Petrology and geochemistry of the Cretaceous Independence volcanic suite, Absaroka Mountains, Montana: Clues to the composition of the Archean sub-Montanan mantle

Abstract

Research Article| February 01, 1987 Petrology and geochemistry of the Cretaceous Independence volcanic suite, Absaroka Mountains, Montana: Clues to the composition of the Archean sub-Montanan mantle JAMES K. MEEN; JAMES K. MEEN 1Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802 Search for other works by this author on: GSW Google Scholar DAVID H. EGGLER DAVID H. EGGLER 1Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802 Search for other works by this author on: GSW Google Scholar Author and Article Information JAMES K. MEEN 1Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802 DAVID H. EGGLER 1Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1987) 98 (2): 238–247. https://doi.org/10.1130/0016-7606(1987)98<238:PAGOTC>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 MailTo Tools Icon Tools Get Permissions Search Site Citation JAMES K. MEEN, DAVID H. EGGLER; Petrology and geochemistry of the Cretaceous Independence volcanic suite, Absaroka Mountains, Montana: Clues to the composition of the Archean sub-Montanan mantle. GSA Bulletin 1987;; 98 (2): 238–247. doi: https://doi.org/10.1130/0016-7606(1987)98<238:PAGOTC>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 Igneous activity at Independence volcano, a major center in the Eastern Absaroka Belt of Montana, occurred between 92 and 84 m.y. ago. Magma series from high-alumina tholeiitic basaltic andesite through shoshonite to high-K dacite and from high-magnesium andesite to banakite are recognized. Major-and trace-elememt compositions of these rocks are modeled by precipitation of observed phenocryst phases. Crystallizing assemblages are dominated by plagioclase and include two pyroxenes and magnetite. Parental rocks of each suite are LILE-enriched, with strong LREK-enrichment (LaN/YbN = 10–15) but do not have high alkali/alkaline-earth ratios (Rb/Sr = 0.020–0.028). Although superficially similar to those observed in many orogenic volcanics, trace-element patterns of Independence volcanics show certain distinctive characteristics, particularly in extreme enrichments in alkaline earths and LREE relative to actinides. Differences between trace-element patterns of Independence volcanics and orogenic andesites argue against significant involvement of a subducted slab in the genesis of the rocks considered here. Rather, trace-element characteristics are interpreted to reflect those of subcontinental mantle of the Beartooth region.Mantle-derived rocks have (87Sr/86Sr)i of 0.7046–0.7054, (143Nd/144Nd)i of 0.5114–0.5119, and (206Pb/204Pb)i of 16.0–17.4, values that are consistent with the trace-element enrichments and with ancient ages of enrichment events. Pb isotopic compositions display correlations of 207Pb/204Pb and 206Pb/204Pb interpreted to be secondary isochrons recording ages of mantle enrichment, 3.8 and 2.0 b.y. Pre–3.8-b.y. mantle had µ = 9.75. 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.