New Mexico Geological Society Annual Spring Meeting — Abstracts

Large-volume travertine deposits in the Lucero Uplift provide an excellent opportunity to understand and quantify Quaternary extension along the western boundary of the Rio Grande rift. Vertical quarried faces expose travertine mounds that have been subsequently cut by multiple systems of extensional fractures. We focus on three quarry sites (Temple Cream, Scheherazade, and Vista Grande), as well as a fourth location, Red Hill, in an attempt to understand the timing and implications of fracture formation.

At each of the quarry sites, at least three fracture sets were observed and measured. Cross-cutting relationships at Temple Cream and Scheherazade indicate that a set of horizontal sills are younger than vertical ~NS - ~NE-SW trending and ~EW - ~NW-SE trending fractures. Vista Grande exposes a more complex history, where vertical and horizontal fractures repeatedly cross-cut one another. Red Hill is a small mesa of Permian sandstone and siltstone capped by travertine. NE-SW trending extensional fractures similar to those observed at the quarry sites cut the Permian rocks and acted as conduits for fluid flow, feeding the overlying travertine deposit. In addition, small-scale (< 1m) normal faults cut the Permian rocks. Preliminary U-series dating of the travertine mound at Scheherazade indicates it was deposited ~750 - 650 ka. The extensional fractures and sills observed at each of the four locations are thus younger than ~ 600 ka.

NS and NE-SW trending fractures observed at all study sites (as well as NE-trending normal faults at Red Hill) indicate ~EW - NW-SE oriented extension that, although of small magnitude, are compatible with Quaternary far field extension related to continued development of the Rio Grande rift. A prominent set of late horizontal sills overprints the subvertical faults and is not consistent with this E-W extension. Instead, these reflect subvertical least compressive stress and suggest a regime of high fluid pressure the reduced the effective normal stress and caused rotation of regional stress fields. This was likely due to upward movement of deeply sourced CO₂-rich fluids to the surface from Socorro magma body-like chambers. We conclude that Quaternary far field extension is ongoing and stress fields are modified in the region of the Socorro magma body by ascending CO₂-rich fluids.