Metamorphic

Metamorphic Rock: Rocks formed via heat and pressure, which change the minerals within the rock.

Geothermal gradient: The average change in temperature that is experienced as material moves into the Earth.

• Average Geothermal Gradient: 1 Degree Fahrenheit/100 Ft

Lithostatic Pressure: The pressure that the weight of the rock above a point exerts on a body of rock or sediment. 

Volatiles: Components of magma which are dissolved until it reaches the surface, where they expand. Examples include water and carbon dioxide. Volatiles also cause flux melting in the mantle, causing volcanism. 

Metamorphism: Rocks and minerals that change within the Earth are called metamorphic, changed by heat and pressure. 

Regional Metamorphism: Metamorphism that occurs with large-scale tectonic processes, like collision zones. HEAT AND PRESSURE

Contact Metamorphism: Metamorphism that occurs when rocks are next to a hot intrusion of magma. HEAT AND VOLATILES

Schist: Rock more metamorphosed than phyllite, to the point that mica grains are visible. Larger porphyroblasts are sometimes present. 

Gneiss: A very high grade metamorphic rock, higher grade than schist, with a separation of light and dark minerals. 

Quartzite: A metamorphosed Sandstone. 

Marble: A metamorphosed Limestone. 

Protolith: The rocks that existed before the changes that lead to a metamorphic rock, i.e. what rock would exist if the metamorphism was reversed. 

Recrystallization: The process of changing a mineral without melting. 

Mineral Rotation and Alignment: A process called foliation that occurs when minerals in rocks realign in response to pressure and heat. 

Foliated Texture: A pervasive layering caused by compositional layering or by the parallel orientation of platy or elongate mineral grains. 

Nonfoliated Texture: A metamorphic rock texture that lacks banding or foliation, and appears granular or crystalline. 

The processes that metamorphose a rock? 

• Heat: Increased temperature can cause existing minerals to recrystallize and form new minerals stable at higher temperatures

• Pressure: Compressive forces can cause minerals to align and create a foliated texture, or can simply compact the rock further

• Chemically Active Fluids and Gasses: Hot, mineral-rich fluids can facilitate chemical reactions within the rock, altering its composition.

Where does regional and contact metamorphism occur?

• Regional Metamorphism - Occurs on a large scale when rocks buried deep beneath the Earth's surface are changed by high temperature and pressure. This usually happens in mountain ranges, where colliding tectonic plates fold and deform rocks.

• Contact Metamorphism - Occurs on a small scale when magma or lava heats and transforms the surrounding rock. This usually happens along the edges of igneous rocks, such as at convergent boundaries with subduction zones.

The protoliths for the different types of metamorphic rocks.

• Foliated: Gneiss - Granite Protolith. Schist - Shale

• Non Foliated: Marble - Limestone, Quartzite - Sandstone Protolith

How regional metamorphism alters the protolith? - Alters the protolith by significantly changing its mineralogy and texture through increased temperature and pressure, causing the original minerals to recrystallize into new minerals that are stable under those conditions, often resulting in a foliated texture due to the directional stress involved in the process. 

How contact metamorphism alters the protolith? - alters the protolith by significantly changing its mineralogy and texture primarily through intense heat generated by the nearby intrusion of magma, causing new minerals to form based on the existing composition of the protolith while also recrystallizing existing grains, often resulting in a finer-grained, more compact rock with a distinct appearance compared to the original rock.