Appalachian Orogen in Canada

1979 ◽  
Vol 16 (3) ◽  
pp. 792-807 ◽  
Author(s):  
Harold Williams
Keyword(s):  
Continental Margin ◽  
Eastern North America ◽  
Early Paleozoic ◽  
The West ◽  
Late Precambrian ◽  
Northwest Africa ◽  
Iapetus Ocean ◽  
History Of ◽  
Appalachian Orogen ◽  
Andean Type

The Appalachian Orogen is divided into five broad zones based on stratigraphic and structural contrasts between Cambrian–Ordovician and older rocks. From west to east, these are the Humber, Dunnage, Gander, Avalon, and Meguma Zones.The westerly three zones fit present models for the development of the orogen through the generation and destruction of a late Precambrian – Early Paleozoic Iapetus Ocean. Thus, the Humber Zone records the development and destruction on an Atlantic-type continental margin, i.e., the ancient continental margin of Eastern North America that lay to the west of Iapetus; the Dunnage Zone represents vestiges of Iapetus with island arc sequences and mélanges built upon oceanic crust; and the Gander Zone records the development and destruction of a continental margin, at least in places of Andean type, that lay to the east of Iapetus.The Precambrian development of the Avalon Zone relates either to rifting and the initiation of Iapetus or to subduction and a cycle that preceded the opening of Iapetus. During the Cambrian Period, the Avalon Zone was a stable platform or marine shelf.Cambrian–Ordovician rocks of the Meguma Zone represent either a remnant of the continental embankment of ancient Northwest Africa or the marine fill of a graben developed within the Avalon Zone.Silurian and younger rocks of the Appalachian Orogen are mixed marine and terrestrial deposits that are unrelated to the earlier Paleozoic zonation of the system. Silurian and later development of the orogen is viewed as the history of deposition and deformation in successor basins that formed across the already destroyed margins and oceanic tract of Iapetus.

Pre-Silurian stratigraphy and tectonic significance of the St. Croix Belt, southeastern Maine

1987 ◽  
Vol 24 (12) ◽  
pp. 2459-2469 ◽  
Author(s):  
Allan Ludman
Keyword(s):  
New Brunswick ◽  
Continental Slope ◽  
Early Paleozoic ◽  
The West ◽  
Early Devonian ◽  
Late Precambrian ◽  
Iapetus Ocean ◽  
Continental Block ◽  
Tectonic Significance ◽  
Anoxic Basin

The St. Croix Belt of southeastern Maine and southwestern New Brunswick is part of a distinctive terrane situated between the Avalon platform and Miramichi arc—two important physiographic components of the Late Precambrian – early Paleozoic Iapetus Ocean. It bears lithologic and stratigraphic similarities to both of those tracts but is identical to neither. Formerly mapped entirely as the Cookson Formation, it is now divided into four formations of Cambrian through Early Orodovician age assigned to the Cookson Group. These rocks record periodic influxes of terrigenous debris into a deep anoxic basin and may have been part of the west-facing continental slope of the Avalonian continental block. The St. Croix Belt has been strongly affected by both pre-Silurian and Early Devonian (Acadian) folding. Facies changes rather than tectonic sutures are used to explain the relationships between the St. Croix Belt and its neighbouring pre-Silurian tracts.

Seismic stratigraphy and structure of the east Canadian continental margin between 41 and 52°N

1985 ◽  
Vol 22 (5) ◽  
pp. 686-703 ◽  
Author(s):  
L. M. Parson ◽  
D. G. Masson ◽  
C. D. Pelton ◽  
A. C. Grant
Keyword(s):  
Early Cretaceous ◽  
Continental Margin ◽  
Magnetic Anomalies ◽  
Seismic Stratigraphy ◽  
Sedimentary Sequence ◽  
The West ◽  
Grand Banks ◽  
Late Precambrian ◽  
Oceanic Basement ◽  
Iberian Margin

The seismic stratigraphy of the eastern Grand Banks continental margin is examined, and a five-fold division of the sedimentary sequence overlying basement is proposed. Oceanic basement of Cretaceous age underlies the eastern part of the study area; to the west, continental basement ranging in age from Late Precambrian to ?Jurassic underlies the Grand Banks. The sediment units, ranging in age from Early Cretaceous to Recent, have been dated by extrapolation of both commercial and DSDP drilling results from the Grand Banks and from the formerly conjugate Iberian margin. Identification of oceanic magnetic anomalies in the Newfoundland Basin agrees with the proposed age of the two oldest, Early Cretaceous units.

scholarly journals Ordovician mafic magmatism in an Ediacaran arc complex, Sibak, northeastern Iran: the eastern tip of the Rheic Ocean

2018 ◽  
Vol 55 (10) ◽  
pp. 1173-1182 ◽  
Author(s):  
Fereshteh Ranjbar Moghadam ◽  
Fariborz Masoudi ◽  
Fernando Corfu ◽  
Seyed Massoud Homam
Keyword(s):  
Indirect Evidence ◽  
Arc Magmatism ◽  
Early Paleozoic ◽  
Northern Margin ◽  
Rheic Ocean ◽  
Late Precambrian ◽  
Sedimentary Sequences ◽  
Appalachian Orogen ◽  
Laurentian Margin ◽  
Clastic Sedimentary

The assembly of Gondwana in the Ediacaran was concluded by extensive arc magmatism along its northern margin. Extensional events in the early Paleozoic led to rifting and the eventual separation of terranes, which were later assimilated in different continents and orogens. The Sibak area of northeastern Iran records these events, including late Precambrian volcanic-sedimentary processes, metamorphism, and magmatism. A granite at Chahak in the Sibak Complex yields a zircon U–Pb age of 548.3 ± 1.1 Ma, whereas a spatially associated gabbro has an age of 471.1 ± 0.9 Ma. The latter corresponds to the earliest stages of rifting in the nearby Alborz domain, with the deposition of clastic sedimentary sequences, basaltic volcanism, and, as indicated by indirect evidence, coeval granitic plutonism. The Chahak gabbro is thus one of the earliest witnesses of the rifting processes that eventually led to the development of the Rheic Ocean and were indirectly linked to subduction of Iapetus at the Laurentian margin and the early development of the Appalachian orogen.

Conversion of Sn to Lg at a continental margin

1975 ◽  
Vol 65 (1) ◽  
pp. 235-244 ◽  
Author(s):  
Bryan L. Isacks ◽  
Christopher Stephens
Keyword(s):  
North America ◽  
Gulf Of Mexico ◽  
Continental Margin ◽  
West Indies ◽  
Wave Train ◽  
Eastern North America ◽  
Substantial Fraction ◽  
The West ◽  
Short Period ◽  
Period Wave

abstract Examination of the seismic phase Sn from earthquakes in the West Indies as recorded by numerous stations in eastern North America reveals that a substantial fraction of the short-period energy carried by Sn across the suboceanic lithosphere of the Atlantic is fed into the continental crust near the continental margin and travels into North America as the crustal phase Lg. As distance within the continent increases, the Lg part of the short-period wave train becomes predominant, and can be identified at stations in northern Canada as far as 58° from the sources. Several estimates of the average Q for the attenuation of Lg in eastern North America agree upon values in the range of 600 to 1,400. Hydrophone recordings at Bermuda indicate an average Q as high as 4,000 for the attenuation of Sn in the suboceanic lithosphere. Conversion of Sn to Lg also appears to occur near the margin between the continental U.S. and the Gulf of Mexico. In this case, Sn travels northward across the Gulf from earthquakes located near the border between Mexico and Guatemala.

Miogeoclines and suspect terranes of the Caledonian–Appalachian Orogen: tectonic patterns in the North Atlantic region

1984 ◽  
Vol 21 (8) ◽  
pp. 887-901 ◽  
Author(s):  
Harold Williams
Keyword(s):  
North Atlantic ◽  
North American ◽  
North Atlantic Ocean ◽  
Continental Margins ◽  
British Isles ◽  
The North ◽  
Northwest Africa ◽  
Iapetus Ocean ◽  
Appalachian Orogen ◽  
The North Atlantic

The Caledonian–Appalachian Orogen was formed by the closing of a Paleozoic Iapetus Ocean. The continental margins of Iapetus are identified in the deformed early Paleozoic miogeoclines of the Caledonian–Appalachian Orogen. Ophiolitic vestiges of Iapetus, its oceanic plateaus, microcontinents, and volcanic arcs are Caledonian–Appalachian suspect terranes. These were assembled in interior parts of the orogen and locally they were emplaced structurally upon the adjacent miogeoclines.The modern North Atlantic Ocean opened along an axis that traversed the Paleozoic orogen longitudinally. Its opening dispersed the elements of the Paleozoic orogen and led to the present arrangement of disjunct Paleozoic miogeoclines and suspect terranes throughout the North Atlantic borderlands.The western or North American margin of Iapetus is represented by the miogeoclines along the west flank of the North American Appalachians and Caledonides of east Greenland. A small North American miogeoclinal segment occurs in the British Isles, and suspect terranes with North American faunal affinities occur in Scandinavia. The eastern margin of Iapetus is represented by the miogeoclines of the Scandinavian Caledonides and the Mauritanides of northwest Africa. Ophiolitic vestiges of Iapetus and suspect terranes occur in the Appalachians, the Caledonides of Scandinavia and the British Isles, and the Variscan foldbelt of Morocco, Iberian Peninsula, and western France.In the scenario of a closing Iapetus and opening North Atlantic, the Paleozoic margin of eastern North America expanded by the acquisition of Appalachian suspect terranes, the Paleozoic margins of Greenland and Scandinavia remained essentially unchanged, and Africa lost parts of its Paleozoic margin.Modern continental margins and the geometry of the North Atlantic mimic Paleozoic miogeoclines and the geometry of Iapetus. The Paleozoic miogeoclines, in turn, follow Grenvillian deformed zones of the Precambrian North Atlantic craton. Thus, patterns for the opening of the North Atlantic may have been set by the geometry of the Grenvillian deformed zones.

Origin and orogenic role of the Chain Lakes massif, Maine and Quebec

2006 ◽  
Vol 43 (3) ◽  
pp. 339-366 ◽  
Author(s):  
C C Gerbi ◽  
S E Johnson ◽  
J N Aleinikoff
Keyword(s):  
Volcanic Rocks ◽  
Metamorphic Event ◽  
Early Paleozoic ◽  
Western Margin ◽  
Middle Ordovician ◽  
Volcanic Sequence ◽  
Iapetus Ocean ◽  
Appalachian Orogen ◽  
New Interpretation

The Chain Lakes massif has long been an enigmatic component of the Appalachian orogen, but new structural, microstructural, and geochronological information provides the basis for the following new interpretation of the massif and its history. In the early Paleozoic, sediments and volcanic rocks from Laurentia or a Laurentian-derived microcontinent were deposited in a fore-arc basin on the western margin of the Iapetus ocean. Following intrusion of arc-related magmas, the sedimentary–volcanic sequence was heated sufficiently to melt in place, resulting in stratigraphic disaggregation and diatexite formation. We dated monazite growth from this metamorphic event at 469 ± 4 Ma. Although some melt may have left the system, much remained, including water dissolved in the melt. Upon crystallization, this water drove thorough retrogression of the massif, causing pervasive pseudomorphism of porphyroblasts. With cooling and crystallization, the Chain Lakes massif became sufficiently rigid that it was not significantly deformed during the Middle Ordovician through Devonian stages of Appalachian orogenesis involving the arrival of several peri-Gondwanan microcontinents.

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