CENTRIFUGE MODELING OF THE EFFECTS OF PLUTON EMPLACEMENT ON SHEARING AND FOLDING IN TRANSTENSIONAL SHEAR ZONES: APPLICATIONS TO THE CARTHAGE COLTON SHEAR ZONE, ADIRONDACK MOUNTAINS, NEW YORK STATE

Centrifuge modeling of the emplacement of analog granitic magma in transtensional environments clearly show that the magma bodies migrate into existing fault/shear zones and boudin necks. In the absence of these structures analog magma bodies beneath competent horizons migrated laterally with little to no vertical migration. Preexisting faults reactivated during tension or transtension provided preferred pathways for diapiric rise of lower density and viscosity putty simulating magma which facilitated fault slip in our models. It appears that the lower density and lower viscosity material, once drawn into the active fault, acted as a lubricant accelerating slip which, in turn, resulted in a marked flattening of the fault surface during extension. Along strike variations in slip caused by differential lubrication of the fault surface resulted in folding of the fault surface during transtension even at low strains (24%). Continued extension rapidly led to formation of accommodation faults between sections with marked differences in slip. In the Adirondack Mountains of northern New York State, Proterozic (Grenville-aged) granitic magmas of the Lyon Mountain Series spatially associated and contemporaneous with transtensional slip along the folded Carthage Colton Shear (CCSZ) provide a natural application of our model results. Fold axis orientations parallel stretching lineations in the zone suggesting that folding of the CCSZ occurred while the shear zone was active. Based on our observations from the analog models, the injection of granitic magmas into the active shear zone may have facilitated slip along segments where these magmas are present. Along strike variations in the volume of magma being drawn into the shear zone is interpreted to have produced differential lubrication of the shear zone leading to its folding comparable to analog models. Detailed mapping of the distribution of Lyon Mountain granite in and adjacent to the CCSZ needs to be done in order to test this hypothesis.