Metamorphism Metamorphic Rocks and Hydrothermal Rocks Chapter 7

Metamorphism, Metamorphic Rocks, and Hydrothermal Rocks Chapter 7 Metamorphic gneiss from Greenland, 3. 7 Ba

Michaelangelo carving of Pieta Looked far and wide for a large pristine marble block He watched the rays of the rising sun strike the block and make it transparent as pink alabaster, with not a hole or hollow or crack or knot in all its massive white weight. It tested out perfect against the hammer, against water, its crystals soft and compacted with fine graining. His Pieta had come home. -Irving Stone (The Agony and Ecstasy) © 2008, John Wiley and Sons, Inc.

Metamorphic Rocks • Metamorphism refers to solid-state changes to rocks in Earth’s interior – Produced by increased heat, pressure, or the action of hot, reactive fluids – Old minerals, unstable under new conditions, recrystallize into stable ones • Rocks produced from pre-existing or parent rocks in this way are called metamorphic rocks

Metamorphic Rocks – are like Cooking * Ingredients added together are cooked at high temperatures to produce a new and different substance with different textures and form. * Rocks © 2008, John Wileyexposed and Sons, Inc. to high temps and pressures react chemically, change

Metamorphic Rocks Metamorphism is the mineralogical, textural, chemical, and structural changes that occur in rocks as a result of exposure to elevated temperatures and/or pressures. Metamorphism occurs in solid state, without any melting processes. So deformation process is preserved in the metamorphic rocks and can be “tracked” in time and through tectonic cycles. © 2008, John Wiley and Sons, Inc.

Metamorphic Rocks Factors effecting metamorphism: Temperature Pressure Rock composition Fluids present Stress environment © 2008, John Wiley and Sons, Inc.

Metamorphic Rocks • Metamorphic rocks common in the old, stable cores of continents, known as cratons *Oldest stable continental core *Seismically fast *Geothermally cold *Buoyant – low density (chemically depleted)

Factors Controlling Metamorphic Rock Characteristics • Temperature during metamorphism – Heat for metamorphism comes from Earth’s deep interior – If temperature gets high enough, melting will occur • Pressure during metamorphism – Confining pressure applied equally in all directions – Pressure proportional to depth within the Earth • increases ~1 kilobar per 3. 3 km of burial within the crust

Temperature and pressure conditions for metamorphism Figure 10. 2 © 2008, John Wiley and Sons, Inc.

Temperature and pressure conditions for metamorphism Figure 10. 2 © 2008, John Wiley and Sons, Inc.

Temperature and pressure conditions for metamorphism Figure 10. 2 Low grade metamorphism: Rocks that are metamorphosed under temperature and pressures upto 400 C and 400 MPa High grade metamorphism: Rocks that are metamorphosed under temperature and pressures higher than 400 C and 400 MPa

Figure 10. 3 From shale to gneiss Diagenesis Shale Low-Grade Slate Medium-Grade Phyllite * Sillmanite and Kyanite Al 2 O 3 with different crystal structures © 2008, John Wiley and Sons, Inc. High-Grade Gneiss

Pore Fluids and Metamorphic Veins The presence of pore space and aqueous fulids can facilitate metamorphic reactions. Porous fluid flow transports mineral chemicals and speeds up mineral growth and recrystallization.

Metamorphic Rocks Under Stress Granite consists of quartz, feldspar, biotite which recrystallized from magma under conditions of uniform stress. Grains are randomly oriented. This gneiss, a high-grade metamorphic rock, contains the same minerals as the rock on the left but deformed in solid state under differential stress. Biotite grains are aligned in a layered texture. Foliation is the planar arrangement of mineral grains giving a layered texture

Compression Bedding Planes Compression Figure 10. 7 Vertical slaty cleavage Horizontal slaty cleavage Bedding planes are perpendicular to the maximum stress direction. Bedding and cleavage planes change if applied stress changes.

Metamorphism and Billiards Wood in early pool tables vibrated and warped. Slate used in 1825 – better table and game. Slaty (low grade met. ) cleavage surface, strong, still. © 2008, John Wiley and Sons, Inc.

Metamorphism: New Rocks from Old Metamorphic Rocks with Foliation Rocks without Foliation © 2008, John Wiley and Sons, Inc.

Metamophism of Sedimentary Rocks Shale Sedimentary Rock © 2008, John Wiley and Sons, Inc. Slate Fine grained, low grade metamorphic rock with slaty cleavage. Phyllite Fine grained, high grade metamorphic rock with foliation.

Metamophism of Sedimentary Rocks Travertine, Getty Museum Limestone Marble

Metamophism of Sedimentary Rocks Sandstone Dominantly quartz minerals Quartzite Very little foliation due to low diversity of minerals.

Metamorphism of Volcanic Rocks Granite Mineral content includes quartz, feldspar, biotite micas © 2008, John Wiley and Sons, Inc. Gneiss Metamorphism of complex mineralogy induces foliation.

Metamorphism of Basalt Increasing grade of metamorphism Increasing pressure (without increasing temperature) Greenschist Blueschist Figure 10. 9 Amphibolite Ecologite

Tectonics and Basalt Metamorphism Basalt Figure 10. 13 Blueschist and eclogite metamorphism

Metamorphic facies © 2008, John Wiley and Sons, Inc. Figure 10. 18

Metamorphism: New Rocks from Old Metamorphic Processes Types of Metamorphism Metamsomatism © 2008, John Wiley and Sons, Inc.

Mechanical deformation Conglomerate pebbles Deformed pebbles due to differential pressure and shear.

Metamorphism: New Rocks from Old Metamorphic Processes Types of Metamorphism © 2008, John Wiley and Sons, Inc.

Types of Metamorphism -Contact metamorphism: Occurs when rocks are heated and chemically changed adjacent to an introduced body of hot magma -Burial: Occurs as a result of burial of sediments in deep sedimentary basins -Regional: Extensive area of crust associated with plate convergence, collision, and subduction.

Contact metamorphism Figure 10. 12 © 2008, John Wiley and Sons, Inc.

Tectonics and Metamorphism Regional metamorphism Zone of burial metamorphism Granitic magma rises and causes contact metamorphism Figure 10. 13 © 2008, John Wiley and Sons, Inc. Blueschist and eclogite metamorphism

Nordlingen Cathedral (in Germany) Constructed within an impact crater. Rock construction include local rocks that were metamorphosed by high heat and pressure during impact Shocked quartz from impact © 2008, John Wiley and Sons, Inc.