PALEOMAGNETISM OF THE KITTERY FORMATION: A RECORD OF TECTONISM AND ROTATION

The Kittery Formation is an early Silurian metaturbidite that formed just before the Acadian Orogeny in central coastal New England. Despite a long history of tectonism and deformation, the Kittery Formation preserves primary stratigraphic features suggesting that paleomagnetic data may further elucidate current tectonic and metamorphic interpretations of the Merribuckfred basin. The tectonostratigraphic history of this basin is difficult to reconstruct due to deformation and lack of abundant fossils. A paleomagnetic study of the Kittery Formation was carried out to determine its original geographic location, to confirm its current age assignment, and to analyze its remagnetization history.

Seven or more cores were drilled from 17 different sites. All cores were demagnetized in thermal increments from 25 to 400⁰C and measured by a SQUID spinner magnetometer at the University of New Hampshire. IRM, XRD, and reflected light microscopy confirm greigite as the only carrier of the ChRM. Greigite likely formed at the expense of iron- bearing sheet silicates during post-depositional deformation. AMS indicates the percent anisotropy of two sites is larger than 20%, while the rest were less than 16%. To a first order, K1 at all sites follows the trend of regional scale folding of the Kittery Formation after bedding correction, suggesting two generations of folding events in this unit. At all localities the Kittery Formation fails the fold test, likely due to internal deformation and strain, irregular fold hinges, or small scale offset between fold limbs. However, it does pass the baked contact test and therefore the magnetization age must be older than Jurassic, but younger than the last folding event. NRM sample directions are well clustered within sites, but comparison of different sites do not cluster in either geographic or tilt adjusted coordinates. Site VGPs cluster more closely with Silurian/Devonian or Carboniferous/Permian paleomagnetic poles for North America after variable amounts of vertical axis rotation. This suggests differential rotation of fault bounded blocks or magmatic shouldering during the Acadian and Alleghanian orogenies in central coastal New England. These results also indicate that greigite can remain stable over hundreds of millions of years, which is significantly longer than previously thought.