The reconstruction of a middle Proterozoic orogenic belt in north-central New Mexico, USA
Christopher G. Daniel, Karl E. Karlstrom, Michael L. Williams, and Jane N. Pedrick
Correlation of Proterozoic rocks and structures in the Tusas, Picuris, Truchas and Rio Mora uplifts in northern New Mexico shows -50 km of post-Precambrian, probably Laramide, right-lateral strike slip across a zone of north-trending faults. Similar peak metamorphic P-T conditions and P-T paths from each uplift suggest that the intersection of subhorizontal isobars with steeply dipping structures can be used as piercing lines to constrain the magnitude of slip. Based on the restoration of Laramide slip, a fundamental crustal boundary separating older, 1700 Ma rocks (Yavapai crustal province) from younger, ~1650 Ma supracrustal rocks (Mazatzal crustal province) is proposed. As the dominant regional deformation appears to be related to the assembly of the younger crustal material to the continental margin at ~1650 Ma, north-central New Mexico is within the area affected by the Mazatzal orogen. In addition to the proposed crustal and orogenic province assignments, several distinctive structural, metamorphic and plutonic belts are recognized. From north to south these include (I) the Cimarron- Taos high-grade metamorphic area characterized by relatively high pressures (6-8 kbar) and abundant 1650 to 1700 Ma plutons; (2) the Ortega ductile thrust belt, a north-vergent, brittle-ductile fold and thrust belt that imbricates rocks of the Vadito and Hondo groups and contains few plutons; and (3) the Yavapai-Mazatzal transition zone, a structurally complex transition from older Yavapai crust to younger Mazatzal crust. This transition zone includes: (1) the Pecos thrust sheet, which places pre-1700 Ma volcanogenic basement that is thrust over the Ortega fold-and-thrust belt; (2) a large ~1650 Ma plutonic complex in the Santa Fe Mountains and southern Pecos river valley; and (3) ~1450 Ma granites in the Nacimiento, Sandia and Pedernal uplifts. The geometry of these belts suggests that heat from ~1650 Ma granitic plutons emplaced below the Ortega thrust sheet and thrust up over the complex (in the Pecos thrust sheet) is responsible for the regional metamorphism of the Ortega thrust belt.
- Daniel, Christopher G.; Karlstrom, Karl E.; Williams, Michael L.; Pedrick, Jane N., 1995, The reconstruction of a middle Proterozoic orogenic belt in north-central New Mexico, USA, in: Geology of the Sante Fe Region, Bauer, Paul W.; Kues, Barry S.; Dunbar, Nelia W.; Karlstrom, K. E.; Harrison, Bruce, New Mexico Geological Society, Guidebook, 46th Field Conference, pp. 193-200.