Migmatite in the Precambrian of Colorado, USA.
Migmatites are very high grade metamorphic rocks that form by partial melting of gneisses. The felsic minerals have melted, cooled, and recrystallized - they form the light-colored, crystalline-textured bands in the rock. The mafic minerals have higher melting temperatures and still retain their metamorphic foliated character.
The outcrop seen here is an Paleoproterozoic-aged migmatite at the Rocky Mountain Front in Colorado. This is part of the local Precambrian basement. Upper Paleozoic redbeds are nonconformably overlying the basement in the area.
Stratigraphy: "Idaho Springs Formation", late Paleoproterozoic, ~1.7 Ga
Locality: Red Rocks Park, west of Denver, north-central Colorado, USA
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