Paleomagnetism of the Todos Santos and La Silla Formations, Chiapas: Implications for the opening of the Gulf of Mexico

Abstract

We report paleomagnetic data for the Lower to Middle Jurassic La Silla and Todos Santos formations of southern Mexico, in west-central Chiapas and the Tehuantepec Isthmus region. Volcanic rocks and red beds of these formations were deposited prior to or during the early stages of Gulf of Mexico opening. Dual-polarity characteristic magnetizations reside primarily in hematite and pass intraformational conglomerate, regional tilt, and reversal tests; they are thus interpreted as primary magnetizations. Our sampling sites are concentrated in three localities; around La Angostura Lake, 17 accepted sites yield a tilt corrected mean of declination (Dec) = 325°, inclination (Inc) = 4.6° (k = 11.9, α 95 = 10.8°); in the Matías Romero region, the mean is Dec = 312.9°, Inc = 3.2° (based on only seven sites); and in the Custepec area, Jurassic andesitic dikes intruding rocks of the Permian Chiapas Massif yield a corrected mean of Dec = 335.0°, Inc = 5.0° (six sites). The mean directions are discordant with respect to expected North America reference directions, and indicate a counterclockwise rotation of 35° to 40°. Inclinations indicate deposition or emplacement at near equatorial paleolatitudes (2.1°N ± 3.4°). This paleolatitude estimate is statistically indistinguishable from those previously observed in the La Boca Formation of the Huizachal Group in northeast Mexico. The localities we sampled in southern Mexico are separated by ~150 km, suggesting that the paleomagnetic signature of these rocks refl ects regionalscale rather than local deformation. These Jurassic paleomagnetic directions support a rotational origin for the Gulf of Mexico. The data are also consistent with an Early to Middle Jurassic reconstruction that places the Chiapas Massif offshore the Tamaulipas state in the western Gulf of Mexico, and an Euler rotation pole for the Maya Block for this time period in the eastern gulf. The apparent polar wander path defi ned by paleomagnetic poles for the Chiapas Massif and Jurassic rocks reported here suggests that relative motion between North America and the Maya Block occurred between Late Permian and Early Jurassic time, during a protracted rifting phase, and then in the Late Jurassic in association with seafl oor formation in the Gulf.

Evolution of the Caribbean plate and origin of the Gulf of Mexico in light of plate motions accommodated by strike-slip faulting

“…Next, we offer an updated model of Gulf of Mexico formation based upon sinistral movement along the Mexico-Alaska megashear that led Schouten and Klitgord (1994) to postulate that the Yucatán rotated in response to edge forces that imposed a "rack and pinion" motion. The rotation, which earlier was recognized during paleomagnetic studies by Molina-Garza et al (1992) and corroborated by Godinez-Urban et al (2011a), involved ~60° of counterclockwise motion. Rotation is inferred to have been accommodated by faults such as the Oaxaca fault (Alaniz-Alvarez et al, 1996) and a precursor of the Chixoy-Polochic fault in Guatemala (Anderson and Schmidt, 1983).…”

“…Next, we summarize recent studies of rift-related clastic sections that reveal stratigraphic relationships and accumulation ages (Godinez-Urban et al, 2011a, 2011bRubio-Cisneros and Lawton, 2011) and, further, note faults such as Oaxaca (Alaniz-Alvarez et al, 1996;Figs. 46 and 49), the Tamaulipas-Golden Lane-Chiapas transform (Pindell, 1985; Fig.…”

“…Extensive strata at this stratigraphic level are buried beneath younger platform sediments of Oligocene or later age (Frost et al, 1998;Larue et al, 1998;Montgomery, 1998). Tertiary deposits to the south form the predominantly tuffaceous Upper Paleocene to Eocene Jacaguas Group (Glover and Mattson, 1967;Mattson, 1967Mattson, , 1968aMattson, , 1968bGlover and Mattson, 1973), the basal unit of which is the Miramar Conglomerate.…”

“…CM-Chiapas massif; YA-Yaqui block. crops out along the western margin of the Veracruz basin and continues southeast as a nearly unbroken outcrop belt along the northeastern margin of the Chiapas massif, from whence exposures extend eastward into western Guatemala along the southern fl ank of the imposing Los Altos Cuchumatanes range (Anderson et al, 1973;Clemons et al, 1974;Godinez-Urban et al, 2011a, 2011bFig. 46).…”

“…As early as 1973, studies by Diller and Vedder (1973) and Uchupi (1973) led each to suggest rotation. The rotation of Yucatán and the surrounding Maya terrane is recorded by paleomagnetic results from the Late Permian Chiapas massif that have been interpreted to refl ect largemagnitude counterclockwise rotation of the Maya block with respect to North America (Molina-Garza et al, 1992;Godinez-Urban et al, 2011a;Fig. 48).…”