Proterozoic geology of the Rincon Range north of Guadalupita, New Mexico
Jeffrey A. Grambling
Proterozoic rocks of the Vadito and Hondo Groups dominate the northern Rincon Range, where the Vadito Group includes metarhyolite, crossbedded quartzofeldspathic gneiss, amphibolite, fragmental silicic metatuff and pelitic schist. The stratigraphically highest beds in the Vadito Group consist of schist rich in kyanite, muscovite, hematite, quartz and manganese andalusite. They are interpreted to represent the metamorphosed equivalent of a lateritic soil that developed along an unconformity separating the Vadito Group from the overlying Hondo Group. Quartzite of the Ortega Formation (Hondo Group), with an exposed stratigraphic thickness of 900 m, overlies the unconformity. The quartzite is similar to but slightly poorer in aluminum silicate minerals than where it has been mapped elsewhere in northern New Mexico. Crossbeds found in both the Vadito and Hondo Groups show that the stratigraphy is everywhere overturned, a consequence of regional deformation. Large-scale, south-dipping ductile shear zones repeat the transition from Vadito to Hondo Groups six times in the mapped area. The shear zones have the geometry of north-verging ductile thrusts. The region experienced its thermal peak following deformation at metamorphic conditions near 500°C, 4 kb. These P-T conditions are common in the Proterozoic rocks of New Mexico, and they may have developed during a period of synmetamorphic extensional deformation.
- Grambling, Jeffrey A., 1990, Proterozoic geology of the Rincon Range north of Guadalupita, New Mexico, in: Tectonic development of the southern Sangre de Cristo Mountains, New Mexico, Bauer, Paul W.; Lucas, Spencer G.; Mawer, Christopher K.; McIntosh, William C., New Mexico Geological Society, Guidebook, 41st Field Conference, pp. 207-210.