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The Geology of Ireland

The Geology of Ireland. Part Two. Donegal Granite. Leinster Granite. Galway Granite. Main Tectonic Zones & Granites. Tectonic Environments of Granites. Ocean Ridge Granites (ORG) Volcanic-Arc Granites Collisional Granites (COLG)

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The Geology of Ireland

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  1. The Geology of Ireland Part Two

  2. Donegal Granite • Leinster Granite • Galway Granite Main Tectonic Zones & Granites

  3. Tectonic Environments of Granites • Ocean Ridge Granites (ORG) • Volcanic-Arc Granites • Collisional Granites (COLG) • Syn-tectonic granites associated with continent-continent collision • Post-tectonic granites associated with continent-continent collision • Syn-tectonic granites associated with continent-arc collision • Within-Plate Granites (WPG)

  4. The Caledonian orogeny

  5. The Caledonian orogeny

  6. The Caledonian orogeny

  7. The Caledonian orogeny

  8. The Caledonian orogeny

  9. The Caledonian orogeny

  10. The Caledonian orogeny

  11. The Caledonian orogeny

  12. The Caledonian orogeny

  13. The Caledonian orogeny

  14. The Caledonian orogeny

  15. The Caledonian orogeny

  16. The Caledonian orogeny

  17. The Caledonian orogeny

  18. The Caledonian orogeny

  19. The Caledonian orogeny

  20. The Caledonian orogeny

  21. The Caledonian orogeny

  22. The Caledonian orogeny

  23. The Caledonian orogeny

  24. The Caledonian orogeny

  25. The Caledonian orogeny

  26. The Caledonian orogeny

  27. The Caledonian orogeny

  28. The Caledonian orogeny

  29. The Caledonian orogeny

  30. The Caledonian orogeny

  31. The Caledonian orogeny

  32. The Caledonian orogeny

  33. The Caledonian orogeny

  34. The Caledonian orogeny

  35. The Caledonian orogeny

  36. The Caledonian orogeny

  37. The Caledonian orogeny

  38. The Caledonian orogeny

  39. The Caledonian orogeny

  40. The Caledonian orogeny

  41. The Caledonian orogeny

  42. Crustal Melting & Granite Magmas • Partial Melting • Segregation • Aggregation • Ascent • Emplacement

  43. Protoliths & Partial Melting • Typical geothermal gradients of 20°C/km do not generate temps >800°C at 35 km depth required to melt most crustal rocks (Thompson 1999). • Three main factors in inducing partial melting: • Increase in temperature • Decrease in pressure (adiabatic decompression) • Introduce H2O-rich volatiles • One or more of these may be met by the influence of proximal mantle-derived basaltic magmas

  44. Partial Melting & Melt Segregation • Melt segregation is the separation of the melt fraction from its restite and source during partial melting • Melt segregation depends on the permeability of the source. • Melts first forms at grain boundaries between mineral phases Image source: www.indiana.edu

  45. Protoliths & Melt Composition • Small degrees of partial melting of an amphibolite will produce a Si-rich melt. • Granitic melts can be produced from a mafic protolith

  46. Granite Mineralogy

  47. Granite Mineralogy

  48. Mafic Enclaves Close-up view of the Drogheda Granite with mafic enclaves (www.gsi.ie)

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