Timing of arrival of the Avalon Zone in the northeastern Appalachians: a new look at the Straddling Granite

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Abstract
The "Straddling Granite" was previously thought to straddle the Hermitage Bay – Dover fault system, which marks the boundary between the Avalon and Gander Zones of eastern Newfoundland, and hence to fix the earliest juxtaposition of these two zones before 504 ± 12 Ma. More detailed investigation shows that these rocks are divisible into two distinct geochemical suites, the Indian Point Granite to the west and the Hardy's Cove intrusive suite to the east. Of the samples that provided the 504 Ma isochron, five were obtained from the Hardy's Cove suite and one from within the fault zone; hence the isochron must be taken as representing only a typical date for plutonic rocks within the Avalon Zone. The Indian Point Granite intrudes the Gaultois Granite, dated at 350 ± 18 Ma, and is thus considerably younger than the Hardy's Cove suite. These observations now allow for juxtaposition of the Avalon and Gander Zones to have been as late as Early Carboniferous.

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