Geochemistry of Quaternary basaltic lavas from the Nuomin volcanic field, Inner Mongolia: Implications for the origin of potassic volcanic rocks in Northeastern China

Abstract

The Nuomin volcanic field (NM for short) in northern Greater Xing'An Mountains is dominated by Quaternary monogenetic eruptions, forming lava flows covering an area of about 600km2. The lavas range from tephrite and basanite to trachybasalts, with high K2O contents between 2.6wt.% and 4.3wt.%, and K2O/Na2O between 0.78 and 1.08. These NM lavas are generally magnesian (Mg# between 0.59 and 0.78) and may contain useful information on the origin of potassic magmas in NE China. The NM lavas are characterized by relatively high (La/Yb)N (21.6–41.9) and enrichments in large ion lithophile elements (LILEs), but low in high field strength element (HSFE) concentrations. The NM lavas have negative εΝd(−0.8–−3.0), 87Sr/86Sr between 0.704661 and 0.704880, 206Pb/204Pb between 17.0 and 17.2, 207Pb/204Pb between 15.41 and 15.43, and 208Pb/204Pb between 37.0 and 37.3. Their trace element spider diagram and chondrite-normalized rare earth element (REE) diagram are similar to those of Wudalianchi lavas, but are different from the Halaha–Chaoer river lavas in central Greater Xing'An Mountains. Their REE characteristics indicate that the NM lavas originate from garnet stability field. Based on petrological and geochemical data, we propose that the delamination of K-rich lithosphere mantle trigger the Quaternary potassic volcanism in Northeastern China.