New insights into Neoarchean-Paleoproterozoic crustal evolution in the North China Craton: Evidence from zircon U-Pb geochronology, Lu-Hf isotopes and geochemistry of TTGs and greenstones from the Luxi Terrane

摘要

Tonalite-trondhjemite-granodiorite (TTG) suites constitute dominant components of Precambrian continental crust and provide important insights into the crustal evolution history of the early Earth. Here we investigate a suite of TTGs and associated greenstones from the Luxi Terrane in the south-eastern part of the North China Craton (NCC). We present data from petrology, geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes to characterize these rocks and understand their genesis. Mineral assemblage in the greenstones and TTGs suggests that the rocks have undergone amphibolite-facies metamorphism with regression under greenschist-facies. Zircon U-Pb data from the magmatic grains yield upper intercept ages of 2753 +/- 37 and 2582 +/- 40 Ma for greenstone, 2552 +/- 13 Ma for TTG gneiss and 2476 +/- 18 Ma for tonalite, and weighted mean Pb-207/Pb-206 age of 2507 +/- 22 Ma for granodiorite. Lu-Hf isotope systematics show et epsilon(Hf)(t) values ranging from -2.13 to 7.29 and crustal model ages (T-DM(C)) in the range of 2603-3125 Ma for the TTGs, whereas the epsilon(H)(t) values are up to 8.53 with T-DM(C) ages of 2644-3006 Ma for the greenstone. The results suggest that the protolith for the greenstone was derived from a Meso- to Neoarchean mantle contaminated by the crust source, whereas the TTGs were mostly sourced from juvenile crustal sources with reworking of older basement. The geochemical features of greenstone are similar to island arc basalt, with low Na2O, K2O and TiO2, low total rare earth elements (REEs) values, relative enrichment in light REEs and depletion in heavy REEs absence of obvious Ce anomaly, and negative Nb, Ta and Ti anomalies. The TTGs show similar features, except for the high K2O content and moderate total REEs values. We propose that the greenstone likely represent a part of the early and initial crustal growth at ca. 2750-2600 Ma, and the TTGs were generated subsequently at ca. 2550-2450 Ma. Our results are consistent with the previou