Metamorphism and Metamorphic Rocks

Flashcards covering key concepts on metamorphism and types of metamorphic rocks.

What is metamorphism?

A solid-state change in composition and/or texture of a rock due to different temperatures and/or pressures or fluids unlike those conditions in which the rock formed.

What are the two sources of heat that drive metamorphism?

Heat from magma (contact metamorphism) and geothermal gradient (an increase in temperature with depth).

What is the average continental geothermal gradient?

About 25-30°C per kilometer of depth.

What is the role of pressure in metamorphism?

Pressure increases with depth and affects the rock's texture and mineral formation through confining pressure and differential stress.

What is hydrothermal metamorphism?

Metamorphism that occurs at mid-ocean ridges or shallow crustal depths where hot fluids facilitate mineral changes.

What are common minerals found in hydrothermally altered rocks?

Gold, Silver, Copper, Magnetite, Fluorite, and Galena.

What defines foliation in metamorphic rocks?

Any planar arrangement of mineral grains or structural features within a rock.

How does foliation develop?

Through rotation of platy minerals, flattening spherical grains, and recrystallization producing new minerals perpendicular to maximum stress.

What texture is referred to as slaty cleavage?

Closely spaced planar surfaces along which rocks split, creating slate.

What is schistosity?

A texture in metamorphic rocks where platy minerals are discernible with the unaided eye, exhibiting a planar structure.

What are porphyroblasts?

Large minerals that grow during metamorphism within a finer-grained matrix.

What is a gneissic texture?

A banded appearance in metamorphic rocks resulting from the segregation of minerals by composition during higher grade metamorphism.