AN OVERVIEW OF THE PINWARE–BARABOO–PICURIS OROGEN: A 1.52–1.37 GA MESOPROTEROZOIC, TRANS–LAURENTIAN OROGENIC BELT

The Pinware orogen of eastern Canada, the Baraboo orogen of the midcontinent, and the Picuris orogen of the southwestern U.S. all preserve a record of volcanism and/or sedimentation between ~1.52 and ~1.44 Ga, followed by metamorphism, deformation, crustal thickening and dominantly granitic magmatism. Together these orogens form a Mesoproterozoic, ~5000 km long orogenic belt across Laurentia. Deposition and magmatism are diachronous across the orogen beginning ~1.52 Ga in eastern Canada and ~1.50 Ga in the southwestern United States. The Pinware orogen reworks older Paleoproterozoic (Labradorian) crust and more juvenile Mesoproterozoic (Quebecia) crust. For the Baraboo and Picuris orogens, Mesoproterozoic deposition covered Paleoproterozoic supracrustal and plutonic rocks of the Penokean-Yavapai-Mazatzal provinces. Metamorphism and deformation in the southwestern U.S. overprints both the Mesoproterozoic supracrustal rocks and the underlying Paleoproterozoic section. The largely buried, more juvenile Granite-Rhyolite Province lies outboard of the Picuris-Baraboo orogens.

A convergent accretionary tectonic margin was proposed to explain the Pinware-Baraboo-Picuris orogenic belt. The Pinware orogen was envisioned as a rifted continental arc, with the formation of a peri-continental island arc that subsequently collided with the continental margin. The formation of a Mesoproterozoic continental arc in the southwest US and midcontinent region was more speculative. For the Picuris and Baraboo orogens an advancing and retreating subduction model, with varying subduction angles was envisioned to allow for both crustal thickening and extension within a continental retroarc or backarc setting. Unfortunately, a fundamental contradiction remains; this model is inconsistent with the dominantly, ferroan magmatism associated with the Mesoproterozoic of Laurentia. One possible modification to this accretionary tectonic model is to call upon the collision of the juvenile Granite-Rhyolite province with the Paleoproterozoic margin of Laurentia to account for the Picuris and Baraboo orogenies. However, finding a tectonic model that fully reconciles the evidence for crustal thickening and a continental scale orogenic belt with the trans-Laurentian ferroan magmatic event remains elusive.