Stratigraphic, geochemical, and isotopic constraints on tectonic and magmatic stages of the Zihuatanejo (Guerrero composite) terrane in Arteaga-Tumbiscatío, Michoacán, Mexico

The Arteaga-Tumbiscatío region of the Zihuatanejo terrane forms the westernmost part of the Guerrero composite terrane. This region contains one of the most complete stratigraphic columns of the terrane. Its evolution is divided into nine main tectonic stages characterized by alternating deformational and volcanic-arc events. The oldest rocks in the region belong to the Arteaga Complex, which is made up of highly sheared and locally metamorphosed turbidites (shale, quartzose sandstone, and black chert) and volcanic siltstone that forms a sedimentary matrix with blocks of mid-ocean-ridge basaltic lavas, banded gabbro, green chert, and limestone. The sedimentary matrix is mostly made up of continent-derived quartzose sandstone that yields 1.2 Ga Nd model ages. The age of deposition of the Arteaga Complex is constrained by Triassic (Norian) radiolarians from chert, Permian–Triassic maximum detrital zircon depositional ages, and a U/Pb zircon age of 180 Ma from a block of gabbro. Lithologic associations, geochemical affinities, and contact relations suggest that rocks of the Arteaga Complex were originally deposited in an oceanic basin that evolved near the paleocontinental margin of Mexico-Gondwana (stage 1). The Arteaga Complex was deformed as a subduction-related accretionary prism sometime between the Late Triassic and Early Jurassic (stage 2, D₁ and D₂) and was intruded by Upper Jurassic granodiorite (stage 3, VA-I) that shows more evolved geochemical and isotopic signatures (peraluminous) than the subsequent magmatic events. These granitoids yielded a ⁴⁰Ar/³⁹Ar age of 152 ± 0.07 Ma and Nd model ages of 1.2 Ga and are interpreted as related to subduction initiation. Rocks of Lower Cretaceous mafic volcanic-arc affinities (stage 4, VA-II) are not exposed in the study area. Jurassic granodiorite intrusive units were deformed, mylonitized, and exhumed (stage 5, D₃) previous to the development of a Cretaceous (Aptian–Albian) volcanic arc (stage 6, VA-III). Four Cretaceous lithostratigraphic units (stage 6, VA-III), the Agua de Los Indios, Pinzán, Resumidero, and Playitas Formations, unconformably overlie the Arteaga Complex and deformed Jurassic intrusive units. All were deposited in an intra-arc basin and record two alternating sea-level transgression/regression cycles. The Cretaceous succession was deformed, causing wide regional folds (stage 7, D₄) that are interpreted as initial pulses of the contractional event that originated the Mexican orogen of the Sierra Madre Oriental fold-and-thrust belt of eastern Mexico. Other areas of the Zihuatanejo terrane recorded Santonian–Maastrichtian arc volcanism (stage 8, VA-IV) that was coeval to late pulses of the Late Cretaceous contractional event that formed the Mexican orogen. This was followed by Eocene magmatism and strike-slip deformation (stage 9, VA-V).