Oxygen Isotopic Ratios for Ultramafic Xenoliths from the Korean Peninsula

Abstract

This study examined the geochemical characteristics, equilibrium temperature and pressure conditions, and oxygen isotopic ratios of mantle xenoliths from the various geological sites of the Korean peninsula. The results are as follows: (1) The ultramafic xenoliths from the Korean peninsula mainly consist of typical high magnesium olivine (MgO : 49.12-50.95 wt.%, Mg value: 90.1-92.2), corresponding to worldwide Cenozoic ultramafic xenoliths in chemical compositions. (2) The pressure-temperature conditions of ultramafic xenoliths in the Korean peninsula are from 854 to 1016℃ and 4.6 to 24.4 kbar. (3) The oxygen isotopic ratios (δ18O) for olivines in ultramafic xenoliths range from 5.06 to 5.51, which are relatively uniform oxygen isotopic values and overlapped by the values of N-MORB and upper mantle peridotite (δ18O: 5.2±0.2). However, olivines of the ultramafic xenoliths from the Baegdusan and Chejudo have a relatively wide δ18O values ranging from 5.07 to 5.51 and 5.07 to 5.45, respectively. Based on the results, this study suggests that the high δ18O signature of the Baegdusan xenoliths give a hint that ~5% of the oxygen in typical EM2 sources originally derived from recycled sediments.