Paleomagnetic investigations have been carried out on latest Cambrian to Early Ordovician alkaline intrusions, their contact intermediate to mafic composition metaigneous rocks, and overlying lower Paleozoic and early Tertiary strata in the Florida Mountains, southwestern New Mexico. A well-defined, predominantly normal polarity magnetization of high median destructive induction and high, usually discrete laboratory unblocking temperatures is isolated from sites in metaigneous rocks in contact with syenites exposed on the northwestern flank of this late Cenozoic uplift. Combinations of stable endpoint and planar data are used in data analysis at the site level (D=262¿, I=-30¿, α95=10¿, k=12; N=22 site means). In addition to the presence of reverse polarity magnetizations at two sites, the dispersion of site mean directions in these rocks (VGP angular standard deviation of 19.6¿) suggests that considerable variation of the geomagnetic field has been averaged. After correction for a combination of early Tertiary (Laramide) deformation and late Tertiary Basin-range block tilting, this magnetization gives a paleomagnetic pole at 6 ¿S, 169 ¿E and is interpreted to have been acquired soon after intrusion of alkaline plutons at 503¿10 Ma, based on published U-Pb zircon isotopic age determinations. A lack of well-defined, coherent magnetizations in the plutonic rocks may reflect the complex subsolidus alteration history of these rocks, as interpreted with Rb-Sr isotopic data. Hematitic sandstones of the earliest Ordovician Bliss Formation, which directly overlie the crystalline rocks in portions of the range, give dual-polarity magnetizations whose directions suggest that these rocks have probably been remagnetized; this remagnetization possibly occurred during deformation in late Cretaceous/Tertiary time.

Ordovician carbonate rocks of the El Paso and Montoya formations give only a Holocene magnetization. Paleocene to earliest Eocene(?) hematite-cemented clastic rocks of the Lobo Formation possess dual-polarity magnetizations. The origin of their magnetization is difficult to assess with the available data. In total, however, paleomagnetic data from the Bliss and Lobo formations argue against any significant vertical axis rotation of the area since Laramide deformation ending in Early Tertiary time. The intermediate to mafic composition metaigneous rocks from the Florida Mountains provide a latest Cambrian-Early Ordovician paleomagnetic pole that compares favorably with other North American paleopoles satisfying several acceptance criteria. The Florida Mountains data further support recent constructions of apparent polar wander paths for North America and thus the hypothesis that significant counterclockwise rotation of North America occurred during the Ordovician. ¿ American Geophysical Union 1991