Geology of Newfoundland and Labrador
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The geology of Newfoundland and Labrador includes basement rocks formed as part of the Grenville Province in the west and Labrador and the Avalonian microcontinent in the east. Extensive tectonic changes, metamorphism and volcanic activity have formed the region throughout Earth history.
In contrast to neighboring Labrador, the island of Newfoundland is largely underlain by younger rocks. The Churchill, Nain, Superior and Grenville Province present in Labrador were all small continents or pieces of continental lithosphere that joined to form sections of the proto-North American continent Laurentia and the broad stable region known as the Canadian Shield. By the end of the Precambrian in the Neoproterozoic, continental crust which had come into existence in the Archean nearly 2.5 billion years had already experienced up to eight supercontinent cycles.[citation needed]
In the late Precambrian and Paleozoic, Avalonia (named after the Avalon Peninsula in Newfoundland) formed as a volcanic island arc off the coast of the supercontinents Pannotia which lost land through rifting and became Gondwana. This volcanic island arc was later split into different areas, but currently underlies southern New England, Maine, Nova Scotia, Prince Edward Island, southern New Brunswick, southern Ireland, England, Wales, Belgium, the Netherlands and much of north Germany. Northwest Newfoundland includes older rocks affected by the Grenville orogeny in the late Proterozoic during the collision of continents to form the previous supercontinent Rodinia.[citation needed]
Examples of ancient rocks from this period include the late Precambrian Harbour Main Group ignimbrite and ash flow tuff with obsidian and augite in the center of the Avalon Peninsula.[1] Rocks of similar age were forming on Grenville Province basement rock in what would become western Newfoundland, such as the Round Pond Granite formed 602 million years ago.[2] Sedimentary and volcanic rocks 15 kilometers thick are exposed in the Avalon Peninsula, deposited in rift basins as flysch and molasse with volcaniclastic rocks in submarine fans. The Gaskiers Formation holds diamictite that may have formed during the Snowball Earth glaciations and Ediacaran fossils and microfossils have been found in some rocks.[3] Northern Newfoundland at the edge of the Laurentian continent witnessed columnar flood basalts in the Cloud Hills area into the Cambrian.[4]
The Avalon Zone is an area of 550 million year old sedimentary and volcanic rocks exposed only in the east that preserves the original geology of the microcontinent and extends 600 kilometers out to sea forming the below water Flemish Cap.[citation needed]
By the early Devonian, the Avalonia microcontinent and the Bronson Hill island arc, collided with Laurentia to form the mid-sized continent Euramerica, causing the Taconic orogeny. The collision closed the Iapetus Ocean and obducted the Laurentian continental margin under the two island arcs. The process produced a strange bulged up area of mantle material to the surface as peridotite in Gros Morne National Park, essentially the only area on the Earth's surface where mantle material is present as cool, crystallized rock. It also created an ophiolite zone where oceanic crust was preserved on land.[citation needed]
Geologists group the rocks in this area into the Humber Zone and the Dunnage Zone, with the Dunnage Zone's southern edge defined by the Gander River Ultrabasic Belt. The neighboring Gander Zone has siltstone, shale and quartz sandstone as well as deformed rocks and granite. The sediments were deposited on the continental margin during the closure of the Iapetus Ocean.[5][unreliable source?]
By 356 million years ago, Gondwana collided with Euramerica, closing the Rheic Ocean and creating the supercontinent Pangea, which left Newfoundland and the Avalonian microcontinent (also known as terrane) far inland and brought widespread interior desert conditions around the world. Newfoundland was re-exposed to the ocean in the Triassic when rifting began to form new oceanic crust and opened the Atlantic Ocean.[citation needed]
