Transition equilibria from the prehnite-pumpellyite to greenschist facies in the Karmutsen metabasites, Vancouver Island, B. C
Thermally-metamorphosed Karmutsen metabasites in NE Vancouver Island, B.C. expose a complete set of progressive mineral assemblages ranging from the zeolite to pyroxene hornfels facies toward the intrusive contact. This study deals with characteristic mineral assemblages ranging from (i) prehnite (pr) + pumpellyite (pp) + epidote (ep), pr + pp + calcite (cc), and pp + ep + cc for prehnite-pumpellyite (PP) facies; through (ii) pr + ep + cc for prehnite-actinolite (PRA) facies; to (iii) actinolite (act) + ep + cc for greenschist (GS) facies. Wairakite with a significant analcime component (wk76am24) coexists with epidote or Al-rich pumpellyite in one PP facies sample. Mg-bearing epidote (up to 1.2 wt % MgO) pseudomorphic after pumpellyite often occurs as a transitional phase in the PRA facies rocks. Mineral compositions of amygdaloidal assemblages from 21 samples were studied in detail. Progressive changes in the compositions and assemblages of Ca-Al silicates are chemographically and theoretically interpreted, on the basis of the predicted P-T grid for the model basaltic system, CaO-MgO-Al/sub 2/O/sub 2/-Fe/sub 2/O/sub 3/-SiO/sub 2/-H/sub 2/O-CO/sub 2/. Although the facies boundaries are gradational due to the multi-variance of the assemblages, two transition equilibria are established for the Karmutsen metabasites: (1) pp + qtz + CO/sub 2/ = pr + ep + cc + chl + H/sub 2/O for the boundary between PP and PRA facies; (2) cc + chl + qtz = ep + act + H/sub 2/O + CO/sub 2/ for that between PRA and GS facies. At constant X/sub H20/, the former is a discontinuous reaction but the latter is of continuous type in the model system. Phase equilibria together with the paragenetic and compositional data of Ca-Al silicates indicate that the PP to GS facies metamorphism occurred at: 14. kb < P < 1.8 kb and 250/sup 0/C < t < 350/sup 0/C.
- Research Organization:
- Stanford Univ., CA (USA)
- OSTI ID:
- 6612079
- 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
BASALT
METAMORPHISM
BRITISH COLUMBIA
HORNFELSES
SCHISTS
GEOCHEMISTRY
MINERALOGY
CALCITE
CHEMICAL COMPOSITION
EPIDOTES
EQUILIBRIUM
GEOLOGIC MODELS
MINERALIZATION
PARAGENESIS
PHASE STUDIES
ZEOLITES
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CALCIUM SILICATES
CANADA
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHEMISTRY
IGNEOUS ROCKS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
IRON COMPOUNDS
IRON SILICATES
MATERIALS
METAMORPHIC ROCKS
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
VOLCANIC ROCKS
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)
580400 - Geochemistry- (-1989)