AGES OF TECTONIC EVENTS IN THE HUDSON HIGHLANDS, NY: RESULTS FROM SHRIMP ANALYSES

New dating of Proterozoic rocks from the Hudson Highlands, NY, using SHRIMP tightly constrains the timing of tectonic events as well as providing evidence for Rodinian plate reconstructions. Three samples were analyzed in fine detail and dates are reported with 1 s errors. All are concordant. The basic geologic setting of the area is 1) deposition of interpreted volcanic, volcaniclastic, and lesser sedimentary sequences, 2) Grenville (Ottawan) nappe emplacement and granulite facies metamorphism, 3) diorite intrusion, and 4) extensive dextral strike-slip shearing. Peak Grenville metamorphic ages from the area yield 1010 +/- 7 Ma and 1007 +/- 4 Ma from two of the samples. The diorite pluton contains deformed and metamorphosed xenoliths of granulite facies gneiss yet it is undeformed. It yields a cluster of concordant ages averaging 1008 +/- 4 Ma. It therefore must be late synkinematic. In other areas, this pluton is deformed in the dextral strike-slip shear zones which were clearly deformed in the solid state. The age therefore provides an upper limit to the strike-slip event. The interpreted metavolcaniclastic gneiss yields a series of apparent protolith ages (cores) ranging from 1230 to 1160 Ma. A metapelite sample contains multiply overgrown cores with a variety of concordant ages. In addition to the typical Grenville ages, there is a 1491 +/- 8 Ma core which could be Pinwarian and a 2041 +/- 23 Ma core which could be TransAmazonian. These ages are consistent with ages of belts from the South American shield and could indicate that it is a sedimentary source for these rocks or that the Hudson Highlands could be an exotic terrane. It may have originated as part of South America.