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 th ...

) 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 d ...

in the northern

Appalachians The Appalachian Mountains, often called the Appalachians, are a mountain range in eastern to northeastern North America. The term "Appalachian" refers to several different regions associated with the mountain range, and its surrounding terrain ...

which broke off the supercontinent

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

(Ma) together with

Avalonia Avalonia was a microcontinent in the Paleozoic era. Crustal fragments of this former microcontinent are terranes in parts of the eastern coast of North America: Atlantic Canada, and parts of the East Coast of the United States, East Coast of the ...

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 The Carolina Terrane, also called the Carolina Superterrane or Carolinia, is an exotic terrane running ~ approximately North-South from central Georgia to central Virginia in the United States. It constitutes a major part of the eastern Piedmont ...

Extent

The microcontinent

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. Siliciclastic rock types include mudrock, sandstone Sandstone is a Clastic ...

rocks of the Gander Zone, the eastern

passive margin A passive margin is the transition between Lithosphere#Oceanic lithosphere, oceanic and Lithosphere#Continental lithosphere, continental lithosphere that is not an active plate continental margin, margin. A passive margin forms by sedimentatio ...

of the

Iapetus Ocean The Iapetus Ocean (; ) existed in the late Neoproterozoic and early Paleozoic eras of the geologic timescale (between 600 and 400 million years ago). It was in the southern hemisphere, between the paleocontinents of Laurentia, Baltica and Avalon ...

, now found in

Newfoundland Newfoundland and Labrador is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region of Labrador, having a total size of . As of 2025 the population ...

New Brunswick New Brunswick is a Provinces and Territories of Canada, province of Canada, bordering Quebec to the north, Nova Scotia to the east, the Gulf of Saint Lawrence to the northeast, the Bay of Fundy to the southeast, and the U.S. state of Maine to ...

, and

New England New England is a region consisting of 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 ...

, 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 (, formerly '; or '; ) is a rugged and irregularly shaped island on the Atlantic coast of North America and part of the province of Nova Scotia, Canada. The island accounts for 18.7% of Nova Scotia's total area. Although ...

, the 550 Ma Upsalquitch

gabbro Gabbro ( ) is a phaneritic (coarse-grained and magnesium- and iron-rich), mafic intrusive igneous rock formed from the slow cooling 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 ( ; ) is an island off the north-west coast of Wales. It forms the bulk of the Principal areas of Wales, county known as the Isle of Anglesey, which also includes Holy Island, Anglesey, Holy Island () and some islets and Skerry, sker ...

Isle of Man The Isle of Man ( , also ), or Mann ( ), is a self-governing British Crown Dependency in the Irish Sea, between Great Britain and Ireland. As head of state, Charles III holds the title Lord of Mann and is represented by a Lieutenant Govern ...

, and the

Lake District The Lake District, also known as ''the Lakes'' or ''Lakeland'', is a mountainous region and National parks of the United Kingdom, national park in Cumbria, North West England. It is famous for its landscape, including its lakes, coast, and mou ...

. The western margin of Ganderia is the

Red Indian There is an ongoing discussion about the 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 primarily by region and age. As Indigenous ...

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 A basement is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...

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 rock, sedimentary formation of rocks, formations (microbialite) that are created mainly by Photosynthesis, photosynthetic microorganisms such as cyanobacteria, sulfate-reducing micr ...

''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. 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 The back-arc region is the area behind a volcanic arc. In island arc, island volcanic arcs, it consists of back-arc basins of oceanic crust with abyssal zone, abyssal depths, which may be separated by remnant arcs, similar to island arcs. In conti ...

system developed along a

clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks by ...

passive margin. The separation of Ganderia opened the northern

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

. 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 Geology of North America, 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 ...

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