Initial magmatism and evolution of the Izu-Bonin-Mariana Arc

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http://abstractsearch.agu.org/meetings/2016/FM/V11E-01.html
Author(s): Arculus, R. J.
Author Affiliation(s): Primary:
Australian National University, Canberra, Australia
Volume Title: AGU 2016 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2016; American Geophysical Union 2016 fall meeting, San Francisco, CA, Dec. 12-16, 2016. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Expedition 351 of the IODP targeted site U1438 in the Amami Sankaku Basin, northwestern Philippine Sea, ∼70 km west of the northern Kyushu-Palau Ridge (KPR). The latter formed a chain of stratovolcanoes of the Izu-Bonin-Mariana (IBM) Arc, and a remnant arc following migration of the volcanic front eastwards during Shikoku backarc basin formation in the Miocene. Unraveling causes of subduction initiation drove the primary aims of the Expedition involving recovery of igneous basement below the KPR, and a history of the magmatic evolution of the KPR preserved in a clastic record. All these aims were achieved, but with some surprises. Out of 1600m drilled in 4700m water depth, 150m of igneous oceanic crust comprising low-K, tholeiitic basalt lava flows were recovered at U1438. The lavas are variably glassy to microphyric, Cr-spinel-olivine-plagioclase-clinopyroxene-bearing, have high V/Ti, very low absolute rare earth element abundances and low La/Yb, and radiogenic Hf at a given 143/144Nd compared to basalts of mid-ocean ridges. The basement is geochemically and petrologically similar to so-called "forearc basalts" recovered trenchward of the active IBM volcanic front, and of similar or older age (≥52Ma). Highly melt-depleted mantle source(s) were involved and high-temperature, low-pressure dehydration of the subducting Pacific Plate. Compositions of glass (formerly melt) inclusions in clinopyroxene-bearing clasts and sandstones in sediments overlying the basement show a change from medium-Fe (aka "calcalkaline") to low-Fe (tholeiitic) magmas during the Eocene-Oligocene evolution of the KPR. Widespread magmatism along- and across-strike of the nascent IBM system coupled with geologic constraints from the western Philippine Sea, indicate subduction initiation at the IBM arc likely propagated adjacent to Mesozoic-aged arcs/basins to the west of the KPR, following plate reorganization subsequent to the demise of the Izanagi-Pacific Ridge along eastern Asia at ∼60Ma. Neither the spontaneous nor induced models of subduction initiation adequately capture the inception of the IBM Arc. Geographic modifiers of basalt types such as "forearc" are overly restrictive and potentially misleading.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 05 Petrology, Igneous and Metamorphic; Cenozoic; Cores; Expedition 351; IODP Site U1438; International Ocean Discovery Program; Izu-Bonin Arc; Marine sediments; North Pacific; Northwest Pacific; Pacific Ocean; Paleogeography; Quaternary; Sediments; West Pacific
Record ID: 2017062762
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States

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