Sediment provenance of Triassic and Jurassic sandstones in central Mexico during activity of the Nazas volcanic arc

Abstract

We have investigated the provenance of Upper Triassic and Jurassic siliciclastic sediments (Zacatecas, Nazas and La Joya formations) in the Mesa Central region (areas of La Ballena, Charcas and Real de Catorce) in central Mexico. The sediments were deposited during activity of the Nazas volcanic arc at the western margin of Pangaea. Provenance characteristics are essential for reconstructing the palaeotectonic setting of the region. Overall, 26 sediment samples and 3 volcanic rock samples from the Nazas volcanic arc were analyzed. The latter are potential source lithologies. Petrographic analysis reveals that the analyzed sediments are mainly composed of monocrystalline quartz, polycrystalline quartz (chert and composite quartz), feldspar, and rock fragments of mainly volcanic origin. Th/Sc vs. Zr/Sc values illustrate low sediment recycling in the source area(s). For the majority of the analyzed samples low Cr and Ni values exclude input from a mafic/ultramafic (ophiolitic) source. The majority of the translucent heavy minerals (Pxn, Amp, Ep, Spn, Grt, Chl, Tur, Ant, Rt) are scarce in almost all samples. The most abundant translucent heavy minerals occurring in the samples are apatite and zircon. Apatite grains decrease from the southeast (La Ballena) towards the northeast (Real de Catorce) either indicating stronger weathering conditions in the area of Real de Catorce or a source area that delivered detritus exclusively for the zone of Real de Catorce. Sediments of the Zacatecas Formation illustrate maximum depositional ages ranging from Norian (Late Triassic) to the Hettangian/Sinemurian boundary (Early Jurassic). Detrital zircon U–Pb ages suggest that they received detritus from the Amazonian craton (~1780–1300?Ma), the Oaxaquia microcontinent (~1290–900?Ma), the Maya (Yucatan–Chiapas), Oaxaquia, Coahuila and possible Chortis, and Florida blocks (~720–450?Ma) and the Permian–Triassic magmatic arc (~300–240?Ma). The Acatlán Complex and the Maya (Yucatan–Chiapas) block are likely source areas for ~445–310?Ma-old zircon grains. The source of the ~240–200?Ma-old detrital zircons are likely magmatic rocks related to the early disassambly of western Pangaea. Detrital zircons from sediments of La Joya Formation provide maximum depositional ages from the Pliensbachian (Early Jurassic) to Oxfordian (Late Jurassic). The most probably source areas are the Oaxaquia microcontinent (~1290–900?Ma), and the Maya (Yucatan–Chiapas), and Coahuila blocks (~720–450?Ma). Zircon ages ranging from ~200 to 150?Ma are indicative of detritus from the Nazas volcanic arc, which explains the presence of the volcanic fragments in La Joya Formation deposits.