ANALYSIS OF DIKE AND VEIN DEFORMATION IN THE APPLETON RIDGE FORMATION SCHIST, CENTRAL ME

Here we analyze deformed dikes and veins to describe the style of deformation in schist of the Appleton Ridge Formation in Central ME. These rocks experienced dextral transpressional deformation ca. 380 Ma (West, 1999). In the study area, the Appleton Ridge Formation is a medium- to coarse-grained quartz-plagioclase-muscovite-biotite-garnet-staurolite schist. The average orientation of the foliation at this locality is 042, 84 SE, and foliation faces often exhibit subhorizontal corrigations. The schist contains numerous folded and boudinaged quartz veins and coarse-grained to pegmatitic leucogranite dikes. We identified three types of deformed dikes and veins: (1) shortened, (2) extended, and (3) shortened-then-extended. We measured dike and vein orientations in horizontal outcrop faces, photographed them, and classified them based on deformation features. We did not observe any particular spatial distribution of quartz or leucogranite structures, and both dikes and veins fall equally into all categories. The strikes of deformed dikes and veins define two sectors of shortened lines at 026-076° and 104°-138°, one sector of extended lines at 025-050°, and one sector of shortened-then-extended lines at 027-073°. Shortened veins exhibit large wave-length isoclinal folding with severe limb attinuation. Isoclinally folded dikes often have an axial-planar foliation. Extended dikes and veins are boudinaged. Individual boudins are generally aligned with the foliation, but boudin trains often step up across discrete shear surfaces. The limbs of isoclinal folds in shortened-then-extended dikes and veins are commonly dismembered along discrete shear planes or high-strain zones. This resulted in the formation of isolated, “s”-shaped pods (fold hinge zones) across extended fold limbs. These pods exhibit both forward and back rotation.

This study originally intended to apply Passchier’s (1990) method to calculate the vorticity of flow using veins and dikes in the Appleton Ridge Formation, but our data do not fit the required parameters. These features do not obey the assumption of homogenous progressive deformation, and we found no structures that fill the gap between the fields of shortening and extension—data essential to define the axes of no longitudinal strain.