LE3 .A278 2023

2023

Barr, Sandra

Acadia University

Bachelor of Science

Honours

Earth and Environmental Science

Earth & Environmental Sciences

Volcanic rocks of the Early Carboniferous Byers Brook and Diamond Brook formations and related plutonic rocks form a linear belt trending NW-SE through the northeastern Cobequid Highlands of northern mainland Nova Scotia. The volcanic rocks, with an exposed stratigraphic thickness of over 5 km and strike-length of about 35 km, include basalt and minor intermediate rocks but are dominated by rhyolite with previously reported U–Pb zircon ages that range from about 358 Ma to 353 Ma. In this study, LiDAR and geophysical imagery were used in combination with petrographic observations and chemical data to corroborate division of the volcanic sequence into at least 8 separate flow units. Rhyolite units include both lava flows and pyroclastic flows, with well-preserved textures such as flow-banded, spherulitic, and granophyric, although reliable distinction between lava flows and pyroclastic flows is difficult based on textures observed in thin section. Chemical data from 55 samples showed that rhyolite is metaluminous to peraluminous, but not peralkaline, with chemical characteristics typical of within-plate A-type magma derived from crustal melting. Chondrite-normalized REE patterns in rhyolite samples are relatively flat and high, ranging from 100 to 1000 times chondritic values with variable but large Eu anomalies. Consistent with previous studies the rhyolite is divided into low-Zr (<650 ppm) and high-Zr (>900 ppm) units. However, samples with ultrahigh-Zr (>1500 ppm) are widely distributed and not confined to specific units. High-Zr rhyolite samples also have high total rare-earth element (REE) abundance, but high-Zr does not correlate with high SiO2 and Rb that characterize the most highly differentiated samples. The associated basalt is subalkalic and has chemical characteristics, including REE patterns, typical of continental tholeiite. Radiometric maps show a large area of high potassium, uranium, and thorium centred on the Warwick Mountain closure area that crosses unit boundaries and extends into the adjacent plutonic rocks. Samples from the area suggest that microgranite dykes intruded both volcanic rocks and adjacent granitic plutons. Samples from the area have high SiO2 and Rb but not characterized by high-Zr or high REE contents.

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https://scholar.acadiau.ca/islandora/object/theses:3984