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Ganderia or Gander Terrane (located near the town Gander, Newfoundland) is a
terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its ow ...
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. The ...
which broke off the supercontinent
Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final st ...
(Ma) together with
Avalonia Avalonia was a microcontinent in the Paleozoic era. Crustal fragments of this former microcontinent underlie south-west Great Britain, southern Ireland, and the eastern coast of North America. It is the source of many of the older rocks of We ...
,
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 ...
, and Carolinia.


Extent

The microcontinent
Avalonia Avalonia was a microcontinent in the Paleozoic era. Crustal fragments of this former microcontinent underlie south-west Great Britain, southern Ireland, and the eastern coast of North America. It is the source of many of the older rocks of We ...
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 Conglome ...
rocks of the Gander Zone, the eastern passive margin of the
Iapetus Ocean The Iapetus Ocean (; ) was an ocean that existed in the late Neoproterozoic and early Paleozoic eras of the geologic timescale (between 600 and 400 million years ago). The Iapetus Ocean was situated in the southern hemisphere, between the paleoc ...
, now found in
Newfoundland Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...
,
New Brunswick New Brunswick (french: Nouveau-Brunswick, , locally ) is one of the thirteen Provinces and territories of Canada, provinces and territories of Canada. It is one of the three Maritime Canada, Maritime provinces and one of the four Atlantic Canad ...
, 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 to the west and by the Canadian province ...
, but they also include the contemporaneous or slightly older rocks of the
Bras d'Or Bras d'Or Lake ( Mi'kmawi'simk: Pitupaq) is an irregular estuary in the centre of Cape Breton Island in Nova Scotia, Canada. It has a connection to the open sea, and is tidal. It also has inflows of fresh water from rivers, making the brackish ...
terrane in
Cape Breton Island Cape Breton Island (french: link=no, île du Cap-Breton, formerly '; gd, Ceap Breatainn or '; mic, Unamaꞌki) is an island on the Atlantic coast of North America and part of the province of Nova Scotia, Canada. The island accounts for 18. ...
, 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 ...
, 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 The South-East is a strategic planning area within the Southern Region in Ireland. It is a NUTS Level III statistical region of Ireland (coded IE052). It includes comprises the counties of Carlow, Kilkenny and Wexford and the city and count ...
,
Anglesey Anglesey (; cy, (Ynys) Môn ) is an island off the north-west coast of Wales. It forms a Local government in Wales, principal area known as the Isle of Anglesey, that includes Holy Island, Anglesey, Holy Island across the narrow Cymyran Strai ...
,
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 Europ ...
, and the Lake District. The western margin of Ganderia is the
Red Indian The Native American name controversy is an ongoing discussion about the changing terminology used by the Indigenous peoples of the Americas to describe themselves, as well as how they prefer to be referred to by others. Preferred terms vary pri ...
Line of the Iapetus Suture.


Tectonic history

The
basement A basement or cellar is one or more Storey, floors of a building that are completely or partly below the storey, ground floor. It generally is used as a utility space for a building, where such items as the Furnace (house heating), furnace, ...
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). ...
''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 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 system developed along a clastic passive margin. The separation of Ganderia opened the northern Rheic Ocean. 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 TetagoucheExploits back-arc basin). Avalonia was subsequently subducted beneath Ganderia during the Silurian and Devonian.


References


Notes


Sources

* * {{Refend Terranes Geology of Canada Paleozoic paleogeography