Magnetic Polarity Stratigraphy and K-Ar Dating in the Camargo Volcanic Field, Northern Mexico: Lateral SW-NE Migration of Volcanic Activity

Abstract

Results of a detailed paleomagnetic study of intraplate mafic alkalic volcanic rocks from the Camargo volcanic field of northern Mexico are presented. The field is formed by >300 eruptive vents and lava flows over an area of 3000 km2, and thus represents an important magmatic episode within the Mexican Basin and Range province. Rock-magnetic properties of the cinder cone field show that remanence is carried in most cases by Ti-poor titanomagnetites, resulting from exsolution and deuteric oxidation of original titanomagnetite during the primary flow cooling. A few units show remanence carried by titanohematite or by secondary titanomaghemite. New radiometric ages and magnetic polarity stratigraphy document a southwest-to-northeast migration of volcanic activity during the Pliocene-Pleistocene (4.7-0.09 Ma). Magnetostratigraphic correlation of dated rocks with the geomagnetic polarity time scale allows improved definition of volcanic stratigraphy. The mean paleomagnetic direction obtained for the Camargo volcanic field is I = 34.7°, D = 351.2°, k = 7, a95 = 16.6°, which deviates about 10° counterclockwise from the expected direction estimated from the North American apparent polar wander path. In the Basin and Range province, extensional faulting is closely related to volcanic activity. The tectonic, structural, and paleomagnetic data for the Camargo field document this association between volcanism and normal faulting, and also indicate the effects of large-scale processes of uplift, extension, block rotation, and regional faults in northern Mexico.