COMPILATION OF GEOCHEMICAL DATA OF META-VOLCANICS FROM THE ROWE-HAWLEY ZONE OF WESTERN NEW ENGLAND ARE CONSISTENT WITH BACKARC, ARC, AND FOREARC REGIONS OF ONE COMPOSITE ARC

The Shelburne Falls Arc (SFA) located within the Rowe-Hawley Zone (RHZ) of western New England has been cited as the colliding terrane during the Taconian Orogeny, but this arc has not been definitively correlated along-strike across western VT, MA, and CT. Geochemical analyses of metabasalts and meta-andesites from the Hawley slices of the eastern RHZ in all three states show them to have suprasubduction zone affinity; these data have been compiled and compared to test correlations of major map units. Subalkaline metabasalts of the Hawley Fm of western MA can be differentiated from subalkaline basalts and basaltic andesites of Collinsville Fm of western CT using MORB-normalized multi-element plots. Hawley samples show large negative Nb, large positive P, and flat Zr to Yb <1, whereas Collinsville samples display small negative Nb, flat Zr to Yb 10 < x > 0.1, and flat to negatively sloping HFSE ≤1; the majority of Collinsville metabasalts are MORB. Mount Norris Intrusive Suite (MNIS) subalkaline basalt from northern Vermont show backarc basin affinity (small negative Nb, Zr to Yb ~1, and relatively flat HFSE ~1). These data and Pearce element ratios indicate that the Hawley and Collinsville rocks could have formed in the forearc and backarc basins, respectively, of one arc complex similar to modern rifted supra-subduction arcs of the western Pacific (e.g., Izu-Bonin). The Taconian orogeny could have been the result of a sequence of accretionary events involving these backarc, arc, and forearc regions of one composite arc. Comparison of these geochemical data along the length of the RHZ have sparked interest in using Pb, Sr, and Nd isotopic compositions of meta-igneous units for analysis of mantle sources, continental and/or sedimentary components, and long-range correlation: 1) Does the MNIS have the same mantle source as the Barnard Gneiss and Hawley Formation? 2) Do Collinsville basalts have the same mantle source as the Barnard Gneiss and Hawley basalts? 3) How do basalts compare from east to west across the RHZ? (4) Can New England meta-igneous units be correlated with volcanics in Newfoundland? Using TIMS thermal ionization mass spectrometry, the Sr, Pb, and Nd isotopic ratios a suite of meta-basalts the RHZ are being analyzed in an attempt to answer these questions.