| Abstract/Notes | In the Eagle Nest area of the Sangre de Cristo Mountains, Precambrian sedimentary and minor igneous lithologies (metamorphosed to metaquartzite, mafic gneiss and granitic gneiss) attain a composite thickness of 18,000 feet. Apparently, emplacement of granite during the Elsonian (1,460-1,280 m.y.) and the formation of migmatites, occurred during the latter stages of regional metamorphism. Foliation is northeasterly.The crystalline terrane, a positive area in early Paleozoic time, is partly overlain by a 13,000- foot section of Mississippian through Paleocene sediments. Repeated crustal warpings during Mississippian and also in Late Triassic and Late Jurassic times formed thin marine and continental deposits, respectively. An aggregate thickness of 711 feet is preserved. In contrast, trough deposition, during the interval between Pennsylvanian (Desmoinesian) and Early Permian accumulated 8,200 feet of marine arkosic 'and continental red-bed sediments. A deepening basin preserved 2,000 feet of Cretaceous marine strata.The evolution of the southern Rocky Mountains geanticline during Laramide time was accomplished by deep-seated basement uplift along upthrust and flattened underthrust contacts with overlying strata. This orogeny is reflected in 1,000 feet of terrestrial Paleocene deposits. Lower to middle Tertiary volcanic units, nearly 3,000 feet thick, contain thin clastics, andesite, latite, and rhyolite. Intrusives include Eocene (51 m.y.) Rio Hondo hornblende granite, Oligocene (34 m.y.) quartz diorite porphyry, and early Miocene (23 m.y.) Questa mine biotite granite. Siliceous intrusives, emplaced along lines of weakness, contributed to uplift by doming.Early Miocene granites produced widespread and locally intense hydrothermal alteration. Contemporaneously, metallization occurred in the Red River district in fissure veins and disseminations. The Questa open-pit stockwork molybdenum deposit, averaging 0.297 percent MoS2, commenced production in 1965. Minor Precambrian quartz-copper mineralization occurs in the Rio Hondo district. In the Elizabethtown-Baldy districts fissure vein gold and contact iron deposits are Oligocene in age. Subsequently placer deposits formed in the Moreno Valley.Middle to late Tertiary high-angle normal faulting dislocated a. mid Tertiary erosion surface. Structural and topographic relief of Laramide features were enhanced, producing several welldefined topographic, tectonic and lithologic features: the Taos horst, Red River graben, Moreno Valley and western flank of the Cimarron Range. Late Pliocene to early Pleistocene gravels accumulated in the Moreno Valley, and drainage integration followed. Radially disposed Wisconsin valley glaciation, coupled with fracture patterns, control drainage in uplifted areas. |
|---|
