The ghost of sutures past: A para-autochthonous origin for the Mazatzal crustal province in southwestern Laurentia demonstrated by structural, geochronologic, and isotopic analysis across the Yavapai-Mazatzal province boundary, central Arizona, USA

The Proterozoic crust of southern Laurentia has been considered for >30 yr to be an archetype of continental growth via the accretion of exotic crustal fragments. In a broadly accepted model, Laurentia grew by the sequential addition of the ca. 1.8−1.7 Ga Yavapai and ca. 1.7−1.6 Ga Mazatzal provinces. These provinces were originally defined in central Arizona, southwestern United States, where the Yavapai and Mazatzal provinces are distinguished by marked differences in lithology, metamorphic grade, and structural style across a proposed suture between the Moore Gulch and Slate Creek shear zones. Here, we tested the hypothesis that rocks of the Mazatzal province are allochthonous with respect to the Yavapai province and that the Moore Gulch shear zone marks the northern edge of the province suture zone. We present: (1) new combined zircon U-Pb and Hf-isotope analyses of plutonic rocks older than 1.7 Ga across the Moore Gulch shear zone, (2) new field and microstructural analysis of the Moore Gulch shear zone, and (3) a compilation of published detrital zircon U-Pb and Hf-isotope data from quartzite successions characteristic of the Mazatzal province. Plutonic rocks on either side of the Moore Gulch shear zone are isotopically juvenile at ca. 1.75−1.74 Ga, with εHf(t) values near +10. Detrital zircon data from post−1.7 Ga quartzites are indistinguishable across the province boundary zone, and stretching lineations in the northeast-striking Moore Gulch shear zone plunge steeply to the east-northeast and record top-to-the-southwest shearing in an oblique sinistral reverse fault geometry. These results do not support the presence of a crustal suture between the Yavapai and Mazatzal provinces. Instead, we favor the interpretation that metasedimentary rocks of the Mazatzal province were deposited unconformably across those of the Yavapai province, and that rocks of the Mazatzal province are para-autochthonous with respect to the Yavapai province. Correlation of Mazatzal Group quartzites across block-bounding shear zones of the Arizona transition zone indicates that deformation attributed to the Mazatzal orogeny in its type locale, and juxtaposition of different crustal levels across block-bounding shear zones, actually occurred during the Mesoproterozoic (ca. 1.49−1.35 Ga) Picuris orogeny. The Mazatzal province is not distinct from the Yavapai province; the two are continuous.