SM-ND ISOTOPIC AND WHOLE-ROCK CHEMICAL COMPOSITIONS OF LATE NEOPROTEROZOIC AND CAMBRIAN SEDIMENTARY AND METASEDIMENTARY ROCKS OF THE CALEDONIAN HIGHLANDS (AVALONIA), SOUTHERN NEW BRUNSWICK

Neoproterozoic though Cambrian clastic sedimentary and/or metasedimentary rocks occur in the Hammondvale Metamorphic Suite (> ca. 620 Ma) and Broad River (ca. 620 Ma), Coldbrook (ca. 560-542 Ma), and Saint John (ca. 540-490 Ma) groups in the Caledonia terrane (Avalonia) of southern New Brunswick. Whole-rock chemical data (major and trace elements) and Nd isotopic compositions are used to compare and contrast the units and to investigate their provenance and tectonic setting during deposition.

Samples from the Hammondvale Metamorphic Suite are chemically most similar to phyllite samples from the Broad River Group, suggesting that they were derived from similar sources. The Coldbrook Group sedimentary rocks show major element patterns similar to the Hammondvale Metamorphic Suite and the Broad River Group metawacke samples, but have more varied trace element patterns, suggesting more varied sediment sources. The Saint John Group sedimentary rocks have varied geochemical patterns that overlap all of the older groups. They had varied source rocks and were possibly derived from a mix of Broad River Group, Hammondvale Metamorphic Suite, and Coldbrook Group sources.

Preliminary Nd isotopic results from this study combined with previously published data show that the Hammondvale Metamorphic Suite and metasedimentary rocks of the Broad River Group have negative ε_Nd values, whereas the sedimentary rocks of the Coldbrook and Saint John groups show more positive ε_Nd values. The Broad River Group and Hammondvale Metamorphic Suite samples fall well outside the Avalonian igneous isotopic window, suggesting a non-Avalonian source. In contrast, Coldbrook Group and Saint John Group samples fall within the main Avalonian isotopic window, suggesting a substantial Avalonian crustal component. Previously published Nd isotopic data from igneous units in the Broad River and Coldbrook groups have mostly positive ε_Nd values, consistent with the Coldbrook and Saint John group sediments being derived from those rocks. The positive values from the igneous units, however, are not consistent with the more negative values for the Broad River and Hammondvale metasedimentary rocks. These sediments must have had a large, isotopically mature source, presumably outside Avalonia.