Geochemical and Sr-Nd-Pb-Mg isotopic constraints on the petrogenesis and mantle source of volcanic rocks from Jeju Island, South Korea
Abstract
Jeju Island is an intraplate volcanic island situated 90 km south of the Korean Peninsula. Volcanic rocks on Jeju Island are predominantly alkaline suites (basalt to trachyte) with subordinate intercalated tholeiitic (TH) basalts. The alkaline suites can be subdivided into high-Al alkaline (HAA) and low-Al alkaline (LAA) suites. In order to better understand the petrogenesis and mantle source characteristics of the three suites, we determined major- and trace-element concentrations, and Sr-Nd-Pb-Mg isotopic compositions for sixty samples from 4 boreholes and 9 outcrops. The whole-rock 40Ar/39Ar ages range from ca. 968 to 24 Ka. The HAA suites formed slightly earlier than other suites, but there are no age differences among the three suites. On a primitive mantle-normalized trace-element distribution diagram, they exhibit typical OIB-like LILE enriched patterns without significant depletion in HFSE. However, some samples, especially the TH and HAA suites, show positive anomalies in Eu and Sr, coupled with elevated 87Sr/86Sr, Δ7/4Pb and Pb/Ce ratios, indicating an significant role of ancient anorthosite assimilation during magma evolution. Also, note that the basaltic rocks (SiO2 < 52 wt%) have fractionated Nb/Ta and Zr/Hf ratios with negative Ti anomalies. They have elevated Dy/Yb ratios which fall within the range of melts derived from garnet lherzolite, but the Yb contents are much higher than those of garnet lherzolite melts, having values close to those of eclogite-derived melts. In addition, they also have high Fe/Mn ratios (>~60) and FeO/CaO-3MgO/SiO2 values (>0.45), similar to melts from pyroxenite/eclogite sources. The Sr-Nd-Pb isotopic compositions display a mixing array between Indian MORB mantle and enriched mantle type 2 (EM2). There are no discernible 143Nd/144Nd, Δ8/4Pb, and δ26Mg isotopic differences in the three suites, implying they derived from a compositionally homogeneous mantle source by different degrees of partial melting. The δ26Mg isotopic compositions (-0.53 to -0.20‰) are extended to much lower values than normal mantle (δ26Mg = -0.25 ± 0.04‰). These observations suggest the presence of recycled rutile-bearing eclogite and carbonate component in the mantle source of Jeju volcanic rocks together with a peridotite component.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V11E0143C
- Keywords:
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- 1033 Intra-plate processes;
- GEOCHEMISTRY;
- 7208 Mantle;
- SEISMOLOGY;
- 8137 Hotspots;
- large igneous provinces;
- and flood basalt volcanism;
- TECTONOPHYSICS;
- 8416 Mid-oceanic ridge processes;
- VOLCANOLOGY