Petrogenesis of the Superstition-Superior Volcanic Area as Inferred from Strontium- and Oxygen-Isotope Studies

Research Article| June 01, 1973 Petrogenesis of the Superstition-Superior Volcanic Area as Inferred from Strontium- and Oxygen-Isotope Studies JOHN S. STUCKLESS; JOHN S. STUCKLESS 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar JAMES R. O'NEIL JAMES R. O'NEIL 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1973) 84 (6): 1987–1998. https://doi.org/10.1130/0016-7606(1973)84<1987:POTSVA>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation JOHN S. STUCKLESS, JAMES R. O'NEIL; Petrogenesis of the Superstition-Superior Volcanic Area as Inferred from Strontium- and Oxygen-Isotope Studies. GSA Bulletin 1973;; 84 (6): 1987–1998. doi: https://doi.org/10.1130/0016-7606(1973)84<1987:POTSVA>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 Apparent initial Sr87/Sr86 ratios of five ash-flow tuffs (0.7063 to 0.7139) and several mafic to silicic lavas (0.7055 to 0.7131) indicate that the magmas were derived below the base of the Precambrian granitic crust (0.7231 to 1.0906). Liquidus compositions in the system Q-Or-Ab-H2O and oxygen-isotope geother-mometry suggest that the silicic magmas started to crystallize quartz, magnetite, and two feldspars in a water-undersaturated environment of high pressure (∼10 kb) and moderate temperature of at least 830°C.During or after ascent into the crust, the magmas underwent varying degrees of crystal-melt re-equilibration. Measured plagioclase-biotite O18 fractionations (0.5 to 0.7) imply a temperature that is too high for the observed mineral assemblage, and the inference is that the two minerals did not crystallize in equilibrium. Prior to eruption, the upper part of the magma column assimilated crustal Sr such that the base of each ash flow is now enriched in Sr87. In some cases, this assimilation was too rapid to allow crystal-melt equilibration of Sr isotopes. δO18 values for the magmas are within the range typical of similar magma types, indicating that no significant interaction took place between the melts and meteoric water; however, some rocks have exchanged oxygen isotopes with meteoric water at low temperatures after eruption.Some of the magma appears to have had a long residence in the crust at lower pressure (1 kb) and temperature (750°C), because two of the ash-flow tuffs and one lava are greatly enriched in Sr87 and have largely re-equilibrated under the P-T conditions of a shallow magma chamber. Even these, however, have retained evidence for a multistage genesis. 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.