Studying an ophiolite in its natural environment; IODP Leg 352 drilling in the Izu-Bonin-Mariana Forearc

Author(s): Stern, Robert J.; Reagan, Mark K.; Pearce, Julian A.
Author Affiliation(s): Primary:
University of Texas at Dallas, Geosciences Department, Richardson, TX, United States
University of Iowa, United States
Cardiff University, United Kingdom
Volume Title: Geological Society of America, 2016 annual meeting & exposition
Source: Abstracts with Programs - Geological Society of America, 48(7); Geological Society of America, 2016 annual meeting & exposition, Denver, CO, Sept. 25-28, 2016. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592 CODEN: GAAPBC
Note: In English
Summary: Increasing evidence supports the interpretation that most ophiolites formed during an episode of massive extension and seafloor spreading accompanying the formation of a new subduction zone. Thus, drilling into the submerged crust of forearcs in convergent margins can test and refine both "ophiolite as fossil forearc lithosphere" and subduction initiation hypotheses. Drilling in the Izu-Bonin-Mariana (IBM) fore-arc during IODP Expedition 352 ≈28°20'N and DSDP Leg 60 ≈18° recovered similar stratigraphic sequences of volcanic rocks. These sequences are like those in many ophiolites, with MORB-like melts early/trench-proximal and arc-like lavas late/trench-distal. IODP 352, in July 30-Sept. 29 2014, cored 1.22 km of igneous basement and 0.46 km of overlying sediment from 4 sites in the forearc east of the Bonin Islands. These cores provided stratigraphically controlled suites of MORB-like fore-arc basalts (FAB) and boninite related to seafloor spreading and earliest arc development above an incipient subduction zone. FAB were recovered at the two bathymetrically-deeper sites (U1440 and U1441; collectively "352-FAB") and boninites at the two sites (U1439 and U1442; collectively "352-BON") upslope to the west. The oldest lavas in IBM forearc sections are FAB with ≈51.5 Ma ages. Boninites began erupting approximately 2-3 m.y. later and further from the trench. First results from IODP Expedition 352 and preliminary post-cruise data suggest that 352-FAB were generated by decompression melting during near-trench sea-floor spreading, and that fluids from the subducting slab were not significantly involved in their genesis. Geochemical data for the IODP 352 and DSDP 60 reveal that mantle became more depleted and more fluid-enriched though time, as spreading rates waned, the volcanic front retreated from the trench and true subduction began. Ophiolites that preserve the vertical sequence MORB-like at the base and arc-like at the top like that seen in IODP site 352 are almost certainly subduction-initiation-related slabs of forearc lithosphere. We expect that the distribution of such ophiolites with time should reflect episodes of plate reorganization.
Year of Publication: 2016
Research Program: DSDP Deep Sea Drilling Project
IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
IPOD International Phase of Ocean Drilling
Key Words: 05 Petrology, Igneous and Metamorphic; Andesites; Boninite; Cenozoic; Deep Sea Drilling Project; Eocene; Expedition 352; IODP Site U1439; IODP Site U1440; IODP Site U1441; IODP Site U1442; IPOD; Igneous rocks; International Ocean Discovery Program; Izu-Bonin Arc; Leg 60; North Pacific; Northwest Pacific; Ophiolite; Pacific Ocean; Paleogene; Tertiary; Volcanic rocks; West Pacific
Coordinates: N282425 N282705 E1424600 E1423600
Record ID: 2017043295
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States