3A8 week 01 lecture 03 rocks and minerals 02

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Geology for Engineers Minerals and Rocks (II) Gneiss Metamorphic Rocks Rocks may be altered through • Temperature • Pressure • Deformation • Fluid influx Metamorphic Rocks • The original rock is termed a protolith • The composition of the protolith and the conditions of metamorphism and deformation will largely determine the end structure and composition of the metamorphic rock Metamorphic Rocks • Protoliths may be sedimentary, igneous or even metamorphic • Metamorphism may result from a general increase (prograde), or decrease (retrograde) of temperature and pressure Pressure-Temperature-Time Metamorphic Rocks Metamorphism may be: • Dynamic (i.e some deformation involved), e.g gneiss • Static (i.e the end rock does not have a preferred shape fabric) e.g hornfels Gneiss Metamorphic Grades • Anchimetamorphic • Greenschist • Amphibolite • Granulite • Eclogite • Blueschist • Increasing temperature and pressure P-T fields of metamorphic grades Index of Metamorphic Minerals csmres.jmu.edu/ Mylonite • Intensely sheared rock Note the recrystallization of feldspar (lightest crystals) and the ribbons of quartz (grey ) in a dark, biotite-rich matrix • Difficult to determine the protolith! Tectonic Settings of Metamorphism Metamorphic Rocks • Sandstone can be metamorphosed to quartzite • Sutured quartz boundaries (changes mechanical properties of the rock) Metamorphic Rocks • A limestone protolith can be metamorphosed into a marble (this example is quite pure, i.e white) Metamorphic Rocks • Mudstone (pelite) Metamorphic Rocks • Phyllite - is the metamorphic step beyond slate New layers of mica minerals give phyllite a shiny, “wavy” appearance Metamorphic Rocks • Schist - heavily foliated rock in which all the original clay minerals are fully transformed Metamorphic Rocks • Greenschist – minerals such as epidote, chlorite and actinolite Metamorphic Rocks • This is a blueschist It was formed in a subduction zone in high pressure and relatively low temperature • Blue mineral = glaucophane Metamorphic Rocks • Migmatite Partial melting of protolith Dark parts = restite Light parts = leucosome Metamorphic Rocks • Garnet Gneiss Metamorphic Rocks • This is an eclogite You can see the presence of garnet (pink) and pyroxene (green) Metamorphic Rocks • This image shows chert (red), which is a sedimentary rock being replaced by silica (SiO2) veins Metamorphic Rocks • This shows a basalt (igneous rock) which has been metamorphose d into an amphibolite (i.e pyroxene changed to amphibole) Metamorphic Rocks • This shows an olivine-rich igneous rock (dunite) which has been metamorphose d into an serpentinite [...]... white) Metamorphic Rocks • Mudstone (pelite) Metamorphic Rocks • Phyllite - is the metamorphic step beyond slate New layers of mica minerals give phyllite a shiny, “wavy” appearance Metamorphic Rocks • Schist - heavily foliated rock in which all the original clay minerals are fully transformed Metamorphic Rocks • Greenschist – minerals such as epidote, chlorite and actinolite Metamorphic Rocks • This is... formed in a subduction zone in high pressure and relatively low temperature • Blue mineral = glaucophane Metamorphic Rocks • Migmatite Partial melting of protolith Dark parts = restite Light parts = leucosome Metamorphic Rocks • Garnet Gneiss Metamorphic Rocks • This is an eclogite You can see the presence of garnet (pink) and pyroxene (green) Metamorphic Rocks • This image shows chert (red), which... Note the recrystallization of feldspar (lightest crystals) and the ribbons of quartz (grey ) in a dark, biotite-rich matrix • Difficult to determine the protolith! Tectonic Settings of Metamorphism Metamorphic Rocks • Sandstone can be metamorphosed to quartzite • Sutured quartz boundaries (changes mechanical properties of the rock) Metamorphic Rocks • A limestone protolith can be metamorphosed into a... (green) Metamorphic Rocks • This image shows chert (red), which is a sedimentary rock being replaced by silica (SiO2) veins Metamorphic Rocks • This shows a basalt (igneous rock) which has been metamorphose d into an amphibolite (i.e pyroxene changed to amphibole) Metamorphic Rocks • This shows an olivine-rich igneous rock (dunite) which has been metamorphose d into an serpentinite ...Index of Metamorphic Minerals csmres.jmu.edu/ Isograd Map Different Styles of Metamorphism • • • • • Barrovian (regional) metamorphism Buchan (regional) metamorphism Contact metamorphism Shock metamorphism Dynamic metamorphism
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