Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
4724253 | Precambrian Research | 2008 | 12 Pages |
The ca. 760 Ma Burin Group occurs in a well-exposed 60 km long northeasterly trending belt on the Burin Peninsula in the Avalon Zone of the southeastern Newfoundland Appalachians. This lithologically distinctive, tectonically bounded succession is characterized by low grade massive and pillowed basalts, abundant gabbro and diabase dykes and sills, mafic pyroclastic and epiclastic rocks and stromatolitic-carbonate-bearing rocks. The Burin Group preserves the oldest known magmatic event in the Avalon terrane, but its tectonic evolution and its relationship to the voluminous 640–570 Ma arc-related magmatism that typifies Avalonia is uncertain. Geochemical analyses confirm that the basalts are predominantly low-K tholeiites. They are characterized by high ratios of LIL/HFS elements, and display depletion to slight enrichment in LREE. Sm–Nd isotopic data reveal that most basalts have juvenile compositions, with ɛNd values similar to contemporaneous depleted mantle, indicating that high LIL/HFS elemental ratios were probably due to coeval subduction which contaminated the mantle source. Other basalts have lower ɛNd values, and the negative correlation of ɛNd with La/Sm, together with a positive correlation of ɛNd with 147Sm/144Nd suggest that their isotopic signatures have been modified by a Mesoproterozoic older oceanic crust or mantle into which the Burin Group mafic magmas were emplaced. The isotopic signature of the Burin mafic rocks is similar to that inferred for the source of the main phase of Avalonian magmatism. These data, together with paleocontinental reconstructions for ca. 760 Ma, suggest that the Burin Group is a local representative of ensimatic arcs within the Panthalassa-type ocean that surrounded Rodinia, possibly as a far-field response to the breakup of Rodinia. Although its low metamorphic grade precludes it being the basement from which Avalonian magmas were extracted, the Burin Group may be representative of the geochemical and isotopic composition of that basement.