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The major Precambrian crustal growth in the North China Craton (NCC) has been thought to have occurred at ∼2.5 Ga. Here we present secondary ion mass spectroscopy (SIMS) and laser ablation-inductively coupled mass spectrometry (LA-ICP-MS) zircon U-Pb ages and Hf isotope compositions from dioritic and tonalite-trondhjemite-granodiorite (TTG) gneisses of the Neoarchean-Paleoproterozoic metamorphic terrane in the central NCC. Zircons from the trondhjemitic samples yield emplacement ages at 2,702±7 and 2,722±9 Ma. Those from the dioritic gneiss yield an age of 2,704±14 Ma. The TTG gneisses are characterized by a Na-rich and K-poor (Na/K ratiosp2.7, 2.6) nature; strongly fractionated rare earth element patterns ([La/Yb] p35, 20); high Sr (418‰, 318‰) and Sr/Y (78, 49); low Y N (5.4‰, 6.4‰) and YbN (3.0, 3.6); and low MgO (0.89%, 1.10%), Mg# (47, 42), Cr (39‰, 20‰), and Ni (11‰, 8‰), Nb/ Ta (16, 12), which suggests that magmas were derived from the partial melting of a flatly subducted oceanic slab. The dioritic gneiss shows higher MgO (3.17%), Mg# (50), Cr (44‰), and Ni (40‰) and lower Sr/Y (22) and (La/Yb)N (8) ratios, which suggests contamination with mantle peridotite. All zircon grains from these Neoarchean gneisses yield high positive εHf (t) values that range from ε3.5 to ε7.7 and Hf model ages between 2.70 and 2.85 Ga. We propose that the widespread ∼2.5-Ga plutonic event found elsewhere in the NCC may represent a major reworking (melting) event, whereas the ∼2.7-Ga magmatism likely represents the main crustal growth of the NCC, comparable to those of other cratons worldwide [ABSTRACT FROM AUTHOR]

Late Mesozoic lithospheric extension in NE Asia resulted in the development of a large extensional province and widespread formation of volcanosedimentary basins. Songliao basin is the biggest in that region, situated between the Siberian and Sino-Korean (North China) cratons. The Songliao basin contains voluminous volcanic rocks as a major part of the basin fill. Volcanic successions form a significant but unexposed part of the late Mesozoic magmatic province in NE China. Here we report zircon U-Pb ages and geochemical data for felsic volcanic rocks from the Songliao basin. Zircon populations of two types of rhyolites with distinct I- and A-type affinities, analyzed by laser ablation inductively coupled plasma mass spectrometry, yielded similar U-Pb ages of 114 ± 2 and 113 ± 2 Ma, respectively. Whole-rock Nd and zircon Hf isotope data of the felsic rocks indicate an origin from newly formed crustal protoliths. The I-type dacites and rhyolites show geochemical signatures with subduction-related affinity, indicating generation by partial melting of juvenile crust that originated from melting of subduction-modified mantle sources, whereas the A-type rhyolites have higher heavy rare earth element and high field strength element concentrations and lower Ba/Nd ratios that are interpreted as evidence for melting of I-type felsic lower crustal sources in an intraplate tectonic environment. Typical geochemical compositions of A-type rhyolites indicate anorthite-rich plagioclase as a residual magmatic phase and imply melting at shallow crustal levels. The A-type felsic rocks were generated during a period of maximum lithospheric extension below eastern China around 110 Ma, and this thinning process was probably related to the retreat of the Paleo-Pacific trench. [ABSTRACT FROM AUTHOR]

The Edong-Jiurui district is located more than 1000 km from the current Pacific subduction zone. It is part of the well-known middle and lower Yangtze River Cu-Fe-Au belt in central eastern China. Cu mineralization in this area is spatially and temporally associated with Late Mesozoic magmatic rocks. These rocks exhibit geochemical features of adakites, but their origin is not yet fully understood. To explore the relationship between Cu mineralization and Mesozoic magmatism, we report geochemical, Sr-Nd-Pb isotopic, and zircon U-Pb age data from adakitic rocks in the Edong-Jiurui area. Zircon U-Pb ages point to a protracted period of magmatic activity from 151 to 139 Ma. This time span coincides with the Cu mineralization (146-137 Ma) in the middle and lower Yangtze River belt. Adakitic features of the rocks are displayed by high contents of SiO2, Al2 O3, Na2O, and Sr; enrichment of light rare earth elements (REEs) and large-ion lithophile elements; depletion of heavy REEs; positive Sr and negative Nb, Ta, and Ti anomalies; and high Sr/Y and La/Yb ratios. We favor a model of melt segregation from a plagioclase-free and garnetbearing residue. Compared to non-Cu-bearing Mesozoic adakitic rocks in the Dabie terrane, adakitic rocks in the Edong-Jiurui area have higher initial εNd values (-3.4 to -6.3), Pb isotopic ratios, and Th contents and lower Pb/Ce values. Altogether, these features indicate that the melts were probably derived from subducted ocean mixed with marine sediment. [ABSTRACT FROM AUTHOR]