TY - JOUR
T1 - Isotopic Characteristics of Neogene-Quaternary Tephra From IODP Site U1438
T2 - A Record of Explosive Volcanic Activity in the Kyushu-Ryukyu Arc
AU - McCarthy, Anders
AU - Yogodzinski, Gene
AU - Tepley, Frank J.
AU - Bizimis, Michael
AU - Arculus, Richard
AU - Ishizuka, Osamu
N1 - Publisher Copyright:
©2019. American Geophysical Union. All Rights Reserved.
PY - 2019/5
Y1 - 2019/5
N2 - International Ocean Discovery program (IODP) Site U1438 is located within the Amami-Sankaku Basin, ~50 km SW of the Kyushu-Palau Ridge and ~500 km SE of the present-day volcanic front of the Kyushu-Ryukyu arc. Thirty-eight rhyolitic tephra layers (1–15 cm thick) deposited over the last 4 Myr were recovered at this site. Representative ash layers dominated by unaltered, colorless glass shards reaching 100–300 μm in size, in association with rare pyroxene, amphibole, biotite, and zircon, were sampled for isotopic analysis. The isotopic compositions of the tephra have a narrow range in 87Sr/86Sr (0.704 to 0.706), 206Pb/204Pb (18.32 to 18.46), 207Pb/204Pb (15.57 to 15.62), and 208Pb/204Pb (38.46 to 38.75) and are more variable in εNd (−3.5 to +4.8) and εHf (+2.0 to +13.3). This record indicates the tephra were not sourced from the Izu-Bonin-Mariana arc or from Central Japan but derived from felsic volcanism from the Kyushu-Ryukyu arc. The 4.8-km-deep Amami-Sankaku Basin was located up to 600–900 km from the Kyushu-Ryukyu arc over the last 4 Ma, which is significantly more distal than other drill sites from which extensive tephra layers sourced from SW Japan have been recovered. Site U1438 tephra are thus likely related to widely distributed (M > 6) rhyolitic eruptions. We propose the unique tephra record and high-precision isotope analysis of recovered tephra from Site U1438 can be used as an important marker to identify submerged calderas within the Ryukyu arc and/or constrain the history of activity (>1 Ma) of major calderas-forming eruptions within the Kyushu-Ryukyu arc.
AB - International Ocean Discovery program (IODP) Site U1438 is located within the Amami-Sankaku Basin, ~50 km SW of the Kyushu-Palau Ridge and ~500 km SE of the present-day volcanic front of the Kyushu-Ryukyu arc. Thirty-eight rhyolitic tephra layers (1–15 cm thick) deposited over the last 4 Myr were recovered at this site. Representative ash layers dominated by unaltered, colorless glass shards reaching 100–300 μm in size, in association with rare pyroxene, amphibole, biotite, and zircon, were sampled for isotopic analysis. The isotopic compositions of the tephra have a narrow range in 87Sr/86Sr (0.704 to 0.706), 206Pb/204Pb (18.32 to 18.46), 207Pb/204Pb (15.57 to 15.62), and 208Pb/204Pb (38.46 to 38.75) and are more variable in εNd (−3.5 to +4.8) and εHf (+2.0 to +13.3). This record indicates the tephra were not sourced from the Izu-Bonin-Mariana arc or from Central Japan but derived from felsic volcanism from the Kyushu-Ryukyu arc. The 4.8-km-deep Amami-Sankaku Basin was located up to 600–900 km from the Kyushu-Ryukyu arc over the last 4 Ma, which is significantly more distal than other drill sites from which extensive tephra layers sourced from SW Japan have been recovered. Site U1438 tephra are thus likely related to widely distributed (M > 6) rhyolitic eruptions. We propose the unique tephra record and high-precision isotope analysis of recovered tephra from Site U1438 can be used as an important marker to identify submerged calderas within the Ryukyu arc and/or constrain the history of activity (>1 Ma) of major calderas-forming eruptions within the Kyushu-Ryukyu arc.
KW - IODP
KW - Izu-Bonin arc
KW - Kyushu-Ryukyu arc
KW - caldera
KW - rhyolite
KW - tephra
UR - http://www.scopus.com/inward/record.url?scp=85066042571&partnerID=8YFLogxK
U2 - 10.1029/2019GC008267
DO - 10.1029/2019GC008267
M3 - Article
SN - 1525-2027
VL - 20
SP - 2318
EP - 2333
JO - Geochemistry, Geophysics, Geosystems
JF - Geochemistry, Geophysics, Geosystems
IS - 5
ER -