RESEARCH

Timing of extension in the Rio Grande rift - Basin and Range transition zone of southern New Mexico: Two distinct tectonic provinces?

Funding: NSF Tectonics grant EAR-1624538 - $166,905

 

The Rio Grande rift is a distinct zone of lithospheric extension from northern Colorado to central New Mexico. In southern New Mexico, however, extension in the rift is more diffuse and it merges with the highly-extended Basin and Range Province. While the Rio Grande rift is one of the best examples of a narrow rift, the Basin and Range remains the archetypal example of a wide rift, and the nature of the boundary between these two provinces remains poorly understood and debated. We are combining apatite and zircon (U-Th)/He with apatite fission-track dating from rocks across southern New Mexico to document periods of cooling due to extensional faulting. These data will help determine whether the southern Rio Grande rift evolved coevally with the Basin and Range or not and whether they should be viewed as two distinct structural entities.

M.S. students: Julian Biddle (UTEP) and Michelle Gavel (NMSU)

B.S. students: Rafael Delfin, Joseadrian Rubio

Chiricahua Mountains of the Basin and Range Province in southeastern Arizona

Geochemical fluctuations of water in extensional fault zones of the Rio Grande rift: Tectonic vs. climatic influences

 

Fluids can be transported along fault zones over short timescales of seconds to months during seismic events or hundreds of thousands of years due to regional changes in climate, making fluid systems highly variable in time and space. Fluid flow is recorded in travertine deposits, which are precipitated from springs along faults in the Rio Grande rift. We are collecting geochronologic, geochemical, and isotopic data from travertine in the Rio Grande rift to document spatial and temporal patterns in travertine deposition and fluid sources. The main hypothesis to be tested is that glacial to interglacial transitions can increase fluid flow in active faults.

Ph.D. student: Victor Garcia

Active and young travertine deposits along the Lucero Uplift, which forms the western edge of the Albuquerque basin

Fault kinematics and paleostrain analysis of the southern Rio Grande rift: A comparative study to the central rift

 

The purpose of this project is to understand fault kinematics that record extension of the southern Rio Grande rift in southern New Mexico. The area of interest preserves multiple faults sets including N – S-trending and NW – SE-trending faults. The main hypothesis to test is that although both fault sets were active during extension of the rift, the NW – SE trending faults may preserve evidence for underlying reactivated older faults, possibly dating back to the Precambrian era. Using exposed faults in southern New Mexico, paleostrain analysis is used to determine maximum extension (S1) and maximum shortening (S3) directions. These data can then be compared to fault kinematic data compiled from the central segment of the rift in northern New Mexico to test models of rift formation. 

M.S. student: Georgina Rodriguez Gonzalez

Exposed fault plane and fault measurements from the Cookes Range, New Mexico

Miocene deformation along the lower Colorado River recorded in the Bear Canyon conglomerate

 

The Bear canyon conglomerate forms an extensive alluvial sequence that crops out in southeastern California along the bank of the Colorado River. It is interstratified with the 9.45 Ma basalt of Black Mountain, and is itself internally faulted and folded. However, the timing of youngest deformation is unknown and detailed mapping of different fluvial units within the Bear Canyon conglomerate is incomplete. To further understand the depositional and deformational history of this unit, we are creating a detailed geologic map of the Bear Canyon conglomerate, focusing on the structures and possible timing constraints obtained from interbedded basalt flows. 

M.S. student: Garrett Goff

Miocene deformation along the lower Colorado River recorded in the Bear Canyon conglomerate

 

The Bear canyon conglomerate forms an extensive alluvial sequence that crops out in southeastern California along the bank of the Colorado River. It is interstratified with the 9.45 Ma basalt of Black Mountain, and is itself internally faulted and folded. However, the timing of youngest deformation is unknown and detailed mapping of different fluvial units within the Bear Canyon conglomerate is incomplete. To further understand the depositional and deformational history of this unit, we are creating a detailed geologic map of the Bear Canyon conglomerate, focusing on the structures and possible timing constraints obtained from interbedded basalt flows. 

M.S. student: Garrett Goff

Zircon (U-Th)/He investigation of the long-term thermal history of Proterozoic rocks in west Texas and southern New Mexico

 

New helium diffusion models in zircon (Guenthner et al. (2013) provide an exciting new technique to explore long-term thermal histories of Precambrian rocks. In this project samples are collected from the Cookes Range, NM, the Franklin Mountains, TX, and the Carrizo Mountains, TX for zircon (U-Th)/He (ZHe) thermochronology. ZHe ages from these locations span hundreds of millions of years, and typically show negative correlations with eU. These relationships are being used to investigate the timing of Precambrian uplift and possible relationships to tectonism along the Grenville Front.

M.S. student: Nathan Reade

Inverse thermal model for the Franklin Mountains, west Texas

Utilizing zircon (U-Th)/He and 40Ar/39Ar thermochronology to refine the thermal history of the Great Unconformity in New Mexico and Colorado

 

The Great Unconformity represents 100-1000 m.y. of missing time in the geologic rock record that formed through extensive weathering and erosion. Despite its global extent, the timing of Precambrian crystalline rock exhumation prior to Phanerozoic sediment deposition remains relatively unresolved in many locations. This project combines new helium diffusion models in zircon (Guenthner et al., 2013) with existing 40Ar/39Ar data to constrain the long-term thermal history of Precambrian rocks in Colorado and New Mexico. These new data will result in a better understanding of the timing of Precambrian exhumation, which has implications for supercontinent cycles, Snowball Earth events, and the explosion of life during the Cambrian. 

M.S. student: Jacoup Roiz

1.1 Ga granitic rocks of the Franklin Mountains, west Texas exposed just beneath the ~500 Ma Bliss Sandstone

© 2019 by Jason Ricketts

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