Geochronology and geochemistry of Neoarchean granitoids from the western Shandong Province, North China Craton, implications for crustal evolution and cratonization

Abstract

Granites are keys to the understanding of crustal stabilization and cratonization processes. Here we present an integrated study of the lithology, geochronology and geochemistry of late Neoarchean granites and associated TTGs (tonalite-trondhjemite-granodiorite) and migmatites from the western Shandong Province (WSP) of the North China Craton (NCC). The TTG xenoliths in the Lushan massive granite formed at 2529±7Ma. The Menglianggu and Yishan migmatite, containing 2.70–2.52Ga inherited zircons, defines regional anatectic event at 2512±6Ma. The Menglianggu, Lushan and Yishan granites yield 207Pb/206Pb ages ranging between 2517 and 2488Ma, which are indistinguishable from the regional metamorphic/anatectic events of the WSP.Based on the SiO2 contents and REE patterns, the late Neoarchean granites exposed in Wande, Sishui, Qixingtai and Menglianggu areas can be subdivided into three groups. Group 1 exhibits, low SiO2 (68.6–69.2wt%), high ΣREE (345.4–475.3ppm) contents, moderate negative Eu anomalies (0.55–0.73) and depletion in U, Nb, Ta and Sr contents. Group 2 is composed of most of the studied samples and show moderate SiO2 (70.1–75.7wt%) and ΣREE (135.8–357.1ppm) content with obvious negative Eu anomalies (0.33–0.58) (excluding an outlier sample TS1310) and pronounced depletions in Ba, Sr, Nb and Ta contents. Group 3 displays high SiO2 (74.9–76.3wt%) and low ΣREE (18.6–71.6ppm) abundance. They are characterized by lack of negative Eu and Sr anomalies. Geology and Geochemical comparisons suggest that the major part of the granitic magma originate from re-melting of TTG type rocks at low pressure. The negative U anomalies of Group 1 granite are inherited from the source which is different from the case of TTGs. The correlation of Sr vs. Ba and Rb suggests fractional crystallization of K-feldspar, plagioclase and minor hornblende in the precursor magmas of Group 2. These geochemical features are similar to those associated with crustal stabilization in other cratons. Our studies on the WSP also suggest that the coeval to slightly earlier regional anatexis is also an important process during cratonization.