ORIGIN OF MYLONITES AND ULTRAMYLONITES IN THE KELLYLAND FAULT ZONE, WASHINGTON COUNTY, MAINE
Major and trace element compositions were measured using combined ICP, INAA and XRF analyses. The mineralogy of the samples was determined using x-ray diffractometry and traditional point counting. Preliminary results show no change in major element composition between undeformed granite, mylonites and ultramylonites, but there is some variability in trace element abundance. During deformation hornblende altered to green biotite, but other major phases were largely unaltered. Quartz, feldspar and biotite are largely dynamically recrystallized in mylonites and ultramylonites. Quartz underwent subgrain rotation dynamic recrystallization while feldspars exhibit deformation lamellae and record grain-boundary bulging recrystallization and ample brittle fracturing. Many ultramylonites contain fine-grained, mineralogically mixed domains interpreted as devitrified pseudotachylite or deformed cataclasite. These observations, coupled with a lack of evidence for solution transfer, indicate deformation under relatively fluid poor conditions. Our data and observations suggest that the localized high-strain zones of the KFZ stemmed from grain size reduction during episodic brittle deformation that catalyzed plastic deformation in the mylonites.