Metamorphism, Metamorphic Rocks, and Hydrothermal Rocks Chapter 7 Metamorphic gneiss from Greenland, 3.7 Ba

© 2008, John Wiley and Sons, Inc. 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)‏

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 breadtoast

© 2008, John Wiley and Sons, Inc. 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 exposed to high temps and pressures react chemically, change mineralogy, and textures.

© 2008, John Wiley and Sons, Inc. 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

Metamorphic rocks common in the old, stable cores of continents, known as cratons Metamorphic Rocks *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 1 kb = 14,500 psi and VW bug = 2000 lbs Pressure at 100 km depth = 239 VW Bugs on 1 square inch area (A bigger area of 1 sq foot would require 34,452 VW bugs!)‏

© 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

Temperature and pressure conditions for metamorphism Figure 10.2 Low grade metamorphism: Rocks that are metamorphosed under temperature and pressures upto 400C and 400 MPa High grade metamorphism: Rocks that are metamorphosed under temperature and pressures higher than 400C and 400 MPa

© 2008, John Wiley and Sons, Inc. From shale to gneiss Figure 10.3 Shale Slate Phyllite Gneiss Diagenesis Low-Grade Medium-Grade High-Grade * Sillmanite and Kyanite Al 2 O 3 with different crystal structures

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

Slaty cleavage Figure 10.7 Horizontal slaty cleavage Compression Vertical slaty cleavage Bedding Planes Bedding planes are perpendicular to the maximum stress direction. Bedding and cleavage planes change if applied stress changes.

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

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

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

© 2008, John Wiley and Sons, Inc. Metamophism of Sedimentary Rocks Limestone Marble Travertine, Getty Museum

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

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

Figure 10.9 GreenschistAmphibolite BlueschistEcologite Increasing grade of metamorphism Increasing pressure (without increasing temperature)‏ Metamorphism of Basalt

Tectonics and Basalt Metamorphism Figure Blueschist and eclogite metamorphism Basalt

© 2008, John Wiley and Sons, Inc. Metamorphic facies Figure 10.18

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

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

Types of Metamorphism Metamorphic Processes Metamorphism: New Rocks from Old © 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.

© 2008, John Wiley and Sons, Inc. Contact metamorphism Figure 10.12

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

© 2008, John Wiley and Sons, Inc. 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