Meta-igneous rocks

Meta-igneous rocks

1. Metamorphic facies

   • Greenschist
     • chlorite, albite, actionlite, epidote, quartz
     • chlorite + green amphibole
   • Amphibolite
     • green amphibole (hornblende = dark green/black amphibole), garnet, plag
   • Hornfels
   • Sanidinite
   • Eclogite
     • high density - transformation of blue schist into something denser and loss of hydrous minerals.
     • green/red colours diagnostic - green pyroxene (jadeite) and garnet
   • Granulite
     • with increasing T, amphibole breaks down to produce pyroxenes: clino and ortho
     • represent unusually hot conditions - greater T than associated with their depth of formation so thought to be formed with crustal thickening and excess heating
     • no hydrous mineral phases - represents deep burial and dehydrated roots of continental crust
     • pyx, garnet/plag
   • Epidote-amphibolite
     • epidote + green amphibole
   • Blueschist
     • Grown under v high pressures - subduction zones
     • characterised by sonic blue amphibole = glaucophane
   • Greenschist --> amphibolite --> granulite corresponds to typical continental geotherm
     • most common facies dries of regional metamorphism - equivalent to classical Barrovian series

2. Hydration of original mafic minerals needed to generate mm mineral assemblages for most facies

   • w/o H2O most igneous rocks will be unaffected whilst surrounding sediments will be metamorphosed
   • coarse-grained intrusions of gabbro are most resistant - low H2O content whilst basalts are most susceptible

3. not much difference between low-P metabolites and med-P

   • distinguish between contact mm facies and medium-pressure regional mm facies if 1) metapelites are present (regional) 2) textures etc

4. metasediments (and barrow zones) tend to give more information that metamorphic facies

Images and files in the map