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Combined U-Pb, hafnium and oxygen isotope analysis of zircons from meta-igneous rocks in the southern North China Craton reveal multiple events in the Late Mesoarchean-Early Neoarchean [查看] DunyiLiu、SimonA.Wilde、YushengWan、ShiyanWang、JohnW.Valley、NorikoKita、ChunyanDong、HangqiangXie、ChangxiuYang、YixinZhang、LinzhiGao

We report the results of a comprehensive isotopic investigation of zircons from metamorphosed tonalites and amphibolites from Lushan in the far south of the Trans-North China Orogen of the North China Craton that reveal the oldest rocks yet dated from the orogen. A detailed investigation of the internal structures of zircons, combined with targeted SIMS U–Pb and oxygen isotope analyses and ICP-MS Hf zircon analyses, has resulted in the discovery of previously unknown geological events in the North China Craton. Magmatic zircon from the tonalite and amphibolite was found to be essentially coeval with a small spread of ages from 2829±18Ma to 2832±11 Ma in the tonalites and from2838±35 Ma to 2845±23Ma in amphibolite. Hafnium isotope data suggest derivation of both tonalite and amphibolite from a depleted mantle source with minor crustal contamination. Oxygen isotope ratios in zircons range from 5.1 to 7.3‰ VSMOW, with high δ18O results recorded only from metamorphic domains. The earliest stage of metamorphic zircon growth, present in all four samples analyzed in this study, occurred between 2772±17/22 in the tonalites and 2776±20 and 2792±12 Ma in the amphibolites. A younger metamorphic event at 2638±61 in the tonalite and between 2671±13 and 2651±13 Ma in the amphibolites is recognized in zircons from three of the four samples investigated. This is the first time that metamorphic events at either of these times have been recorded in the North China Craton. Importantly, there is no evidence for the 1.8 Ga high-grade metamorphic event that is manifest in the northern and central parts of the Trans-North China Orogen.

SHRIMP U-Pb and CAMECA 1280 oxygen isotope results from ancient detrital zircons in the Caozhuang quartzite, Eastern Hebei, North China Craton Evidence for crustal reworking 3.8 Ga ago [查看] SIMONA.WILDE、JOHNW.VALLEY、NORIKOT.KITA、AARONJ.CAVOSIE、DUNYILIU

ABSTRACT. The Caozhuang quartzite, located in Eastern Hebei Province in the eastern part of the North China Craton, has long been known to contain the oldest detrital zircon population in China. A suite of 30 zircons with preliminary ages >3.7 Ga were selected for detailed SHRIMP U-Pb and CAMECA 1280 oxygen isotope analyses.SHRIMP U-Pb dating reveals that ages range from 3860 to 3135 Ma, the former being the oldest 207Pb/206Pb zircon age so far obtained from the North China Craton. Values of 18O range from 5.4 to 7.5 permil, similar to Archean igneous zircons worldwide, but the average value for the 30 zircons is 6.6 permil, which is 0.3 permil higher than suite averages for detrital zircons from the Jack Hills and Beartooth Mountains and nearly 1 permil higher than magmatic zircons from igneous rocks of the Superior Province and Barberton. These elevated values of 18O suggest reworking of a significant amount of juvenile crust, older than 3.8 Ga, that underwent a low temperature supracrustal history and was distributed throughout the source region in northeast China.

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