Search Constraints
1 - 3 of 3
Number of results to display per page
View results as:
Search Results
-
- Creator:
- Murray, Kendra E., Niemi, Nathan A., Clark, Marin K., and Siddoway, Christine
- Description:
- The Front Range of the Southern Rocky Mountains near Boulder, CO contains a rock record that spans nearly 1.7 billion years. Zircon U-Pb geochronology is an isotopically-based chronometer for measuring deep earth time. We apply this method to a series of small igneous intrusive bodies from the Front Range west of Boulder, CO. These instrusives are collectively known as the Colorado Mineral Belt (CMB) for the economic mineral deposits associated with the instrusives. Past geochronological methods have provided only rudimentary constraints on the geologic timing of emplacement of these bodies. We demonstrate the CMB magmatic activity in the Front Range occurred in two discrete pulses, one at ~67 Ma (million years ago) and one at ~47 Ma. Additional application of the same methodology to a sedimentary rock, the Neoproterozoic Tavakiav Quartzite, uses the zircon U-Pb ages as tracers to constrain the provenance and depositional age of this unique sand body.
- Keyword:
- zircon, Colorado, Front Range, geochronology, Tava, Colorado Mineral Belt, Eldorado stock, Bryan Mountain stock, Sugarloaf, Sunset stock, Bald Mountain, Caribou stock, North Fork, CMB, Front Range mineral belt, and Jamestown
- Citation to related publication:
- Murray, K. E., Niemi, N. A., & Clark, M. K. (2025). Evidence for the Neoproterozoic rifting of Rodinia in the Rocky Mountain Front Range. Tectonics, 44, e2023TC008216.
- Discipline:
- Science
-
- 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
-
- 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