Browsing by Subject "Geology -- Colorado"
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Item A study of clays from the lower part of a soil developed on tertiary basalt in south-eastern Colorado(Texas Tech University, 1961-05) Panichapong, SamarnNot availableItem Precambrian geology of the northern Sangre De Cristo Range, Chaffee, Fremont, and Saguache counties, Colorado(Texas Tech University, 1972-12) Normand, David E.Precambrian metamorphic and igneous rocks, Paleozoic sedimentary rocks, and Tertiary igneous and sedimentary rocks crop out in the northern Sangre de Cristo Range. Miocene (?) age normal faults, Late Cretaceous or Early Tertiary thrust faults, and Paleozoic (?) reverse faults have displaced Precambrian and Paleozoic rocks. The complex structural relationships between the Sangre de Cristo, Sawatch, and Mosquito Ranges are interpreted as typical basin-and-range block faulting. Precambrian rocks consisting of foliated and nonfoliated metaigneous and metasedimentary rocks crop out over approximately 98 square miles. Metasedimentary rocks are subdivided into mappable units of migmatitic gneiss, porphyroblastic gneiss, granitic gneiss, and quartzite. Rb-Sr age dates record thermal events at 1.7 b. y. and between 1.3 and 1.2 b. y. ago. Field mapping and metamorphic textures suggest three regional thermal events and six periods of igneous activity during Precambrian time. The earliest recognized thermal event is recorded in statically recrystallized minerals of upper amphibolite facies. The second thermal event produced synkinematically recrystallized minerals characteristic of lower amphibolite facies. The latest thermal event is recorded by upper amphibolite facies minerals which have recrystallized statically. The earliest thermal event is not recognized in the quartzite unit. Metasediments dip north and northeast. Correlation of metasedimentary units with similar metasedimentary rock in an adjacent area to the north corroborates the presence of an east-plunging synform. Mineral composition, bedding character, and primary structures suggest that the original sediments were largely arkosic sands, calcareous or dolomitic shales, thin limestones, and well-sorted quartzitic sands. An unstable continental shelf environment is inferredItem Preliminary investigation of the geology and geochronology of the Precambrian core of the northern Wet Mountains, Colorado(Texas Tech University, 1960-08) Himmelberg, Glen RThe Wet Mountain block is an asymmetrical anticlincal structure oriented en echelon with the Colorado Front Range. The Precambrian rocks of the northern Wet Mountains are of diverse texture and composition. Migmatities, granitic gneisses, and granites comprise the western half; the eastern portion is composed of metasediments, meta-igneous rocks, and large bodies of pegmatites. Metamorphism to the highest amphibolite fades is represented in the metasedlments. The age of the metamorphism has been dated at approximately 1.4 billion years. Morphological studies of zircons reveal rounded grains in the metasediments and euhedral and rounded grains In the granitic rocks, indicating a partial replacement origin for the crystallines. Precambrian history of the area thus far indicated is; deposition of diverse sediments, intrusion of igneous plugs, metamorphism to the amphibolite facies, alkali metasomatism, intrusion of granites with associated pegmatites, uplifted peneplanation.