39 The Mesozoic Convergent Margin of Alta and Baja California

This session will cover aspects including the structure, petrology, geochronology, and stratigraphy of the Mesozoic convergent margin of North America from Alta California to Baja California Sur.

Friday, 24 April 2026
1:30 PM - 5:30 PM
LMH, Deli

Rapid Cretaceous Forearc Accumulation and Arc Unroofing in Baja California: New Constraints from the Vizcaíno Basin

Paper number: 39-3
Program: Technical Sessions
Time: 2:05 PM – 2:20 PM

Authors

Abstract

Recent years have seen renewed debate over the tectonic evolution of the western North American Cordillera, including the timing and magnitude of terrane translation and the role of proposed hit-and-run collisions. These controversies hinge in part on uncertainties in the paleogeography and kinematic histories of terranes along the continental margin. The Baja California peninsula represents the southern continuation of U.S. Cordillera, yet remains comparatively underutilized in these discussions. Here, we reconstruct the tectono-stratigraphic evolution of the Vizcaíno forearc basin in Baja California Sur, Mexico, using new stratigraphic, geochronologic, and provenance data.

We present new LA-ICP-MS U–Pb zircon geochronology from tuffs and sandstone maximum depositional ages, Bayesian stratigraphic age modeling, sedimentary provenance data, and analyses of sediment accumulation and tectonic subsidence. Mid- to Late Cretaceous forearc sandstones from the Vizcaíno Peninsula and El Rosario area are dominated by mid-Cretaceous zircons sourced from the Peninsular Ranges Batholith. Sandstone compositions evolve from undissected to dissected arc provenance fields and have increasing monocrystalline quartz and feldspar, which we interpret as progressive arc unroofing. Stratigraphic age modeling of a revised chronostratigraphy for the Asunción and Valle formations indicates rapid accumulation rates (~100–1000 m/My) between ca. 108 and 92 Ma. Rapid accumulation rates coincide with peaks in detrital zircon age modes, inferred arc unroofing, and a previously proposed transition from extension to contraction in the overriding plate, inboard migration of arc magmatism, and rapid batholith exhumation. Our results highlight links among deformation regime, arc magmatism, batholith exhumation, and deep-water forearc sedimentation, with implications for competing models of Cordilleran tectonic evolution.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410929

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