Insights into tectonostratigraphic zone identification in southwestern Newfoundland based on isotopic (Nd, O, Pb) and geochemical data

Abstract

Plutonic and supracrustal rocks sampled from various tectonostratigraphic divisions in southwestern Newfoundland exhibit a large range in SiO2 (49 to 77 wt%), K2O (0.9 to 4.2 wt%),εNd (T) (-9.2 to +8.1), δ18O (+6.3 to +12.7 ‰) and Pb isotopic ratios. In general, isotopic plus geochemical data are either compatible with, or substantiate, structurally and lithologically based correlations between southwestern Newfoundland and the Central Mobile Belt further north. Such data can thus represent a robust terrane identification tool in highly telescoped or segmented portions of orogenic belts, such as southwestern Newfoundland, and can also provide significant insights into orogen evaluation. For example the Port aux Basques granite (tonalite), which is characterised by MORB-like εNd (+8.1) and δ18O (+7.5‰) and radiogenic Pb (207Pb/204Pb = 15.818), is interpreted as a Late Ordovician partial-melt of a juvenile source added to the Gander Zone during Early Ordovician opening of the Exploits back-arc basin. Strongly negative εNd (T), mantle-like δ18O, variable Pb isotopic ratios and metaluminous characteristics of Ordovician plutonism in the Notre Dame arc suggest derivation from Paleoproterozoic or older infracrustal sources. The data indicate formation in an Andean-type continental arc formed on the edge of the Laurentian margin.