Magma differentiation processes that develop an "enriched" signature in the Izu Bonin rear arc; evidence from drilling at IODP Site U1437

Author(s): Heywood, Luan Jean; DeBari, Susan M.; Schindlbeck, Julie Christin; Escobar-Burciaga, Ricardo Daniel
Author Affiliation(s): Primary:
Western Washington University, Bellingham, WA, United States
Other:
Helmholtz Centre for Ocean Research, Germany
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: The Izu Bonin rear arc represents a unique laboratory to study the development of continental crust precursors at an intraoceanic subduction zone., Volcanic output in the Izu Bonin rear arc is compositionally distinct from the Izu Bonin main volcanic front, with med- to high-K and LREE-enrichment similar to the average composition of the continental crust. Drilling at IODP Expedition 350 Site U1437 in the Izu Bonin rear arc obtained volcaniclastic material that was deposited from at least 13.5 Ma to present. IODP Expedition 350 represents the first drilling mission in the Izu Bonin rear arc region. This study presents fresh glass and mineral compositions (obtained via EMP and LA-ICP-MS) from unaltered tephra layers in mud/mudstone (Lithostratigraphic Unit I) and lapillistone (Lithostratigraphic Unit II) <4.5 Ma to examine the geochemical signature of Izu Bonin rear arc magmas. Unit II samples are coarse-grained tephras that are mainly rhyolitic in composition (72.1-77.5 wt.% SiO2, 3.2-3.9 wt.% K2O and average Mg# 24) and LREE-enriched. These rear-arc rhyolites have an average La/Sm of 2.6 with flat HREEs, average Th/La of 0.15, and Zr/Y of 4.86. Rear-arc rhyolite trace element signature is distinct from felsic eruptive products from the Izu Bonin main volcanic front, which have lower La/Sm and Th/La as well as significantly lower incompatible element concentrations. Rear arc rhyolites have similar trace element ratios to rhyolites from the adjacent but younger backarc knolls and actively-extending rift regions, but the latter is typified by lower K2O, as well as a smaller degree of enrichment in incompatible elements. Given these unique characteristics, we explore models for felsic magma formation and intracrustal differentiation in the Izu Bonin rear arc.
Year of Publication: 2015
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Expedition 350; IODP Site U1437; International Ocean Discovery Program; Izu-Bonin Arc; Magmatism; North Pacific; Northwest Pacific; Pacific Ocean; West Pacific
Coordinates: N314723 N314724 E1390136 E1390134
Record ID: 2016106176
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