Image: Large anorthosite xenolith in ophitic ilmenite gabbro (anorthosite series, Duluth Complex, Mesoproterozoic, 1099 Ma; Keene Creek East Skyline Parkway roadcut, Duluth, Minnesota, USA) 1 (22039818790)

Description: Large anorthosite xenolith in ophitic ilmenite gabbro in the Precambrian of Minnesota, USA. These rocks are part of the widespread Duluth Complex, a ~1.1 billion year old suite of igneous rocks in northeastern Minnesota that is associated with volcanism in the Lake Superior segment of the ancient Mid-Continent Rift System. The dark-colored rocks are gabbro. The light-colored mass is a single large anorthosite xenolith within the gabbro. Xenoliths are "foreign rocks" that sometimes occur in igneous rocks - they form by detachment of magma chamber wall rocks. In this case, the magma chamber contained gabbroic magma and the walls were anorthosite. Gabbro is a mafic, phaneritic (coarsely-crystalline), intrusive igneous rock dominated by the minerals plagioclase feldspar and pyroxene. Anorthosite is a mafic, phaneritic, intrusive igneous rock dominated by just plagioclase feldspar. Geologic unit & age of gabbros: anorthosite series, Duluth Complex, late Mesoproterozoic, 1099 Ma Age of anorthosite xenolith: unknown, but Precambrian, likely derived from the lower crust Locality: Keene Creek East outcrop - roadcut along the northern side of Skyline Parkway, Duluth, northeastern Minnesota, USA (46° 45’ 08.52” North, 92° 10’ 29.93” West)
Title: Large anorthosite xenolith in ophitic ilmenite gabbro (anorthosite series, Duluth Complex, Mesoproterozoic, 1099 Ma; Keene Creek East Skyline Parkway roadcut, Duluth, Minnesota, USA) 1 (22039818790)
Credit: Large anorthosite xenolith in ophitic ilmenite gabbro (anorthosite series, Duluth Complex, Mesoproterozoic, 1099 Ma; Keene Creek East Skyline Parkway roadcut, Duluth, Minnesota, USA) 1
Author: James St. John
Usage Terms: Creative Commons Attribution 2.0
License: CC BY 2.0
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