THE YAVAPAI AND MAZATZAL PROVINCES ARE NOT JUVENILE OCEANIC ARC TERRANES: IMPLICATIONS FOR LAURENTIAN CRUSTAL EVOLUTION IN THE PALEOPROTEROZOIC

A popular view is that Laurentia grew during the Paleoproterozoic by accretion of juvenile oceanic arcs along an active southern margin. The ca. 1.75 Ga Yavapai and ca. 1.65 Ga Mazatzal Provinces have long been thought to be such juvenile arcs. However, new Hf isotopic data from detrital zircons from the Pinal schist, as well as ages of detrital zircons in the Vishnu schist and metasedimentary rocks in the Little Chino Valley region of northern Arizona, indicate that Paleoproterozoic crust in this region includes an older (pre-Yavapai) component. This older component requires a physical connection to continental crust that includes Archean and older Paleoproterozoic rocks, and is consistent with the well-known isotopic complexities of the adjoining Mojave Province. The 1.84 Ga Elves Chasm terrane of the Grand Canyon may be an exhumed remnant of this older component. If so, the Yavapai and Mazatzal Provinces should be considered marginal continental arcs. A further implication is that by ca. 1.85 Ga the basement infrastructure for these provinces was present in southern Laurentia. Although the simplest interpretation is that Mojave, Yavapai, and Mazatzal Provinces evolved on Laurentian crust, there have been recent suggestions that these provinces are in fact exotic to Laurentia, having been formed outboard of the Australian-Antarctic (Mawson) continent and accreted to Laurentia during a ca. 1.65 Ga continent-continent collision. Geochronologic and isotopic studies in the Gawler and Northern Australian cratons show striking similarities to the Mojave, Yavapai, and Mazatzal Provinces, including evidence that older crust was involved in the genesis of ca. 1.75 and 1.65 Ga rocks.