ABSTRACT

The tectonic style of the late Mesozoic Sevier orogenic belt in Utah was greatly affected by preexisting structural trends that date from the late Precambrian rifting and fragmentation of the North American continent.

The late Precambrian cratonic margin (Cordilleran hinge line) was marked by a system of prominent faults including the north-south-trending ancestral Wasatch and ancient Ephraim faults and the southwest-northeast-trending Leamington, Scipio, Cove Fort, and Paragonah faults.

During the Paleozoic and Mesozoic, renewed activity on these faults affected the geometries of the late Paleozoic Paradox and Oquirrh basins, the boundaries of the Jurassic Arapien Formation, and the sedimentary pattern of the Cretaceous foreland basin.

Many of these fault zones were reactivated as tectonic ramps (e.g., the ancient Ephraim fault) and tear faults (e.g., the Leamington fault) during the compressional Sevier tectonism. The Fillmore arch and some other structural highs situated along the edge of the late Precambrian craton caused ramping of the inner Keystone-Pavant-Canyon thrust sheets and telescoping of the frontal thrust sheets.

Post-thrust uplift of basement highs led to tectonic denudation and to the development of low-angle, extensional faults, such as the Sevier detachment. Northeast-trending lineaments, such as the Cove Fort and Paragonah lineaments, were reactivated as right-lateral strike-slip faults. They also affected the extent of the Marysvale volcanic field.

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