DETRITAL ZIRCON AGES FROM CONGLOMERATE AND SANDSTONE UNITS OF NEW BRUNSWICK AND COASTAL MAINE: PALEOGEOGRAPHIC IMPLICATIONS FOR GANDERIA AND THE CONTINENTAL MARGIN OF WESTERN GONDWANA

Detrital zircon ages were determined from conglomerate and sandstone samples from six fault-bounded belts in New Brunswick and coastal Maine. Formations sampled included Martinon (Brookville belt), Flagg Cove (Grand Manan Island belt), Matthews Lake (New River belt), Ellsworth (Ellsworth belt), Calais (St. Croix belt), and Baskahegan Lake (Miramichi belt). Their range of depositional ages based on the youngest detrital zircon population and stratigraphic, paleontological, and cross-cutting intrusive relationships are: Martinon between 602 ± 8 and 546 ± 2 Ma; Flagg Cove between 574 ± 7 and 535 ± 3 Ma; Matthews Lake between 539 ± 5 and 514 ± 2 Ma; Ellsworth between 507 ± 6 and 504 ± 3 Ma; Calais between 510 ± 8 and 479 ± 2 Ma; and Baskahegan Lake between 525 ± 6 and 488 ± 2 Ma.

All of the samples are dominated by Neoproterozoic (pan-African) zircon populations. The Paleozoic Matthews Lake, Ellsworth, and Calais formations contain main population peaks at 539 ± 5 Ma, 545 ± 4 Ma, and 556 ± 7 Ma, respectively, consistent with derivation mainly from magmatic rocks of the Brookville, Grand Manan Island, and/or New River belts, previously dated at 553 to 528 Ma. In contrast, the main peak in the Paleozoic Baskahegan Lake Formation is older at 585 ± 5 Ma. The main peak in the Neoproterozoic to Early Cambrian Flagg Cove Formation is at 611 ± 7 Ma with a secondary peak at 574 ± 7 Ma; the former was likely derived from locally exposed igneous units dated at ~618 to ~611 Ma. The Neoproterozoic Martinon Formation exhibits dominant peaks at 674 ± 8 Ma and 635 ± 4 Ma. Ganderian basement gneiss dated at ~675 Ma and intruded by plutonic rocks dated at ~584 Ma in the Hermitage Flexure of Newfoundland are possible sources for these older zircon components in the Martinon and Baskahegan Lake formations. Plutonic rocks in the New River belt dated at ~629 to ~622 Ma may be the source of the younger component in the Martinon Formation.

The samples also contain a small number of Mesoproterozoic, Paleoproterozoic, and Archean zircon grains, the latter as old as 3.23 Ga. The presence of zircons in the range 1.07 to 1.61 Ga is consistent with an origin along the peri-Gondwanan margin of Amazonia rather than West Africa. The general similarity of zircon provenance for samples from New Brunswick and coastal Maine suggests that all the Ganderian belts were part of a single microcontinent.