mid-ocean ridges: a connected system hydrothermal circulation links ocean, seafloor, and crust,...
TRANSCRIPT
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