Decompression melting: an isothermal polybaric liquidus diagram for charnockites
Partial melting in the crust is likely to be most effective, in the absence of abundant aqueous vapor, where hydrates are present. Melting under vapor-absent conditions give rise to magma or migma that is upwardly mobile. Hence equilibria may be usefully shown in isothermal polybaric liquidus diagrams. The present schematic diagram involves quartz (QTZ), K-feldspar (KFS), biotite (BIO), orthopyroxene (OPX), liquid (L) and vapor (V) in the system KAlO/sub 2/-MgO-SiO/sub 2/-H/sub 2/O, for a temperature of about 850/sup 0/C, above the low-pressure invariant point. MgO-contents of liquids are exaggerated for clarity. Arrows indicate decreasing pressure, and relations at high pressures are analogous to those shown by Eggler (1972). Primary phase fields are for KFS, OPX and BIO, contoured in terms of pressure. Only liquids on the outer curved boundary are H/sub 2/O-saturated; the other boundary lines are vapor-absent, intersecting at a ternary peritectic point. For example, for a QTZ-BIO protolith, melting starts at this ternary peritectic and continues with melting of KFS and OPX until KFS is exhausted. The L changes towards OPX until it becomes H/sub 2/O-saturated, whence crystallization of OPX and dehydration occur until the low-pressure ternary eutectic is attained and a charnockite with aqueous vapor results. Given the low MgO-contents expected in liquids in this system, it is likely that any reasonable liquids produced would be orthopyroxene-bearing granites of restricted composition, whereas restites segregated after melting would have much more variable compositions, very dependent on the protoliths.
- Research Organization:
- Univ. of Minnesota, Duluth (USA)
- OSTI ID:
- 6863014
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Vol. 17; ISSN GAAPB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580400* -- Geochemistry-- (-1989)
ACTIVATION ENERGY
BIOTITE
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMICAL REACTION KINETICS
EARTH CRUST
ENERGY
FELDSPARS
IGNEOUS ROCKS
ISOTHERMAL PROCESSES
KINETICS
MAGMA
MAGMATISM
MICA
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PETROCHEMISTRY
PETROGENESIS
PRESSURE EFFECTS
PYROXENES
QUARTZ
REACTION KINETICS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
TEMPERATURE EFFECTS