Petrology of Andesitic, Spilitic, and Keratophyric Flow Rock, North-Central Puerto Rico

Abstract

Research Article| January 01, 1965 Petrology of Andesitic, Spilitic, and Keratophyric Flow Rock, North-Central Puerto Rico EDWARD G LIDIAK EDWARD G LIDIAK Dept. Earth and Planetary Sciences, University of Pittsburgh, Pittsburgh, Pa. Search for other works by this author on: GSW Google Scholar Author and Article Information EDWARD G LIDIAK Dept. Earth and Planetary Sciences, University of Pittsburgh, Pittsburgh, Pa. Publisher: Geological Society of America Received: 06 Mar 1964 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1965, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1965) 76 (1): 57–88. https://doi.org/10.1130/0016-7606(1965)76[57:POASAK]2.0.CO;2 Article history Received: 06 Mar 1964 First Online: 02 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 EDWARD G LIDIAK; Petrology of Andesitic, Spilitic, and Keratophyric Flow Rock, North-Central Puerto Rico. GSA Bulletin 1965;; 76 (1): 57–88. doi: https://doi.org/10.1130/0016-7606(1965)76[57:POASAK]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 Chemical, mineralogical, and petro-graphical variations in a thick accumulation of andesitic, spilitic, and keratophyric flow rock result mainly from compositional differences and crystallization history.Together, the clinopyroxene-rich and plagioclase-rich andesitic rocks (1) range from andesitic basalt to dacite, (2) show a calc-alkalic chemical trend, (3) contain plagioclase and clinopyroxene rich in Ca, (4) generally contain no olivine, and (5) show no Fe enrichment. Their origin is attributed to partial fusion under hydrous conditions: magmas of plagioclase-rich rocks formed at depths where basaltic phases existed; magmas of clinopyroxene-rich rocks where eclogitic phases existed.Plagioclase-rich spilitic rocks generally differ from their andesitic counterparts in having (1) higher Na and K, and lower Ca, Mg, and Al; (2) lower phenocryst content; (3) greater alteration; (4) greater cloudiness of plagioclase; (5) slightly lower inferred Ca content in some clinopyroxenes; and (6) no actinolite. Clinopyroxene-rich rocks show the same differences but are more variable chemically. High-K andesitic rocks otherwise resemble normal andesitic rocks. Spilitic rocks resemble andesitic rocks in matrix textures and in apparent simultaneous crystallization of plagioclase and clinopyroxene. Calcic plagioclase is relict in some spilitic rocks, and Ca-rich secondary minerals occur in both. The spilitic rocks are interpreted as having formed from andesitic rocks during the late-magmatic or deuteric stage, although they may have resulted from postconsolidation metasomatism.Keratophyric rocks occur only in plagioclase-rich associations. Quartz content suggests that most keratophyres are felsic magmatic rocks; other felsic rocks in the map area contain excess quartz and are products of hydrothermal silicification. 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.