PETROGENESIS AND GEOCHEMICAL CORRELATION OF THE META-IGNEOUS ROCKS OF THE SIERRA EL ARCO WITH THE CEDROS-VIZCAINO REGION, CENTRAL BAJA CALIFORNIA PENINSULA: MIDDLE JURASSIC-EARLY CRETACEOUS ISLAND ARC MAGMATISM OF NW MEXICO

In the central part of the Baja California peninsula, the Vizcaino (Jurassic-Early Cretaceous) and Alisitos (Early Cretaceous) terranes are separated ~100 km by the Vizcaino basin (Late Cretaceous-Eocene). The geographic separation, age differences, and the absence of observable contact-relationships preclude a direct correlation between the two terranes. In this study, we focus on the petrogenesis of a meta-igneous suite and metamorphic host rocks in the Sierra El Arco-Calmalli region, which are the southernmost exposures of the Alisitos terrane. The results were integrated with data from the volcano-plutonic suite of the Cedros-Vizcaino region (Vizcaino terrane) to propose a coherent geologic history of the Baja California peninsula.

In the Sierra El Arco, the magmatic suite ranges from peridotite to granodiorite, with associated basaltic to dacitic volcanic rocks, with greenschist-facies metamorphism. The suite shows an island arc affinity, and their Sr-Nd isotopic composition suggests a depleted mantle source with no discernible assimilation of isotopically evolved material. Northward, in the Calmalli area, amphibolite and paragneiss dominate. The geochemistry and isotope composition of the amphibolites suggest a protolith similar to the meta-igneous rocks of the Sierra El Arco, whereas the paragneisses display evolved Sr-Nd isotope compositions. Their Nd crustal residence ages of 1.5 Ga suggest continentally derived detritus, similar to Triassic-Middle Jurassic metasedimentary rocks that crop out along the Baja California peninsula and southwestern Mexico. The Jurassic magmatism of the Sierra El Arco (Alisitos terrane) and the Vizcaino-Cedros (Vizcaino terrane) regions are geochemically and isotopically similar, suggesting a common origin within the same island arc subduction setting, close to the continental margin. Coeval magmatism of continental affinity in the Baja California peninsula and southwestern Mexico could be explained by the assimilation of different amounts of Late Triassic metasedimentary rocks, which differs from the Precambrian crystalline basement of northwestern Mexico.