CONTRASTING SEQUENCES OF METAPELITIC MINERAL-ASSEMBLAGES IN THE AUREOLE OF THE TILTED NELSON BATHOLITH, BRITISH COLUMBIA: IMPLICATIONS FOR PHASE EQUILIBRIA AND PRESSURE DETERMINATION IN ANDALUSITE SILLIMANITE-TYPE SETTINGS

2005 ◽  
Vol 43 (1) ◽  
pp. 51-88 ◽  
Author(s):  
D. R.M. Pattison ◽  
J. J. Vogl
Keyword(s):  
British Columbia ◽  
Phase Equilibria ◽  
Mineral Assemblages

Metamorphism of the Settler Schist, southwest of Yale, British Columbia

1976 ◽  
Vol 13 (3) ◽  
pp. 405-421 ◽  
Author(s):  
Lee C. Pigage
Keyword(s):  
British Columbia ◽  
Linear Regression ◽  
Microprobe Analysis ◽  
Regional Metamorphism ◽  
Fluid Phase ◽  
Contact Metamorphism ◽  
Major Constituent ◽  
Minor Components ◽  
Mineral Assemblages ◽  
Regression Techniques

Pelitic metasediments immediately southwest of Yale, British Columbia contain mineral assemblages characteristic of staurolite through sillimanite zones of the Barrovian facies series. Microprobe analyses of major constituent phases in the pelites are combined with linear regression techniques to formulate probable kyanite- and sillimanite-forming reactions.A zone some 3 km wide contains the assemblage staurolite–kyanite–garnet–biotite–muscovite–quartz–plagioclase-ilmenite-rutile, which is univariant in AFM projection. Within precision limits of microprobe analysis, this assemblage is also univariant using linear regression techniques. Univariant relations are possible if [Formula: see text] with the composition of the fluid phase being buffered by the progressing reaction. This assemblage emphasizes the need for precise analyses when using the regression method, since minor components are often within permissible error limits rather than being balanced.Pelitic and calc-silicate assemblages from the metasediments restrict estimates of pressure–temperature conditions during regional metamorphism to 6–8 kbar and 550–770 °C. Pseudomorphs after andalusite indicate that contact metamorphism preceded regional upgrading of the pelites.

Phase equilibria and mixed parageneses of metabasites in lowgrade metamorphism

1985 ◽  
Vol 49 (352) ◽  
pp. 321-333 ◽  
Author(s):  
J. G. Liou ◽  
S. Maruyama ◽  
M. Cho
Keyword(s):  
Phase Equilibria ◽  
Model System ◽  
Metamorphic Grade ◽  
Low Grade ◽  
Qualitative And Quantitative ◽  
Basaltic Rocks ◽  
Mineral Assemblages ◽  
The Common ◽  
Invariant Points ◽  
Model Phase

AbstractThe system Na2O-CaO-MgO Al2O3-SiO2-H2O is proposed to model phase equilibria and mineral parageneses for low-temperature metamorphism of basaltic rocks. Univariant reactions marking the transitions between various sub-greenschist facies are identified and some have been experimentally determined. The introduction of Fe2O3 into the model system at fixed FeO/MgO ratio creates continuous reactions for facies boundaries and discontinuous reactions for invariant points of the model system. Both qualitative and quantitative effects on P-T displacement and phase compositions are discussed. The XFe3+ isopleths for epidote were plotted to exemplify the transition from the zeolite through prehnite-pumpellyite to prehnite-actinolite facies. T-XFe3+ relations were established for continuous and discontinuous reactions relating such facies transitions. Because of the common occurrence of two or three Ca-Al hydrosilicates in low-grade metabasites, an isobaric Al-Ca-Fe3+ projection from chlorite may be used to illustrate mineral assemblages and compositions of the coexisting Ca-Al silicates in the presence of quartz, albite, and chlorite. Reported occurrences in several classic burial metamorphic terrains and ocean-floor metabasites in ophiolites are described. Only the composition of a mineral from a buffered assemblage can constrain the intensive properties for metamorphism; previously reported compositional trends for pumpellyite and epidote with increasing metamorphic grade are oversimplified.

Calculated phase equilibria in K2O-FeO-MgO-Al2O3-SiO2-H2O for sapphirine-quartz-bearing mineral assemblages

2004 ◽  
Vol 22 (6) ◽  
pp. 559-578 ◽  
Author(s):  
D. E. Kelsey ◽  
R. W. White ◽  
T. J. B. Holland ◽  
R. Powell
Keyword(s):  
Phase Equilibria ◽  
Calculated Phase ◽  
Mineral Assemblages

Granulite Facies Metamorphism in the Coast Range Crystalline Belt

1975 ◽  
Vol 12 (11) ◽  
pp. 1953-1955 ◽  
Author(s):  
Lincoln S. Hollister
Keyword(s):  
British Columbia ◽  
Granulite Facies ◽  
Coast Range ◽  
Geologic History ◽  
Granulite Facies Metamorphism ◽  
Mineral Assemblages ◽  
Facies Metamorphism ◽  
History Of

Mineral assemblages diagnostic of the granulite facies of metamorphism occur between Terrace and Prince Rupert, British Columbia. The estimated pressure (5–8 kb) and temperature (750–850 °C) of metamorphism are important constraints in unravelling the geologic history of the Coast Range batholithic complex.

Phase Equilibria in the System MgO-Al2O3-SiO2-H2O: Chlorites and Associated Minerals

1973 ◽  
Vol 39 (303) ◽  
pp. 297-312 ◽  
Author(s):  
Bruce Velde
Keyword(s):  
Solid Solution ◽  
Chemical Composition ◽  
Low Temperature ◽  
Phase Equilibria ◽  
Water Pressure ◽  
Positive Slope ◽  
Natural Mineral ◽  
Natural Minerals ◽  
Cell Dimensions ◽  
Mineral Assemblages

SummaryTwenty-six compositions in the system MgO-Al2O3-SiO2-H2O were investigated under conditions of 1 and 2 Kb water pressure and temperatures between 300 and 700°C. The solid solution for 7 Å and 14 Å chlorites has been delimited as well as that of the expanding phases (tri- and dioctahedral montmorillonites and expanding chlorites). Negative slopes were found for the transformation montmorillonite → expanding chlorite, and expanding chlorite → chlorite+quartz and a positive slope for 7Å → 4 Å transformation. The relative positions of the reactions chlorite+quartz → cordierite+talc, chlorite+andalusite → cordierite and chlorite+corundum → cordierite+spinel are located between 500 and 65°C.Cell dimensions of the synthetic chlorites can be correlated with their chemical composition. Solid solution in synthetic minerals compares well with 325 analysis of natural minerals from the literature, indicating that the chemiographic relations between phases in the simplified synthetic system are applicable to natural mineral assemblages. The phase relations indicate that at low temperature the 7Å aluminous chlorite is not stable with quartz or another silica phase.

Calc-silicate isograds in the Riondel area, southeastern British Columbia

1976 ◽  
Vol 13 (8) ◽  
pp. 1093-1104 ◽  
Author(s):  
Trygve Höy
Keyword(s):  
British Columbia ◽  
Regional Metamorphism ◽  
Fluid Phase ◽  
Lower Grade ◽  
Binary Fluid ◽  
Physical Conditions ◽  
Mineral Assemblages ◽  
Maximum Temperatures ◽  
Wide Zone ◽  
Model Reactions

Five metamorphic isograds have been mapped in the calc-schists of the Riondel area, British Columbia. These isograds are based on the following model reactions:[Formula: see text]The first four of these isograds represent discontinuities in the observed mineral assemblages and are located by plotting all occurrences of the complete reactant and product assemblages. The fifth isograd occurs over a wide zone in which the anorthite component of the plagioclase in the assemblage Ep–Ac–Q–Di–Pl increases with increasing metamorphic grade, from approximately An30 in the lower grade eastern part of the area to approximately An60 in the western part.The distribution of isograds and the systematic variation in plagioclase compositions in the Ep–Ac–Q–Di–Pl assemblage is modelled using [Formula: see text]diagrams that have been calculated at 5000 bars pressure under the simplifying constraint that[Formula: see text]. These diagrams provide a basis for estimating the physical conditions of regional metamorphism in the Riondel area. Maximum temperatures exceeded 600 °C in the highest grade part of the area and the composition of the hypothetical binary fluid phase varied from approximately [Formula: see text]in the lower grade to 0.5 or 0.6 in the higher grade areas.

New insights into the age and metamorphic evolution of the Irumide orogeny in Malawi

2021 ◽  
Author(s):  
Sofia C. Böhme ◽  
Steven D. Boger
Keyword(s):  
Phase Equilibria ◽  
Island Arc ◽  
Zircon Geochronology ◽  
The South ◽  
Metamorphic Evolution ◽  
Temperature Conditions ◽  
The North ◽  
Southern Margin ◽  
Mineral Assemblages

<p>Metapelitic rocks of the Irumide Domain in central Malawi contain detrital and metamorphic zircons. U-Pb zircon geochronology yielded two age populations, which have been dated at c. 1995 Ma and 1050 Ma. The ages demonstrate that the precursor sediments to these rocks were derived from erosion of the Palaeoproterozoic Ubendian Domain, which is adjacent to the north, and at a later stage were affected by the Irumide orogeny. The metapelitic rocks are characterised by garnet + sillimanite + biotite ± muscovite ± K-feldspar mineral assemblages. Phase equilibria modelling shows that they equilibrated under pressure-temperature conditions of about 7 kbar and 700–740˚C.  In combination with the metamorphic ages this is interpreted to record late Mesoproterozoic (c. 1050 Ma) accretion of a juvenile island arc, the South Irumide Domain, to the southern margin of the Tanzania-Congo Craton.</p>

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