12 Tectonics, Volcanism, and Sediment Dispersal Within and Proximal to the Rio Grande Rift and Southern Rocky Mountains

This session integrates research on coupled tectonics, volcanism, and sediment dispersal in the Rio Grande Rift and southern Rockies. We examine how extensional faulting controls volcanic processes and reshapes sediment routing from Colorado through Texas.

Monday, 18 May 2026
1:30 PM - 4:30 PM
Alvarado A

Subsurface Structure of the Northern Jemez Mountains

Paper number: 12-3
Program: Technical Sessions
Time: 2:15 PM – 2:35 PM

Authors

Abstract

Interpretations of gravity data collected in the northern Jemez Mountains by students attending the Summer of Applied Geophysical Experience field program in recent years have been key in locating the western boundary of the Rio Grande rift, which is buried beneath the Jemez Mountains volcanic field. High quality gravity data with precise GPS elevation control has been added to the north, south and within the Valles Caldera. The older legacy gravity database has been reviewed, edited and recomputed resulting in better definition of sub-volcanic field structures.  A gravity low that coincides with mapped normal faults defines a broad, shallow early Miocene rift basin overlain by 10 to 2.8 Ma volcanic rocks (Lobato, La Grulla, Tschicoma formations) between the northern rim of the Valles Caldera to the south and the village of Abiquiu to the north. A sequence of 2-D EW profile models reveals the development of an extensive rift basin. The faults bounding the gravity low include the Coyote, Gonzales, and Cañones fault zones. Outcrops of rift-related Abiquiu Formation and Santa Fe Group on the south side of the Rio Chama valley and on the northern rim of the Valles Caldera are offset by these faults, but these faults do not cut the 2.8 Ma basalt-of-Cañones-Mesa flow or the Bandelier Tuff. Gravity data collected in the Toledo embayment during the last two years revealed a narrow, deep graben, a buried, high-density intrusion along the northern rim of the caldera, and strong east-west trending gravity gradients that are interpreted to represent a section of the Toledo Caldera ring fracture. The location of the buried intrusion is supported by magnetotelluric data, which indicate a locally resistive region at the location of the high-density body.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410701

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