AMS Studies on Flaser Gneiss, Piseco Lake, Adirondack Mountains

Flaser gneisses are strongly foliated and strongly lineated gneisses with pronounced ribbon-like lineations. We analyzed the anisotropy of magnetic susceptibility (AMS) on oriented cores (average 6 cores per site) from 10 sites along a profile across the Piseco antiform, east of Piseco Lake in the SW Adirondack Mts. Mainly these are quartz-feldspar-hornblende-biotite gneisses of granitic to syenitic composition. The degree of anisotropy Pj is high, ranging from 1.2 to 3, and increases from the flanks to the axial zone of the fold. The shape parameter (U) for the core samples varied from 0.6 (oblate) to -0.8 (prolate). Prolate sites are dominant in this fold structure, suggesting that longitudinal extension along the fold axis occurred during the formation of these flaser gneisses.