Temporal Evolution of Boron Flux in the Honshu and Izu Arcs measured by Ion Microprobe from the forearc tephra record.
- Clift, Peter D.
- Layne, Graham D.
- Najman, Yani
- Kopf, Achim
- Shimizu, Nobumichi
- Hunt, John
DOIAbstract
The enrichment of boron relative to similarly incompatible elements, such as Be, in arc volcanic rocks has been used as a proxy for the involvement of slab flux in petrogenesis. New ion microprobe analyses of single glass shards in tephra layers recovered by the Ocean Drilling Program (ODP) in the Izu and NE Japan forearc basins now allow the temporal variation in slab flux to be charted since 7 and 5 Ma, respectively. B/Be ratios are typically <70 in NE Japan and <130 in Izu, with no single grain exceeding 200. Although moderate to high for modern arcs, these values are much less than those recorded in the Marianas and Tonga at 3–4 Ma, shortly after the start of rifting of their back-arc basins. This observation suggests that the peak B/Be...
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