Paleoproterozoic tectonic history ofthe Cerbat Mountains, northwestern Arizona:Implications for crustal assembly in the southwestern United States

摘要

Structural mapping, metamorphic anal- ysis, and U-Pb geochronology from the Cerbat Mountains of northwestern Arizona place new constraints on the tectonic sig- nificance and timing of the boundary be- tween the Mojave and Yavapai Proterozoic crustal provinces in the southwestern Unit- ed States. The Cerbat Mountains are the easternmost range that exhibits wholly Mo- jave Pb isotopic signatures, yet their Paleo- proterozoic structural history is strikingly similar to that of the Yavapai province. Two pervasive deformational events are recognized in the Cerbat Mountains. Dl fabrics are well preserved in the northern Cerbat Mountains, and are characterized bya north-northwest-striking, moderately northeast-dipping foliation (SJ that is axial planar to macroscopic recumbent folds that we interpret to be west to southwest ver- gent. Similar structures have been docu- mented locally in the Yavapai province. Dl 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 cen- tral and southern Cerbat Mountains and include a subvertical, northeast-striking fo- liation that truncates and transposes Sl. 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 Dl and D2 fabrics in the Cer- bat 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 ear- ly 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 Yava- pai provinces were sutured together be- tween ca. 1740 and 1720 Ma during region- al Dl deformation. Collisional orogenesis in the eastern Mojave province may have re- sulted in the tectonic burial of rocks in the Cerbat Mountains to depths of 20 km. D2, between l720 and 1682 Ma, corresponds to the widespread Yavapai orogeny, and is in- terpreted to record accretion of the amal- gamated Mojave- Yavapai terrane to Pro- terozoic terranes that are now located in Colorado.