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Correlation of ash-flow tuffs

1985; Geological Society of America; Volume: 96; Issue: 7 Linguagem: Inglês

10.1130/0016-7606(1985)96 2.0.co;2

1943-2674

Wes Hildreth, Gail A. Mahood,

High-pressure geophysics and materials

Research Article| July 01, 1985 Correlation of ash-flow tuffs WES HILDRETH; WES HILDRETH 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar GAIL MAHOOD GAIL MAHOOD 2Department of Geology, Stanford University, Stanford, California 94305 Search for other works by this author on: GSW Google Scholar Author and Article Information WES HILDRETH 1U.S. Geological Survey, Menlo Park, California 94025 GAIL MAHOOD 2Department of Geology, Stanford University, Stanford, California 94305 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1985) 96 (7): 968–974. https://doi.org/10.1130/0016-7606(1985)96 2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation WES HILDRETH, GAIL MAHOOD; Correlation of ash-flow tuffs. GSA Bulletin 1985;; 96 (7): 968–974. doi: https://doi.org/10.1130/0016-7606(1985)96 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 Discrimination and correlation of ash-flow sheets is important in structurally complex, long-lived volcanic fields where such sheets provide the best keys to the regional stratigraphic framework. Three-dimensional complexities resulting from pulsatory eruptions, sectorial emplacement, mechanical sorting during outflow, thermal and compositional zoning of magmas, the physical zoning of cooling units, and structural and erosional disruption can make such correlation and discrimination difficult. When lithologic, magnetic, petrographic, chemical, and isotopic criteria for correlating ash-flow sheets are critically evaluated, many problems and pitfalls can be identified. Distinctive phenocrysts, pumice clasts, and lithic fragments are among the more reliable criteria, as are high-precision K-Ar ages and thermal remanent magnetization (TRM) directions in unaltered welded tuff. Chemical correlation methods should rely principally upon welded or nonwelded pumice blocks, not upon the ash-flow matrix, which is subject to fractionation, mixing, and contamination during emplacement. Compositional zoning of most large sheets requires that many samples be analyzed before phenocryst, glass, or whole-rock chemical trends can be used confidently as correlation criteria. This content is PDF only. Please click on the PDF icon to access. 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.