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Contributions to Mineralogy and Petrology

, Volume 110, Issue 1, pp 121–132 | Cite as

Phase relationships in Buchan facies series pelitic assemblages: calculations with application to andalusite-staurolite parageneses in the Mount Lofty Ranges, South Australia

  • Peter Dymoke
  • Michael Sandiford
Article

Abstract

Low-pressure, medium- to high-temperature (Buchan-type) regional metamorphism of pelitic rocks in the Mount Lofty Ranges, South Australia, is defined by the development of biotite, staurolite-andalusite, fibrolite, prismatic sillimanite and migmatite zones. K-feldspar makes its first appearance in the prismatic sillimanite zone and here we restrict our discussion to lower grade assemblages containing prograde muscovite, concentrating particularly on well-developed andalusitestaurolite parageneses. In general, the spatial distribution and mineral chemical variation of these assemblages accord with the predictions of petrogenetic grids and P-T and T-XFe pseudo-sections constructed from the internally consistent data set of Holland and Powell (1990) in the system KFMASH, assuming a(H2O) ∼1, although analysed white mica compositions are systematically more aluminous than predicted. Importantly, the stability ranges of most critical assemblages predicted by these grids and pseudo-sections coincide closely with P-T estimates calculated using the data set of Holland and Powell (1990) from the Mount Lofty Ranges assemblages. With the exception of Mn in garnet and Zn in one staurolite-cordierite-muscovite assemblage non-KFMASH components do not significantly appear to have affected the stability ranges of the observed assemblages. An apparent local reversal in isograd zonation in which andalusite first appears down-grade of staurolite suggests a metamorphic field gradient concave towards the temperature axis and, together with evidence for essentially isobaric heating of individual rocks, is consistent with the exposures representing an oblique profile through a terrain in which heat was dissipated from intrusive bodies at discrete structural levels.

Keywords

Stability Range Regional Metamorphism Andalusite White Mica Pelitic Rock 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Mineral abbreviations used in figures

als

Al2SiO5 phase

bi

biotite

chl

chlorite

ky

kyanite

ph

phengite

sill

sillimanite

and

andalusite

cd

cordieritc

gt

garnet

mu

muscovite

q

quartz

st

staurolite

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Copyright information

© Springer-Verlag 1992

Authors and Affiliations

  • Peter Dymoke
    • 1
  • Michael Sandiford
    • 1
  1. 1.Department of Geology and GeophysicsUniversity of AdelaideAustralia

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