How Project IBM can help understand tHow Project IBM can help understand the Central America Subduction Factoryhe Central America Subduction Factory

R.J. STERN and Y. TATSUMIR.J. STERN and Y. TATSUMI

MARGINS-IFREE MARGINS-IFREE Workshop on IBM Workshop on IBM Subduction FactorySubduction Factory

NOV. 7-10 2007HONOLULU HAWAII

Application Deadline July 15, 2007Information on MARGINS webpage

Outline of TalkOutline 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

IODP Initial Science PlanIODP Initial Science PlanFocus on Recycling of Oceanic Lithosphere Into the Focus on Recycling of Oceanic Lithosphere Into the Deeper Mantle and Formation of Continental CrustDeeper 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.

Why IBM ?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 spati

al magmatic variations- Arc-arc collision zone- NSF-MARGINS & Japan Cont

inental Shelf Project

IBM IBM Tectonic EvolutionTectonic 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 sin

ce 7Ma

Temporal Variation in Temporal Variation in MagmatismMagmatism

- 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.

~300 ~3000 km long IBM Arc is mostly ~3000 km long IBM Arc is mostly submarinesubmarine

Seismic Imaging by IFREESeismic Imaging by IFREE

Seismic Structure of Seismic Structure of Crust/MantleCrust/Mantle

A A’

B B’

C

C’

Well-documentedacross- and along-arccrust/mantle structure

Seismic Structure of Crust/MantleSeismic Structure of Crust/Mantle

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

Project IBMProject 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 @H

onolulu 2002- IFREE-JOI IBM Mini-Workshop @Yokohama 2006

Project IBMProject IBM

Objectives: Nature of the original crust

/mantle Initial arc crust formation Rear-arc magmatism and c

rust formation Formation and evolution o

f the middle crust

IBM-1 @ Amami Sankaku BasinIBM-1 @ Amami Sankaku Basin

Objectives: Nature of the original, pre-subduction crust/mantle Initiation of IBM subduction Volcanic evolution 50-25 Ma

IBM-2 @ Izu ForearcIBM-2 @ Izu Forearc

Objectives: Understand the nature of initial arc magmatism Drill through sheeted dikes into gabbro Test the SSZ ophiolite model

Deepen ODP 786

IBM-3 & 5 @ Izu ReararcIBM-3 & 5 @ Izu Reararc

Objectives: Characterize rear-arc mag

matic evolution: the missing half of arc crust

IBM-4 @ near volcanic arcIBM-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)

Scheduled seismic & heatflow expeditScheduled seismic & heatflow expeditionsions

• 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

Continental Shelf Project & IFREE Research Project

Heat-Flow Measurements

DSDP Leg 60 was greatODP Legs 125 & 126 were fantastic IODP Project IBM will be incredible!

Why not join Project IBM?