Lithospheric architecture and tectonic evolution of the southwestern U.S. Cordillera: Constraints from zircon Hf and O isotopic data

Fate of the lower lithosphere during shallow-angle subduction: The Laramide example

“…Our new results indicate that studied arclogitic xenoliths are coeval with the 1 GSA data repository item 2019368, field observations, sample descriptions, analytical methods, and zircon U-Pb data, is online at www.geosociety.org/datarepository/2019. SCB and, with the exception of a small proportion (<10% of analyzed grains) of Latest Cretaceous-early Cenozoic grains, are older than Arizona porphyry copper deposits (Vikre et al, 2014;Chapman et al, 2018;Fig. 2).…”

“…160-140 Ma) and Late Cretaceous (90-70 Ma) arc plutonic assemblages with relatively small amounts of Mesozoic to Neoproterozoic metasedimentary rocks (Wells and Hoisch, 2008;Barth et al, 2008;Needy et al, 2009;Chapman et al, 2018 Repository Fig. DR1 1 ; e.g., Vikre et al, 2014;Tosdal and Wooden, 2015;Chapman et al, 2018). Hence, Latest Cretaceous-early Cenozoic and Early-Middle Jurassic xenolith zircon ages, readily distinguishable from Late Cretaceous and Late Jurassic ages expected from the Mojave Desert, may point to a SW Arizona origin.…”

“…For example, the Mojave Desert is underlain chiefly by Middle Jurassic-Early Cretaceous (ca. 160-140 Ma) and Late Cretaceous (90-70 Ma) arc plutonic assemblages with relatively small amounts of Mesozoic to Neoproterozoic metasedimentary rocks (Wells and Hoisch, 2008;Barth et al, 2008;Needy et al, 2009;Chapman et al, 2018 Repository Fig. DR1 1 ; e.g., Vikre et al, 2014;Tosdal and Wooden, 2015;Chapman et al, 2018).…”

Geochemical evidence for an orogenic plateau in the southern U.S. and northern Mexican Cordillera during the Laramide orogeny

“…Unlike the central United States Cordillera (the location of the Nevadaplano), the southern United States Cordillera was marked by extension associated with the Bisbee-Mc-Coy-Sabinas rift system during Late Jurassic to Early Cretaceous time (Dickinson and Lawton, 2001). Aptian-Albian marine limestone in southern Arizona suggests that the region was at or below sea level during mid-Cretaceous time (Dickinson and Lawton, 2001) and only transitioned to a contractional regime at the start of the Laramide orogeny (Chapman et al, 2018). Structural studies in the area indicate that deformation primarily occurred by folding or slip associated with high-angle reverse faults, which only accumulated a few to several tens of kilometers of horizontal shortening (Davis, 1979;Krantz et al, 1989;Clinkscales and Lawton, 2017;Favorito and Seedorff, 2018).…”

“…2) during the Laramide orogeny as the subduction angle of the Farallon slab shallowed (Coney and Reynolds, 1977). Laramide igneous rocks in southern Arizona and northern Sonora are mainly intermediate, metaluminous, and calc-alkaline rocks that have radiogenic isotopic compositions inherited from the lithospheric province into which they were emplaced (Lang and Titley, 1998;González-León et al, 2011;Chapman et al, 2018). During mid-Eocene time, toward the end of the Laramide orogeny and after arc magmatism had migrated through the region, silicic (SiO 2 >70 wt%), peraluminous granitoids were emplaced as sills, dikes, and plutons interpreted as products of crustal melting (Miller and Bradfish, 1980;Haxel et al, 1984;Miller and Barton, 1990;Fornash et al, 2013).…”