Arizona Geological Society
2026 Speaker Series
Tuesday, 3 March 2026 | 5:30 - 8:00 PM
Location: Hexagon Mining Division Office
40 East Congress Street, Suite 150, Tucson, Arizona 85701
Parking: On the street or parking garage (Old Pueblo Parking)
Social Hour - Sandwiches from Beyond Bread (5:30-6:20 PM MST), Presentation (6:25 PM MST)
NOTE: This event will not be livestreamed.
AGS and SEG Publications will be available
for sale at Tuesday's meeting.
Will need cash or check (no credit cards)
For those planning to attend the event, please register by 6:00 PM on Sunday, March 1, 2026. Please register early so we have an accurate number of attendees to order the right amount of food.
The Arizona Geological Society thanks Hexagon
for generously providing the venue and drinks
The Sangre Taphrogeny: Neogene/Quaternary Stress Distribution and Kinematics of the Clockwise Rotation of the Colorado Plateau Microplate
by Vince Matthews, Retired,
Director, Colorado Geological Survey
Abstract: The Sangre Taphrogeny is a unifying kinematic model that links the late Cenozoic (Neogene and Quaternary) mountain building, rifting, magmatism, regional elevation, sedimentation, and incision surrounding a roughly circular, lithospheric microplate. The taphrogen is characterized as a rift-chain feature (g3/k22/d1 in Sëngor and Natalin’s classification), composed of ten linear rift segments along with their associated damage zones. The linked tectonic elements are approximately 2300 km long and average about 150 km in width. They surround and define a Colorado Plateau Microplate (CPM) that is larger than the physiographic province. Clockwise-rotation of the microplate creates rifting of the craton on the east and north. Regional elevation is caused by mantle buoyancy in response to extension and thinning of the lithosphere, as seen at oceanic spreading centers and the East African Rift. The late Cenozoic taphrogen is coeval with, and kinematically related to, the regional extension caused by changing plate interactions along the west coast. This extensional tectonic belt is superimposed on a regional erosion surface that greatly subdued the topography of the Late Cretaceous/Early Paleogene structures of the Laramide orogeny.
A variety of 21st century databases provide documentation of the Neogene/Quaternary taphrogen. Distribution and orientation of stress (SHmax) and strain (faults and dikes) within the 150-km-wide taphrogen are parallel to the principal rift segments. Kilometer-scale displacement of Neogene/Quaternary fault blocks creates ultra-high topography (more than 900 peaks >3962 meters AMSL) and is supported by thermochronological transects and geologic relations. GPS vectors are normal to the rift segments and indicate that the taphrogeny is ongoing at present. Most of the taphrogen correlates with high crustal attenuation (Q0) and high heat flow (mW/m2).
Igneous activity with mantle signatures is widespread throughout the taphrogen. Multiple grabens contain thick syntectonic strata. Rivers emanating from mountains formed by the taphrogeny have deeply incised the CPM and Great Plains as well as transported substantial volumes of sediment to both the Gulf Coast and the Gulf of California. The Western Uinta Mountains arose during the tectonism of the Sangre taphrogeny and are not a remnant of the Laramide orogeny.
Three types of physical modeling in the laboratory help in understanding the distribution of stress and strain that is observed within the taphrogen. The Sangre Taphrogen model is a synthesis of old ideas and 21st century datasets and tools.
Bio: Vincent Matthews received his PhD in Earth Science from the University of California for his research on the San Andreas fault. His B.S. and M.S are from the University of Georgia. Both departments awarded him distinguished alumni recognition.
Vince’s varied career included teaching at seven institutions of higher education, two of which were tenured positions, and one where he was President of the Faculty Senate. He also held executive positions in four natural resource companies, two of them with Fortune 500 companies. He retired from the Senior Executive Service of the State of Colorado as Director of the Colorado Geological Survey and State Geologist of Colorado in 2013. He is a Senior Fellow in the Geological Society of America and recipient of the “Pioneer Award” from the American Association of Petroleum Geologists. He remains professionally active. In 2024. the Rocky Mountain Association of Geologists gave him their “Outstanding Scientist” Award and in 2025 his book, “Land of Ice: Jaunts into Colorado’s Glacial Landscape” was a Winner of the Colorado Humanities and Center for the Book Award. He is a member of The Arizona Geological Society and usually attends by ZOOM from Wisconsin.
Hexagon Mining Division Office - 40 East Congress Street,
Suite 150, Tucson, Arizona 85701
