Granites b Petrography b Field relations b Origin

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

Petrography b Fabric b Classification b Alteration

Fabric b Hypidiomorphic granular b Equigranular b Porphyritic b Pegmatitic b Graphic

Anisotropy • • • Foliatiation Lineation Segregation layers

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

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

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

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

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

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

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