Neoarchean crustal evolution in western Shandong Province of the North China Craton: The role of 2.7-2.6 Ga magmatism

The Neoarchean era is an important period for the formation of continental crust in the early earth. The North China Craton (NCC) records magmatism during 2.8-2.7 Ga and 2.6-2.5 Ga with the latter more extensive. However, the similar to 2.7 Ga rock assemblages are significantly different from those of the similar to 2.5 Ga rocks. Based on detailed field investigation, we present results of zircon geochronology by using SHRIMP and LA-ICP-MS techniques on the Shanggang pluton in the central belt of the western Shandong Province (WSP). The Shanggang pluton is composed of 2.71-2.69 Ga strongly deformed tonalite on the eastern and northern margins with the central part occupied by younger (2.67-2.65 Ga and 2.63-2.61 Ga) trondhjemite. Most zircon grains with apparent Pb-207/Pb-206 ages of 2.67-2.66 Ga in our samples have low Th/U ratios (0.05-0.20) resulted from low to moderate Th contents of 10-130 ppm and relatively higher U contents of 100-3000 ppm, consistent with those of anatectic zircons. Some of grains carry similar to 2.7 Ga inherited cores. Our study reveals that the crustal re-working event at 2.67-2.66 Ga might have been more widespread than currently known, although the 2.67-2.66 Ga zircons have positive epsilon(Hf)(t) values close to that of coeval depleted mantle (Wan et al., 2014). Together with data from previous studies, it is notable that more trondhjemite and even some granite were generated during 2.67-2.60 Ga. Relative to the older TTG suites (2.72-2.69 Ga), the younger ones (2.67-2.60 Ga) are dominated by trondhjemite. The compositional variations of TTG suites through the early to middle Neoarchean suggest that the 2.67-2.60 Ga magmatic and anatectic events should be related to the compositional differentiation of the Archean continental crust of the WSP. (C) 2016 Elsevier B.V. All rights reserved.