Proterozoic geology of northern New Mexico: Recent advances and ongoing questions
Michael L. Williams
Proterozoic supracrustal rocks in northern New Mexico have been divided into four lithotectonic packages: (1) mafic metavolcanic sequences (1765-1720 Ma), interpreted to have formed in volcanic arcs; (2) the Vadito Group, felsic metavolcanics and metasediments (1720-1700 Ma), deposited in a continental rift or back-arc basin; (3) the Hondo Group interbedded quartzites and pelitic schists (1700–ca. 1690 Ma), deposited on a shallow marine shelf; and (4) a sequence of felsic metavolcanic and metasedimentary rocks (1660-1650 Ma), suggested to have formed in an arc or back-arc setting. The rocks record a major, northwest-directed, crustal shortening event that involved ductile thrusting in massive units and multiple generations of folds in schistose units. Evidence exists for at least two subsequent deformational events: south-directed shearing on subhorizontal ductile faults and right-lateral shearing and faulting on steep north-trending structures. Most rocks were metamorphosed in the amphibolite facies (500°C, 4 kb) although granulite facies gneisses occur in two ranges below subhorizontal ductile faults. Although significant refinements have been made in tectonic models for the evolution of the Proterozoic rocks, important questions remain in several areas including: the tectonic setting of the major lithotectonic units and the nature of their contacts; the timing of deformation and metamorphism; controls on the production of regionally constant metamorphic conditions; and the timing and controls on uplift and stabilization of the Proterozoic crust.
- Williams, Michael L., 1990, Proterozoic geology of northern New Mexico: Recent advances and ongoing questions, 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. 151-159.