Petrological evidence of an anhydrous carbonatitic peridotite source for the Xiaogulihe ultrapotassic volcanic rocks, northeastern China

This study presents new olivine and whole-rock geochemical data for the Xiaogulihe ultrapotassic volcanic rocks of northeastern China. These data provide insights into the petrogenesis of the rocks of the Erkeshan–Wudalianchi–Keluo–Xiaogulihe (EWKX) potassic–ultrapotassic volcanic belt. The petrography and whole-rock geochemical compositions of the Xiaogulihe volcanic rocks are indicative of formation from magmas that primarily underwent olivine + clinopyroxene fractionation with insignificant crustal contamination and post-magmatic alteration. The high-Fo (87–90) olivine within the Xiaogulihe volcanic rocks has high Ni (2050–3800 ppm) and Mn (1190–1750 ppm) contents, high 10000Zn/Fe values (12–15), low Ca (1310–1800 ppm) contents, and low Fe/Mn (56–72) and Mn/Zn (10–14) values. Their high Mn contents and low Fe/Mn values together with their low FC3MS (<0.65; FC3MS = FeO/CaO – 3MgO/SiO2), low FCKANTMS (<0.37; FCKANTMS = ln(FeO/CaO) − 0.08ln(K2O/Al2O3) − 0.052ln(TiO2/Na2O) − 0.036ln(Na2O/K2O) ln(Na2O/TiO2) − 0.062(ln(MgO/SiO2))3–0.641(ln(MgO/SiO2))2–1.871ln(MgO/SiO2) − 1.473) and low CaO–Al2O3–Fe2O3Total values are indicative of derivation from a mantle source containing refractory peridotite. The Xiaogulihe olivines have slightly higher Zn/Fe and lower Mn/Zn values than expected for olivines formed from typical peridotite-derived melts, suggesting that the source for these lavas was previously metasomatized by interaction with Zn-rich sedimentary carbonatitic melts. The low magmatic water contents of the Xiaogulihe lavas (<1 wt% determined by use of the Ca-in-olivine geohygrometer) is also indicative of derivation from an anhydrous mantle source. These data suggest that the Xiaogulihe ultrapotassic lavas represent partial melts of anhydrous refractory subcontinental lithospheric mantle peridotite. The K-rich nature of these volcanic rocks is indicative of derivation from the K-rich reservoir of the mantle, which is closely associated with carbonatitic metasomatism, indicating the role of this process in the generation of the K-rich EWKX volcanics.