105_07-metamorphics_part_2 - Types of Metamorphism Dynamic...

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Unformatted text preview: Types of Metamorphism Dynamic Dynamic Metamorphism – Associated with faults – Rocks subjected to high pressure – Form narrow bands of metamorphic rocks along fault zones (mylonites) Hard Hard Dense Dense Fine Fine grained Thinly Thinly laminated Types of Metamorphism Mylonite Mylonite Types of Metamorphism Regional Regional Metamorphism – produces most metamorphic rocks; makes up the shields – results from extreme heat and pressure generated by the processes at convergent plate boundaries – covers large geographic areas, and usually shows a gradation of deformation corresponding to areas of the most intense heat/pressure Types of Metamorphism? Regional Regional Metamorphism – certain minerals are known to form under specific conditions of temperature and pressure index minerals Petrogenetic grid Index minerals Kyanite Andalusite Sillimanite Types of Metamorphism Regional Regional Metamorphism – low, intermediate, and high grades of metamorphism are recognized, based on conditions and the resulting mineral assemblages • Polymorphs of Al2SiO5 Other famous polymorph pair? 1 Index minerals How are Metamorphic Rocks Classified? Texture: Texture: – Foliated Parallel Parallel layers of platy, flat minerals Muscovite or biotite – Non-foliated NonNo No platy minerals No muscovite or biotite Metamorphic Rocks Let’s bake mud! Foliated Foliated Metamorphic Rocks Shale Shale ⇒ Slate ~ 200°C – Minerals align – Shiny surface Foliated Rocks (from mud) Slate: Slate: – Exhibits slaty cleavage Slate Slate Slaty cleavage 2 Foliated Rocks (from mud) Slate Slate Slate Slate roof Metamorphic Rocks Let’s bake mud! Foliated Rocks (from mud) Phyllite Phyllite Slate Slate ⇒ Phyllite ~ 300°C – Larger mica Metamorphic Rocks Let’s bake mud! Foliated Rocks (from mud) Schist Schist – “Tough schist!” – “Schist happens!” Phyllite Phyllite ⇒ Schist ~ 400°C – Crystals can be seen with unaided eye 3 Foliated rocks (from mud) Garnet Garnet Schist Garnet Talc tremolite schist Metamorphic Rocks Let’s bake mud! Foliated Rocks (from mud) Gneiss Gneiss – “have a gneiss day!” Schist Schist ⇒ Gneiss ~ 500 – 700°C – Felsic and mafic minerals start to separate Foliated textures Gneiss Metamorphic Rocks Let’s bake mud! Gneiss Gneiss ⇒ Migmatite ~ 600 – 800°C – Felsic minerals melt – Mafic minerals stay metamorphic – Both igneous and metamorphic rock 4 Nonfoliated metamorphic rocks minerals minerals do not show a discernible preferred orientation Nonfoliated Rocks Fine Fine grained (microgranular) Equal Equal sized visible (crystalline) Metamorphic Rocks Nonfoliated Nonfoliated – Sandstone ⇒ Quartzite Metamorphic Rocks Nonfoliated Nonfoliated – Limestone ⇒ Marble Metamorphism - overview How Does Metamorphism Relate to Plate Tectonics? Convergent Convergent boundaries – temperature and pressure increase in collisions – several facies are recognized in this model, defined by the temp/pressure conditions 5 Metamorphism and Metamorphic Rocks Chapter 7 6 ...
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