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: