The following new U–Pb dates are provided for zircons from volcanic and intrusive rocks of the Avalon Terrane of Newfoundland: Burin Group ophiolite (Wandsworth pegmatitic gabbro), [Formula: see text]; Marystown Group ash-flow tuff, [Formula: see text]; Rock Harbour Group rhyolite clast in conglomerate, [Formula: see text]; Harbour Main Group ash-flow tuff, [Formula: see text]; Harbour Main Group flow-banded rhyolite, [Formula: see text]; porphyritic rhyolite plug intruding Harbour Main Group, 632 ± 2 Ma; Holyrood Granite, [Formula: see text]; rhyolite dyke, Harbour Main Group, [Formula: see text]; and welded ash-flow tuff, "Grand Beach porphyry," [Formula: see text]. All of the dated zircons are simple, single-age populations with no trace of inheritance. These dates confirm that the ophiolitic Burin Group represents an older and separate event that correlates precisely with the Bou Azzer ophiolite of Morocco and that the Rock Harbour Group does not represent continental volcanism that preceded that event. The Rock Harbour, Marystown, and Harbour Main groups and the Holyrood Granite (632–608 Ma) are all part of the younger 650–550 Ma pulse of Pan-African orogenesis that affected a broad area extending through Africa, Asia, western Europe, southern England and Wales, and eastern North America. However, a shortage of high-precision dates throughout these terranes precludes very exact correlations and thus very exact interpretations in terms of specific tectonic or magmatic events. Although these dates require some revisions in the stratigraphy of the Newfoundland Avalon Terrane, they do not support suggestions that the Avalon Terrane comprises a "collage of suspect terranes." The age of the Grand Beach porphyry (394 Ma) places it squarely with the Acadian granites of the Appalachians and removes it from consideration as part of the Marystown Group.

Lower to Middle Cambrian volcanic rocks occur within the Avalon Zone of southern New Brunswick at Beaver Harbour and in the Long Reach area. The Beaver Harbour rocks are intensely altered, but the major- and trace-element geochemistry indicates that they could be highly evolved (basaltic andesites) within-plate basalts. The mafic flows from the Long Reach area form two chemically and petrologically distinct groups: (1) basalts with feldspar phenocrysts that represent evolved continental tholeiites with some oceanic characteristics; and (2) a group of aphyric basalts showing extremely primitive continental tholeiite compositions, also with oceanic affinities and resembling some rift-related Jurassic basalts on the eastern seaboard. Felsic pyroclastic rocks in the Long Reach area make the suite bimodal. This distribution of rock types supports conclusions from the mafic rocks that the area experienced tension throughout the Early to Middle Cambrian.

The early Mesozoic, quartz normative, North Mountain basalts in southwestern Nova Scotia (Digby area) form three units: a coarse massive lower flow (~190 m) bearing minor lenses of mafic pegmatite, a middle unit of thin amygdaloidal basaltic flows (~50 m), and an upper flow unit of massive phenocryst-rich basalt (~160 m). The two thick units show phenocrysts of orthopyroxene (bronzite) and (or) pigeonite, augite, and zoned plagioclase in a granular matrix of augite, pigeonite, and plagioclase. Variation diagrams and chondrite-normalized rare-earth-element patterns relate all chemical diversity between and within flows to removal and (or) accumulation of plagioclase and pyroxene phenocrysts (~1:1). High K, Rb, and Ba, appear related to assimilation of continental crust. Constancy of fractionation-independent element ratios and variations in phenocryst content vertically and along the 200 km strike of the basalts suggest (1) crystal settling and accumulation together with assimilation and mixing in a lower crustal magma chamber, (2) rise to upper crustal levels in a central conduit followed by northeast-ward emplacement along a tension-induced dyke system, and (3) extrusion along a fissure in two major and numerous minor pulses that formed the lower, upper, and middle units. Assimilation did not occur as magma moved through the dyke system, for assimilation-related variations in composition do not occur along strike.

A diabase dike about 140 km long (the Shelburne dike) cuts in a northeasterly direction across the southwestern part of Nova Scotia. The dike, recently dated at 201 Ma, forms part of a major Appalachian system of diabase dikes and basaltic flows of early Mesozoic age, emplaced during the first stages of opening of the present Atlantic Ocean.The Shelburne dike is tholeiitic and quartz normative. Its chemistry resembles that of the Palisade sill of New Jersey, but differs substantially from the more primitive magnesian composition of a similar dike on the Avalon Peninsula of Newfoundland. A more advanced stage of differentiation is reflected also in the composition of its main minerals (augite, pigeonite, zoned orthopyroxene, calcic plagioclase). Such chemical variations among the roughly contemporaneous diabase dikes of the northern Appalachians complicate the existing petrogenetic and tectonic models of the development of the Appalachian dike swarm.

Basalts totalling 236 m in thickness were intersected in the wildcat oil well Mobil Gulf Chinampas N-37 in the Bay of Fundy. A 5.5 m section of conventional core retrieved from the middle of the basalt section sampled two fine-grained, phenocryst-poor, amygdaloidal basalt flows. The basalts, though somewhat altered, show concentrations of ferromagnesian elements (e.g., Fe, Mg, Cr, Ni) and immobile elements (e.g., Zr, Nb, Ta, Hf) as well as chondrite-normalized REE patterns typical of high-Ti quartz-normative tholeiites and are identical to more evolved samples of the North Mountain basalts at Digby. These petrographic and geochemical characteristics allow correlation with middle unit flows of the North Mountain basalts. The lower unit of North Mountain basalt may be as thick in the well as in the Digby area (~200 m), but the upper unit is either missing or very thin (< 68 m). A 25 m thick sedimentary section just above the conventional core but within the basalt sequence has not been reported on land and hints at the existence of a basalt unit not present on North Mountain. The conclusion that North Mountain basalts occur in the Chinampas well suggests that the flows underlie most of the Bay of Fundy, originally covered 9400 km2, and had a total volume of 2350 km3.