Magma degassing buffered by vapor flow through brecciated conduit margins

Research Article| April 01, 2004 Magma degassing buffered by vapor flow through brecciated conduit margins A.C. Rust; A.C. Rust 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA Search for other works by this author on: GSW Google Scholar K.V. Cashman; K.V. Cashman 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA Search for other works by this author on: GSW Google Scholar P.J. Wallace P.J. Wallace 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA Search for other works by this author on: GSW Google Scholar Author and Article Information A.C. Rust 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA K.V. Cashman 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA P.J. Wallace 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA Publisher: Geological Society of America Received: 03 Dec 2003 Revision Received: 04 Jan 2004 Accepted: 05 Jan 2004 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2004) 32 (4): 349–352. https://doi.org/10.1130/G20388.2 Article history Received: 03 Dec 2003 Revision Received: 04 Jan 2004 Accepted: 05 Jan 2004 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation A.C. Rust, K.V. Cashman, P.J. Wallace; Magma degassing buffered by vapor flow through brecciated conduit margins. Geology 2004;; 32 (4): 349–352. doi: https://doi.org/10.1130/G20388.2 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 SocietyGeology Search Advanced Search Abstract Obsidian pyroclasts, a common component of rhyolitic tephra, preserve a range of volatile contents, which has been used to infer syneruptive conditions of magmatic degassing. Here we show that the textures of obsidian pyroclasts provide information on physical mechanisms of magma flow and degassing along conduit margins. Obsidian clasts often contain xenoliths, sheared bands of lithic powder, and textures consistent with magma autobrecciation. These features suggest that pyroclastic obsidian primarily forms near conduit walls where magma fragments and reanneals during ascent. We use these observations to develop a degassing model for pyroclastic obsidian from the A.D. 1340 Mono Craters, California, eruptions. We suggest that degassing was buffered by continual flux of vapor through highly permeable, brecciated magma along conduit walls. Continuous reequilibration of magma with vapor of relatively constant composition not only explains the CO2-H2O and δD-H2O data from Mono Craters pyroclastic obsidian, but also requires much lower magmatic CO2 values than the commonly accepted model of closed-system degassing. Taken together, the chemical and physical evidence suggests that magma brecciation along conduit walls aids the degassing of ascending rhyolite. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.