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Title: Geochemistry of high-potassium rocks from the mid-Tertiary Guffey volcanic center, Thirtynine Mile volcanic field, central Colorado

The Guffey volcanic center is the largest within the 2000 km{sup 2} mid-Tertiary Thirtynine Mile volcanic field of central Colorado. This study is the first to provide extensive chemical data for these alkalic volcanic and subvolcanic rocks, which present the eroded remnants of a large stratovolcano of Oligocene age. Formation of early domes and flows of latite and trachyte within the Guffey center was followed by extrusion of a thick series of basalt, trachybasalt, and shoshonite flows and lahars. Plugs, dikes, and vents ranging from basalt to rhyolite cut the thick mafic deposits, and felsic tuffs breccias chemically identical to the small rhyolitic plutons are locally preserved. Whole-rack major and trace element analyses of 80 samples, ranging almost continuously from 47% to 78% SiO{sub 2}, indicate that the rocks of the Guffey center are among the most highly enriched in K{sub 2}O (up to 6%) and rare earth elements (typically 200-300 ppm) of any volcanic rocks in Colorado. These observations, along with the relatively high concentrations of Ba and Rb and the depletion of Cr and Ni, suggest an appreciable contribution of lower crustal material to the magmas that produced the Thirtynine Mile volcanic rocks.
Authors:
;  [1] ; ; ;  [2] ; ;  [3] ; ;  [4] ;  [5] ;  [6] ;  [7]
  1. (Williams College, Williamstown, MA (USA))
  2. (Franklin Marshall College, Lancaster, PA (USA))
  3. (Colorado College, Colorado Springs (USA))
  4. (Carleton College, Northfield, MN (USA))
  5. (Smith College, Northampton, MA (USA))
  6. (Beloit College, WI (USA))
  7. (Whitman College, Walla Walla, WA (USA))
Publication Date:
OSTI Identifier:
6140437
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geology; (USA); Journal Volume: 18:7
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; COLORADO; VOLCANIC REGIONS; GEOCHEMISTRY; BARIUM; BASALT; CHEMICAL ANALYSIS; CHROMIUM; CONTINENTAL CRUST; DIKES; ENRICHMENT; EROSION; EXTRUSION; MAGMA; MIXING; MULTI-ELEMENT ANALYSIS; NICKEL; POTASSIUM OXIDES; RARE EARTHS; RHYOLITES; RUBIDIUM; SILICON OXIDES; SOLIDS FLOW; TERTIARY PERIOD; TRACE AMOUNTS; TUFF; VOLCANIC ROCKS; ALKALI METAL COMPOUNDS; ALKALI METALS; ALKALINE EARTH METALS; CENOZOIC ERA; CHALCOGENIDES; CHEMISTRY; EARTH CRUST; ELEMENTS; FABRICATION; FEDERAL REGION VIII; FLUID FLOW; GEOLOGIC AGES; GEOLOGIC STRUCTURES; IGNEOUS ROCKS; MATERIALS WORKING; METALS; NORTH AMERICA; OXIDES; OXYGEN COMPOUNDS; POTASSIUM COMPOUNDS; ROCKS; SILICON COMPOUNDS; TRANSITION ELEMENTS; USA 580000* -- Geosciences