Petrogenesis and tectonic significance of the plagiogranites in the Zhaheba ophiolite, Eastern Junggar orogen, Xinjiang, China

• The Zhaheba albitites were formed by early stage albite accumulation.
• The albite granites were formed by residual magma consolidation.
• The plagiogranites were derived from the anatexis of metasomatised gabbro.
• The Zhaheba–Armantai ophiolites were formed at intra-oceanic backarc basin.

Plagiogranites (albitite and albite granite dikes/lenses) occur in the western section of the Zhaheba ophiolite, middle part of the Eastern Junggar orogen. The Zhaheba albitites (498.0 ± 5.8 Ma) and albite granites (494.6 ± 6.9 Ma) were roughly coeval and with distinct petrographic textures, i.e., cumulus texture for the albitites and granitic texture for albite granites. The Zhaheba plagiogranites are Na-enriched and LILE-depleted, resembling typical plagiogranites. Geochemical characteristics and cumulus texture of the albitites indicate that they may have been formed by early stage accumulation of albite, whereas the albite granites may have been the products of the residual magma consolidation. The εNd(t) values of the albitites and albite granites vary in the ranges of 7.2–7.7 and 6.4–7.3, respectively, whereas the εHf(t) values vary in the ranges of 11.5–17.9 and 9.8–13.9, respectively. Isotopic compositions and Zr/Hf ratios of the Zhaheba plagiogranites are similar to those of typical MORB, implying a genetic relationship with the oceanic crust. The low TiO2, Nb, Ta content, LREE enrichment and elevated (87Sr/86Sr)i values of the Zhaheba plagiogranites indicate that the rocks were likely derived from the anatexis of amphibolites, which were related to hydrothermal alteration of gabbros in intra-oceanic backarc basin. U–Pb geochronology of the Zhaheba plagiogranites indicates that it is more reasonable to connect the Zhaheba–Armantai and Karamay ophiolites to the Zaysan collision zone.

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