Palaeomagnetic assessment of plutons from the southern Peninsular Ranges batholith and the Jurassic Vizcaino igneous suites, Baja California, Mexico

摘要

We report geological and palaeomagnetic data from five discrete plutons in the southern part of the Peninsular Ranges batholith (PRB) and one pluton that is part of the Jurassic plutonic suite in the Vizcaino peninsula. The PRB plutons are Cretaceous and belong to the Alisitos island arc. The Jurassic pluton intrudes a Triassic-Jurassic ophiolite.Our study was designed to evaluate the palaeomagnetic homogeneity of the batholith from the Sierra San Pedro Martir, at similar to 31 degrees N, to about similar to 28.3 degrees N. The Punta Prieta, Nuevo Rosarito, San Jeronimo, and La Rinconada plutons in the western zone of the PRB are characterized by magnetizations residing in magnetite. The Compostela pluton is emplaced in a transition zone and has a magnetization that resides in haematite. The five Cretaceous plutons yield a combined palaeopole at 80.3 degrees N, 162.1 degrees E, A(95)=9.8 degrees, N=5 that after correcting for the opening of the Gulf of California rotates to 77.6 degrees N, 173.6 degrees E, the rotated pole being in angular distance of only 4.4 degrees from the North America reference pole. The Jurassic San Roque pluton yields a mean 0.6 degrees N, 306.1 degrees E, A(95)=9.2 degrees, N=10, which is discordant, showing a clockwise rotation of about 131 degrees +/- 16 degrees and flattening of 9.5 degrees +/- 12.9 degrees with respect to the 150Ma cratonic reference palaeopole. The results suggest that the intrusion of the undeformed Cretaceous Punta Prieta to Compostela plutons (128.1 +/- 1.4 and 100.5 +/- 2.7Ma, respectively) restricts tectonic accretion of the Jurassic-Early Cretaceous sequences to the North America margin to the time before mid-Cretaceous magmatism (similar to 100Ma) in the PRB near present latitude 28 degrees N. Mesozoic and Cenozoic strike-slip faulting along the Vizcaino margin can account for the 131 degrees clockwise rotation of the San Roque pluton. Our results do not support significant latitudinal movement between Vizcaino, the PRB, and mainland Mexico with the exception of the Neogene San Andreas Fault-related right lateral movement.