Paper No. 13-9
Presentation Time: 10:55 AM
CHASING CAMERON’S LINE: DETRITAL ZIRCON RESULTS FROM THE MANHATTAN AND HARTLAND SCHIST IN NEW YORK CITY
New York City lies within the broader physiographic province referred to as the Manhattan Prong, which includes the boroughs of NYC and much of southern Westchester County. Structurally, the Manhattan Prong sits at an important junction of the Appalachian Mountain belt, marking the boundary between the northern and southern Appalachians and is generally considered to be at (or near) the major boundary between rocks of Laurentian and Gondwanan affinities. This major terrane boundary referred to as Cameron’s Line separating Laurentian derived units from accreted exotic terranes, however, is poorly defined in southern New England. Previous mapping frequently – although not entirely consistently – interprets the Manhattan Schist as Laurentia, and the Hartland Schist as correlative with exotic terrane derived units farther north. However, previous work has not included detailed provenance studies or comparative detrital zircon analyses of these schist units. Here we present Nd isotope and detrital zircon results from multiple locations of both Hartland and Manhattan Schists. These results are consistent with both units being primarily derived from Laurentia: 1) eNd isotopic values for all samples range between -7 and -13, and 2) detrital zircon populations are dominated by Grenville aged zircons (1000 Ma and 1400 Ma). Hartland Schist from the east side of Central Park does contain a small population of 610 Ma zircon grains. We interpret to reflect a small input of material deposited from exotic terranes through minor mixing of sediment in the Iapetus Ocean but overwhelmingly, these rocks all have Laurentian affinities. Therefore, we suggest that the difference in texture and subtle chemistries of schists in New York City reflect a combination of tectonic pathway during deformation and/or subtle facies differences in the sediment prior to metamorphism and that the major terrane boundary likely likes to the east or southeast of New York City.