How and When
The Sevier fold and thrust belt was active between late Jurassic through Eocene time. The actual age of initiation of the belt is not entirely agreed upon by researchers. The beginning of deformation in the earliest stages of the orogeny started about 120-80 Ma (millions of years ago) with the formation and continuation of a magmatic arc and foreland fold-thrust belt. However, data from the southern portion of the belt shows contraction in southern Nevada and southeastern California beginning about 200 to 92 Ma largely based on intrusions and the formation of the Lavinia Wash conglomerate sequence due to mountain building and erosion. This deformation continued and intensified around 105 to 100 Ma caused by the continued subduction of the Farallon plate beneath the North American plate. Deformation spread eastward starting around 80 to 75 Ma. At this time the elevated crust ran into the Colorado Plateau. The collision resulted in lateral spreading of deformation and led to a weakened lithosphere and crustal thickening. Metamorphism due to the crustal heating and thickening is prevalent between 90 to 70 Ma in the present Great Basin region.
Read more about this topic: Sevier Orogeny
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