1 / 29

Geology for Engineers

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

reyna
Download Presentation

Geology for Engineers

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Geology for Engineers Minerals and Rocks (II) Gneiss

  2. Metamorphic Rocks Rocks may be altered through • Temperature • Pressure • Deformation • Fluid influx

  3. 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

  4. 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

  5. Pressure-Temperature-Time

  6. 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

  7. Gneiss

  8. Metamorphic Grades • Anchi-metamorphic • Greenschist • Amphibolite • Granulite • Eclogite • Blueschist • Increasing temperature and pressure

  9. P-T fields of metamorphic grades

  10. Index of Metamorphic Minerals csmres.jmu.edu/

  11. Index of Metamorphic Minerals csmres.jmu.edu/

  12. Isograd Map

  13. Different Styles of Metamorphism • Barrovian (regional) metamorphism • Buchan (regional) metamorphism • Contact metamorphism • Shock metamorphism • Dynamic metamorphism (e.g. shearing)

  14. ContactMetamorphism • This shows a basalt (igneous rock) intruding into a limestone. You can see that it has been metamorphosed into marble near the contact with the basalt.

  15. 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!

  16. Tectonic Settings of Metamorphism

  17. Metamorphic Rocks • Sandstone can be metamorphosed to quartzite. • Sutured quartz boundaries (changes mechanical properties of the rock)

  18. Metamorphic Rocks • A limestone protolith can be metamorphosed into a marble (this example is quite pure, i.e. white).

  19. Metamorphic Rocks • Mudstone (pelite)

  20. Metamorphic Rocks • Phyllite - is the metamorphic step beyond slate. New layers of mica minerals give phyllite a shiny, “wavy” appearance.

  21. Metamorphic Rocks • Schist - heavily foliated rock in which all the original clay minerals are fully transformed

  22. Metamorphic Rocks • Greenschist – minerals such as epidote, chlorite and actinolite

  23. Metamorphic Rocks • This is a blueschist. It was formed in a subduction zone in high pressure and relatively low temperature • Blue mineral = glaucophane

  24. Metamorphic Rocks • Migmatite Partial melting of protolith Dark parts = restite Light parts = leucosome

  25. Metamorphic Rocks • Garnet Gneiss

  26. Metamorphic Rocks • This is an eclogite. You can see the presence of garnet (pink) and pyroxene (green)

  27. Metamorphic Rocks • This image shows chert (red), which is a sedimentary rock being replaced by silica (SiO2) veins.

  28. Metamorphic Rocks • This shows a basalt (igneous rock) which has been metamorphosed into an amphibolite (i.e. pyroxene changed to amphibole)

  29. Metamorphic Rocks • This shows an olivine-rich igneous rock (dunite) which has been metamorphosed into an serpentinite

More Related