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

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• 作者：Dunyi Liu ; Simon A. Wilde ; Yusheng Wan ; Shiyan Wang ; John W. Valley ; Noriko Kita ; Chunyan Dong ; Hangqiang Xie ; Changxiu Yang ; Yixin Zhang ; Linzhi Gao
• 关键词：Tonalite ; Supracrustal rocks ; Mesoarchean ; SHRIMP dating ; Hf isotopes ; Oxygen isotopes ; North China Craton
• 刊名：Chemical Geology
• 出版年：2009
• 出版时间：15 April 2009
• 年：2009
• 卷：261
• 期：1-2
• 页码：140-154
• 全文大小：2335 K

文摘

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 ± 18 Ma to 2832 ± 11 Ma in the tonalites and from 2838 ± 35 Ma to 2845 ± 23 Ma 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.