A northwest trending, Jurassic Fold Nappe, northernmost Zacatecas, Mexico

Abstract

The Caopas, Rodeo, and Nazas formations exposed in the San Julifin uplift of northern Zacatecas are distinguished principally on the basis of style and intensity of deformation; they are parts of the same early Mesozoic(?) volcanogenic suite. This suite was the source for overlying volcanidastic conglomerate and sandstone (La Joya Formation) that appears transitional into succeeding Late Jurassic (Oxfordian?) Zuloaga Limestone. Deformation that was contemporaneous with the deposition of the lower part of the Zuloaga produced an asymmetrical northwest trending fold nappe that was driven somhwestward. The massive quartz-porphyry core of the structure (Caopas Formation) moved somewhat independently of the encasing, more ductile rocks (Rodeo and Nazas formations). Phyllonite developed in the nose of the nappe; the upright limb was attenuated and ruptured. In zones where deformation due to the nappeforming process was weaker, a gemly dipping foliation, possibly related to an older episode of recumbent folding, is preserved. Orientation, age, and location of the nappe suggest that it is a manifestation of tr.anspressional stress developed along the Mojave-Sonora megashear as left-lateral movement carried the Jurassic arc toward the southeast. INTRODUCTION AND PURPOSEAbout 50 years ago a series of geologic studies established the basic regional stratigraphic framework of These works were supplemented 'by a second generation of field mapping that began with de Cserna's [1956] preparations for the Twentieth International Geological Congress and were followed by the publication of several key quadrangle maps [C6rdoba, 1964, 1965; Enciso de la Vega, 1963; Pantoja-Alor, 1963; Mayer Perez Rul, 1967; Clemons and McLeroy, 1966; McLeroy and Clemons, 1965] and ancillary research [Rogers et al., 1961]. Interest in the belt of Cross Ranges, which separates Coahuila Island from the Meseta Central to the south, was rekindled by the development of plate tectonic theory and the widespread search for prospective hydrocarbon sources [e.g. Carillo-Bravo

The Mesozoic successions of western Sierra de Zacatecas, Central Mexico: provenance and tectonic implications

“…Whereas the rifting processes were dominant in the east of nuclear Mexico, the palaeo-Pacific margin was subject to compressive and transpressive tectonic processes. Transpressional tectonics could be related to the reorganization of the peri-Gondwanan blocks as result of the break-up of Pangaea (Anderson, McKee & Jones, 1991; Sedlock, Ortega-Gutiérrez & Speed, 1993) or the oblique subduction (Silver & Anderson, 1974). Transpressional faults were active during Late Jurassic time (Anderson, McKee & Jones, 1991; McKee, Jones & Anderson, 1999), and could have originated from compressional structures (D1) documented in the Zacatecas and La Pimienta formations; the latter demonstrate a NW–SE–shortening direction, a similar orientation to that of the transpressional structures.…”

Pre–Late Jurassic, fossil-bearing volcanic and sedimentary red beds of Huizachal Canyon, Tamaulipas, Mexico

“…As the La Boca Formation is thought to be correlative to the Nazas Formation (Imlay et al, 1948;Belcher, 1979;Gose et al, 1982;Anderson and Schmidt, 1983;Cohen et al, 1986;Salvador, 1987;Maher et al, 1991;Anderson et al, 1991;Jones et al, 1995;McKee et al, 1997), a similar origin is likely for any volcanic material found therein. If the VES also originated from Pacifi c subduction, then these two volcanic rock sequences might be from the same arc system or its earlier analog.…”