Actinolite-forming reaction at low pressure and the role of Fe2+-Mg substitution

Terabayashi, Masaru

doi:10.1007/bf00379738

Cited by 15 publications

(21 citation statements)

References 32 publications

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“…A close field association or coexistence of the phases prehnite, pumpellyite, and actinolite have been reported in (1) Aroostook County, Maine (Richter and Roy, 1976); (2) the Swiss Alps (Coombs et al, 1976); (3) the Welsh basin (Roberts, 1981;Bevins and Rowbotham, 1983;Merriman et al, 1986;Bevins and Merriman, 1988); (4) the South Island of New Zealand (Bishop, 1972;Houghton, 1982); (5) the Hamersley basin of West Australia (Smith et al, 1982); (6) the Precambrian of Sweden (Nystrom, 1983); (7) New South Wales, Australia (Offler, 1984); (8) the Karmutsen Volcanics, Vancouver Island, British Columbia (B.C.) Terabayashi, 1988); and (9) the Smartville Complex, California Springer et al, 1992). Liou et al (1987) proposed that the disappearance of prehnite and pumpellyite in chlorite-rich bulk compositions should mark the beginning of the greenschist facies.…”

Section: Boundaries Among the Faciesmentioning

confidence: 99%

“…In rocks that include ferrous and ferric iron as major components, this assemblage may be at least divariant and coexist over a wide range of physical conditions, and the boundaries among the P-T fields assigned to the various facies may be high variance continuous reactions. The high variance of the natural assemblages undoubtedly lies at the heart of recent proposals for a prehnite-bearing subfacies of the pumpellyiteactinolite facies (Smith et al, 1982) and for a redefinition of the prehnite-actinolite facies to include both pumpellyite-bearing rocks and prehnite-absent rocks (Terabayashi, 1988). Frey et al (1991) showed that there is a high degree of overlap of pressures and temperatures in which assemblages of the key index minerals prehnite, pumpellyite, epidote, and actinolite are stable.…”

Section: Boundaries Among the Faciesmentioning

confidence: 99%

“…Coombs et al 1977Evarts and Schiffman 1983Liou et al 1983Terabayashi 1988 South lar progress for low-grade mafic rocks. Most investigations of the mineralogy of low-grade rocks have focused on attempts to correlate relative metamorphic grades and P-T conditions with the compositions of the individual common minerals.…”

Section: Oliver and Leggett 1980mentioning

confidence: 99%

“…Nakajima et al (1977) and Nakajima (1982) proposed that Fe 3+ /(Fe 3+ + Al) in epidote could be used as a geothermometer in pumpellyite-actinolite facies schists. However, according to Terabayashi (1988), Aiba (1982) demonstrated that Fe 3+ /(Fe 3+ + Al) in epidote is sensitive to bulkrock Fe 2+ /(Fe 2+ + Mg). Cho et al (1986) and Terabayashi (1988) documented opposite trends in the composition of epidote versus metamorphic grade in two traverses through the Karmutsen Volcanics, located -20 km apart on Vancouver Island, B.C.…”

Section: Epidotementioning

confidence: 99%

“…However, according to Terabayashi (1988), Aiba (1982) demonstrated that Fe 3+ /(Fe 3+ + Al) in epidote is sensitive to bulkrock Fe 2+ /(Fe 2+ + Mg). Cho et al (1986) and Terabayashi (1988) documented opposite trends in the composition of epidote versus metamorphic grade in two traverses through the Karmutsen Volcanics, located -20 km apart on Vancouver Island, B.C. A miscibility gap from 12%-22% Fe/(Fe + Al) has been proposed by several authors (Strens, 1965;Hietanen, 1974;Raith, 1976).…”

Section: Epidotementioning

confidence: 99%

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Mineral paragenesis of pumpellyite in low-grade mafic rocks

Beiersdorfsser

Day

1995

Low-Grade Metamorphism of Mafic Rocks

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Our understanding of low-grade, mafic, metamorphic rocks is relatively primitive compared to higher grade equivalents, in large part because of the abundance of relict minerals, the difficulties of studying fine-grained rocks, and the difficulties of establishing the existence and scale of chemical equilibrium. However, work carried out during the past decade has identified the systematic correspondence between effective bulk compositions and mineral assemblage that is required by the metamorphic facies concept, and a large body of data defines the mineral pangeneses of coexisting pumpellyite (Pmp), prehnite (Prh), amphibole (Ab), and epidote (Ep). At pressures and temperatures typical of many regional metamorphic ter- rains, rocks containing Ep + Ab + quartz (Qtz) may have, in addition, chlorite (Chi) + actinolite (Act) in magnesian bulk compositions, Chi + Pmp in more ferroan compositions, and Prh in compositions relatively lower in aluminum and ferric iron. Act + Pmp ± Chi ± Prh may coexist in a narrow range of compositions with intermediate values of Mg/(Mg + Fe 2+ ). Improvements in thermodynamics data bases now permit calculation of pressures and temperatures for low variance assemblages.The results of systematic examination of mineral assemblages and calculations of petrogenetic grids for epidote-bearing rocks suggest that the stability field of the Prh-Pmp facies is entirely contained within the overlapping stability fields of the Pmp-Act and Prh-Act facies. At pressures typical of the most common metamorphic field gradients, the stability fields of the three facies cannot be distinguished.The predictability of mineral assemblages and the recent success in calculating meaningful pressure and temperature for low-grade rocks suggest that, under favorable circumstances, mineralogical approaches rooted in the assumptions of equilibrium thermodynamics are likely to prove as useful for determining the physical conditions of low-grade metamorphism as they have been for high-grade rocks.

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