ISSN:
1525-1314
Quelle:
Blackwell Publishing Journal Backfiles 1879-2005
Thema:
Geologie und Paläontologie
Notizen:
Calcsilicate granulites of probable Middle Proterozoic age (c.1000–1100 Ma) in the vicinity of Battye Glacier, northern Prince Charles Mountains, East Antarctica, contain prograde metamorphic assemblages comprising various combinations of wollastonite, scapolite, clinopyroxene, An-rich plagioclase, calcite, quartz, titanite and, rarely, orthoclase, ilmenite, phlogopite and graphite. Comparison of the prograde assemblages with calculated and experimentally determined phase relations in the simple CaO–Al2O3–SiO2–CO2–H2O system suggests peak metamorphism at ≥835 °C in the presence (in wollastonite-bearing assemblages at least) of a CO2-bearing fluid (XCO≥0.3) at a probable pressure of 6–7 kbar.Well-preserved retrograde reaction textures represent: (1) breakdown of scapolite to anorthite+calcite±quartz; (2) formation of grossular–andradite garnet and, locally, (3) epidote, both principally by reactions involving scapolite breakdown products and clinopyroxene; (4) local coupled replacement of clinopyroxene and ilmenite by hornblende and titanite, respectively; and finally (5) local sericitization of prograde and retrograde plagioclase. These retrograde reactions are interpreted to be the result of cooling and variable infiltration by H2O-rich fluids, possibly derived from crystallizing pegmatitic intrusions and segregations that may be partial melts, which are common throughout the area.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1111/j.1525-1314.1997.00024.x
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