RELATIONSHIP BETWEEN REMAGNETIZATION, MAGNETIC FABRIC AND DEFORMATIONIN PALEOZOIC CARBONATES

We have studied the magnetic fabric of Paleozoic carbonates from numer ous sites in the North American midcontinent, for comparison with pale omagnetic behavior and calcite twinning strains. Sites carrying a Kiam an remagnetization have significantly lower anhysteretic remanent magn etization (ARM) anisotropy (less than 3%) than other sites. Minimum ax es of ARM ellipsoids are distributed in a vertical plane trending appr oximately SE-NW. This trend is very similar to the orientation of Alle ghenian layer-parallel shortening, as inferred by mechanical twinning in calcite. Sites lacking a Kiaman overprint invariably have steeply-o riented minimum ARM axes and relatively strong anisotropy, whereas the most strongly remagnetized sites have nearly horizontal minima and we ak anisotropy. These observations suggest that diagenetic/authigenic m agnetites formed independently of any pre-existing fabric of precursor sulphides and host rock, and that the magnetic fabric of the whole mi dcontinent was at least partially affected by Alleghenian syn-orogenic activity.