Mid-Ocean Ridges: A Connected System Hydrothermal circulation links ocean, seafloor, and crust,...

Mid-Ocean Ridges: A Connected SystemMid-Ocean Ridges: A Connected System

• Hydrothermal circulation links ocean, seafloor, and crust, including vent communities

• How is fluid circulation controlled by faulting, fracture systems, and magma chamber?

• How does crust evolve?– Layer 2A – Magma chamber

• 3-D seismic reflection can tie seafloor geology to subsurface at 50-100 m resolution

Nedimovic et al. (2008)

Carbotte et al. (2006), Van Ark et al. (2007)

2-D Seismic Survey over Endeavour Segment 2-D Seismic Survey over Endeavour Segment

• Along-axis and cross-axis seismic lines acquired in 2002 (Carbotte et al, 2006)

• 2-D surveys have much lower resolution than 3-D

• Microseismicity studies around vent fields (Wilcock et al., 2002)

Along-Axis Seismic Line Along-Axis Seismic Line

• Reflector from layer 2A: alteration boundary or top intrusives

• Underlying axial magma lens correlates with seismicity under vent fields

• Melt reflector is out-of-plane of 2-D profile: correct positioning requires 3-D

Van Ark et al. (2007)

Cross-Axis Seismic LineCross-Axis Seismic Line

• Reflector from layer 2A: alteration boundary or top intrusives or both

• Underlying restricted axial magma lens dips to east, and sometimes correlates with seismicity under vent fields

Van Ark et al. (2007)

Seismicity Above Axial Magma ChamberSeismicity Above Axial Magma Chamber

• Seismicity pattern consistent with fracturing above inflating magma sill

• Inflation of AMC facilitates heat transfer, and may control seafloor vent distribution

• Can these faults be imaged by 3-D surveys?

Wilcock et al. (2009)

Streamer Tomography and Hydrothermal Circulation Streamer Tomography and Hydrothermal Circulation

• High resolution seismic velocity models from towed streamer recording

• Fluid migration in oceanic crust inferred from velocities and disruption of reflector at base of layer 2A

Newman et al. (in prep)

3-D / 4-D Seismic Proposal (Carbotte, Nedimovic et al.)3-D / 4-D Seismic Proposal (Carbotte, Nedimovic et al.)

• Endeavour is focus of a broad range of geoscience studies

• Understanding seafloor and ocean processes requires detailed knowledge of subsurface

• 3-D seismic reflection surveys can image structures at a “geological scale”

• Long-term monitoring also requires knowledge of subsurface changes from repeat surveys

• Velocity models can be used for earthquake location

3-D / 4-D Seismic Proposal (Carbotte, Nedimovic et al.)3-D / 4-D Seismic Proposal (Carbotte, Nedimovic et al.)

• 3-D seafloor topography and fine-scale structure require 3-D seismic imaging

– Relation between faulting and magma distribution

– Controls on hydrothermal venting by faults, crack systems, and melt

– 3-D fluid circulation constraints

• Baseline 3-D survey for long-term site monitoring of seismicity, fluid chemistry, microbiology etc. by NEPTUNE Canada

– Subsurface evolution by differencing of monitoring surveys (10 year intervals?)

• Possible survey sites: Endeavour vent fields, Axial Volcano, East Pacific Rise

– Long-term monitoring of Endeavour by Neptune Canada

EPR OSC Kent et al. (2001)

3-D Result with 1980s Technology