Abstract

Structural mapping, metamorphic analysis, and U-Pb geochronology from the Cerbat Mountains of northwestern Arizona place new constraints on the tectonic significance and timing of the boundary between the Mojave and Yavapai Proterozoic crustal provinces in the southwestern United States. The Cerbat Mountains are the easternmost range that exhibits wholly Mojave Pb isotopic signatures, yet their Paleoproterozoic structural history is strikingly similar to that of the Yavapai province.

Two pervasive deformational events are recognized in the Cerbat Mountains. D1 fabrics are well preserved in the northern Cerbat Mountains, and are characterized by a north-northwest−striking, moderately northeast-dipping foliation (S1) that is axial planar to macroscopic recumbent folds that we interpret to be west to southwest vergent. Similar structures have been documented locally in the Yavapai province. D1 is bracketed between 1740 and 1721 Ma in the Cerbat Mountains on the basis of U-Pb zircon ages of the Big Wash granite (1737 ± 4.3 Ma) and the Diana and Chloride granites (1719 ± 1.2 and 1721 ± 2.4 Ma, respectively). D2 fabrics dominate the central and southern Cerbat Mountains and include a subvertical, northeast-striking foliation that truncates and transposes S1. D2 is bracketed between 1721 and 1682 Ma, on the basis of U-Pb ages of the Diana and Chloride granites and post-D2 granite dikes in the eastern Cerbat Mountains (1682.5 ± 2.4 Ma). The structural style, orientation, and timing of D1 and D2 fabrics in the Cerbat Mountains are identical to those of the Yavapai province.

Supracrustal rocks within the Cerbat Mountains were subjected to two periods of metamorphism that correspond temporally to the two periods of deformation. The early phase occurred at 675–725 °C and 5–6 kilobars. The later phase occurred at 650– 700 °C and 3.5–4.5 kilobars.

We propose that the Mojave and Yavapai provinces were sutured together between ca. 1740 and 1720 Ma during regional D1 deformation. Collisional orogenesis in the eastern Mojave province may have resulted in the tectonic burial of rocks in the Cerbat Mountains to depths of 20 km. D2, between 1720 and 1682 Ma, corresponds to the widespread Yavapai orogeny, and is interpreted to record accretion of the amalgamated Mojave-Yavapai terrane to Proterozoic terranes that are now located in Colorado.

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