Petrological evidence for magma recharge and mixing beneath the Ma'anshan monogenetic volcano of Xiaogulihe in Northeast China

Geochemical compositions of rocks from monogenetic volcanoes in intraplate settings are commonly used to constrain their mantle source and melting processes; however, the subsequent magmatic evolution of such small-volume volcanic systems is commonly ignored. Here we present petrographic observations, mineral chemistry, whole-rock major and trace element data, and thermodynamic modeling for Quaternary ultrapotassic rocks from the Ma'anshan monogenetic volcano of Xiaogulihe in Northeast China. We use these data to evaluate the crystallization conditions and recharge and mixing processes that the magmas have experienced within the crust. The Ma'anshan volcanic products are predominantly phonotephrite and tephriphonolite. These rocks have small variations in geochemical composition with moderate SiO2 (47.29–49.4 wt%), high total alkali contents (K2O + Na2O = 9.85–11.87 wt%), and high K2O/Na2O ratios (3.18–4.21). Two types of assemblages were identified in these ultrapotassic rocks: Type-1 antecrysts (olivine and leucite) and hybrid crystals (clinopyroxene, formed by incongruent replacement of antecrysts) and type-2 autocrysts (olivine and leucite). For the type-2, normally zoned olivines, Ni decreases and Mn increases more rapidly with decreasing %Fo than for oceanic basalts, which can be explained by abundant olivine and leucite fractionation in strongly alkaline melts at shallow crustal levels (