Testing models of Laramide orogenic initiation by investigation of Late Cretaceous magmatic-tectonic evolution of the central Mojave Sector of the California Arc

• Published in: Geosphere (Boulder, Colo.) Colo.), 2021-12, Vol.17 (6), p.2042-2061
• Main Authors: Economos, Rita C, Barth, Andrew P, Wooden, Joseph L, Paterson, Scott R, Friesenhahn, Brody, Wiegand, Bettina A, Anderson, J. Lawford, Roell, Jennifer L, Palmer, Emerson F, Ianno, Adam J, Howard, Keith A
• Format: Article
• Language: English
• Subjects: absolute age; alkaline earth metals; batholiths; Cadiz Valley Batholith; California; California Arc; chemical composition; correlation; Cretaceous; crustal thinning; Geochemistry; Geochronology; igneous and metamorphic rocks; igneous rocks; intrusions; isotope ratios; isotopes; Joshua Tree National Monument; Laramide Orogeny; magmatism; Mesozoic; metals; Mojave Desert; Nd-144/Nd-143; neodymium; nesosilicates; orogeny; orthosilicates; Petrology; rare earths; Riverside County California; San Bernardino County California; San Bernardino Mountains; silicates; Sr-87/Sr-86; stable isotopes; strontium; tectonics; Transverse Ranges; U/Pb; United States; Upper Cretaceous; zircon; zircon group
• ISSN: 1553-040X; 1553-040X
• DOI: 10.1130/GES02225.1

The Mojave Desert region is in a critical position for assessing models of Laramide orogenesis, which is hypothesized to have initiated as one or more seamounts subducted beneath the Cretaceous continental margin. Geochronological and geochemical characteristics of Late Cretaceous magmatic products provide the opportunity to test the validity of Laramide orogenic models. Laramide-aged plutons are exposed along a transect across the Cordilleran Mesozoic magmatic system from Joshua Tree National Park in the Eastern Transverse Ranges eastward into the central Mojave Desert. A transect at latitude ∼33.5°N to 34.5°N includes: (1) the large upper-crustal Late Cretaceous Cadiz Valley batholith, (2) a thick section of Proterozoic to Jurassic host rocks, (3) Late Cretaceous stock to pluton-sized bodies at mesozonal depths, and (4) a Jurassic to Late Cretaceous midcrustal sheeted complex emplaced at ∼20 km depth that transitions into a migmatite complex truncated along the San Andreas fault. This magmatic section is structurally correlative with the Big Bear Lake intrusive suite in the San Bernardino Mountains and similar sheeted rocks recovered in the Cajon Pass Deep Scientific Drillhole. Zircon U-Pb geochronology of 12 samples via secondary ionization mass spectrometry (SIMS) (six from the Cadiz Valley batholith and six from the Cajon Pass Deep Scientific Drillhole) indicates that all Cretaceous igneous units investigated were intruded between 83 and 74 Ma, and Cajon Pass samples include a Jurassic age component. A compilation of new and published SIMS geochronological data demonstrates that voluminous magmatism in the Eastern Transverse Ranges and central Mojave Desert was continuous throughout the period suggested for the intersection and flat-slab subduction of the Shatsky Rise conjugate deep into the interior of western North America. Whole-rock major-element, trace-element, and isotope geochemistry data from samples from a suite of 106 igneous rocks represent the breadth of Late Cretaceous units in the transect. Geochemistry indicates an origin in a subduction environment and intrusion into a crust thick enough to generate residual garnet. The lack of significant deflections of compositional characteristics and isotopic ratios in igneous products through space and time argues against a delamination event prior to 74 Ma. We argue that Late Cretaceous plutonism from the Eastern Transverse Ranges to the central Mojave Desert represents subduction zone arc magmat