Heterogeneous mantle beneath the Neo-Tethys Ocean revealed by ultramafic rocks from the Xiugugabu Ophiolite in the Yarlung-Tsangpo Suture Zone, southwestern Tibet

摘要: Ultramafic rocks of the Yarlung-Tsangpo ophiolites (lherzolites, harzburgites, dunites and pyroxenites) have been interpreted as lithospheric mantle relics of the Cretaceous Neo-Tethys Ocean (NTO). Studying these rocks could provide key constraints on the NTO’s evolution and invaluable information on sub-ridge mantle heterogeneity. The Xiugugabu ophiolite crops out in the western segment of the Yarlung-Tsangpo Suture Zone (YTSZ) and is dominantly composed of mantle components with minor crustal material. Here we report a comprehensive field, petrological and geochemical study of the ultramafic rocks from this ophiolitic massif. The lherzolites and harzburgites are less refractory than the Xigaze ultramafic rocks in the middle part of the YTSZ. Petrology and simple models are consistent with 10–20% fractional melting from an anhydrous, depleted mantle source, within the spinel and garnet stability fields …