Ganderia or Gander Terrane (located near the town

Gander, Newfoundland Gander is a town located in the northeastern part of the island of Newfoundland in the Canadian province of Newfoundland and Labrador, approximately south of Gander Bay, south of Twillingate and east of Grand Falls-Windsor. Located on the nor ...

) is a

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust (geology), crust fragment formed on a tectonic plate (or broken off from it) and Accretion (geology), accreted or "Suture (geology), sutured" to crust lying on another pla ...

in the northern

Appalachians The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...

which broke off the supercontinent Gondwana (Ma) together with Avalonia,

Megumia The Meguma terrane, also known as Megumia, is a terrane exposed in southern Nova Scotia, that became joined to the present North American landmass as part of the Appalachian orogeny. The exposed part of the Meguma terrane, the Meguma Group, is l ...

, and Carolinia.

Extent

The microcontinent Avalonia broke off Gondwana in the Late Neoproterozoic together with a series of terranes that either formed its eastern coast or a separate block called Ganderia in front of it, if so separated from the Avalon Zone by the several hundred metres-wide Dover Fault. These terranes include the Early Palaeozoic

siliciclastic Siliciclastic (or ''siliclastic'') rocks are clastic noncarbonate sedimentary rocks that are composed primarily of silicate minerals, such as quartz or clay minerals. Siliciclasic rock types include mudrock, sandstone, and conglomerate Conglomera ...

rocks of the Gander Zone, the eastern

passive margin A passive margin is the transition between oceanic and continental lithosphere that is not an active plate margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional lithosphere. Continental rifting cre ...

of the Iapetus Ocean, now found in Newfoundland,

New Brunswick New Brunswick (french: Nouveau-Brunswick, , locally ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. It is the only province with both English and ...

, and

New England New England is a region comprising six states in the Northeastern United States: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. It is bordered by the state of New York (state), New York to the west and by the Can ...

, but they also include the contemporaneous or slightly older rocks of the Bras d'Or terrane in Cape Breton Island, the 550 Ma Upsalquitch

gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...

, the Brookville and New River terranes in New Brunswick, and the Seven Hundred Acre Island in Maine. The Gander Zone also extends to the British Isles: Southeast Ireland,

Anglesey Anglesey (; cy, (Ynys) Môn ) is an island off the north-west coast of Wales. It forms a principal area known as the Isle of Anglesey, that includes Holy Island across the narrow Cymyran Strait and some islets and skerries. Anglesey island ...

Isle of Man ) , anthem = "O Land of Our Birth" , image = Isle of Man by Sentinel-2.jpg , image_map = Europe-Isle_of_Man.svg , mapsize = , map_alt = Location of the Isle of Man in Europe , map_caption = Location of the Isle of Man (green) in Europe ...

, and the Lake District. The western margin of Ganderia is the Red Indian Line of the

Iapetus Suture The Iapetus Suture is one of several major Fault (geology), geological faults caused by the collision of several ancient land masses forming a suture (geology), suture. It represents in part the remains of what was once the Iapetus Ocean. Iapet ...

Tectonic history

The basement beneath Ganderia is unexposed, but the rock of the Green Head Group in southern New Brunswick, the oldest known, contains the Precambrian

stromatolite Stromatolites () or stromatoliths () are layered sedimentary formations ( microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). T ...

''Archaeozoon acadiense'', and the Seven Hundred Acre Island Formation in coastal Maine has been dated to c. 670–1230 Ma, similar in age to that of the

Amazonian Craton The Amazonian Craton is a geologic province located in South America. It occupies a large portion of the central, north and eastern part of the continent and represents one of Earth's largest cratonic regions. The Guiana Shield and Central Braz ...

. Between 640 and 455 Ma intermittent arc

magmatism Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of ...

were separated by soft collisional events, first in the Late Ediacaran and Early Cambrian while Ganderia was part of Gondwana, and then in the Ordovician when Ganderia was an isolated microcontinent. The first early phase of arc magmatism occurred 625–605 Ma in the Brookville and New River terranes, but also in Anglesey. The next phase of arc magmatism accompanied by metamorphism occurred at the end of the Precambrian in Newfoundland, New Brunswick and on Cape Breton Island. Ganderia probably separated from Gondwana near the Cambrian-Ordovician boundary when subduction ceased and a arc-

back-arc A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most o ...

system developed along a clastic passive margin. The separation of Ganderia opened the northern

Rheic Ocean The Rheic Ocean was an ocean which separated two major palaeocontinents, Gondwana and Laurussia (Laurentia- Baltica-Avalonia). One of the principal oceans of the Palaeozoic, its sutures today stretch from Mexico to Turkey and its closure result ...

. Ganderia and Carolinia were probably connected during the Late Ediacaran and, if so, were collectively separated from Avalonia during the Early Palaeozoic. When Ganderia was finally accreted to

Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, althoug ...

during the Late Ordovician and Silurian large scale magmatism accompanied its subduction. Its accretion to Laurentia during the Late Ordovician closed large parts of the Iapetus Ocean and the accretion of its trailing edge resulted in the Salinic orogeny (the closure of the Tetagouche– Exploits back-arc basin). Avalonia was subsequently subducted beneath Ganderia during the Silurian and Devonian.

References

Notes

Sources

* * {{Refend Terranes Geology of Canada Paleozoic paleogeography