A CASE FOR REVISING THE TIMING, REGIONAL EXTENT, AND SIGNIFICANCE OF THE MAZATZAL OROGENY IN ITS TYPE AREA

Recently published detrital zircon data and new regional correlations across Tonto Basin of central Arizona, revise the timing of the Mazatzal orogeny, in its type area, to ca. 1.485-1.45 Ga, contemporaneous with the Picuris orogeny of New Mexico. The new timing does not affect well documented deformation ca. 1.7-1.65 Ga including deformation recently extended, temporally and spatially, to 1.58 Ga per Duebendorfer et al. (2015). The 2 km thick Mazatzal Group (MG) in the northern Mazatzal Mountains (MM) is deformed by northwest-directed folding and thrusting, recording 35-50% shortening. Deformation in this area has long been interpreted as one of the type localities for the Paleoproterozoic Mazatzal Orogeny. The MG includes the basal Deadman quartzite, Maverick shale, and Mazatzal Peak quartzite. The upper most MG is conformably overlain by erosional remnants of the Hopi Springs Shale (HSS). The basal HSS has a maximum depositional age (MDA) of 1.57 Ga and is folded beneath the Barnhardt Thrust, long viewed as one of characteristic structures of the Mazatzal Orogeny. A correlative metapelite with a MDA of 1.58 Ga outcrops within the core of the Four Peaks quartzite synform in the southern MM. The lower quartzite at Four Peaks was deposited on a ca. 1.657 Ga rhyolitic ashflow that is variably deformed. The MG also correlates to the post-1.657 Ga White Ledge Formation (WLF) in the upper Salt River Canyon (USRC). The WLF is disconformably overlain by the Yankee Joe Group (YJG), which is now known to have been deposited after ca. 1.485 Ga. The YJG and quartzite at Four Peaks are intruded by post-tectonic 1.436 - 1.45 Ga granite constraining deformation between the 1.49-1.436 Ga. Collectively, the synform at Four Peaks, the WLF, and YJG are all deformed by NW-directed contraction attributed to the ca. 1.65 Ga Mazatzal orogeny. However, recognition that much of the strata were deposited during the Mesoproterozoic requires reconsideration of the nature, extent, and significance of the Mazatzal Orogeny. This revised timing for the Mazatzal orogeny is contemporaneous with the Picuris orogeny. Across Tonto Basin, stratigraphic evidence suggest little, if any, tectonism between 1.66 – 1.485 Ga although detrital zircon and ash deposits between 1.6 – 1.5 Ga suggest active volcanism in the region.