Upcoming Meetings

Please note, our virtual happy half-hour will begin at 6:00 pm, with our speaker presenting at approximately 6:30pm.

GENERAL INFORMATION: All participants will sign up via Eventbrite (using the button to the right).  A link to the meeting will be emailed to all participants approximately 30 minutes prior to the meeting start time.  Registration for this meeting will close at 5:30pm on March 7th.  This month’s meeting is free; however, donations are appreciated and can be given via Eventbrite during sign-up or via PayPal to scgs.mgmt@gmail.com. For those who have not used Zoom, it is free to sign up and you do not need a paid account to attend the meeting.  We suggest logging in at least 10-15 minutes early if this is your first time using Zoom or you have not recently updated your Zoom account.  SCGS officers will be standing by to assist as best we can. If you have any issues, please email us at scgs.mgmt@gmail.com

Please note, the meeting may be recorded for future use.

Next Meeting

Speaker: Dr. Alyssa Abbey

Topic: A Growing Rift: Understanding the Development of the Rio Grande Rift Through Faulting and Magmatism.

When: Monday, March 7th (6:00PM – 8:00PM)


Analysis of low-temperature thermochronometric data in the Rio Grande rift (RGR) in New Mexico and Colorado, USA provides the means to assess the timing of fault initiation, as well as patterns in growth and linkage of rift faults. Evaluating spatiotemporal patterns in faulting and rift-related magmatism reveals insights into processes behind extension accommodation and helps to distinguish between possible rift models. Apatite (U-Th-Sm)/He (AHe), zircon (U-Th)/He (ZHe) and apatite fission track (AFT) thermochronometric data were combined to compile 14 vertical transects, spanning more than >800 km along the RGR axis. Thermal history modeling of these data, in the program QTQt, reveals contemporaneous rift initiation at ca. 25 Ma in both the northern and southern RGR with continued fault initiation, growth, and linkage progressing from ca. 25 to ca. 15 Ma. The central RGR, however, shows no evidence of Cenozoic fault-related exhumation as observed with thermochronometry and instead chronicles exhumation related to the Laramide Orogeny rather than rift related exhumation. Thus, extension appears to be accommodated through Late Cenozoic magmatic injection. Major structures associated with rift formation in the northern and southern sections of the RGR are spatially coincident with recognized north-south oriented Ancestral Rockies structures (the Central Colorado Trough, Orogrande and Estancia Basins, and Frontrange, Apishipa Sierra Grande, and Pedernal uplifts). Conversely, the central, non-exhumed section of the RGR is coincident with the southwest-northeast striking Jemez lineament, which is recognized as a possible boundary between the Yavapai and Mazatzal terranes. The central RGR is also spatially coincident with a south-to-north transition from thinner to thicker lithosphere that accompanies a change from a wide rift with multiple faults accommodating extension to a narrow rift focused on single basin-bounding structures. This suggests that rift structure and geometry are at least partly controlled by inherited structure and/or lithospheric properties, such that rift structures in the RGR preferentially localize along pre-existing crustal weaknesses inherited from earlier orogenic events including the Ancestral Rocky Mountain and Laramide orogenies, and that rift style and extension mechanisms are controlled by lithospheric-scale structure. These data and observations lead to the proposal of a new evolutionary model for the RGR involving initiation of fault-accommodated extension by oblique strain followed by block rotation of the Colorado Plateau, where extension in the RGR is accommodated by a combination of faulting (southern and northern RGR) and magmatism (central RGR).

Speaker Bio: 

Dr. Alyssa Abbey is an Assistant Professor in the department of Geoscience at California State University Long Beach (CSULB). She studied Geology and French at the University of Arizona and then completed her PhD at the University of Michigan researching continental rifting and fault growth using various geological dating methods. Her postdoctoral work, at the University of California Berkeley, took her into new fields, studying young faults in Argentina, and water-rock interactions combining geochemistry, geochronology, and modeling. At CSULB, her lab is split into both tectonics and fault research and field science education research (more information can be found on her website: alyssalabbey.com).