Petrogenesis of the meta-igneous rocks of the Sierra El Arco and coeval magmatic rocks in Baja California: Middle Jurassic-Early Cretaceous (166-140 Ma) island arc magmatism of NW México

Abstract

ABSTRACT The Jurassic-Early Cretaceous Vizcaíno and Alisitos terranes are juxtaposed in the central part of the Baja California Peninsula, México. The southernmost outcrops of the Alisitos terrane are located in the Sierra El Arco, which consists of greenschist-facies meta-igneous rocks. Further east in the Calmallí area, amphibolite and paragneiss dominate. The meta-igneous rocks constitute a magmatic system ranging from peridotite to granodiorite, with associated basaltic to dacitic volcanic rocks. The suite displays negative εSrt (average −8.4, n = 23) and positive εNdt values (average +5.8, n = 23), suggesting mantle-derived melts with no discernible assimilation of continental crustal material. Geochemical and isotopic data of the amphibolite suggests a protolith similar to the meta-igneous rocks. Paragneiss samples display εSrt of +166 and εNdt around −7, with Nd crustal residence ages of 1.5 Ga. The isotopic data of the paragneiss suggest provenance from continental sources. Similar to Triassic-Middle Jurassic metasedimentary rocks from the Baja California Peninsula and western México. Middle Jurassic magmatism on Cedros Island (Vizcaíno terrane) and the Sierra El Arco (Alisitos terrane) define an εSrt vs. εNdt evolutionary trend that is mostly within the mantle array, suggesting a common origin within the same island arc subduction setting. Jurassic magmatism of continental affinity, defined by positive εSrt (average +39, n = 15) and negative εNdt values (average −4.2, n = 15), is widespread in the Baja California Peninsula and western México. Our Sr-Nd isotope mixing curves suggest that the assimilation of Late Triassic metasedimentary rocks or a lower crust could explain the isotopic composition of the continental affinity Jurassic magmatism.