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Understanding Intrusive Igneous Structures and the Role of Viscosity in Magma Dynamics

This concise overview explores essential concepts related to intrusive igneous structures, highlighting the significance of viscosity in magma behavior and volcanic activity. It addresses how pressure and time (measured in pascal-seconds) influence fluid dynamics, discusses the differences between viscous and pseudoviscous materials, and examines the buoyancy of magma versus surrounding rock. Moreover, it outlines how gas pressure contributes to volcanic eruptions and the effect of plate tectonics on magma movement. Case studies from various geological formations illustrate these principles.

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Understanding Intrusive Igneous Structures and the Role of Viscosity in Magma Dynamics

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  1. Igneous Structures: Intrusive

  2. Viscosity • Units: pascal-seconds (kg/m-sec) • How many pascals pressure x how many seconds to squash fluid flat? • Viscous: Material flows as long as pressure is applied, however small • Pseudoviscous: Material flows after some threshold stress

  3. Viscosity of Common Materials

  4. Geologic Viscosities

  5. What Drives Magma? • Magma is typically 10% lighter than equivalent solid rock • Why pressure inhibits melting • Buoyancy drives magma upward • Weight of rock around volcanic conduit > weight of magma • Gas pressure powers volcanic eruptions • Mafic (dense) rocks can sink in crust by viscous flow

  6. Plate Tectonics and Volcanoes

  7. Cullain Layered Complex, Scotland

  8. Cullain Layered Complex, Scotland

  9. Cullain Layered Complex, Scotland

  10. Cullain Layered Complex, Scotland

  11. Cullain Layered Complex, Scotland

  12. Filter Pressing, Scotland

  13. Filter Pressing? Scotland

  14. Lava Flows and Dike, Scotland

  15. Magma Mixing, Scotland

  16. Pseudotachylite, Scotland

  17. Sill, Scotland

  18. Extrusion Striae, Scotland

  19. Keeweenawan Sills, Ontario

  20. Keeweenawan Sills, Ontario

  21. Columnar Jointing, Ontario

  22. Batholith, California

  23. Sierra Nevada Batholith

  24. Roof Pendants, Sierra Nevada

  25. Columnar Jointing, Devil’s Postpile, California

  26. Columnar Jointing, Devil’s Postpile, California

  27. Columnar Jointing, Idaho

  28. Columnar Jointing, Scotland

  29. Devil’s Tower, Wyoming

  30. Phonolite, Devils Tower, Wyoming

  31. Jointing, Devils Tower, Wyoming

  32. Laccolith, Bear Mountain SD

  33. Laccolith, Wyoming

  34. How Laccoliths Form

  35. How Devil’s Tower Formed

  36. Intrusions, Mount Rushmore

  37. A Rarely Seen Perspective

  38. Granite Intrusion, Black Hills

  39. Dike and Shear Zone, Washington

  40. Dikes, Lead, South Dakota

  41. Dike, Redgranite, Wisconsin

  42. Dike, Redgranite, Wisconsin

  43. Dike, Black Hills, SD

  44. Palisades, New Jersey

  45. The Palisades

  46. Base of Palisades Sill, NJ

  47. Intrusion Breccia

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