Petrogenesis of Mount Rainier andesite: Magma flux and geologic controls on the contrasting differentiation styles at stratovolcanoes of the southern Washington Cascades

Research Article| January 01, 2014 Petrogenesis of Mount Rainier andesite: Magma flux and geologic controls on the contrasting differentiation styles at stratovolcanoes of the southern Washington Cascades T.W. Sisson; T.W. Sisson † 1U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA †E-mail: tsisson@usgs.gov (Sisson, corresponding); salters@magnet.fsu.edu (Salters); plarson@wsu.edu (Larson). Search for other works by this author on: GSW Google Scholar V.J.M. Salters; V.J.M. Salters † 2National High Magnetic Field Laboratory, Isotope Geochemistry, and Department of Geological Sciences, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310, USA †E-mail: tsisson@usgs.gov (Sisson, corresponding); salters@magnet.fsu.edu (Salters); plarson@wsu.edu (Larson). Search for other works by this author on: GSW Google Scholar P.B. Larson P.B. Larson † 3Department of Geology, Washington State University, Pullman, Washington 99164, USA †E-mail: tsisson@usgs.gov (Sisson, corresponding); salters@magnet.fsu.edu (Salters); plarson@wsu.edu (Larson). Search for other works by this author on: GSW Google Scholar GSA Bulletin (2014) 126 (1-2): 122–144. https://doi.org/10.1130/B30852.1 Article history received: 15 Jan 2013 rev-recd: 17 Jun 2013 accepted: 23 Sep 2013 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation T.W. Sisson, V.J.M. Salters, P.B. Larson; Petrogenesis of Mount Rainier andesite: Magma flux and geologic controls on the contrasting differentiation styles at stratovolcanoes of the southern Washington Cascades. GSA Bulletin 2014;; 126 (1-2): 122–144. doi: https://doi.org/10.1130/B30852.1 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 Quaternary Mount Rainier (Washington, USA) of the Cascades magmatic arc consists of porphyritic calc-alkaline andesites and subordinate dacites, with common evidence for mingling and mixing with less evolved magmas encompassing andesites, basaltic andesites, and rarely, basalts. Basaltic andesites and amphibole andesites (spessartites) that erupted from vents at the north foot of the volcano represent some of Mount Rainier's immediate parents and overlap in composition with regional basalts and basaltic andesites. Geochemical (major and trace elements) and isotopic (Sr, Nd, Pb, O) compositions of Mount Rainier andesites and dacites are consistent with modest assimilation (typically ≤20 wt%) of evolved sediment or sediment partial melt. Sandstones and shales of the Eocene Puget Group, derived from the continental interior, are exposed in regional anticlines flanking the volcano, and probably underlie it in the middle to lower crust, accounting for their assimilation. Mesozoic and Cenozoic igneous basement rocks are unsuitable as assimilants due to their high 143Nd/144Nd, diverse 206Pb/204Pb, and generally high δ18O.The dominant cause of magmatic evolution at Mount Rainier, however, is inferred to be a version of in situ crystallization-differentiation and mixing (Langmuir, 1989) wherein small magma batches stall as crustal intrusions and solidify extensively, yielding silicic residual liquids with trace element concentrations influenced by accessory mineral saturation. Subsequent magmas ascending through the intrusive plexus entrain and mix with the residual liquids and low-degree re-melts of those antecedent intrusions, producing hybrid andesites and dacites. Mount St. Helens volcanic rocks have geochemical similarities to those at Mount Rainier, and may also result from in situ differentiation and mixing due to low and intermittent long-term magma supply, accompanied by modest crustal assimilation. Andesites and dacites of Mount Adams isotopically overlap the least contaminated Mount Rainier magmas and derive from similar parental magma types, but have trace element variations more consistent with progressive crystallization-differentiation, probably due to higher magma fluxes leading to slower crystallization of large magma batches, allowing time for progressive separation of minerals from melt. Mount Adams also sits atop the southern projection of a regional anticlinorium, so Eocene sediments are absent, or are at shallow crustal levels, and so are cold and difficult to assimilate. Differences between southwest Washington stratovolcanoes highlight some ways that crustal geology and magma flux are primary factors in andesite generation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.