Phase equilibrium constraints on conditions of granulite-facies metamorphism at Scourie, NW Scotland
T.E. Johnson
R.W. White
10.6084/m9.figshare.3454916.v1
https://geolsoc.figshare.com/articles/dataset/Phase_equilibrium_constraints_on_conditions_of_granulite-facies_metamorphism_at_Scourie_NW_Scotland/3454916
<p>The metamorphic evolution of a metapyroxenite and metagabbro from Scourie, NW Scotland, is investigated using phase equilibria
modelled in the NCFMASHTO (Na<sub>2</sub>O–CaO–FeO–MgO–Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub>–H<sub>2</sub>O–TiO<sub>2</sub>–O) system. The calculated stability fields for the observed assemblages in each rock overlap and imply conditions of 8.5–11.5
kbar and 875–975 °C for the peak of granulite-facies (Badcallian) metamorphism. The lack of any evidence for the former presence
of garnet in the metapyroxenite suggests that the rocks cannot have reached pressures much in excess of those recorded at
the metamorphic peak. The growth of coronas of plagioclase, orthopyroxene and magnetite replacing garnet in the metagabbro
is consistent with near-isothermal retrograde decompression from the metamorphic peak to pressures of 7–9 kbar. The constraints
on the pressure–temperature evolution imposed by the modelled phase equilibria are more consistent with a process of crustal
growth dominated by magmatic accretion rather than by significant tectonic thickening during the early Scourian.
</p>
2016-06-21 12:26:30
metamorphism
metagabbro
NCFMASHTO
modelled phase equilibria
metapyroxenite
Scourie
Phase equilibrium constraints
evolution
phase equilibria modelled
kbar
garnet
NW Scotland
Geology