Thermobarometry of cumulate xenoliths: implications for basalt ponding under the Colorado Plateau, Arizona
Many recent studies in petrology have alluded to ponding of basaltic magma at the base of the crust as a heat source for simultaneous assimilation/fractional crystallization and metamorphic processes. New thermodynamic data permit calibration of thermobarometers involving common gabbroic assemblages in the system CMAS. Two reactions involving the mineral assemblages opx, cpx, plag, and spinel can be combined to yield unique solutions for pressure and temperature. A third relationship applicable to this assemblage is the two pyroxene thermometer. Activity models are available for all of these components. These relationships have been applied to mafic cumulate xenoliths entrained in basalt lavas of the San Francisco Peaks Volcanic Field, yielding equilibration conditions of P = 12.2-14.5 kbars and T = 1200-1100/sup 0/C. These pressures are coincident with a MOHO depth of 40-45kms and may be an excellent example of massively accumulated and fractionated alkaline basalt underlying anorogenic continental crust, giving rise to crustal melting processes manifested by the Quaternary silicic volcanism of the field.
- Research Organization:
- Univ. of Michigan, Ann Arbor (USA)
- OSTI ID:
- 6459225
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ARIZONA
BASALT
GEOBAROMETRY
GEOTHERMOMETRY
PETROGENESIS
PETROLOGY
CHEMICAL REACTIONS
COLORADO PLATEAU
CRYSTALLIZATION
GEOCHEMISTRY
GEOTHERMOMETERS
INCLUSIONS
MAGMA
MAGMATISM
METAMORPHISM
PRESSURE EFFECTS
TEMPERATURE EFFECTS
THERMODYNAMIC PROPERTIES
CHEMISTRY
FEDERAL REGION IX
GEOLOGY
IGNEOUS ROCKS
MEASURING INSTRUMENTS
MOUNTAINS
NORTH AMERICA
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
ROCKS
THERMOMETERS
USA
VOLCANIC ROCKS
580400* - Geochemistry- (-1989)
580300 - Mineralogy
Petrology
& Rock Mechanics- (-1989)