HR: 11:50h
AN: T32B-06    [Abstracts]
TI: Thermal-Mechanical Behavior of Oceanic Transform Faults- Implications for Hydration of the Upper Oceanic Mantle
AU: * Roland, E C
EM: eroland@mit.edu
AF: MIT/WHOI Joint Program, Woods Hole Oceanographic Inst. Clark 242 - MS 24, Woods Hole, MA 02543, United States
AU: Behn, M D
EM: mbehn@whoi.edu
AF: Woods Hole Oceanographic Institution, Dept. Geology and Geophysics Clark 260B, MS#22, Woods Hole, MA 02543, United States
AU: Hirth, G
EM: Greg_Hirth@Brown.edu
AF: Brown University, Geological Sciences 324 Brook Street Box 1846, Providence, RI 02912, United States
AB: The presence of water at oceanic transform faults influences the thermal structure, rheology, and petrology of the upper mantle. Serpentinization at ridges and transforms plays an important role for the large-scale water budget of the mantle and eventual flux melting that is responsible for arc volcanism at convergent margins. The extent to which hydrous minerals (e.g., serpentine and talc) are incorporated into the upper mantle at oceanic transform faults is highly dependent on the thermal structure and stress state. Previous numerical modeling studies have suggested that the mantle beneath oceanic transform faults is anomalously cold, with depressed isotherms relative to a half-space cooling model [1,2,3]. However, recent models, that incorporate brittle rheology, show that transform faults may represent a region of enhanced mantle upwelling and elevated temperatures [4]. To investigate the thermal-mechanical behavior of oceanic transform faults, we utilize a 3D finite element model, assuming mantle convection, conduction, and steady-state incompressible mantle flow. Our model incorporates a non-linear viscous rheology with a visco-plastic approximation to simulate lithospheric brittle failure. The introduction of water into the lithosphere causes rheological changes with additional feedbacks on the thermal and rheologic structure such as enhanced conductive cooling and changes in frictional behavior. We incorporate the effects of these feedbacks, and our derived thermal structures are integrated with the estimated zone of permeable fluid flow to approximate the stability fields of hydrous phases in the upper mantle. Through examining a rage of parameters, including spreading rate, fault length, and the efficiency of hydrothermal circulation, we constrain the potential for transform faults to act as a source for mantle hydration, and estimate the amount of water that could be bound in hydrous phases as a result of brittle cracking at oceanic faults. 1. Furlong et al., The Nature and Tectonic Significance of Fault Zone Weakening 2001; 2. Phipps Morgan and Forsyth, JGR 1988; 3. Shen and Forsyth, JGR 1992; 4. Behn et al., Geology 2007
DE: 0545 Modeling (4255)
DE: 3035 Midocean ridge processes
DE: 3039 Oceanic transform and fracture zone processes
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8162 Rheology: mantle (8033)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting