Review of Late Jurassic-early Miocene sedimentation and plate-tectonic evolution of northern California: illuminating example of an accretionary margin

Growth and provenance of a Paleozoic subduction complex in the Broken River Province, Mossman Orogen: evidence from detrital zircon ages

“…The inboard magmatic arc linkage for the Broken River subduction complex demonstrated here is similar to that documented from detrital zircon studies for the Franciscan complex of California (Dumitru et al, 2015;Ernst, 2015) and subduction complexes of southern Alaska (Amato & Pavlis, 2010;Davidson & Garver, 2017) and Japan (Isozaki et al, 2010).…”

“…Detrital zircon age spectra from subduction complex sandstones commonly includes a prominent, in some cases dominant, cluster that reflects derivation from a magmatic arc generated by the subduction system. For example, this has proven to be the case for the succession of subduction complexes represented in the Japanese islands (Isozaki, Akoli, Nakama, & Yanai, 2010), the Chugach complex of southern Alaska (Amato & Pavlis, 2010), the Franciscan complex of California (Dumitru, Ernst, Hourigan, & McLaughlin, 2015;Ernst, 2015) and the subduction complex developed in the New England Orogen of Australia (Korsch et al, 2009). Given the general magmatic arc-subduction complex association of Cawood, Hawkesworth and Dhuime (2012), maximum depositional ages (MDA) obtained from the youngest zircon grains in populations from subduction complex sandstone samples are likely to approximate the age of deposition.…”

Subduction initiation and early evolution of the Easton metamorphic suite, northwest Cascades, Washington

“…Preservation of amphibolite with a subordinate blueschist overprint suggests accretion, cooling, and exhumation rapidly followed early subduction metamorphism, without sufficient time for thorough recrystallization (Anczkiewicz et al, 2004;Agard et al, 2008;Plunder et al, 2016). More intensely retrograded amphibolite in the Franciscan and in Chile is interpreted to have been retrograded and dismembered into tectonic blocks in mélange during a prolonged residence time at depth (e.g., Wakabayashi, 1990;Ernst, 2015;Hyppolito et al, 2016;Mulcahy et al, 2018). The tectonic interpretation of amphibolite and Na-amphibole schist as metamorphic soles of the Easton metamorphic suite is similar to accretion and exhumation of the well-preserved metamorphic sole in the Semail ophiolite, which occurred over ~5 m.y.…”

“…Blueschist-and eclogite-facies rocks along the western North American margin record ~200 m.y. of subduction and accretion (e.g., Brown and Blake, 1987;Anczkiewicz et al, 2004;Dumitru et al, 2010;Ernst, 2015). Understanding the structural, metamorphic, and thermal evolution of these high-pressure-low-temperature (HP/LT) rocks is critical to reconstructing the assembly of western North America and provides insight into the evolution of long-lived subduction-accretion systems.…”

“…Geochronology of Franciscan rocks records continuous subduction metamorphism from 180 Ma until ca. 80 Ma (Anczkiewicz et al, 2004;Wakabayashi and Dumitru, 2007;Ukar et al, 2012;Ernst, 2015;Mulcahy et al, 2018). The structural and metamorphic evolution of early Franciscan subduction, however, is complicated by the fact that early high-grade rocks commonly occur as blocks in a younger lower-grade mélange (Cloos, 1985;Wakabayashi, 1992;Ukar et al, 2012), and only locally as coherent slabs at high structural levels that are faulted against younger lower-grade units (e.g., Wakabayashi and Dumitru, 2007).…”