TY - JOUR

T1 - Magma Source Evolution Following Subduction Initiation

T2 - Evidence From the Element Concentrations, Stable Isotope Ratios, and Water Contents of Volcanic Glasses From the Bonin Forearc (IODP Expedition 352)

AU - Coulthard, Daniel A.

AU - Reagan, Mark K.

AU - Shimizu, Kenji

AU - Bindeman, Ilya N.

AU - Brounce, Maryjo

AU - Almeev, Renat R.

AU - Ryan, Jeffrey

AU - Chapman, Timothy

AU - Shervais, John

AU - Pearce, Julian A.

N1 - Funding Information: This research used samples and data provided by the International Ocean Discovery Program (IODP). We thank the crew of the JOIDES Resolution, the science team, and the technical support staff for IODP Expedition 352 for making this research possible. We particularly thank staff scientist Katerina Petronotis for her guidance throughout the expedition. Ben Maunder provided P-T paths for subducted materials. Postexpedition awards from the US Science Support Program to Reagan, Shervais, and Ryan, and US-NSF grants OCE1558647 (Reagan). OCE1558689 (Shervais) and OCE1558855 (Ryan) supported this research. Almeev was supported by the German Science Foundation (DFG Project AL1189/8-1). Brounce acknowledges support from the University of California Riverside. Pearce thanks the NERC (UK) for grant NE/M012034/1. Chapman was supported by the Australia-New Zealand IODP consortium and the ARC LIEF scheme (LE140100047). This paper benefitted significantly from reviews by Karsten Haase, Heather Handley, Michael Perfit, and Kaj Hoernle. Funding Information: This research used samples and data provided by the International Ocean Discovery Program (IODP). We thank the crew of the JOIDES Resolution, the science team, and the technical support staff for IODP Expedition 352 for making this research possible. We particularly thank staff scientist Katerina Petronotis for her guidance throughout the expedition. Ben Maunder provided P‐T paths for subducted materials. Postexpedition awards from the US Science Support Program to Reagan, Shervais, and Ryan, and US‐NSF grants OCE1558647 (Reagan). OCE1558689 (Shervais) and OCE1558855 (Ryan) supported this research. Almeev was supported by the German Science Foundation (DFG Project AL1189/8‐1). Brounce acknowledges support from the University of California Riverside. Pearce thanks the NERC (UK) for grant NE/M012034/1. Chapman was supported by the Australia‐New Zealand IODP consortium and the ARC LIEF scheme (LE140100047). This paper benefitted significantly from reviews by Karsten Haase, Heather Handley, Michael Perfit, and Kaj Hoernle.

PY - 2021/1/12

Y1 - 2021/1/12

N2 - International Ocean Discovery Program Expedition 352 to the Bonin forearc drilled the sequence of volcanic rocks erupted in the immediate aftermath of subduction initiation along the western margin of the Pacific Plate. Pristine volcanic glasses collected during this expedition were analyzed for major and trace elements, halogens, sulfur, and H and O isotopes with goals of characterizing the fluids and melts of subducted materials that were involved in generating the nascent upper plate crust. Incompatible trace element compositions of the oldest lavas (forearc basalts [FAB]) are similar to those of the most depleted mid-ocean ridge basalts globally. Most FAB were generated by decompression melting during seafloor spreading in a near-trench, supra-subduction zone environment with only minor involvement of diverse and generally dilute water-rich fluids from the subducting plate. Boninite series glasses are enriched in incompatible trace elements mobilized from the subducting plate, but strongly depleted in other elements, such as the middle-heavy rare-earth elements. These traits are attributed to generation of boninites largely by flux melting involving water-rich melts first derived from the leading edge of subducted basaltic crust and then from both subducted crust and sediment. These melts were generated at low pressures as the shallow, embryonic slab extracted heat from hot asthenosphere near the trench. The progressive depletion of the mantle source for the FAB-through-boninite sequence suggests that the asthenospheric mantle remained trapped above the nascent subducting plate for the first several million years of subduction beneath the Philippine Sea Plate.

AB - International Ocean Discovery Program Expedition 352 to the Bonin forearc drilled the sequence of volcanic rocks erupted in the immediate aftermath of subduction initiation along the western margin of the Pacific Plate. Pristine volcanic glasses collected during this expedition were analyzed for major and trace elements, halogens, sulfur, and H and O isotopes with goals of characterizing the fluids and melts of subducted materials that were involved in generating the nascent upper plate crust. Incompatible trace element compositions of the oldest lavas (forearc basalts [FAB]) are similar to those of the most depleted mid-ocean ridge basalts globally. Most FAB were generated by decompression melting during seafloor spreading in a near-trench, supra-subduction zone environment with only minor involvement of diverse and generally dilute water-rich fluids from the subducting plate. Boninite series glasses are enriched in incompatible trace elements mobilized from the subducting plate, but strongly depleted in other elements, such as the middle-heavy rare-earth elements. These traits are attributed to generation of boninites largely by flux melting involving water-rich melts first derived from the leading edge of subducted basaltic crust and then from both subducted crust and sediment. These melts were generated at low pressures as the shallow, embryonic slab extracted heat from hot asthenosphere near the trench. The progressive depletion of the mantle source for the FAB-through-boninite sequence suggests that the asthenospheric mantle remained trapped above the nascent subducting plate for the first several million years of subduction beneath the Philippine Sea Plate.

KW - boninites

KW - forearc basalts

KW - IODP Expedition 352

KW - Izu-Bonin-Mariana

KW - JOIDES Resolution

KW - Site U1439

KW - Site U1440

KW - Site U1441

KW - Site U1442

KW - subduction initiation

UR - http://www.scopus.com/inward/record.url?scp=85100031988&partnerID=8YFLogxK

U2 - 10.1029/2020GC009054

DO - 10.1029/2020GC009054

M3 - Article

AN - SCOPUS:85100031988

VL - 22

JO - Geochemistry, Geophysics, Geosystems

JF - Geochemistry, Geophysics, Geosystems

SN - 1525-2027

IS - 1

M1 - e2020GC009054

ER -