochemical isotopic compositions suggest that the porphyritic garnet-bearing syenogranite and garnet-bearing monzogranite originated from the partial melting of pre-existing crust of heterogeneous compositions with the addition of mantle-derived material. On the basis of our results, combined with geological data on the Paleoproterozoic structural evolution of the Khondalite Belt, we assume that the timing of the metamorphism and anatexis in the Jining–Liangcheng area is correlated with a regional metamorphism and mantle-derived magmatism.