METAMORPHISM AND METAMORPHIC ROCKS FACTORS INFLUENCING METAMORPHISM PRESSURE

METAMORPHISM AND METAMORPHIC ROCKS FACTORS INFLUENCING METAMORPHISM PRESSURE More pressure is exerted on rocks at depth than at Earth’s surface. LITHOSTATIC or CONFINING PRESSURE pushes on rocks in all directions. Grains become smaller and denser at depth.

METAMORPHISM AND METAMORPHIC ROCKS FACTORS INFLUENCING METAMORPHISM PRESSURE Pressure is greatest at the contact point between grains. Bonds can break. Ions migrate and re-bond. Rock becomes compressed.

METAMORPHISM AND METAMORPHIC ROCKS FACTORS INFLUENCING METAMORPHISM PRESSURE Pressure may be greater in some directions. DIRECTED PRESSURE Flattens rock in the direction at which the greatest pressure is applied. Lengthens rock in the direction to the greatest pressure.

METAMORPHISM AND METAMORPHIC ROCKS FACTORS INFLUENCING METAMORPHISM PRESSURE Causes existing minerals and features to deform. Doesn’t affect minerals in the rocks. Induces FOLIATION, in which the tabular minerals are aligned to the direction of greatest directed pressure.

METAMORPHISM AND METAMORPHIC ROCKS FACTORS INFLUENCING METAMORPHISM FOLIATION

METAMORPHISM AND METAMORPHIC ROCKS FACTORS INFLUENCING METAMORPHISM PRESSURE For metamorphism to occur, 1 kilobar of pressure is required. 1 Bar = pressure applied to the Earth’s surface by the atmosphere. 1 Bar = 1. 02 kg/cm 2 1 kilobar = 1000 Bar (or 1020 kg/ cm 2) These pressures occur at ~ 3 km depth.

METAMORPHISM AND METAMORPHIC ROCKS FACTORS INFLUENCING METAMORPHISM CIRCULATING FLUIDS Water greatly influences metamorphism. Aids in migration of unbonded atoms and ions. Allows for exchange of ions between adjacent grains. Water comes from a variety of sources Ground water Subducted oceanic crust Crystallization of magma Decomposition of water-rich minerals like amphiboles and clays

METAMORPHISM AND METAMORPHIC ROCKS FACTORS INFLUENCING METAMORPHISM CIRCULATING FLUIDS Influence production of new minerals by ionic exchange. Speed up reactions and change overall composition of the rock.

METAMORPHISM AND METAMORPHIC ROCKS FACTORS INFLUENCING METAMORPHISM PARENT ROCK Composition of parent rock influences the type of metamorphic rock produced.

METAMORPHISM AND METAMORPHIC ROCKS TYPES OF METAMORPHISM CONTACT METAMORPHISM Solid rocks in close proximity to magma will change in response to heating and circulation of hot fluids, i. e. , INTRUSIONS. Produces a “baked zone” in the adjacent country rock. Pressure is not significant in reaction. Impact of the intrusion is local. Only rocks in immediate contact with the intrusion will be highly metamorphosed.

METAMORPHISM AND METAMORPHIC ROCKS CONTACT METAMORPHISM Minerals stable at high temperatures will be formed closest to the intrusion. Coarser grained metamorphic minerals will also be formed closest to the intrusion. Size of the intrusion also influences the amount of metamorphism. Differences in temperature is also significant.

METAMORPHISM AND METAMORPHIC ROCKS CONTACT METAMORPHISM

METAMORPHISM AND METAMORPHIC ROCKS REGIONAL METAMORPHISM Alters rocks over a large geographic region. Appalachians of New England North Cascades of Washington-British Columbia

METAMORPHISM AND METAMORPHIC ROCKS REGIONAL METAMORPHISM BURIAL METAMORPHISM Occurs deep in sedimentary basins. Requires depths > 10 km At these depths and greater, lithostatic pressure and geothermal heat drive metamorphic reactions and recrystallization. Does not require a tectonic process. Does not create mountain belts. Generally no foliation because no directed pressure.

METAMORPHISM AND METAMORPHIC ROCKS REGIONAL METAMORPHISM BURIAL METAMORPHISM

METAMORPHISM AND METAMORPHIC ROCKS REGIONAL METAMORPHISM DYNAMOTHERMAL METAMORPHISM Affected by pressure (squeezing) and heat (magma). Occurs when converging plates squeeze rock caught between the plates. Crust generally thickens. Surface rocks get taken deep into the Earth. Rocks are subjected to high temperatures, lithostatic pressure and directed pressure. Rocks become foliated.

METAMORPHISM AND METAMORPHIC ROCKS REGIONAL METAMORPHISM DYNAMOTHERMAL METAMORPHISM Produced metamorphic rocks found in the Alps, Himalaya, and Appalachian Mountains. Also produced the greatly eroded metamorphic rocks in the Great Lakes region. These rocks are exposed by uplift (faulting) and rapid erosion. The process doesn’t reverse itself.

METAMORPHISM AND METAMORPHIC ROCKS OTHER TYPES OF METAMORPHISM HYDROTHERMAL METAMORPISM Chemical alteration of pre-existing rocks by hot water. Occurs primarily beneath ocean floor near divergent plate boundaries. Creates water-rich minerals. Includes serpentine, talc, and chlorite In addition, when steam hits ocean water and cools rapidly, valuable metals such as Cu, Ni, Fe and Pb are precipitated.

METAMORPHISM AND METAMORPHIC ROCKS OTHER TYPES OF METAMORPHISM FAULT ZONE METAMORPISM Produced by rocks grinding past each other at a fault. Produced by directed pressure and frictional heat.

METAMORPHISM AND METAMORPHIC ROCKS OTHER TYPES OF METAMORPHISM SHOCK METAMORPISM Produced by meteorite impact. Forms shock varieties of quartz. Stishovite Coesite

METAMORPHISM AND METAMORPHIC ROCKS OTHER TYPES OF METAMORPHISM PRYOMETAMORPHISM Results from ultra-high temperatures that occur in low pressure environments. Usually produced by lightning hitting surface rocks or sediments. Fulgurite

METAMORPHISM AND METAMORPHIC ROCKS OTHER TYPES OF METAMORPHISM PRYOMETAMORPHISM Fulgurite