Petrogenesis of the Neoarchean granitoids and crustal oxidation states in the Western Shandong Province, North China Craton

摘要

Na-rich and K-rich granitoid rocks contain geological signatures that are crucial for understanding the global evolution and oxidation states of the Archean crust. Here we present an integrated investigation of the lithology, geochronology, and geochemistry of Neoarchean plutonic granitoid gneisses and supracrustal rocks from Xintai to Feixian within the Western Shandong Province (WSP) granite-greenstone belt of the North China Craton (NCC). Six main lithological assemblages are identified within the WSP granite-greenstone belt: (1) The similar to 2.69-2.68 Ga tonalite-trondhjemite-granodiorite (TTG) gneisses, which were derived from the partial melting of low-K mafic rocks at lower crust, have low MgO contents (0.68-2.11 wt%) and high (La/Yb)(N) ratios (16.7-92). (2) The similar to 2.53 Ga granodioritic gneisses exhibit a low MgO content (0.87-1.91 wt%) but high K2O content (3.06-4.66 wt%), their magma originated from the partial melting of high-K mafic rocks. (3) The similar to 2.54-2.49 Ga monzogranitic gneisses show the highest SiO2 content (71.67-75.26 wt%), and their magma was formed from the partial melting of metagreywackes. (4) The similar to 2.56-2.52 Ga TTG gneisses also have low MgO content (1.42-1.69 wt%) and relatively low (La/Yb)(N) ratios (17.1-23); their magma was produced by the partial melting of low-K mafic rocks at lower crustal levels. (5) The similar to 2.53-2.52 Ga quartz syenites have the highest alkali content (9.66-11.23 wt%) but relatively low MgO content (0.71-1.50 wt%), and their magma was generated by the partial melting of juvenile basaltic rocks associated with recycled sediments. (6) An similar to 2.73 Ga xenolith of plagioclase amphibolite is characterized by high positive epsilon Hf(t(2)) values from + 5.2 to + 8.8, and fractionated chondrite-normalized REE patterns, indicating it may have been derived from a depleted mantle source enriched either by the addition of melt or by fluid metasomatism.