Tectonic significance of Cretaceous-Tertiary magmatic and structural evolution of the northern margin of the Xolapa Complex, Tierra Colorada area, southern Mexico

Abstract

The Tierra Colorada area sits along the northern limit of the Xolapa Complex, where it is juxtaposed against the Mixteco (Paleozoic) and Guerrero (Mesozoic) terranes of southern Mexico, just north of Acapulco. This paper presents combined structural and geochronological data from Tierra Colorada area that show evidence of four deformational events and several episodes of arc magmatism during Mesozoic and Cenozoic time. The oldest magmatism is represented by ca. 165 Ma granitoids and was followed by intrusion of the foliated El Pozuelo granite (129 ± 0.5 Ma; concordant U-Pb zircon analysis). This intrusion postdates D 1 metamorphism and migmatization in the Xolapa Complex. The next magmatic episode is represented by the peraluminous, foliated El Salitre granite (55.3 ± 3.3 Ma; mineral-whole-rock Rb-Sr isochron) and the protomylonitic Las Piñas I-type granite (54.2 ± 5.8 Ma; lower intercept U-Pb zircon). Las Piñas granite is characterized by D 2 ductile fabric with normal, top-tothe north-northwest sense of shear, deformed at 45-50 Ma (Rb-Sr and K-Ar ages). The ca. 34 Ma undeformed granites correspond to the last intrusive pulse in the area, postdating both D 3 south-southwest-verging thrusting of the Cretaceous Morelos Formation over sheared granites and Lower Cretaceous volcanic rocks, and open folding during D 4. These four pulses of subduction-related magmatism in the Tierra Colorada area indicate a regular northeastward subduction at the Mesoamerican trench since Jurassic time, and alternate with contractile and/or extensional tectonic events. The gap in magmatic activity ca. 90-100 Ma roughly coincides with deposition of platformal limestones of the Morelos Formation during the middle Cretaceous. The stable conditions during deposition of the Morelos Formation may have resulted from a combination of backarc extension and development of a passive margin during the Early-middle Cretaceous, which postdated the accretion of an exotic block, either the Guerrero terrane or the Chortís block. Following the Laramide orogeny in southern Mexico (roughly during the Late Cretaceous) the Paleocene-Miocene tectonic evolution in the Tierra Colorada area involved an alternation of magmatic pulses with extensional and contractile events. This was the result of a combination of several factors, including the geometry of the subducted slab, convergence rate, stress transmission between the subducting and overlying plates, and the rate of subduction erosion.

U–Pb geochronological constraints on the Triassic–Jurassic Ayú Complex, southern Mexico: Derivation from the western margin of Pangea-A

“…Keppie, 2004;Solari et al, 2007;Pérez-Gutiérrez et al, 2009). These rocks were displaced sinistrally along the La VentaChacalapa Fault during Eocene-Oligocene time (Ratschbacher et al, 1991;Riller et al, 1992;Tolson, 2005;Solari et al, 2007;Ratschbacher et al, 2009). The Acatlán and Oaxacan complexes are unconformably overlain by unmetamorphosed continental redbeds, siliciclastic fluvial deposits and shallow marine shelf sediments of Upper Permian to Middle Jurassic age (Fig.…”

Crust and upper-mantle seismic anisotropy variations from the coast to inland in central and Southern Mexico

“…In this simplified model, it is possible to approximate such a setting as transverse isotropy (TI) with a horizontal symmetry axis in which pre-existing cracks that are approximately parallel to the direction of maximum compressive horizontal stress may have been opened while others are closed. We suggest that the anisotropy direction near the boundary of the Xolapa terrane is influenced by the E-W to WNW-ESE striking shear zone that bounds it (Solari et al 2007).…”

An Evaluation of Proposed Mechanisms of Slab Flattening in Central Mexico

“…The western Mexican margin has been a subduction margin for the past 160 million years (KEPPIE, 2004;SOLARI et al, 2007). The Sierra Madre Occidental, the subduction-related arc of western Mexico, initiated in the Jurassic and contains a continuous record of subduction-related magmatism from the Cretaceous and throughout the Cenozoic.…”