AMPHIBOLES AND ISOTOPES BELOW AND ABOVE THE PROSPECT ROCK THRUST, CENTRAL AND NORTHERN VERMONT: INTERCONNECTED AND/OR DISCONNECTED HISTORIES OF MAFIC SUBDUCTION ZONE ROCKS?
This contribution interprets Nd isotopic data from mafic whole-rocks above and below the PRT in the context of existing amphibole compositions, modal space paths, and geochemical data to determine if magmatic origins have bearing on subsequent metamorphic pressure-temperature-time paths. This may help resolve tectonometamorphic links between sodium and calcium-sodium amphibole-bearing mafic bodies throughout central and northern Vermont. Magmatic similarities between mafic bodies would be more consistent with a shared subduction history and imply that barroisite-bearing amphibolites and greenstones may represent different parts of a coherent terrane-scale P-T-t loop. Magmatic contrasts on the other hand favor an interpretation where individual mafic bodies preserve unique P-T-t paths that are not part of the same metamorphic loop.
Mafic rocks below the PRT associated with medium-high to high pressure facies amphiboles preserve lower age-corrected εNd (t) values than mafic rocks above the PRT in the Rowe/Prospect Rock slice (R/PRS). A range of εNd (t) values is observed in mafic rocks of the R/PRS and there does not appear to be a correlation with depth within the slice. Contrasting εNd (t) values and amphibole compositions for mafic rocks intercalated over 10s of meters within the R/PRS supports a petrologic model where individual mafic units preserve independent P-T-t paths. Comparable amphibole compositions are observed in mafic rocks above and below the PRS that display distinct εNd (t) values, suggesting that P-T-t paths may be locally independent of magmatic origin. Perhaps the most appropriate terrane-scale tectonometamorphic model is one that allows for both interconnected and disconnected P-T-t paths and loops for mafic rocks of diverse origins.