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A crustal-upper-mantle model for the Colorado Plateau based on observations of crystalline rock fragments in the Moses Rock Dike

McGetchin, Thomas R. and Silver, Leon T. (1972) A crustal-upper-mantle model for the Colorado Plateau based on observations of crystalline rock fragments in the Moses Rock Dike. Journal of Geophysical Research, 77 (35). pp. 7022-7037. ISSN 0148-0227. doi:10.1029/JB077i035p07022.

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On the basis of the size, the abundance, and the petrographic character of xenoliths in the Moses Rock dike, a model for the vertical stratigraphy of crystalline rocks beneath the dike is proposed extending from near the surface to a depth of about 200 km. Sedimentary clasts, whose original position in the undisturbed vent walls is known but which are now within the intrusive breccia of the Moses Rock dike, show a decrease in size with distance of upward transport from their original position in the vent walls. This inverse relationship between fragment size and known depth of origin provides an empirical basis for a reconstructed model for the distribution of rocks on the basis of the particle size of fragments in the intrusive breccia. Metabasalt, granite, and granite gneiss are abundant in the upper part of the crust along the dike walls; diorite, gabbro, and amphibole schists of basic composition constitute intermediate layers, and garnet-bearing metagabbro (basic granulite gneiss) and serpentine schist are present in the lower crust. The crustal rock suite is predominantly metavolcanic and metaplutonic and basic in composition. Dense ultramafic rocks, possibly derived from the mantle, constitute about 0.3% of the breccia filling the dike and include jadeite-rich clinopyroxenite, eclogite, spinel-websterite, spinel-lherzolite, and garnet-lherzolite. The M discontinuity appraently occurs within a petrologically complex region and may coincide with phase and compositional transitions, which include hydration. A compositional transition within the upper mantle between spinel- and garnet-peridotite (lherzolite) is inferred. The variety and the abundance of ultramafic and dense types, together with the complexity of their textures, suggest that the mantle may be as complicated as the crust in composition and history.

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Additional Information:Copyright 1972 by the American Geophysical Union. (Received February 25, 1972; revised August 8, 1972.) We are grateful for reviews by E. Wolfe and D. Stuart-Alexander of the U.S. Geological Survey, and Herwart Helmstaedt of McGill University, and for helpful discussions with many colleagues. In particular, we thank E. M. Shoemaker for advice, stimulation, and support over many years. This report summarizes research carried on from 1965 to the present. It was supported by the National Aeronautics and Space Administration through grants to M.I.T. (NGR-22-009-637) and to the U.S. Geological Survey's Center for Astrogeology (R-66), by the Geological Society of America (Penrose grant 1040-65), by the Atomic Energy Commission under contract to the California Institute of Technology (AT (04-3)-767, CALT-767P7-61), by the U.S. Air Force (under faculty research project AFIT-68-14, Air Force Institute of Technology and AFIT-OAR contract F-33601-69-C-0568), and by the National Science Foundation (GA-31728). The senior author held a NASA graduate traineeship at Cal Tech from 1965 to 1967 at the inception of the project; from 1967 to 1969, he was an active duty captain in the U.S. Air Force assigned as assistant professor in the School of Engineering, AFIT, Wright-Patterson Air Force Base, Ohio; he is currently assistant professor, Department of Earth and Planetary Sciences, M.I.T. Division of Geological and Planetary Sciences, California Institute of Technology contribution 1919.
Funding AgencyGrant Number
Geological Society of America Penrose Bequest Research Grants1040-65
Atomic Energy CommissionAT (04-3)-767
Air Force Institute of TechnologyAFIT-68-14
Air Force Institute of TechnologyF-33601-69-C-0568
NASA Graduate FellowshipUNSPECIFIED
Subject Keywords:Crust; Igneous Rocks; Inclusions; Mantle; Metamorphic Rocks; Utah
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Caltech Division of Geological and Planetary Sciences1919
Issue or Number:35
Record Number:CaltechAUTHORS:20141111-135550881
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Official Citation:McGetchin, T. R., and L. T. Silver (1972), A crustal-upper-mantle model for the Colorado Plateau based on observations of crystalline rock fragments in the Moses Rock Dike, J. Geophys. Res., 77(35), 7022–7037, doi:10.1029/JB077i035p07022.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51593
Deposited By: George Porter
Deposited On:11 Nov 2014 22:20
Last Modified:10 Nov 2021 19:13

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