We found a match
Your institution may have rights to this item. Sign in to continue.
- Title
The First 10 Million Years of Rear‐Arc Magmas Following Backarc Basin Formation Behind the Izu Arc.
- Authors
Miyazaki, T.; Gill, J. B.; Hamelin, C.; DeBari, S. M.; Sato, T.; Tamura, Y.; Kimura, J.‐I.; Vaglarov, B. S.; Chang, Q.; Senda, R.; Haraguchi, S.
- Abstract
IODP Site U1437 is located in the Izu rear‐arc region, approximately 330 km west of the Izu‐Bonin trench axis. The oldest four units (Units IV through Unit VII) include volcaniclastic sediment and in situ hyaloclastites. They have ages of about 6–15 Ma, shortly after cessation of Shikoku backarc basin opening. Three magma types are identified by their distinct geochemistry; they are similar types to those found in the modern Izu arc (Rear Arc Seamount Chain [RASC]‐type, Rift‐type, and volcanic front [VF]‐type). RASC‐type has the most enriched Nd and Hf isotope and fluid‐immobile trace element ratios and dominates from 9 to 6 Ma. Rift‐type, dominant from 15 to 9 Ma, is similar to VF‐type in Nd‐Hf isotopes but has the least radiogenic Sr and Pb, and intermediate La/Yb and Nb/Yb, indicating a more fertile mantle source and less hydrous slab component than VF‐type. Less common and randomly distributed VF‐type sediments have the most radiogenic Sr and Pb, and the highest Ba/(Th, LREE [light rare earth element]) ratios, and are interpreted to be distally derived. The genesis of mafic Unit VII samples (~15 Ma) was modeled using the Arc Basalt Simulator. Results are most similar to those for basalts in the modern rift environment indicating the addition of ~1% of a melt‐rich slab component generated at ~125 km, to a Philippine Sea Plate ambient mantle that was more depleted than DMM (depleted MORB mantle). The initial post‐Shikoku basin magmatism in the Izu rear‐arc generated Rift‐type magmas for about 6 million years before the distinctive RASC‐type magmatism began, which then became increasingly enriched. Plain Language Summary: We explore the history of magma genesis in the Izu rear‐arc, Japan, by studying the geochemistry of volcaniclastic sediments that were obtained by ocean drilling. This paper presents their Sr‐Pb‐Nd‐Hf isotope ratios and numerical models of magma genesis. We identify the presence of three geochemical types that change through time. Rift‐type formed soon after cessation of seafloor spreading in the Shikoku Basin at ~15 Ma and came from a more fertile mantle source with a less hydrous slab component than at the contemporaneous volcanic front. This type is most like basalts from rifts behind the current volcanic front and was unknown before drilling. RASC‐type dominates from 9 to 6 Ma and has more enriched Nd and Hf isotope and fluid‐immobile trace element ratios that are like those of rocks dredged from the coeval rear‐arc seamount chains. VF‐type is uncommon, randomly dispersed, and interpreted as derived from the distal volcanic front. The results confirm that the arc front has migrated trenchward since the Miocene. Key Points: The geochemistry of the volcaniclastics and hyaloclastites of IODP Site U1437 is reportedTwo magma types and one magma type of distal origin existed in the Izu rear‐arc after spreading in the Shikoku Basin endedThe initial post backarc basin magmatism generated magmas similar to Quaternary Rift‐type and evolved to rear‐arc seamount chain type
- Subjects
MAGMAS; PLATE tectonics; OCEANIC crust; EARTH sciences; BIG data
- Publication
Geochemistry, Geophysics, Geosystems: G3, 2020, Vol 21, Issue 10, p1
- ISSN
1525-2027
- Publication type
Article
- DOI
10.1029/2020GC009114