Arc volcanic suite from a Miocene subduction system in SW Japan: A geochemical and zircon U-Pb-Lu-Hf study

Arc volcanic rocks are important products of the subduction factory in convergent plate margins and contribute significantly to crust building in the evolving Earth. Southwest Japan provides a window to gain insights into the ongoing subduction-related processes and the early stages of crust building. In this study, we investigate a suite of volcanic rocks from the central segment of the Setouchi volcanic belt (SVB) including dacites and andesite from northeast Shikoku island in southwestern Japan based on petrologic, geochemical, zircon U-Pb, REE (rare-earth element), and Lu-Hf analyses. The dacites and andesite from this region are peraluminous, medium-K, and calcalkalic, with LREEs (light rare-earth elements) enrichment and depleted in HREEs (heavy rare-earth elements) and HFSEs (high field-strength elements). Two groups of zircon grains occur in these volcanic rocks as revealed from U-Pb studies. The older magmatic zircon grains are of late Cretaceous age and show typical oscillatory zoning yielding Pb-206/U-238 age peaks at 83.6 Ma with dominantly negative epsilon(Hf)(t) values (-3.7 to +0.9), indicating older reworked crustal sources. The second group is represented by thin elongated prismatic grains with banded structure, which yield 206Pb/238U age peaks at 13.8 Ma and displaying more positive epsilon(Hf)(t) values (+2.4 to +7.7), indicating juvenile sources. A compilation and comparison of the available geochemical and geochronological data on the volcanic suites in the SVB reveal a common source for the coeval island-arc volcanic rocks (andesite-dacites-rhyolite) and HMA (high magnesium andesites). Compared with the HMA, the other volcanics are more evolved through crustal contamination and fractionation. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study revealed the mineral composition and age characteristics of volcanic rocks in the central segment of the Setouchi volcanic belt in southwest Japan, showing two groups of different zircon grains representing crustal and juvenile sources respectively. Analysis of geochemical and geochronological data showed that the volcanic rocks in this area have evolved through processes of crustal contamination and fractionation, differing from HMA.