Trans-Hudson Orogeny - Overview

Overview

The Trans-Hudson orogeny was the culminating event of the Paleoproterozoic Laurentian assembly, which occurred after the Wopmay orogeny (West of Hudson Bay, ca. 2.1-1.9 Ga.). The Trans-Hudson orogeny resulted from the collision of the Superior craton of eastern Canada with the Hearne craton in northern Saskatchewan and the Wyoming craton of the western United States, with the Archaen microcontinent Sask craton trapped in the THO western interior. The northern edge of the THO is marked by an exposed continental collision zone on Baffin Island (Canada) that occurred between ca. 1.85-1.835 Ga. On Baffin Island, ca. 1.845 Ga. crustal thickening occurred that was associated with accretion of an intra-oceanic arc terrane and subsequent regional metamorphic activity characterized by the growth of retrograde, upper amphibolite-facies assemblages that define a clockwise, decompressive P–T path (pressure-temperature) path. Final mineral growth on Baffin Island occurred between 1.82-1.81 Ga. and occurred as a progressive change from plate-margin to intraplate processes within an evolving convergent orogeny. Collectively, these collisions resulted in a mountain range that rivaled the grandeur of the Himalayas. Similar to the Himalayas, the Trans-Hudson orogeny was also the result of continent-continent collision along a suture zone. Only the roots of this mountain chain remain, but these can be seen in northeastern Saskatchewan and in the Black Hills of South Dakota. The Trans-Hudson orogeny and the consequent upheaval of the continental crust in the middle Proterozoic eon caused the area around the Great Lakes to become a flattened plain, which in turn led to the creation of the intercontinental basin and the interior and central plains of the United States (the Great Plains are the westernmost portion of North America's Interior Plains, which extend east to the Appalachian Plateau).

The Black Hills of South Dakota is one of the few remaining exposed portions of the Trans-Hudson orogenic belt. It is a huge, elliptically domed area in northwestern South Dakota and northeastern Wyoming about 125 miles long and 65 miles wide where the THO uplift caused erosion to remove the overlying cover of the Proterozoic marine sedimentary rocks and expose the granite and metamorphic rocks that formed the core of the dome. The peaks of the Black Hills are 3,000 to 4,000 feet above the surrounding plains, while Harney Peak - the highest point in South Dakota - has an altitude of 7,242 feet above sea level. These central spires and peaks all are carved from granite and other igneous and metamorphic rocks that form the core of the uplift. The nature and timing of this portion of the THO event in southern Laurentia is poorly understood compared to the exposed northern segments in Canada. The Black Hills offer the only surface exposure of the deformed and metamorphosed belt of Paleoproterozoic continental margin rocks in the collisional zone between the Archean Wyoming and Superior provinces. Based on geophysical evidence, this zone has been broadly interpreted to be the southern extension of the THO that was later truncated by the ~1.680 Ga. Central Plains orogen.