LE3 .A278 2011

2011

Barr, Sandra

Acadia University

Master of Science

Masters

Geology

Earth & Environmental Sciences

The Lower Coverdale plutonic suite underlies an area of 35 km2 south of Moncton, New Brunswick, based on the extent of the associated positive aeromagnetic anomaly. The pluton does not outcrop at surface, but has been intersected in 11 drill holes at depths of 100-200 m below unconformably overlying Carboniferous sedimentary rocks, and extends to a depth of at least 1100 m. The host rock is unknown, but based on regional trends, the pluton is located in the Ganderian Brookville terrane of the northern Appalachian orogen. Based on petrological studies of core samples, the plutonic suite consists dominantly of anorthosite, mafic anorthosite, ferronorite and interlayered Fe-Ti-P rocks. A ferronorite sample yielded an Early Neoproterozoic age of 975.5+7.8/-6.9 Ma, interpreted to be the igneous crystallization age of the plutonic suite. Based on petrological similarities to other anorthosite suites, abundant mafic and minor felsic dykes are interpreted to be coeval with the anorthosite-ferronorite. Quartz monzonite at the bottom of one hole is Devonian and unrelated to the older suite. The anorthosite has characteristics of alkali anorthosite massifs, including plagioclase of andesine composition (An30-35) and exsolution lamellae of K-feldspar with up to 1.5% BaO. Orthopyroxene in the ferronorite is magnesian (En62-70). Apatite contains 3-4% F. Whole-rock chemical analyses show that the anorthosite contain 50-60% silica, with high Na and Ba, whereas the ferronorite has SiO2 ranging from 45-25%, with 25-14% Fe2O3, 14-3% TiO2, and up to 8% P2O5. With increasing abundance of interstitial apatite and ilmenite, the ferronorite grades to Fe-Ti-P rocks. The mafic dykes are high-aluminum tholeiite compositions. It is inferred that the Lower Coverdale anorthosite massif may have formed in a Mesoproterozoic orogenic belt in Amazonia, which separated from Laurentia during breakup of Rodinia.

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https://scholar.acadiau.ca/islandora/object/theses:214