Fore‐arc basalts and subduction initiation in the Izu‐Bonin‐Mariana system

Recent diving with the JAMSTEC Shinkai 6500 manned submersible in the Mariana fore arc southeast of Guam has discovered that MORB‐like tholeiitic basalts crop out over large areas. These “fore‐arc basalts” (FAB) underlie boninites and overlie diabasic and gabbroic rocks. Potential origins include eruption at a spreading center before subduction began or eruption during near‐trench spreading after subduction began. FAB trace element patterns are similar to those of MORB and most Izu‐Bonin‐Mariana (IBM) back‐arc lavas. However, Ti/V and Yb/V ratios are lower in FAB reflecting a stronger prior depletion of their mantle source compared to the source of basalts from mid‐ocean ridges and back‐arc basins. Some FAB…

• NS
  National Science Foundation

  Award: 0827817
• UO
  University of Illinois at Urbana-Champaign
• JA
  Japan Agency for Marine-Earth Science and Technology
• IN
  Institut national des sciences de l'Univers