Stratigraphy, petrology and geochemistry of volcanic rocks of Long Island, Newfoundland

Kean, B. F. (1973) Stratigraphy, petrology and geochemistry of volcanic rocks of Long Island, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The map area lies at the north of Halls Bay, Notre Dame Bay in the Central Mobile Belt of Newfoundland, i.e., at the northeastern extremity of the Appalachian mountain system. -- The map units consist of a south-dipping, south-facing pile of Ordovician pillow lavas, pyroclastics and volcaniclastic sediments approximately 17,000 feet in thickness. There is a lateral facies change from predominantly pyroclastics with minor lava tongues in the northwest to predominantly lava with intercalated discontinuous lenses of pyroclastics in the southeast. -- The pyroclastics and volcaniclastic sediments are mainly intermediate-composition reworked tuffs with common agglomeratic horizons. There are minor lenses of acid pyroclastics and pseudo-iron formation. -- The flows vary from massive, glassy pillow basalt, crystalline pillow basalt and associated pillow breccia with rare intercalated pyroclastics or sediments at the base to highly vesicular and porphyritic pillowed andesites with numerous and in places thick intercalated pyroclastic lenses. Chemically the flows form two distinct chemical groups corresponding to the stratigraphic level in the pile thus suggesting a general but consistent differentiation sequence from the lower basalts to the upper andesites. The chemistry and stratigraphy suggest that the succession is of island-arc affinity rather than oceanic affinity. -- Each type or group has a mineral assemblage characteristic of the lower greenschist facies epidotite, chlorite, actinolite, calcite, albite; however, the originally igneous mineralogy can generally be recognized. -- A shallowing environment is suggested by the presence of shallow water limestone and limestone breccias and current bedded greywackes near the top of the sequence. However, the recurrence of pillow-lavas and reworked tuffs above this unit suggest either not a completely emergence or a resubmergence. -- The early gabbro, diabase and andesite type intrusions predate the regional, probably Acadian deformation and are probably genetically related to the volcanism. The Long Island pluton and quartz-feldspar porphyries are post-deformation. -- One phase of regional deformation is represented by a locally or zonally developed steep, generally E-W penetrative cleavage. This cleavage is obscured and/or intensified by faulting in the southern area of Long Island. Small scale folds, angular relationships and cleavage-bedding relationships combined with stratigraphic tops suggest that the sequence occupies the south limb of a west plunging anticline. Kink bands fold the earlier fabric but are restricted to fault zones and may be related to faulting. Similarly minor local crenulations of the first cleavage seem to be related to intrusions.

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