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Ab-An Binary vs. Water Pressure
Johannes, 1978; Morse, 1980
Hypersolvus vs. Subsolvus Granites
Yoder et al., 1957; Morse, 1970
An-Ab-Kfsp Ternary - Flattened
An-Kfsp Binary
An-Ab BinaryAb-Kfsp Binary
Nekvasil & Lindsley, 1990; Brown, 1993
Intersection of Liquidus Surfaces
Temperature fallsfrom E toward Min Thermal Valley
An-Ab-Kfsp Perspective
Solvus or Miscibility Gap
Feldspar Tielines
Smith & Carmichael, 1969; Fuhrman & Lindsley, 1988; Best et al., 1995
Rhyolite Pumice
Trachybasalt
An-Ab-Kfsp Ternary Liquid Line of Descent
Water Saturated Granite System
Effect of Pressure and Granite Modes
Origin of Granitoids• Phase equilibria support either that granitoids are
either the end product of fractional crystallization of a mafic parent or the partial melt generated from the melting of sialic crust - large corresponding extrusive equivalents suggests large magma chambers of equivalent composition.
• Field relations suggest that large plutons have diffuse boundaries and many seem to show variable and locally pervasive overprint of subsolidus recrystallization indicative of metamorphic origin.
Granitic System Liquid Line of Descent
Initial Bulk Composition
Pyroxene Quadrilateral
Mica and Amphibole - Melt Equilibria
Wones & Eugster, 1965
Thermal Stability of Volatile Minerals
thermal energy + volatile-richmineral = volatile-free or volatile-poor mineral(s) +volatile fluid
Assessing States of Equilibrium
• Isolated anhedral grains that resulted from partial resorption or dissolution into the melt
• Reaction rims of one or more phases surrounding another anhedral crystalline phase.
• Compositionally zoned grains originate through incomplete reaction relations within a single solid solutions, e.g. plagioclase.
• Presence of minerals or a mineral assemblage that is known to be unstable or unlikely in an evolutionary sense, e.g. Mg-olivine and qtz together.
Disequilibrium states are suggested by the following: