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  • Reverse faulting within a continental plate boundary transform system [Data set]

    work
    Creator:
    Townsend, Kirk F., Clark, Marin K., and Niemi, Nathan A.
    Description:
    These datasets support the findings of Townsend et al. (in review) investigating the timing of faulting relative to changes in the orientation of the North American-Pacific plate boundary. Coeval with development of an oblique plate boundary segment (i.e. the “Big Bend” of the San Andreas fault), active shortening is inferred to have initiated at ~5 Ma in the Western Transverse Ranges (WTR). However, new low-temperature thermochronometric transects yield Miocene to Pleistocene apatite (U-Th-Sm)/He cooling ages and partially reset zircon (U-Th)/He ages. Inverse thermal modelling indicate that reverse faulting initiated as early as 10 Ma, several million years prior to our current understanding of the timing of the Big Bend. New and existing thermochronometry data delineate the WTR as the locus of rapid post-Miocene exhumation, and demonstrate that similar exhumation is not present in the broader region surrounding the Big Bend. We posit that reverse faulting is localized in the WTR because of a weak underlying lithosphere and predates the more recent geometric anomaly of the restraining bend in the transform margin.
    Keyword:
    Reverse faults, Fault initiation, Fault propagation, Low-temperature thermochronometry, Western Transverse Ranges, and San Andreas Fault
    Citation to related publication:
    Townsend, K. F., Clark, M. K., & Niemi, N. A., in review, Reverse faulting within a continental plate boundary transform system. Tectonics
    Discipline:
    Science

  • Dataset of apatite and zircon (U-Th)/He thermochronologic analyses from the Rio Grande Rift, Colorado and New Mexico, USA to accompany Abbey and Niemi, 2019, Tectonics.

    work
    Creator:
    Niemi, Nathan A. and Abbey, Alyssa L.
    Description:
    These data were produced in the scope of research into the timing, rate, and magnitude of extensional exhumation along the length of the Rio Grande Rift in Colorado and New Mexico. The low-temperature (apatite and zircon (U-Th)/He) thermochronometric ages presented in this data set are sensitive to near-surface temperatures (~80C and 180C, respectively) and record the progressive exhumation of the rock mass from which the samples were collected towards the Earth's surface. These thermochronometric ages, and the differences between them, provide insight into the absolute timing, exhumation rate and total magnitude of exhumation on the normal faults that bound the Rio Grande Rift. and The QTQt program mentioned (Version QTQt64R5.6.2a was used for the data presented in this deposit) is not openly available for download, but is described in the Gallagher 2012 publication referenced, and can be requested from its author. For more information on the request process and a user guide, see  http://www.iearth.org.au/codes/QTQt/
    Keyword:
    thermochronology, helium dating, (U-Th)/He, Rio Grande Rift, New Mexico, Colorado, and extensional tectonics
    Citation to related publication:
    Abbey, A. L., & Niemi, N. A. (2020). Perspectives on Continental Rifting Processes From Spatiotemporal Patterns of Faulting and Magmatism in the Rio Grande Rift, USA. Tectonics, 39(1), e2019TC005635.  https://doi.org/10.1029/2019TC005635
    Discipline:
    Science