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Overview of geology, stratigraphy, and thermal features of the Jemez Mountains Volcanic Field, including the Valles Caldera. The objective of the field trip is to acquaint the students with the geologic setting for their upcoming exercises.
Outcrop sketches and description of stratigraphic sections are undertaken in superb outcrops of the ~60 ka El Cajete Pumice within the Valles Caldera with the objective to evaluate criteria for recognizing fall, surge, and flow deposits.
Students measure and describe a section through the Pleistocene Bandelier Tuff with emphasis on recognizing, and distinguishing, eruptive units, flow units, and zonation of the deposits in terms of welding, devitrification and vapor-phase mineralization. The outcrops studied are in Eagle Canyon only a few kilometers from the field station.
Field excursion to west-central New Mexico to examine (a) basaltic lava flow (including inflated flow), lava tubes, and vent features associated with late Pleistocene to middle Holocene basalts and (b) the stratigraphy and petrology of Mt. Taylor, a Pliocene composite volcano. Lodging for one night at motel in Grants, NM, included in course fee.
This project involves mapping a small area of andesitic lavas and associated pyroclastics and volcaniclastic sediments that form part of the flanking apron to late Miocene composite volcanoes. Detailed stratigraphic study will also permit students to contemplate how to distinguish primary pyroclastic deposits from reworked sedimentary facies, the distinction of debris-flow and fluvial deposits, and the comparative record of compositions represented by lavas, pyroclastics, and sediment clasts.
Students construct a geologic map of a dissected upper Miocene rhyolite vent in Bland Canyon to evaluate relationships between precursor pyroclastics and extruded lava, distribution of glassy and devitrified zones within the rhyolite, and relationship of flow foliation to processes of intrusion and extrusion.
Students map Pliocene near-vent basaltic deposits of both hydromagmatic and strombolian character that are exposed in a steep tributary to the Rio Grande in White Rock Canyon. They also study stratigraphic relationships to the overlying Bandelier Tuff ignimbrite, which buried a complex landscape with both constructional and erosional topography. Distinction of magmatic and hydromagmatic eruptive products and measurement of flow directions in surge deposits and lavas are among the objectives in this project. This exercise is undertaken during a three-day, whitewater raft trip through White Rock Canyon, which will also include opportunities to examine other basaltic-vent features and to visit the famous 13th-14th century Anasazi ruins in Bandelier National Monument.
Students measure sections through proximal hydromagmatic deposits at scenic Tent Rocks, which are associated with late Miocene rhyolite dome extrusion. Emphasis is placed on reconstructing the history of water-magma interaction during the eruption, the origin of the water that was involved in the eruption, and determining the location of the vent from which the debris was erupted.
Students conduct a mapping exercise at Sulphur Springs in the western moat of the Valles Caldera in order to understand the complexities of caldera-fill geology and experience the challenge of mapping lavas, tuffs, and moat-fill sediments that have been highly altered in an acid-sulfate hydrothermal system. Students also learn how to sample gas and water from fumaroles, mudpots and hot springs and the rudiments of identifying alteration minerals in the field.
Detailed examination of an andesite lava exposed in an abandoned quarry emphasizes recognition of primary flow features and those related to later alteration, including hydrolthermal explosion breccias. The lava studied also exhibits outstanding outcrop-scale evidence for magma mixing, providing an opportunity to discuss this important petrologic phenomena.
The synthesis project, this exercise involves mapping and interpretation of a variety of pyroclastic fall, flow, and surge deposits, rhyolite lava and related breccias of various origins in addition to sediments derived from both the lava and the pyroclastics. The small map area provides outstanding outcrops to provide insights into the relationship of different deposits to the evolving constructional topography of a volcanic landscape and the controls on the distribution of different types of deposits.
Students have one day off each week. This time is generally used to finish up projects, do laundry in a nearby town, hike the canyons and mesas surrounding the field station, visit local pueblos, or sorties for shopping and dining in Santa Fe. One off day coincides with the traditional corn dances and feast at nearby Santo Domingo Pueblo. Evenings are generally used for working on projects, examining thin sections of rocks collected in the exercise areas, and brief lectures and discussion sessions before each new project.
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