14 Mineralogy and Petrology (Posters)

Friday, 14 March 2003
8:00 AM - 12:00 PM

TIMING OF DEFORMATION IN THE GOLD HILL FAULT ZONE, CAROLINA ZONE, NORTH CAROLINA

Paper number: 14-4
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

The accretion of the Carolina zone to Laurentia constituted one of the key events in the tectonic history of the southern Appalachians. However, the timing of accretion is controversial, as previous geochronologic data can be interpreted to indicate either a late Silurian/Devonian age or an Ordovician age for this event, and the original suture between the Carolina zone and Laurentia has been either tectonically buried or totally obliterated by late Paleozoic Alleghanian motion on the central Piedmont shear zone (the western-most boundary of the Carolina zone). Therefore, the history of accretion must be indirectly deduced from structures and tectonostratigraphic sequences that formed outside the suture zone.

The Gold Hill fault zone (GHfz) is the most prominent structure in the western part of the Carolina zone, the area closest to the suture with Laurentia, and provides an alternative to looking at the original suture. Samples of deformed mylonitic granite and phyllites collected from the GHfz in North Carolina show mineral recrystallization associated with low grade (lower greenschist facies) metamorphism. Quartz and calcite retain intracrystalline strain features (subgrains, undulose extinction, etc.) suggesting deformation occurred at low temperatures and was followed by relatively rapid cooling. Pseudotachylyte has been found in some of the hanging wall phyllites of the GHfz, also suggesting high strain rates and relatively rapid cooling. This style of deformation should prove ideal to date through 40Ar/39Ar analysis of muscovite. Our geochronologic study in progress focuses on dating recrystallized, neoblastic muscovite from different lithologies in the GHfz in order to constrain the timing of deformation.