### Abstract

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 L_{S}, 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 (L_{S}) , we define three degrees of segmentation: first-degree, corresponding to type I step overs ≥ 3); second-degree, corresponding to type II step overs (1 ≤ < 3); and third-degree, corresponding to type III step overs <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.

Original language | English |
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Pages (from-to) | 3405-3418 |

Number of pages | 14 |

Journal | Geochemistry, Geophysics, Geosystems |

Volume | 18 |

Issue number | 9 |

DOIs | |

Publication status | Published - 1 Sep 2017 |

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*Geochemistry, Geophysics, Geosystems*,

*18*(9), 3405-3418. https://doi.org/10.1002/2017GC006967

}

*Geochemistry, Geophysics, Geosystems*, vol. 18, no. 9, pp. 3405-3418. https://doi.org/10.1002/2017GC006967

**Thermal segmentation of mid-ocean ridge-transform faults.** / Wolfson-Schwehr, Monica; Boettcher, Margaret S.; Behn, Mark D.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Thermal segmentation of mid-ocean ridge-transform faults

AU - Wolfson-Schwehr, Monica

AU - Boettcher, Margaret S.

AU - Behn, Mark D.

PY - 2017/9/1

Y1 - 2017/9/1

N2 - 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 LS, 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) , we define three degrees of segmentation: first-degree, corresponding to type I step overs ≥ 3); second-degree, corresponding to type II step overs (1 ≤ < 3); and third-degree, corresponding to type III step overs <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.

AB - 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 LS, 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) , we define three degrees of segmentation: first-degree, corresponding to type I step overs ≥ 3); second-degree, corresponding to type II step overs (1 ≤ < 3); and third-degree, corresponding to type III step overs <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.

KW - fault segmentation

KW - fault thermal structure

KW - intratransform spreading center

KW - melt transport

KW - oceanic transform fault

UR - http://www.scopus.com/inward/record.url?scp=85029354468&partnerID=8YFLogxK

U2 - 10.1002/2017GC006967

DO - 10.1002/2017GC006967

M3 - Article

VL - 18

SP - 3405

EP - 3418

JO - Geochemistry Geophysics Geosystems

JF - Geochemistry Geophysics Geosystems

SN - 1525-2027

IS - 9

ER -