--> --> Detailed Geologic Map of the Santana Caldera, Santa Elena Canyon Protected Area, Chihuahua, Mexico

AAPG Southwest Section Annual Convention

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Detailed Geologic Map of the Santana Caldera, Santa Elena Canyon Protected Area, Chihuahua, Mexico

Abstract

Detailed geologic mapping of the Santana and San Carlos calderas near Manuel Benavides, Chihuahua reveals map- and outcrop-scale folds that differ in orientation from Chihuahua tectonic belt folds. Folds mapped to date could be caldera-caused circumferential folds. The overlapping Santana and San Carlos calderas are located within the Oligocene Trans - Pecos Volcanic Belt, south of the Jurassic-Cretaceous Chihuahua trough, and between the Chihuahua tectonic belt and the Sabinas fold belt (reference on poster). The most detailed previous mapping of the caldera was at 1:30,000 scale. We map on a 1:12,000-scale ESRI ArcGIS satellite image base. We describe and measure map- and outcrop -scale folds while mapping. Stereonet 10 software displays bedding, fold, and fault orientations. Thin- section petrography and SEM analyses improve map unit descriptions. A grid of cross-sections provides a three-dimensional view. We correlate formation names used by the Mexican Geological Survey (SGM) with names used in the Solitario. We apply Solitario formation names to distinguish nine Cretaceous and one Carboniferous map units. Early NNW-trending folds were refolded by an Oligocene granite pluton that also produced a contact metamorphic aureole. A Tertiary sill cross-cuts Tesnus and Yucca formations. Discoveries include: a) Santana Caldera Cretaceous section is 5,700 ft thick, compared to 3,300 ft in the Solitario and 13,600 ft in the eastern Chihuahua trough, b) folds contain axial plane orientations averaging 355 68 NE and fold axis trends and plunges of 000 10, c) boudins within the Carboniferous Tesnus formation adjacent to Tertiary granite pluton support forceful intrusion, d) a previously mapped thrust on the eastern caldera margin does not exist, e) unusual fracture sets within Tertiary granite strike 345 and 088 which may be related to caldera collapse or inflation. New hypotheses include applying a circumferential fold model to caldera margin folds. The Alba Mons caldera, Mars, displays similar circumferential folds. Future work will include geochemical analyses of water samples which, together with more mapping, will assist in predicting groundwater flow.