Early Cretaceous pre-batholith dextral-transpression in the central Baja California peninsula: the record of the La Unión complex, Baja California, Mexico

Abstract

The La Unión volcanic-plutonic complex is located near the southwestern margin of the Peninsular Ranges batholith (PRb). La Unión complex rocks are grouped into prebatholithic and batholithic rock units. Batholithic rocks are assigned to the Cretaceous western zone of the PRb, which is associated with the Alisitos island arc. Prebatholithic rocks are composed of Upper Jurassic volcanic rocks and granitoids containing screens of metamorphic rocks. Prebatholithic rocks recorded ductile deformation with steeply dipping fabrics and overturned strata in response to a dextral transpression (D1) generated between ca. 128 and 132 Ma. The La Unión complex interfingers with the Nuevo Rosarito plutonic suite. Intrusive rocks of both composite plutonic bodies are composed of two mafic and three younger felsic units. The emplacement of the felsic units initiated at~108 Ma synchronously with an oblique (?) contractional event (D2), for which deformation was accommodated in part by a magma-assisted fan-like structure ≥5-7 km wide. The strain regime and age of D2 is placed in a regional context, where reverse faults and thrusts developed along the axial zone of Baja California as a result of the juxtaposition between the Alisitos arc and the North America margin. The incorporation of D1 and D2 into the geologic record of the Baja California peninsula allows us to propose a regional scenario where deformation associated to the final arc-continent juxtaposition began at least as early as 130 Ma and was a discontinuous process generated at two different stages.

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

“…Undeformed granitoids from Punta Prieta to Compostela that yield U-Pb zircon dates between 128.1 ± 1.4 Ma and 100.5 ± 2.7 Ma, restrict the timing of the accretion of the Jurassic-Early Cretaceous sequences with the North America margin to before mid-Cretaceous magmatism (~100 Ma) in the southern part of the PRB. This interpretation agrees with the model proposed by Peña-Alonso et al (2015). They suggested that a prebatholithic deformation event, characterized by a dextral transpression, may have occurred in the study area during the Early Cretaceous between 132 and 128 Ma.…”

“…Johnson et al (1999), , and Johnson et al (2003) observed that the plutons with ages ranging from about 110 to 100 Ma that intrude the suture zone at SSPM show syn-and post-deformational structures, including west-vergent mylonite shear zones. In our study area, Peña-Alonso et al (2015) observed Jurassic-Early Cretaceous dextral transpression recorded by the La Unión volcanic-plutonic complex in the southern part of the PRB at 28°-29°N. The authors interpret that this deformation may be a consequence of non-orthogonal or oblique convergence between the Farallon plate and the trench at ca.…”

“…The average foliation in the NR mafic and tonalitic rocks is parallel to the regional structural trend, and the elongation of the plutonic bodies is NW-SE ( Figure 2). The pluton emplacement occurred after the deformational event responsible for the foliation and metamorphism of the host rocks, which is dated between~132 and~128 Ma (Peña-Alonso et al 2015).…”

“…Titanite is a common accessory in this pluton; this is important because titanite is also a characteristic mineral in intrusions of the transition and eastern zones of the PRB. Deformation displayed as frequent shearing planes is interpreted to be coeval with the La Unión pluton(Figure 2), for which emplacement is interpreted to have occurred under a transpressive regime(Peña-Alonso et al 2015).…”

Transecto magnetotelúrico en el área transfronteriza de Sonora-Arizona: Identificación del límite nororiental del rift del Golfo de California

“…La evolución del arco continental cordillerano durante el Mesozoico es compleja e incluye varios eventos de ruptura continental y acreción de arcos de islas al margen occidental de México, ocurriendo los más importantes -o mejor conocidos-durante el Cretácico (e.g., Gastil et al, 1981;Busby et al, 1998;Centeno-García, 2008;Peña-Alonso et al, 2015). Durante el Cretácico Superior-Eoceno se produjo un aumento generalizado de la tasa de convergencia entre la placa subducida (Farallón) y el continente de Norteamérica (orogenia Larámide sensu lato) que resultó en la construcción de un arco magmático continental de tipo andino a lo largo del margen cordillerano (e.g., Coney y Reynolds, 1977;Engebretson et al, 1985;Yonkee y Weil, 2015).…”