Abstract

Peralkaline granites, representing the most volumetrically significant component of the Topsails igneous complex, occur throughout the northern Appalachians in Newfoundland, the Gulf of Maine, northern New Hampshire, and eastern Massachusetts. They are divisible into three temporal groups: Silurian-Early Devonian, Late Carboniferous, and Late Triassic-Jurassic. The division reflects the episodic nature of peralkaline magmatism. These groups chronologically parallel those recorded for the Niger-Nigeria province of west Africa where the peralkaline granites are thought to represent anorogenic magmatism associated with local crustal extension in cratonic environments. Such tectonic-magmatic episodes reflect the repeated operation of large-scale mantle processes throughout the North Atlantic region from middle Paleozoic to Mesozoic time.

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