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1 Department of Earth Sciences, University of Windsor, Windsor, Ontario N9B 3P4, Canada
2 Department of Geological Sciences, Rutgers University, New Brunswick, New Jersey 08903, USA
3 Institut für Mineralogie, Universität Münster, Corrensstrasse 24, 48149 Münster, Germany, and Mineralogisch-Petrologisches Institut, Universität Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany
4 Department of Geological Sciences, Rutgers University, New Brunswick, New Jersey 08903, USA
5 Department of Earth and Atmospheric Sciences, Saint Louis University, St. Louis, Missouri 63103, USA
6 Department of Geology, Peking University, Beijing 100871, China
7 Department of Earth Sciences, University of Windsor, Windsor, Ontario N9B 3P4, Canada, and Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ontario N9B 3P4, Canada
8 Department of Geological Sciences, Rutgers University, New Brunswick, New Jersey 08903, USA
The 2.55–2.50 Ga Zunhua and Wutaishan belts within the central orogenic belt of the North China craton contain variably metamorphosed and deformed tectonic blocks of peridotites and amphibolites that occur in a sheared metasedimentary matrix. In the Zunhua belt, dunites comprise podiform chromitites with high and uniform Cr-numbers (88). Peridotites and associated picritic amphibolites are characterized by light rare earth element (LREE)–enriched patterns and negative high field strength element (HFSE: Nb, Zr, and Ti) anomalies. They have positive initial 
Hf values (+7.9 to +10.4), which are consistent with an extremely depleted mantle composition. Mass-balance calculations indicate that the composition of the 2.55 Ga mantle beneath the Zunhua belt was enriched in SiO2 and FeOT compared to modern abyssal peridotites. These geochemical signatures are consistent with a suprasubduction zone geodynamic setting. Metasomatism of the subarc mantle by slab-derived hydrous melts and/or fluids at ca. 2.55 Ga is likely to have been the cause of the subduction zone geochemical signatures in peridotites of the Zunhua belt.
In the Wutaishan belt, chromitite-hosting harzburgites and dunites display U-shaped rare earth element (REE) patterns and have high Mg-numbers (91.1–94.5). These geochemical characteristics are similar to those of Phanerozoic forearc peridotites. The dunites might have formed by dissolution of orthopyroxene in reactive melt channels, similar to those in modern ophiolites. However, they differ in detail, and they might be residues of Archean komatiites. Following the initiation of an intra-oceanic subduction zone, they were trapped as a forearc mantle wedge between the subducting slab and magmatic arc. Slab-derived hydrous melts infiltrating through the mantle wedge metasomatized the depleted mantle residue, resulting in U-shaped rare earth element (REE) patterns.
Key Words: Archean • peridotite • suprasubduction • picrite • spinel • trace element • North China craton
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