Re–Os isotope systematics of mantle xenoliths from South Korea: Evidence for complex growth and loss of lithospheric mantle beneath East Asia

We report Re–Os isotopic data for seventeen mantle xenoliths from the Jeju and Baekryeong Islands, Pyeongtaek, and Boeun, South Korea. All are spinel peridotites, hosted by late Tertiary to Quaternary (∼5.0 Ma to historic) alkali basalt flows and range in composition from depleted harzburgites to variably depleted lherzolites. All of the measured 187Os / 188Os and 187Re / 188Os ratios are subchondritic to chondritic (0.1155 to 0.1285 and 0.022 to 0.391, respectively), with the exception of two samples with 187Re / 188Os (> 0.6). Model Os TRD ages of ∼1.9 to 1.8 Ga for three strongly depleted harzburgites (Mg# = 90.6 to 91.2) indicate that Paleoproterozoic subcontinental lithospheric mantle (SCLM) is currently preserved beneath the Korean peninsula. The slopes of linear trends of 187Os / 188Os vs. Al2O3 are also consistent with this interpretation, although a lack of correlation between 187Re / 188Os and 187Os / 188Os indicates likely recent perturbations in Re concentrations, especially in the lherzolites. Collectively, the new data indicate that the age of the current SCLM beneath South Korea is considerably younger than the overlying Archean crust, suggesting possible removal and replacement of the Archean SCLM during the Proterozoic. This replacement event may be temporally coincident with widespread intracrustal reworking events that occurred in South Korea during the Paleoproterozoic (∼2.1 to 1.8 Ga). The results of this study and previous studies of other East Asian tectonic blocks provide strong evidence for the periodic construction and destruction of SCLM beneath East Asia during the Archean, Proterozoic, and Phanerozoic, and extend to the east the range of known complicated age structure of the current SCLM beneath East Asia.