Compositional diversity among Late Devonian peraluminous granitoid intrusions in the Meguma Zone of Nova Scotia, Canada

Abstract

Late Devonian (385−370 Ma) granitoid intrusions in the Meguma Zone of southwestern Nova Scotia represent two geographically separate magmatic suites that show subtly different lithological, geochemical and isotopic characteristics. “Central intrusions” crop out with satellite mafic-intermediate intrusions, range in composition from granodiorite to leucogranite, contain two micas, have exclusively peraluminous compositions (molar A/CNK 1.1-1.3), variably high values for FeO T (0.4–6.0 wt.%), Ba (5–980 ppm), Y (6–50 ppm), Pb (2–50 ppm), Ga (11–53 ppm), 87Sr 86Sr i (0.7081-0.7130), δ 18O (9.8–13.0) and δ 34S (4.5–11.9), in conjunction with low values for ϵNd (−1 to −6.5). In contrast, “peripheral plutons” crop out with synplutonic mafic-intermediate intrusions, range in composition from tonalite to leucogranite, may contain minor hornblende, have dominantly peraluminous compositions (molar A/CNK 0.9-1.3), variably high concentrations of TiO 2 (0.1-1.1 wt.%), Al 2O 3 (12.0–19.7 wt.%), CaO (0.2–4.9 wt.%), Sr (7–720 ppm), Cr (3–111 ppm) and V (1–136 ppm), higher ϵNd values (−2.0 to 3.2), and lower values for 87Sr 86Sr i (0.7040-0.7079), δ 188O (7.6–10.5) and δ 34S (0–4.6). Such regional diversity is explained by inferring that upper crustal contamination dominated the central granitoid compositions and mixing with mantle-derived mafic-intermediate magmas dominated peripheral granitoid compositions. However, additional contributions from heterogeneous lower crust cannot be excluded.