Migmatite Garnet Gneiss), Welcome Springs, Utah
Migmatites have undergone partial melting with one or more minerals in a liquid state (usually the lightly colored feldspar and quartz) and the rest (dark colored minerals) remains in a solid to semi-solid state. These two components are mixed to form a migmatite. Here, both metamorphism and mixing are the result of subducting oceanic sediment deposited at the passive margin of ancient North America into an oceanic trench, thus exposing the sediment both to heat and pressure. This metamophosis happened about 1.7 billion years ago.
Some of the migmatites resulting from subduction into an oceanic trench show a completely appearance depending on the direction o view.
When viewed perpendicular to the movement into the trench (left), sometimes wild curly schlieren pattern appear, giving these migmatites a unique appearance. However, when viewed indirection of the movement into the trench (right), the curly pattern are disappear, just plain foliated parallel lines in the gneiss.
Common in this area are also migmatites based on amphibolites.
Migmatite Garnet Gneiss), Welcome Springs, Utah
Migmatites have undergone partial melting with one or more minerals in a liquid state (usually the lightly colored feldspar and quartz) and the rest (dark colored minerals) remains in a solid to semi-solid state. These two components are mixed to form a migmatite. Here, both metamorphism and mixing are the result of subducting oceanic sediment deposited at the passive margin of ancient North America into an oceanic trench, thus exposing the sediment both to heat and pressure. This metamophosis happened about 1.7 billion years ago.
Some of the migmatites resulting from subduction into an oceanic trench show a completely appearance depending on the direction o view.
When viewed perpendicular to the movement into the trench (left), sometimes wild curly schlieren pattern appear, giving these migmatites a unique appearance. However, when viewed indirection of the movement into the trench (right), the curly pattern are disappear, just plain foliated parallel lines in the gneiss.
Common in this area are also migmatites based on amphibolites.