Paleoproterozoic metamorphic, structural, and tectonic evolution of the Hartville Uplift, Southeastern Wyoming

Abstract

The Hartville Uplift (HU) of southeastern Wyoming lies near the intersection of two major Paleoproterozoic crustal boundaries, the Cheyenne Belt (CB) and the Dakotan Orogen. Previous structural and geochronologic studies in the HU, Laramie Mountains, and the Black Hills show that temporal and kinematic relationships are complex and suggest an earlier episode of east-west compression and metamorphism prior to accretion along the CB and a younger (ca. 1715 Ma) suturing of the Wyoming and Superior Province. This study aims to unravel the polydeformational and polymetamorphic tectonic history of the HU by analyzing geologic structures and the metamorphic history of metapelites and other rocks during the Paleoproterozoic orogenies. The HU is bisected by the vertical to steeply east dipping, north-northwest striking, Hartville-Rawhide Fault Zone (HRFZ) that separates greenschist facies assemblages on its western side from the upper amphibolite assemblages on its eastern side. The first documented deformational event on the western side is a nappe-forming event, D1, that is associated with relict metamorphism recognized by biotite, chlorite, and quartz pseudomorphing garnet. Although there are no clear noses of nappes exposed, north-trending, variably plunging hinges of parasitic folds suggest an east-west vergence.