DescriptionLayered Gabbro of the Duluth Complex in Minnesota USA 01.jpg
English: Layered gabbros of the troctolitic series in the Duluth Complex at a roadcut next to parking lot for the Thomson Hill Information Center, Skyline Parkway, northern side of Interstate 35, just west of the Route 2-Interstate 35 intersection, west of Duluth, Minnesota, USA. (Geology hammer for scale). The gabbro formed 1099 million years ago.
This is gabbro, a mafic, phaneritic, intrusive igneous rock composed principally of plagioclase feldspar and pyroxene. This rock is 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. Layering is not commonly seen in intrusive igneous rocks. These layered gabbros are the result of repeated episodes of crystal settling in a magma chamber.
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