Ex 7 Metamorphic Rocks

Rocks that have experienced _____ are metamorphosed at high pressures and relatively low temperatures.

subduction zone metamorphism

Rocks that have experienced ____ are metamorphosed at intermediate pressures and temperatures.

mountain belt metamorphism

Rocks that are “cooked” by an igneous intrusion have experienced ____, and are metamorphosed at very low pressures at a variety of temperatures (very low to very high).

contact metamorphism

What two types of metamorphism would result in foliated rocks?

mountain-building, subduction zone

What is true of low-grade and high-grade rocks?

Low-grade rocks are fine grained, high-grade rocks are coarse-grained

Slaty

fine-grained texture in which mica grains are aligned, causing the rock to break into flat pieces (foliated)

Phyllitic

fine-grained texture characterized by breaks which are shiny, but also wrinkled or corrugated. Mica grains are aligned to create this type of foliation (foliated)

Schistose

fine- to-coarse grained texture in which clearly visible minerals are aligned to give the rock a foliation. Schists are composed of ~50% micas giving them a characteristic brilliant shine. The minerals are not segregated into continuous, alternating dark and light layers (foliated)

Porphyroblastic Schistose

refer to rocks with a classic schistose texture and very large minerals called porphyroblasts (usually garnets or staurolite crystals) embedded in the rock (foliated)

Gneissic

fine to coarse grained texture in which clearly visible, usually aligned, mineral grains are segregated into continuous, alternating dark and light layers (foliated)

Hornfels

fine-grained, minerals often too small to see, rock breaks in irregular chunks rather than layers or sheets (non-foliated)

Granoblastic

sugary, crystalline, minerals usually same general size and do not have preferred orientation (non-foliated)