A tale of two Walker Lane pull-apart basins in the ancestral Cascades arc, central Sierra Nevada, California

Abstract

We integrate new geochronological, petrographic, and geochemical data with previously published (Sierra Crest-Little Walker volcanic center) and new (Ebbetts Pass volcanic center) structural and stratigraphic data to describe two deeply dissected, spectacularly well-exposed Walker Lane pull-apart basins in the ancestral Cascades arc. The Miocene (ca. 12-5 Ma) Sierra Crest-Little Walker arc volcanic center and the Miocene-Pliocene (ca. 6-4.6 Ma) Ebbetts Pass arc volcanic center formed in pull-apart basins in the Walker Lane, a NNW-trending zone of dextral strike-slip and oblique normal faults at the western edge of the Basin and Range Province. The Sierra Crest-Little Walker arc volcanic center is a transtensional arc volcanic field that is as areally extensive (~4000 km Volcano-tectonic activity continued for a longer period (ca. 12-6 Ma) in the northern half of the Sierra Crest-Little Walker volcanic center than it did in the southern half (ca. 12-9 Ma), overlapping for ~1 m.y. with the onset of volcano-tectonic activity at the Ebbetts Pass volcanic center to the north. This provides local-scale confirmation of the regional-scale interpretation that a transtensional rift tip propagated northward with time within the arc axis, in concert with northward migration of the Mendocino triple junction. Transtensional rift magmatism followed in its wake and continues today at various points along the length of the Walker Lane. "Tectono-stratigraphic recycling" was a key geologic process throughout the development of these ancestral Cascades arc pull-apart basins, and it consisted of the transfer of megaslide slabs, up to 2 km long and tens to hundreds of meters thick, from footwall to hanging-wall blocks in the transtensional rift. A time-slice series of block diagrams is used to illustrate the structural controls on arc volcanism in the early stages of Walker Lane transtensional faulting (ca. 12-4.6 Ma).

Graben type calderas: The Bolaños case, Sierra Madre Occidental, Mexico

“…This particular type of calderas was named as graben calderas by Aguirre-Díaz and Labarthe-Hernández ( 2003), and Aguirre -Diaz et al (2008) because of the association between the caldera volcanism and the graben that hosts it. However, these characteristics are shared by tectonically controlled collapse calderas developed in other tectonic environments (e.g., Williams, 1941;Van-Bemmelen, 1949;Williams and Meyer-Abich, 1955;Martí, 1991;Cummings et al, 2000;Cole et al, 2006;Molina-Zúñiga et al, 2012;Saxby et al, 2016;Busby, 2013;Gudmunsson, 2016;Busby et al, 2018;Sunyé-Puchol et al, 2019a, 2019bNavarrete et al, 2020), so this particular caldera dynamics may have a more general applicability than in the specific case described in this study.…”

4D volcanic geology of Hachijo-jima islet, Izu-Bonin arc

“…Island arcs are among the fundamental geotectonic environments on Earth, and studies of them provide information on plate tectonic mechanisms and history, as well as igneous processes. Whereas most research of island arc geology has focused on petrology, geochemistry, and geochronology of the igneous rocks (e.g., Ishizuka et al 2011, important new insights into tectonic and igneous processes can be gained by analytical research integrated with detailed geologic mapping (e.g., Busby et al 2018).…”