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Precambrian Ancestry of the Colorado Mineral Belt

1963; Geological Society of America; Volume: 74; Issue: 8 Linguagem: Inglês

10.1130/0016-7606(1963)74[991

1943-2674

Ogden Tweto, P.K. Sims,

Mineralogy and Gemology Studies

Research Article| August 01, 1963 Precambrian Ancestry of the Colorado Mineral Belt OGDEN TWETO; OGDEN TWETO U. S. Geological Survey, Denver, Colo Search for other works by this author on: GSW Google Scholar P. K SIMS P. K SIMS Minnesota Geological Survey, Minneapolis, Minn Search for other works by this author on: GSW Google Scholar Author and Article Information OGDEN TWETO U. S. Geological Survey, Denver, Colo P. K SIMS Minnesota Geological Survey, Minneapolis, Minn Publisher: Geological Society of America Received: 14 Nov 1960 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1963, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1963) 74 (8): 991–1014. https://doi.org/10.1130/0016-7606(1963)74[991:PAOTCM]2.0.CO;2 Article history Received: 14 Nov 1960 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation OGDEN TWETO, P. K SIMS; Precambrian Ancestry of the Colorado Mineral Belt. GSA Bulletin 1963;; 74 (8): 991–1014. doi: https://doi.org/10.1130/0016-7606(1963)74[991:PAOTCM]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The narrow northeast-trending Colorado mineral belt, the site of most of the major mining districts of Colorado, is characterized by intrusive porphyries and associated ore deposits of Laramide age and, in some places, by fissures and faults of northeasterly trend. The belt, about 250 miles long, extends diagonally across the generally north-trending mountain ranges of Colorado, occupies several different geologic environments, and seems to be independent of the present mountain structure.The mineral belt follows an ancient zone of weakness defined by northeast-trending shear zones of Precambrian age in a belt 10–35 miles wide. Individual shear zones or clusters of zones are spaced from a mile or less to many miles apart. In most parts of the belt, a major northeast-trending shear zone is flanked by lesser shear zones in an echelon arrangement.Movement occurred along the belt of shear zones through most of the Precambrian time recorded in the region. During this time, deformation progressed from a deep-seated environment characterized by folding and plastic flow to a more shallow environment characterized by fracture and retrograde metamorphism. The earliest movement occurred during regional folding, when folds were oriented parallel to the shear zones or were bent where they impinged upon the shear zones. Cataclastic deformation began after the folds had formed, but the earliest products of cataclasis re-crystallized as new gneisses, indicating that relatively intense metamorphic conditions either still prevailed or recurred. Later, when pressure and temperature were lower, cataclastic gneisses, pseudotachylyte, mylonite, and broad granulated zones formed, and in some places small crossfolds formed in layers of incompetent gneiss between cataclastically deformed competent layers. Still later in the Precambrian, gouge and breccia formed, partly by the degradation of earlier shear products of higher rank.During Paleozoic and Mesozoic time, minor differential movements occurred repeatedly in the regional zone of shearing, as recorded by thinning, wedgeouts, and changes in facies of several sedimentary formations along the zone.With the onset of the Laramide orogeny, magma invaded the regional zone of shearing and imparted to it the conspicuous features that characterize the mineral belt—intrusive igneous bodies and ore deposits. Fault movement occurred along the zone at this stage also but was on a smaller scale than it had been previously. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.