Geochemistry of volcanic rocks from International Ocean Discovery Program (IODP) Site 1438, Amami Sankaku Basin; implications for Izu-Bonin-Mariana (IBM) arc initiation

Author(s): Hickey-Vargas, Rosemary; Ishizuka, O.; Yogodzinski, G. M.; Bizimis, Michael; Savov, I. P.; McCarthy, A. J.; Arculus, R. J.; Bogus, K.
Author Affiliation(s): Primary:
Florida International University, Miami, FL, United States
Geological Survey of Japan, Tsukuba, Japan
University of South Carolina, Columbia, SC, United States
University of Leeds, Leeds, United Kingdom
Universite de Lausanne, Lausanne, Switzerland
Australian National University, Canberra, A.C.T., Australia
International Ocean Discovery Program, College Station, TX, United States
Volume Title: AGU 2015 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2015; American Geophysical Union 2015 fall meeting, San Francisco, CA, Dec. 14-18, 2015. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: IODP Expedition 351 drilled 150 m of volcanic basement overlain by 1461 m of sedimentary material at Site 1438 in the Amami Sankaku basin, just west of the Kyushu Palau Ridge, the locus of IBM arc initiation. Age interpretations based on biostratigraphy (Arculus et al., Nat. Geosci., in-press) determined that the age of the basement section is between 64 and 51 Ma, encompassing the age of the earliest volcanic products of the IBM arc. The Site 1438 volcanic basement consists of multiple flows of aphyric microcrystalline to finely crystalline basalts containing plagioclase and clinopyroxene with rare olivine pseudomorphs. New XRF major and ICPMS trace element data confirm findings of shipboard analysis that the basalts are moderately differentiated (6-14 % MgO; Mg# = 51-83; 73-490 ppm Cr and 58-350 ppm Ni) with downcore variations related to flow units. Ti/V and Ti/Sc ratios are 16-27 and 75-152, respectively, with lowest values at the base of the core. One prominent characteristic of the basalts is their depletion of immobile highly incompatible elements compared with MORB. Basalts have MORB-normalized La/Nd of 0.5 to 0.9, and most have Th/La < 0.05. Although all basalts are LREE-depleted, La/Nd ratios increase slightly upcore, and Th enrichment compared with LREE occurs in the uppermost 5 meters. Cs, Rb, K, Ba and U are concomitantly enriched relative to LREE in several intervals as a probable result of seawater alteration, but ratios less than those of MORB are found in other areas. In contrast to basement, andesites from three sills in the lowermost sedimentary unit have arc-like trace element patterns with La/Nb > 3 and primitive mantle normalized La/Yb > 1. Our results suggest that mantle melting at the onset of subduction involved exceptionally depleted sources. Enrichment over time may be related to increasing subduction inputs and/or other processes, such as entrainment of fertile asthenosphere during extension of the overriding plate.
Year of Publication: 2015
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Asia; Chemical composition; Far East; Geochemistry; IODP Site U1438; Igneous rocks; International Ocean Discovery Program; Izu-Bonin Arc; Japan; Kagoshima Japan; Kyushu; Mariana Islands; Micronesia; North Pacific; Northwest Pacific; Oceania; Oshima; Pacific Ocean; Ryukyu Islands; Sankaku Basin; Volcanic rocks; West Pacific
Record ID: 2016066767
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States

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