2 metamorphic textures

25 5 0
  • Loading ...
1/25 trang

Thông tin tài liệu

Ngày đăng: 30/11/2016, 16:04

Metamorphic Textures Recrystallization: Minimization of Interfacial Free Energy by Minimizing Surface Area Sandstone Quartzite Crack Recrystallization Cement Crack Crack Recrystallization of a Bi-minerallic Rock  a) interfacial free energy of AA = AB; dihedral angle (θ) is thus 120o  b) interfacial free energy of AA > AB; dihedral angle decreases to decrease surface area of AA Plagioclase Cpx Recrystallization of Quartz-Mica Rock  Interfacial free energy of Quartz-Mica >> Quartz-Quartz  Interfacial angle increases from 120o to 180o Decussate Texture Aggregate of mica grains in which most interfaces are parallel to {001} This occurs because the surface energy of the {001} face is substantially lower than that of other faces, e.g {110} The texture may also be developed by other minerals Granoblastic/Decussate Textures (Characteristic of Contact or Thermal Metamorphism) Porphyroblast development  Nucleation of new crystals requires excess free energy  If the nucleation energy is high, growth is favoured and porphyroblasts form  Porphyroblasts will be euhedral if their faces have high energy Crystalloblastic Series Most Euhedral Titanite, rutile, pyrite, spinel Garnet, sillimanite, staurolite, tourmaline Epidote, magnetite, ilmenite Andalusite, pyroxene, amphibole Mica, chlorite, dolomite, kyanite Calcite, vesuvianite, scapolite Feldspar, quartz, cordierite Least Euhedral Textural Effects of Differential Stress Stressed grains store strain energy released during metamorphism by clearing defects and dislocations (polygonization) Undulose extinction Subgrain development Defects Dislocations and Deformation Defects Dislocation Deformation by Dislocation Pressure Solution Differential stress produces serated grain boundaries Foliation Development σ1 S1 Schistocity S1 flattened around garnet porphyroblasts S2 S1 Crenulation cleavage S2 developed by folding S1 Pressure Shadows Chlorite in shadow around garnet Quartz in shadow around staurolite Pressure Fringes Staurolite Pyrite Muscovite Sillimanite Metamorphic Mineral Growth Relative to Deformation Pre-tectonic Textures Undulose extinction Pressure shadows Pressure fringes Micro-boudinage Crenulation cleavage Deformation twins Syn-tectonic Texture Snowball Garnet with Pressure Shadows Post-tectonic Textures Helicitic folds Chiastolite Randomly oriented crystals Overgrowth on snowball Polygonal arc Pseudomorph Polymetamorphism Stages in Polymetamorphism (S0, S1) Stages in Polymetamorphism (S2) Stages in Polymetamorphism (S3) Corona Textures [...]... Development σ1 S1 Schistocity S1 flattened around garnet porphyroblasts S2 S1 Crenulation cleavage S2 developed by folding S1 Pressure Shadows Chlorite in shadow around garnet Quartz in shadow around staurolite Pressure Fringes Staurolite Pyrite Muscovite Sillimanite Metamorphic Mineral Growth Relative to Deformation Pre-tectonic Textures Undulose extinction Pressure shadows Pressure fringes Micro-boudinage... Deformation twins Syn-tectonic Texture Snowball Garnet with Pressure Shadows Post-tectonic Textures Helicitic folds Chiastolite Randomly oriented crystals Overgrowth on snowball Polygonal arc Pseudomorph Polymetamorphism Stages in Polymetamorphism (S0, S1) Stages in Polymetamorphism (S2) Stages in Polymetamorphism (S3) Corona Textures
- Xem thêm -

Xem thêm: 2 metamorphic textures , 2 metamorphic textures , 2 metamorphic textures

Gợi ý tài liệu liên quan cho bạn

Nạp tiền Tải lên
Đăng ký
Đăng nhập