MIDDLE PROTEROZOIC DEXTRAL STRIKE-SLIP EVENT IN THE CENTRAL APPALACHIANS - EVIDENCE FROM THE RESERVOIR FAULT, NJ

Unequivocal kinematic indicators in cataclasites and mylonites of the Reservoir fault zone, New Jersey, show consistent dextral strike-slip shear sense and provide evidence for an extensive strike-slip event su bsequent to the peak of the Grenvillian (Ottawan) Orogeny. The fault z one occurs in layered granitic gneiss and minor amphibolite of Precamb rian age in the New Jersey Highlands (northern Reading Prong). The fau lt rocks underwent extensive synkinematic hydrothermal retrogression t hat produced amphibole-rich assemblages from all previous phases. Retr ogression of the protolith shows sequential reactions to assemblages d ominated by F-magnesiohastingsite, Cl-magnesiohastingsite, ferro-actin olite, actinolite, and finally actinolite + chlorite. Although deforma tion was purely brittle within the granitic protolith (quartz shows ma rginal plasticity), reaction enhanced ductility and plasticity of some phases produced S-C mylonites in amphibole mineralized fault rocks. C planes are composed of fine aligned grains of ferro-actinolite and ac tinolite and define tails on sigma-type amphibole porphyroclasts. The porphyroclast cores are composed of F-magnesiohastingsite and/or Cl-ma gnesiohastingsite and commonly define S-planes. Some porphyroclast cor es show brittle pull-apart textures and SEM analysis shows that virtua lly all have micro-brecciated rims that are indurated with epitaxial a mphibole over-growths from a more retrograde assemblage. C' planes are locally developed and defined by fine-grained chlorite and actinolite . All kinematic indicators show a consistent dextral strike-slip shear sense. Because retrogression was facilitated by fluids that evolved f rom F-rich to Cl-rich, as recorded by the amphiboles, they are interpr eted as Proterozoic which is characterized by F-rich metamorphic fluid s. Conditions of retrogression were lower greenschist facies as indica ted by both mineralogy and dynamic response of minerals. Therefore the strike-slip event postdates granulite facies metamorphism which occur red in this area as late as ca 1000 Ma. Dextral strike-slip shearing w as reported on the Canopus shear zone segment of the Ramapo fault, in the Hudson Highlands, New York. These examples of dextral shearing ind icate a significant event that may have resulted from escape tectonism during a Himalayan-type orogeny.