Paper No. 12
Presentation Time: 8:00 AM-12:00 PM
LATE GRANITE INTRUSIVES, NORMAL FAULTING, AND THE NATURE OF THE CARTHAGE COLTON SHEAR ZONE
Detailed mapping (1:24,000) of the central portion of the Carthage Colton Shear Zone in northern New York State reveals a complex structural and petrologic history. The CCSZ detachment surface records ductile to brittle thrust displacement to the SE separating rocks of the Adirondack lowlands (LL:Central Metasedimentary Belt) from those of the Adirondack Highlands (HL:Central Granulite Terrane). The Diana (DIA) complex is a stacked thrust sheet with the eastern-most thrust forming the present day detachment surface. The thrust faults are locally offset by E-W trending faults of oblique to strike slip character. Offsets are typically on the order of a few tens of meters and one of these faults clearly offsets the HH/LL detachment fault. Throughout, the DIA is strongly deformed with marked c/s fabric development that record NNW and gently plunging transport lineations. Regions of mylonitic to ultramylonitic fabric development are common at or near to the HL/LL boundary. Internally, small (2-5cm width) ductile shear zones in the DIA record both thrust and normal shear movements. These shear zones contain upper greenschist to amphibolite assemblages and record U/Pb sphene (recrystallization) ages of 1041 +/- 2 Ma and 40Ar/39Ar hornblende cooling age of 979+/- 8.6Ma. The DIA is thrust onto a strongly-deformed isoclinally folded complex of calcsilicate and granitic gneisses which are intruded by a weakly deformed I-A type hornblende granite. REE and Spider plots for this granite most resemble those of continental arc granitoids, yet plot within the WPG (within plate granite) field on Pierce discrimination diagrams. To the west, this granite body truncates against a NE trending SE dipping normal fault that cuts into and displaces the HL/LL detachment. A set of gently plunging open folds with NW trending hinge lines cross the HL/LL boundary and rotate all structures forming a weak hook and eye interference pattern. These data clearly point to a prolonged and active history for the CCSZ that includes intrusive activity, faulting and folding after juxtaposition of the Adirondack Highland and Lowland Terranes. In addition, the newly recognized E-W trending fault set pass through many of the active and abandoned mines in the region indicating that these fault systems played an important role in mineralization in both terranes.