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METAMORPHIC-LECTURE 5 - Coggle Diagram
METAMORPHIC-LECTURE 5
Granulite
Metamorphism at depths up to 50 km, T can be >900°C, defined by incoming of opx. opx+cpx+plag+qtz+/-grt, hbl, bt
Distribution in space: continental shield areas, recent mountain belts, exhumed arc foundations
Distribution in time: archean terranes, proterozoic, neoproterozoic to cambiran, phanerozoic
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Most granulites: 6-9 kbar, 750-900 °C
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Evidence of low H2O activity: calculations on mineral asseblages at T, TE depletions, high density CO2-rich fluid inclusions
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Assemblages in pelites
Lower T 700-800 °C, bt+sill+kfs
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As T increases, crd/grt will appear, driven by entropy change of reaction favouring the development of more liquid/crd/grt
Upper T range, bt+qtz produce opx, which coexists w/ grt+crd+kfs+qtz+melt
T range >750 to >900°C, 4-9kbar
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Grt+crd+sill+qtz+kfs, aluminous.
Grt+crd+bt+qtz+kfs, subaluminous
High P T: low-alumina rocks grt+opx, high-alumina rocks grt+sill+/-crd
UHT pelites
900°C, 6-12 kbar, beyond stability of grt+crd+sill
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Spr: Mg2Al4SiO10, low silica phase, equivalent to spl+qtz
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Crd+kfs can react w/ melt at T around 900-930°C and <7-8 kbar to produce osumilite. Osu is very Mg-rich, coexists w/ crd+opx+qtz
UHT indicators
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Osu+symplectite (intergrowth of 2 or more crystals, texture deriving from breakdown of unstable phases)