Disciplinary Groups: Seafloor Geology/ Morphology

Moderator: Adam Soule; Co-moderator: Deb Kelley

Participants (list your name here):
    •    Vicki Ferrini
    •    Jeff Standish
    •    Scott White
    •    Allison Fundis
    •    Adam Soule
    •    Garrett Ito
    •    Dan Curewitz
    •    Roger Buck
    •    Jeff Karson
    •    Milene Cormier

Discussion topics (list ideas and suggestions here):
    •    Variability and interaction of tectonic & magmatic accretionary processes
    •    Ridge morphology related to eruption frequency
    •    Volcanic repaving of tectonic disruption (and vice versa)
    •    Axial segmentation: top down or bottom up?
    •    How does faulting influence hydrothermal circulation and vice versa?
    ◦    How faithfully does venting (behavior or location) reflect shallow permeability and/or structural architecture?
    ▪    Can magmatic controls be distinguished from structural controls?
    ◦    What sort of geological record of venting might be preserved (biological, mineralogical, alteration, microbiological, etc)?
    •    How does the shape/size/xtallinity of the axial melt lens influence eruption style?
    •    What is the time and spatial scale of variability of the substrate? How to characterize it?

Summary of breakout group discussion:

COMPARABLE DATA ACROSS ISS:
Regional bathymetry (Seabeam, EM300): Available at all three ISS
Local bathymetry (ABE, Jason): Available at all three ISS, but at a variety of scales.
Acoustic backscatter (DSL120, IMI30): Available at EPR and Lau, Endeavor data not available.

TASKS:
-Identify cross-ISS morphology/geology problems that we have made progress on.
-Methods for comparing large-scale ridge crest morphology (e.g. Small, 1998; Scheirer & Macdonald, 1993; Ito & Behn, 2008)
-Identify specific opportunities for cross-ISS integration/synthesis with existing databsets
-Identify specific datasets that would allow cross-ISS integration/synthesis/comparisons.

QUESTIONS:
-Controls on ridge-crest morphology from spreading rate / melt supply
-Variations in tectonic distuption and colvanit accretion within and between ISS ridge crests (eruption frequency)
-Links between morphology and permeability structure / vent location
-Timescales over which ridge-crest morphologi geatures (axial troughs, etc.) persist / develop
-How does faulting infuence hydrothermal venting (and vice versa)

Geologic Maps:

Geologic maps generated in order to understand the volcanic/tectonic history of the ridge crest and the relationship between ridge crest features/structures and the distribution of hydrothermal vents (for example). The data is in place to generate such maps at a variety of scales at each ISS, but in general have only been constructed for small areas.

-Make available geologic maps from different ISSs to facilitate comparisons?
-Define as a group what features for each ISS should be digitized/quantified?
-Develop a set of standards in symbols used in geologic maps?
-Define a standard mode of presentation? Scale, rock types?
-Gather and make available existing interpretations to identify where there are spatial gaps.
-Photos being brought into database and GeoMapApp (Alvin, Jason, ABE, TowCam, Argo) will help this effort
-Existing available datasets could be interpreted to help toward this (e.g. EM300 at JdF, DSL120 at Lau)
-What is eruption frequency?
-Dating has been done at EPR, is in process at JdF, and Lau (Standish)

Is there geologic evidence to help understand magmatic processes?
-- frequency of eruptions?
-- spatial extent?
-- magma lens height?
-- composition?

What is the architecture, permeability structure etc between AMC reflector and seafloor surface?
-- near-bottom magnetics helps with this (some is published for JdF (Tivey), more is being processed (Denny); being processed for EPR (Tivey); data exists for Lau, but no project funded for processing)

Yucca Mountain paper about faulting/diking (reference?)

Cross-ISS Comparison Ideas
How wide is area of magmatic accretion across axis?
JdF and EPR could be used for this and results could be used to help understand at other sites.
--at JdF - lots of heterogeneity of basalts along western wall - not a symmetric system - eastern flank v. different from western
--magma lens dips to the east - what's the interaction between faulting along western wall and diking from magma lens?

AST at EPR - new data suggests eruption processes may be different from what we'd previously thought.

JdF and EPR, hydrothermal activity found above magma bodies.
Have we fully identified the presence of off axis hydrothermal venting?
Not well explored, but evidence for off axis venting exists at several sites.

Big Topics for Cross-ISS investigation:
    •    Large-scale axial morphology (axial highs, valleys, & transitional morphology). The formation of axial highs, axial valleys, or transition between the two can be broadly understood in terms of the competition between tectonic extension which tends to reduce topography and magmatic processes which tends to build topography. The ISS’s show a wide range of long-wavelength topographic characteristics in which the above competition probably varies, between different ridge segments as well as along individual segments. Does the thermal structure of the crust influence axial topography/depth? Is there a relationship between axial morphology/depth and the abundance of hydrothermal vents?
    •    Fault characteristics and creating abyssal hill fabric. Various mechanisms have been proposed for generating the faults at mid-ocean ridges, which forms seafloor abyssal hill fabric, perhaps the most common topographic fabric on earth. These mechanisms include: (i) magmatic intrusions, which accommodate extension and break the overlying rock, (ii) caldera-like collapse over the crustal magma storage zone, (iii) flexing of the axial lithosphere as the seafloor migrates away from the accretion zone, and (iv) far-field plate forces driving extension and normal faulting. Examining new and existing data among the ISS’s will allow R2K to distinguish among the above processes and determine in what environments they are most important.
    •    How do variations in morphology and the processes that are responsible for them influence the hydrogeology of the ridge crest at each site. How do structural parameters and the thermal state of the crust vary between the sites and how is that manifest in the along axis spacing and thermal output of vents.
    •    Volcanic accretion at mid-ocean ridges: What is the frequency-size distribution of volcanic eruptions at each ISS? What controls extrusion v. intrusion at ridge crests? What is the width of the magma injection zone and does is correlate with spreading rate? How do dikes and faults interact?
    •    What is the timescale of formation of ridge crest features such as axial troughs/valleys and how persistent are they in time?