Intense Heat and/or Pressure, Yo! Metamorphic Rocks
AIM: What are the characteristics of metamorphic rocks? Metamorphic rocks are formed from existing bedrock by the action of heat, pressure, and chemical action within the Earth’s crust.
Heat/Pressure causing recrystallization
Meta Rox Pressure: (Regional/Dynamic Metamorphism) At 6 miles beneath the surface, The downward pressure ~ 20 tons/in2 Horizontal pressure is present during mountain building
Orogeny (Mountain Building)
The REALLY smart version…. College Definition: Metamorphic rock is created when heat and pressure break the bonds between some of the ions in a mineral, allowing them to migrate to other sites in the rock and re-bond. Such migration of ions, usually through fluids circulating through the rock, results in recrystallization of the mineral. Metamorphism occurs when heat and pressure exceed certain threshold levels, destabilizing the minerals in rocks, but do not become high enough to cause melting.
Meta Rox Heat and Chemical Action (Thermal or Contact Metamorphism) High temps may cause partial melting and re-crystallization A “baked” zone is present along the edge of an igneous intrusion. This will contain contact metamorphosed rocks
Rock Metamorphism Rock Transformations: (Original Morphed) Limestone Marble (acid test reveals carbonate) Sandstone Quartzite (harder and denser) ShaleSlatePhylliteSchistGneiss ConglomerateMeta-conglomerate (pebbles stretched and squished)
NOTE!! Quartzite and Marble may result from regional / dynamic metamorphism but they do not show foliation (see ESRT)
What is Foliation? Foliation – under intense pressure and heat, some minerals may partially melt and re-crystallize as new minerals or larger crystals. They may also align themselves in sheets or plates (distorted layers)of mineral crystals (Schist)
Foliated Meta Rox
Foliation or they may arrange into bands of alternating light and dark minerals (Gneiss)
Foliation High-grade metamorphism will also show distorted layering and banding
Meta Rox/Foliation