Water content of ultrapotassic basalts: a case study from Xiaogulihe Cenozoic basalts, NE China

• 1、CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Science, University of Science and Technology of China, Hefei, 230026, China

Abstract：Water is an important factor of magmatic process, to determine the water content of mantle source of the Xiaoguolihe ultrapotassic basatls, this paper measured the water content in clinopyroxene (cpx) phenocrysts by Fourier transform infrared spectrometry (FTIR) and calculated H2O contents of equilibrated melts using the partition coefficient of H2O between cpx and basaltic melt. The calculated H2O content of the "primary" magmas is low (0.38±0.11 wt%), falling in the range of mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs). The low water content of "primary" melt show that the temperature of melting in the mantle source may high, which is consistent with the high melting temperature of Wudalianchi potassic basalt. Meanwhile, the low water content of "primary" melt also show that the K-rich component is unlikely to come from the hydrous mineral phlogopite, and may from the dehydrated sediment (e.g., dry K-hollandite).

Keywords： Geochemistry clinopyroxene phenocryst Ultrapotassic basalts Water FTIR