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Granites

Granites. Petrography Field relations Origin Time-space patterns in plutons S-Type and I-Type compositions. Petrography. Fabric Classification Alteration. Fabric. Hypidiomorphic granular Equigranular Porphyritic Pegmatitic Graphic. Anisotropy. Foliatiation Lineation

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Granites

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  1. Granites • Petrography • Field relations • Origin • Time-space patterns in plutons • S-Type and I-Type compositions

  2. Petrography • Fabric • Classification • Alteration

  3. Fabric • Hypidiomorphic granular • Equigranular • Porphyritic • Pegmatitic • Graphic

  4. Anisotropy • Foliatiation • Lineation • Segregation layers

  5. Compositional Classification • Q-Ab-Or diagram • Chemical classification is useful • Quartz, K-spar, Plagioclase diagram • Modal classification also is good

  6. Textural classification • Porphyry • Large crystals in a fine-grained matrix • Aplite • Leucocratic, fine sugary texture • Pegmatite • Extremely coarse-grained with rare euhedral minerals • Li, Be, Zr, Nb, Mo, Sn, Ta, W,Th, U concentrated • Granophyre • Micrographic texture

  7. Alteration • Most granites show some degree of alteration • High temperature minerals replaced by low T ones

  8. Field relations • General distribution • External contacts • From of intrusions • Internal features • Time and depth of emplacement

  9. General distribution of granites • Concentrated in orogenic belts • Located at the margins of continents • Also in deeply eroded Precambrian shields • Alkaline granites occur in rift zones

  10. Origin • Magmas vs. granitization • Room problem • Form of large batholiths • Zoned plutons • Origin of magmas

  11. Time-space patterns in plutons • S-Type granites’ • I-Type granites • Mesozoic Andean granites • Mesozoic Batholiths of western USA

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