How Project IBM can help understand the Central America Subduction Factory

1. How Project IBM can help understand the Central America Subduction Factory R.J. STERN and Y. TATSUMI

2. MARGINS-IFREE Workshop on IBM Subduction Factory NOV. 7-10 2007 HONOLULU HAWAII Application Deadline July 15, 2007 Information on MARGINS webpage

3. Outline of Talk • Importance of drilling intra-oceanic arcs • Why IBM (Izu-Bonin-Mariana)? ・Simple and well-known tectonic evolution ・Minimal contamination of magmas ・Well-defined crustal structure • Project IBM ・CDP proposals (umbrella + 4 expedition proposals) ・A working hypothesis: crust/mantle transformation ・Drilling strategies

4. IODP Initial Science Plan Focus on Recycling of Oceanic Lithosphere Into the Deeper Mantle and Formation of Continental Crust Probing the possible new ‘continental root’ beneath juvenile oceanic arcs by IODP will be a tremendous step towards understanding the origin of the continental crust.

5. Why IBM ? IBM is an outstanding and well-studied example of a juvenile intra-oceanic arc • Middle crust (Vp=6.0 km/s) • Simple tectonic history allows tracking of crustal growth • Simple magmagenesis • Significant temporal and spatial magmatic variations • Arc-arc collision zone • NSF-MARGINS & Japan Continental Shelf Project

6. IBM Tectonic Evolution • Lithospheric subsidence and subduction initiated ~50Ma • Forearc spreading & ophiolite formation • Arc magmatism localized in Oligocene (~35 Ma) • Backarc opening at 25-15Ma (Kyushu-Palau Ridge remnant arc) • arc-arc collision since 15Ma • Mariana Trough opening since 7Ma

7. Temporal Variation in Magmatism • Earliest arc magmas were boninitic to tholeiitic • Arc magmatic lull at 25-15Ma (Time of Parece Vela Basin opening) • Mantle component varied from highly depleted to Indian-MORB type • Subduction component consists of fluids from dehydrated oceanic crust and serpentinites; also fluids and melts from subducted sediments.

8. ~3000 km long IBM Arc is mostly submarine ~300

9. Seismic Imaging by IFREE

10. Seismic Structure of Crust/Mantle C A A’ C’ B B’ Well-documented across- and along-arc crust/mantle structure

11. Seismic Structure of Crust/Mantle

12. Well-defined Crustal Structure = Opportunity to Study Early Stages in the Growth of Continental Crust

13. Project IBM • A Complex Drilling Project umbrella full proposal • 4 proposals for each expedition • Outcome of international dialogue in: • IFREE-NSFMARGINS Workshop on the Izu-Bonin-Mariana Subduction System @Honolulu 2002 • IFREE-JOI IBM Mini-Workshop @Yokohama 2006

14. Project IBM Objectives: • Nature of the original crust/mantle • Initial arc crust formation • Rear-arc magmatism and crust formation • Formation and evolution of the middle crust

15. IBM-1 @ Amami Sankaku Basin Objectives: • Nature of the original, pre-subduction crust/mantle • Initiation of IBM subduction • Volcanic evolution 50-25 Ma

16. IBM-2 @ Izu Forearc Deepen ODP 786 Objectives: • Understand the nature of initial arc magmatism • Drill through sheeted dikes into gabbro • Test the SSZ ophiolite model

17. IBM-3 & 5 @ Izu Reararc Objectives: • Characterize rear-arc magmatic evolution: the missing half of arc crust

18. IBM-4 @ near volcanic arc -Characterize upper and middle crust of IBM ・Drill several kilometers into arc crust ・Constraints from technical requirements (e.g., T<250°C)

19. Continental Shelf Project & IFREE Research Project • Combined MCS and wide-angle seismic survey using super-densely deployed OBS arrays (1-2 km interval of OBS) • Seismic refraction tomography • New migration technique for wide-angle reflection data Heat-Flow Measurements Scheduled seismic & heatflow expeditions

20. DSDP Leg 60 was greatODP Legs 125 & 126 were fantastic IODP Project IBM will be incredible!Why not join Project IBM?