PROTEROZOIC ACCRETIONARY TECTONIC HISTORY OF SOUTHWESTERN LAURENTIA: MULTIPLE HYPOTHESES, AND THE SEARCH FOR ANALOGUES (Invited Presentation)

Proterozoic crust of southern Laurentia has been regarded as an example of lithospheric growth through accretionary orogenesis for over 30 years. A broadly accepted model posits that supracrustal and plutonic rocks of the 1.8-1.7 Ga Mojave and Yavapai provinces and 1.7-1.6 Ga Mazatzal province were accreted to the margin of southern Laurentia during the successive 1.74-1.66 Ga, 1.65-1.60 Ga, and 1.45-1.38 Ga orogenies. Crucial aspects of this model remain debated, including the tectonic setting(s) of crust formation, nature and location of province boundaries, and the timing, duration, and tectonic drivers of orogenesis. An extensive regional dataset of paired zircon U-Pb geochronology and Hf isotopes from the oldest metasedimentary and plutonic rocks across all three crustal provinces delineates distinct packages of supracrustal rocks associated with each province and highlights the cyclic nature of tectonism across the region. These data provide new constraints and raise new questions concerning the nature of province boundaries and how and when provinces became juxtaposed. The Mojave province is dominated by schists and paragneisses with distinctive 2.0-1.8 Ga and 2.7-2.4 Ga detrital zircon populations interpreted to represent a magmatic arc(s) and arc-related basins built on and/or sourced by older Archean crust between 1.79-1.74 Ga. In stark contrast, metasedimentary rocks of the Yavapai province show prominently unimodal detrital zircon age peaks with juvenile Hf-isotope signatures that perfectly match the plutonic basement of the province, suggesting juvenile arc and arc-basin development. Both the Mojave and Yavapai provinces were deformed and metamorphosed from 1.74-1.66 Ga, reaching peak metamorphic conditions at 1.7 Ga. The Mazatzal province preserves evidence of multiple cycles of sedimentation and magmatism at 1.71 Ga, 1.66 Ga, and at the end of the 1.60-1.48 Ga North American Tectonic Gap. Tectonism following the latter necessitates refined models for the Proterozoic evolution of southwestern Laurentia and the stabilization of continental lithosphere that include repeated episodes of basin formation and inversion and amalgamation of continental margin arcs. We explore possible analogues for crustal growth including the Tasmanides and the North American Cordillera.