leucogranite - an orogenic collision-related igneous rock - hand specimen
Leucogranite is a characteristic feature of collisional orogenic zones. It is a light-colored granitic rock composed of quartz, plagioclase feldspar with almost no dark minerals. In this Proterozoic leucogranite, from a dike in the Beaver Dam Mountains of Utah, large garnet crystals are common.
Leucogranite forms by the melting of metamorphosed fine-grained sedimentary rocks in the upper portions of thickened crust. In the western United States, the presence of leucogranite suggests the possible locations of collisional suture zones for Precambrian terranes accreted to Laurentia.
Mont Saint-Michel in Normandy, France, is composed of leucogranite, emplaced during the Cambrian, about 525 million years ago. Leucogranite in the Black Hills is related to the Proterozoic Trans-Hudson orogeny. Leucogranites are associated with the Blue Ridge basement complex and in Maine, the Paleozoic Appalachian orogeny.
The name is derived from the Greek, leukos, for white.
Click and click again to enlarge the QAPF diagram. See how this rock fits into the classification of intrusive igneous rocks.
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