Thermal segmentation of mid-ocean ridge-transform faults
Boettcher, Margaret S.
Behn, Mark D.
MetadataShow full item record
KeywordOceanic transform fault; Intratransform spreading center; Fault segmentation; Fault thermal structure; Melt transport
3-D finite element simulations are used to calculate thermal structures and mantle flow fields underlying mid-ocean ridge-transform faults (RTFs) composed of two fault segments separated by an orthogonal step over. Using fault lengths and slip rates, we derive an empirical scaling relation for the critical step over length ( inline image), which marks the transition from predominantly horizontal to predominantly vertical mantle flow at the base of the lithosphere under a step over. Using the ratio of step over length (LS) to inline image, we define three degrees of segmentation: first-degree, corresponding to type I step overs ( inline image ≥ 3); second-degree, corresponding to type II step overs (1 ≤ inline image < 3); and third-degree, corresponding to type III step overs ( inline image <1). In first-degree segmentation, thermal structures and mantle upwelling patterns under a step over are similar to those of mature ridges, where normal mid-ocean ridge basalts (MORBs) form. The seismogenic area under first-degree segmentation is characteristic of two, isolated faults. Second-degree segmentation creates pull-apart basins with subdued melt generation, and intratransform spreading centers with enriched MORBs. The seismogenic area of RTFs under second-degree segmentation is greater than that of two isolated faults, but less than that of an unsegmented RTF. Under third-degree segmentation, mantle flow is predominantly horizontal, resulting in little lithospheric thinning and little to no melt generation. The total seismogenic area under third-degree segmentation approaches that of an unsegmented RTF. Our scaling relations characterize the degree of segmentation due to step overs along transform faults and provide insight into RTF frictional processes, seismogenic behavior, and melt transport.
Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 18 (2017): 3405–3418, doi:10.1002/2017GC006967.
Suggested CitationGeochemistry, Geophysics, Geosystems 18 (2017): 3405–3418
Showing items related by title, author, creator and subject.
Thermal-mechanical behavior of oceanic transform faults : implications for the spatial distribution of seismicity Roland, Emily C.; Behn, Mark D.; Hirth, Greg (American Geophysical Union, 2010-07-01)To investigate the spatial distribution of earthquakes along oceanic transform faults, we utilize a 3-D finite element model to calculate the mantle flow field and temperature structure associated with a ridge-transform-ridge ...
Behn, Mark D.; Boettcher, Margaret S.; Hirth, Greg (Geological Society of America, 2007-04)We use three-dimensional finite element simulations to investigate the temperature structure beneath oceanic transform faults. We show that using a rheology that incorporates brittle weakening of the lithosphere generates ...
Gregg, Patricia M.; Behn, Mark D.; Lin, Jian; Grove, Timothy L. (American Geophysical Union, 2009-11-13)We examine mantle melting, fractional crystallization, and melt extraction beneath fast slipping, segmented oceanic transform fault systems. Three-dimensional mantle flow and thermal structures are calculated using a ...