Abstract
AbstractWe report a detailed paleomagnetic and rock-magnetic study of 19 independent lava flows belonging to the Eastern Alkaline Province (EAP) in Mexico. In total, 162 oriented samples were collected in four areas (Sierra de Tantima-Alamo, Tlanchinol, Chiconquiaco-Palma Sola and Poza Rica). All sites analyzed in this study were previously dated by means of theunspikedK-Ar geochronological method (Ferrariet al., J. Volcanol. Geotherm. Res.,146, 284–306, 2005) and span from 14.6 to 1.5 Ma. Rock-magnetic experiments point to simple magnetic mineralogy. In most cases, the remanence is carried by Ti-poor titanomagnetite of pseudosingle-domain grain size. In a few cases, Ti-rich titanomagnetites are responsible for the magnetization. The characteristic paleodirections are successfully isolated for all of the studied units. The mean paleodirection, discarding two intermediate polarity sites, isD=359.5°,I=32.9°,n=17,k=30, α95=6.7°. This direction is practically undistinguishable from the expected Mio-Pliocene paleodirections, as derived from reference poles for the North American polar wander curve, and is in agreement with the previously reported directions from the western Trans-Mexican Volcanic Belt. This suggests that no major tectonic rotation occurred in studied area since the middle Miocene to Present. The paleosecular variation is estimated through the study of the scatter of virtual geomagnetic poles, givingSF=12.7 withSU=16.5 andSL=10.3 (upper and lower limits, respectively). These values are consistent with those predicted by the latitude-dependent variation model of McFaddenet al.(Geophys. Res.,93, 11583–11588, 1991) for the last 5 Myr. Eleven sites yielded reverse magnetic polarity, six are normally magnetized and two lava flows provided apparently intermediate paleodirections. An interesting feature of the paleomagnetic record obtained from EAP volcanics is that two independent lava flows, dated as 2.04±0.04 and 1.97±0.04 Ma, respectively, both yield normal paleodirections during the reverse Matuyama period. These sites were apparently formed during the Réunion geomagnetic event worldwide observed.
Highlights
The Trans-Mexican Volcanic Belt (TMVB), one of the largest continental volcanic arcs on the American continent, is related to Neogene subduction of the Cocos and Rivera plates beneath the southwestern margin of the North American plate
We report a detailed paleomagnetic and rock-magnetic study of 19 independent lava flows belonging to the Eastern Alkaline Province (EAP) in Mexico
Alkaline volcanic fields runs from the U.S border to the southern part of the Mexican state of Veracruz (Fig. 1), intersecting the subduction-related TMVB in Central Veracruz
Summary
The Trans-Mexican Volcanic Belt (TMVB), one of the largest continental volcanic arcs on the American continent, is related to Neogene subduction of the Cocos and Rivera plates beneath the southwestern margin of the North American plate. Urrutia-Fucugauchi (1994), provides a substantially lower value (7.4◦), which is in clear disagreement with the latitude-dependent paleosecular variation models. Paleomagnetic studies of the Plio-Quaternary volcanic sequences have focused on the paleosecular variation (PSV) characteristics for Central Mexico, with contrasting conclusions in terms of the amount of paleosecular variation as estimated by the angular dispersion of virtual geomagnetic poles (VGP). This author argued that the area may form part of the Central Pacific non-dipole region. As early as 1968, Cox predicted that there should be numerous undiscovered geomagnetic
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