83 Structural Geology and Tectonics (Posters)

PRELIMINARY PALEOMAGNETIC DATA FROM EARLY PERMIAN ROCKS FROM NORTHERN IBERIA, IMPLICATIONS FOR THE TIMING OF LATE VARISCAN OROCLINAL BENDING

Paper number: 83-85
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

Preliminary paleomagnetic data from 20 sites in Early Permian redbeds and volcano-clastic rocks from the northern arm of the Cantabrian-Asturian Arc (CAA) yield a mean tilt-corrected paleopole that indicates a near-primary magnetization. These data show no perceptible vertical-axis rotations with respect to previously published paleopoles from the stable Iberian meseta. Previous work from remagnetized Paleozoic carbonates from throughout the CAA suggests major vertical-axis rotations of the limbs of the arc during late-stage oroclinal bending of the Western European Variscan Belt (WEVB). These previous paleomagnetic data suggest that orocline formation resulted from a two stage tectonic history: first an east-west compression event during the Carboniferous that resulted in a complex and well developed fold-thrust belt architecture with an almost linear shape, and second a north-south shortening event around the Carboniferous-Permian boundary (recently dated as 299 Ma), which resulted in oroclinal bending of the WEVB (both in present-day coordinates). The timing of deformation is bracketed by the acquisition of successive remagnetizations, each recording a distinct kinematic, fluid, and thermal history. Previous upper age limits of vertical-axis rotations in the CAA come from later Permian and Triassic rocks from throughout Iberia that show no comparable rotations.

Together, the previous remagnetization data and our new Early Permian data bracket the main phase of oroclinal bending in the WEVB to a short time interval between 300 – 290 Ma. This time interval coincides directly with independently confirmed ID-TIMS zircon and monazite U-Pb ages of voluminous tonalite-granodiorite-monzogranite plutonism with subordinate mafic-ultramafic intrusions that occurred across the entire WEVB, including the foreland basin in the Cantabrian-Asturian Arc. Together these data temporally and kinematically bracket a large-scale lithospheric buckling event that strongly suggests that the entire lithosphere was involved in oroclinal generation.