THE PROTEROZOIC TECTONIC EVOLUTION OF ARIZONA (PRECAMBRIAN, PLATE TECTONICS, VOLCANIC, STRATIGRAPHY).

Abstract

Archean tectonics are irreconcilable with modern plate tectonics without clearly understanding Proterozoic tectonic accretionary prosesses. Arizona best displays a convergent margin where Proterozoic accretion to an Archean craton generated a new Proterozoic crust from 1800 to 160 Ma. This 12 year study independently formulated a definitive understanding of Arizona's Proterozoic tectonic evolution with new lithologic, petrologic, geochemical, structural and relative age data, and extensive new mapping. The Northwest Gneiss Belt contains an early Proterozoic arkosic clastic wedge at the Wyoming Archean edge, but only intraoceanic elements--Antler-Valentine and Bagdad volcanic belts--on Proterozoic oceanic crust south of the wedge. The Central Volcanic Belt evolved diachronously on oceanic crust: 1800-1750 Ma formative volcanism (Bradshaw Mountain, Mayer, Ash Creek and Black Canyon Creek Groups) stepped SE to form the Prescott-Jerome island arc above a SE-dipping subduction zone; a 1740 Ma NW subduction flip accreted the arc to the Archean craton, evolved I-type plutons of NW alkali-enrichment opposit to arc tholeiites, and formed calc-alkaline Union Hills Group volcanics at the southeast arc front. Except for hiatal Alder Group deposition in structural troughs, the central magmatic arc emerged as the trench stepped southeastward across SE Arizona with flattening of subduction, growth of the Pinal Schist fore-arc basin, 1700 Ma accretion of the Dos Cabenzas arc to the margin, eruption of felsic ignimbrite fans across the central arc front, and Mazatzal Group shallow marine sedimentation across the emergent arc. Proterozoic plate tectonics were subtly different from modern plate tectonics, producing oceanic crust, island arcs and other features very different in detail from modern and Archean analogs. The Proterozoic Plate Tectonic Style warrants clear distinction from those of other eras. This study establishes for Arizona an extensive, accurate and new Proterozoic data base, for central Arizona a detailed relative chronology surpassing isotopic resolution, and a new formal stratigraphic framework to be the foundation for future studies. This dissertation is superceded by a new book on Arizona's Proterozoic Tectonic Evolution, published by the Precambrian Research Institute, 810 Owens Lane, Payson, Arizona, 85541.