Petrology, structure and exhumation of the southern Sawatch mountains, south-central Colorado

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Show simple item record Robbins, Rebecca en 2005-06-07T18:05:24Z 2005-06-07T18:05:24Z 2005-06-07T18:05:24Z
dc.description.abstract The southern Sawatch Range of the Southern Rocky Mountains of south-central Colorado is composed of Precambrian crystalline igneous and metamorphic rocks that have undergone at least three major mountain building events during the Phanerozoic, the Ancestral Rockies Orogeny, the Laramide Orogeny, and Rio Grande rifting. In order to determine how the ancient basement structures might have influenced later episodes of deformation, a small area of basement terrain was mapped along the western margin of the Poncha Pass transfer zone between the San Luis and Upper Arkansas basins in the northern Rio Grande rift. The two dominant rock types in the map area, (hornblendic) amphibolite gneiss and (felsic) quartzofeldspathic gneiss, may represent interlayered metabasalt/metadiorite and metarhyolite/metagranite, with lenses of exotic lithologies throughout. Metamorphic foliations were found to be oriented predominantly N35ºW 47ºNE and to have had an influence on younger brittle structures related to the rifting episode. Lineations and fractures in the gneissic fabric also are parallel to brittle deformation structures. Apatite Fission-Track (AFT) analysis provided a means of determining when this crust was exhumed and cooled by the removal of overburden in response to erosion and/or tectonics. The resultant AFT age distribution revealed that exhumation occurred at the higher elevations during the Laramide orogeny (~299-46 Ma), and at lower elevations during Rio Grande rifting (~29-19 Ma). Although it is commonly thought that these mountains were exhumed during the rifting episode, the results of this study indicate that older events played a significant role in the exhumation. en
dc.format.extent 22672234 bytes
dc.format.mimetype application/pdf
dc.language.iso en_US en
dc.publisher Kansas State University en
dc.subject Precambrian paleoproterozoic en
dc.subject Southern Sawatch range en
dc.subject Felsic hornblendic gneiss en
dc.subject Exhumation en
dc.subject Apatite fission-track en
dc.subject Thermochronology en
dc.title Petrology, structure and exhumation of the southern Sawatch mountains, south-central Colorado en
dc.type Thesis en Master of Science en
dc.description.level Masters en
dc.description.department Department of Geology en
dc.description.advisor Mary Hubbard en
dc.subject.umi Geology (0372) en 2005 en May en

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