Mg–Sr–Nd Isotopic Insights into Petrogenesis of the Xiarihamu Mafic–Ultramafic Intrusion, Northern Tibetan Plateau, China

Abstract To characterize the integrated magmatic processes for magma plumbing systems from mantle sources to chambers, we present Mg–Sr–Nd isotopic data a representative mafic–ultramafic intrusion in Xiarihamu, northern Tibetan Plateau, China. The hosts largest Ni–Cu sulfide deposit an orogenic setting world and is composed predominantly of harzburgite, orthopyroxenite, websterite, gabbronorite. cumulate harzburgites have relatively low ?26Mg orthopyroxene (–0·49 –0·34‰) moderately high (87Sr/86Sr)i positive ?Nd(t) values (0·7067–0·7080 +0·4 +1·8, respectively). Most orthopyroxenites, websterites, gabbronorites slightly higher (–0·34 –0·21‰) lower (0·7087–0·7118 –4·0 –1·4, respectively) than harzburgites. On other hand, marginal facies (i.e. few centimeters meters contact between country rocks schist, gneiss, marble) including websterite gabbronorite are marked by (–0·44 –0·33‰) extremely negative (0·7127–0·7172 –5·4 –4·8, ?26Mg, (87Sr/86Sr)i, best interpreted inheritance source, which was previously metasomatized subducted Mg-rich carbonates. Given fact that solidus carbonated significantly volatile-free mantle, metasomatism carbonates may be critical generate voluminous mafic magmas form giant Xiarihamu deposits convergent settings worldwide. most were produced extensive contamination isotopically heavy crustal deep-seated chamber. facies, compared with websterites gabbronorites, governed assimilation local low-?26Mg (e.g. gneiss at chamber during emplacement. These observations indicate cumulates away can preserve their primitive isotope signatures inherited deep even sources, negligible ascent findings first time, our knowledge, provide observational evidence single system source sheds light on petrogenesis mineralization intrusions.