Estudio petrogenético de las rocas ígneas en las formaciones Huizachal y Nazas

http://dx.doi.org/10.18268/BSGM1986v47n2a1

Manuel López Infanzón*

*Subdirección de Tecnología de Exploración, Instituto Mexicano del Petróleo

Abstract

Petrologic and geochronometric studies of samples collected in thirteen sites where red beds outcrop in Northeastern Mexico, reveal two petrogenetically distinctive continental sedimentary cycles during the Mesozoic.

The first cycle is the Huizachal Formation deposited in the Late Triassic. Erosion of basement rocks and deposition in rift basins formed during the early phases of the Pangea break up, are indicated by its petrogenesis. This formation, involves red beds exposed in the Huizachal-Peregrina Antielinorium and Miquihuana, Tam., El Alamar Canyon and SW of Galeana, N.L., and El Jabalí, Coah.

The second cyce is defined by the Nazas Formation; it consists of a vulcanosedimentary sequence deposited in the Middle Jurassic. Late cycles of sedimentation were associated to faulting and magmatism; so in parts, this sequence suffered progressive cataclasis and thermal effects that caused it to be considered previously as metamorphic units in the Sector Transversal de Parras and Northeastern Zacatecas.

Petrlogy, K-Ar data and stratigraphic relationships lead to propose the next units to be included in the Nazas Formation; the red beds underlying post-oxfordian rocks in the Sector Transversal de Parras (El Numero and Jimulco areas); the Rodeo Formation (Rogers et al., 1961) consisting of interbedded andesite flows and tuffs (183±8 m.y.); a cataclastic granitic-dioritic hypabisal intrusive first described as the "Caopas Schist" (Rogers et al., op. cit) and red beds overlying the Zacatecas Formation in the Sierra de Catorce, S.L.P.

The petrologic data lead to consider the basal portion of the Rodeo Formation, first described by Cordoba (1964) to the Northeast of Caopas, Zac., as a part of the Taray Formation.

The geological oboervations made, suggest that the Altiplano and the Sierra Madre Oriental have a historical geology linked to the North American Craton since the Late Proterozoic.