METAMORPHIC ROCKS Heat Temperature Recognizing Metamorphic Rocks Meta

METAMORPHIC ROCKS Heat + Temperature

Recognizing Metamorphic Rocks • Meta = Greek for change • Morphe = Greek form • Under enough heat, any rock will become igneous; • But if there is enough pressure to keep it solid, it may just change without reaching its melting point!

Metamorphic Minerals • Remember Fractional Crystallization? Bowen? • All minerals are stable at certain temperatures and crystallize at different temperatures. • If rocks containing minerals change due to heat + pressure, scientists can tell what conditions created the new minerals. Talc, Mica and Garnet

Metamorphic Textures • Two main groups: • Foliated • Nonfoliated • Geologists use metamorphic textures and mineral composition to identify metamorphic rocks.

Foliated Rocks • Layers and bands of minerals are characteristics of foliated metamorphic rocks. • High pressure flat, needle- like crystals with long axes perpendicular to the pressure. • Parallel alignment of minerals.

Nonfoliated Rocks • Composed mainly of minerals that form with blocky crystal shapes. • Quartzite (sandstone) and marble (limestone) are common examples • Porophyroblasts: new metamorphic crystals that grow large while surrounding minerals remain small.

Grades of Metamorphism • Combos of temperature + pressure result in different ‘grades’ of metamorphism. • Low-grade: Low temp and pressure with specific minerals/textures • High-grade: High temp and pressure with specific minerals/textures • Intermediate: between

Regional Metamorphism • Temperature and pressure affect large areas of the Earth’s crust. • Ranges in grade from low to high grade. • Results: changes in rock type, foliation and folding/deforming of rock layers in an area.

Contact Metamorphism • When molten material— igneous intrusion—comes in contact with a solid rock. • High temp, low to moderate pressure • Much more abundant with intrusive igneous rocks than with extrusive; affects surrounding rocks.

Hydrothermal Metamorphism • Super hot water reacts with rock and alters its chemical and mineral composition. • Fluids coming in and out of rock alter mineral composition and texture. • Chemical changes common. • Valuable ores (gold, copper, zinc, lead) can be formed.

Economic Importance • Modern life is only as convenient as it is because of naturally occurring Earth materials. • Metamorphic processes create gold, silver, copper and lead as well as many non-metallic resources.

Metallic Mineral Resources • Occur mostly in the form of metal ores. • Precipitated through hydrothermal solutions: • Concentrated in veins • Spread throughout rock mass • Most deposits are metal sulfides such as galena or pyrite.

Nonmetallic Mineral Resources • Metamorphism of ultrabasic igneous rocks produces the minerals talc and asbestos. • Talc: very soft; used as dusting powder and texture in paints. • Asbestos: not combustible; used in fireproofing / insulating materials. • Graphite: formed by metamorphism of coal!

The Rock Cycle • Metamorphic rocks form when other rocks change. • Igneous crystallize magma under Earth or on surface. • Sedimentary form from lithified minerals and sediments • Metamorphic change both with temperature and pressure.

The Rock Cycle • Will rocks stay the same? • Probably not. • Any rock can be changed into any other type of rock. • Continuous changing and remaking of rocks is called the rock cycle. • No one single way; many different ways to convert rocks.