Compositions of melts coexisting with plagioclase, augite, and olivine,or low-calcium pyroxene, at anhydrous and hydrous conditions and pressures from 1 atm. to 8 kbar: application to the petrogenesis of Aleutian and Mariana Island arc rocks and Columbia River basalts

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6898740

Baker, D R; Eggler, D H

Anhydrous and hydrous, 2% water in the melt, experiments have been performed on a suite of high-alumina basalts and andesites from the Aleutian and Mariana island arcs. Compositions of experimentally produced melts coexisting with plagioclase (plag), augite (aug), and olivine (ol), or low-calcium pyroxene (lpx) have been used to construct liquid lines of multiple saturation (LLMS's) on pseudoternary diagrams. Anhydrous LLMS's at 1 atm. and 8 kbar and hydrous LLMS's at 2 and 5 kbar were determined. At 1 atm. and under hydrous conditions orthopyroxene (opx) is the stable lpx; at 8 kbar pigeonite (pig) is the stable lpx. Comparison of the plotted positions of the LLMS's and the compositions of rocks from the Aleutians suggest that basaltic andesites and andesites were produced by crystal fractionation of plag+aug+ol or plag+aug+opx from basaltic magmas with less than 2% water content at pressure between 2 and 5 kbar. Comparison of the LLMS's with the compositions of Columbia River Basalts indicates that crystal fractionation of plag+aug+ol (or lpx) in magma chambers at Moho depths cannot alone account for the observed compositional trend; instead the trend is probably due to some combination of polybaric fractionation, contamination, and possibly mixing of magmas between deep and shallow magma chambers.

• Research Organization: Smithsonian Institution, Washington, DC (USA)
• OSTI ID: 6898740
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

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54 ENVIRONMENTAL SCIENCES
ALEUTIAN ISLANDS
ALKALINE EARTH METAL COMPOUNDS
ANDESITES
ANORTHOSITES
BASALT
CHEMICAL COMPOSITION
COMPARATIVE EVALUATIONS
GABBROS
IGNEOUS ROCKS
IRON COMPOUNDS
IRON SILICATES
ISLANDS
MAGMATISM
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MARIANA ISLANDS
MINERALOGY
MINERALS
NORTH AMERICA
OLIVINE
OXYGEN COMPOUNDS
PETROCHEMISTRY
PETROGENESIS
PLUTONIC ROCKS
PRESSURE EFFECTS
PYROXENES
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRUST TERRITORY OF THE PACIFIC ISLANDS
USA
VOLCANIC ROCKS