Geothermal gradient of the upper mantle beneath Jeju Island, Korea: Evidence from mantle xenoliths |
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Authors: | Seong Hee Choi Yong-Joo Jwa Han Yeang Lee |
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Institution: | Department of Earth Science Education, Seoul National University, Seoul, 151-742, Korea (email:;),Department of Earth and Environmental Sciences, Gyeongsang National University, Jinju, 660-701, Korea and;Korea Institute of Geology, Mining, and Materials (KIGAM), Daejeon, 305-350, Korea |
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Abstract: | Abstract Ultramafic xenoliths found in alkali basalts from Jeju Island, Korea are mostly spinel lherzolites accompanied by subordinate amount of spinel harzburgites and pyroxenites. The combination of results from a two-pyroxene geothermometer and Ca-in-olivine geobarometer yields temperature–pressure (T–P) estimates for spinel peridotites that fall in experimentally determined spinel lherzolite field in CaO-Fe-MgO-Al2O3-SiO2-Cr2O3 (CFMASCr) system. These T–P data sets have been used to construct the Quaternary Jeju Island geotherm, which defines a locus from about 13 kbar at 880°C to 26 kbar at 1040°C. The geothermal gradient of Jeju Island is greater than that of the conventional conductive models, and may be as a result of a thermal perturbation by the heat input into the lithospheric mantle via the passage and emplacement of magma. Spinel–lherzolite is the main constituent rock-type of the lithospheric mantle beneath Jeju Island. Pyroxenites may be intercalated in peridotites at similar depth and temperature as re-equilibrated veins or lenses. |
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Keywords: | Jeju Island lithospheric mantle Quaternary geotherm spinel lherzolite |
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