Strike-slip terranes and a model for the evolution of the British and Irish Caledonides

1987 ◽  
Vol 124 (5) ◽  
pp. 405-425 ◽  
Author(s):  
Donald H. W. Hutton
Keyword(s):  
North America ◽  
Continental Margin ◽  
Strike Slip ◽  
Slip Zone ◽  
Lake District ◽  
Early Ordovician ◽  
Boundary Fault ◽  
Lower Ordovician ◽  
Major Strike ◽  
Back Arc

AbstractEvidence is presented that many of the major strike faults in the British and Irish Caledonides were active as sinistral strike-slip zones in the end-Silurian to pre-mid-Devonian period. Some, such as the Highland Boundary Fault, moved in this way at an earlier stage in the Ordovician. These data allow the Caledonian rocks lying between the Laurentian miogeocline (whose basement is represented by the Lewisian, Moine and possibly the Dalradian) and the Gondwanaland miogeocline (Midland Platform and Welsh Basin) to be re-analysed as a group of disorganized terranes which originated to the southwest in North America and southwest Europe/Africa prior to the Silurian. The Highland Border Terrane and Northern Belt Terrane are interpreted as duplicated pieces of a mid-Ordovician sequence which was a back are to northwest subduction. The Midland Valley Terrane is interpreted as a slice of Laurentian foreland onto which ophiolites were obducted in the lower Ordovician but which became the basement of a continental margin arc to northwest subduction in the mid-Ordovician. The Cockburnland Terrane is inferred to be part of the same arc repeated and then broken up and dispersed by continuing strike slip. The Connemara Terrane is regarded as an allochthonous piece of the Dalradian miogeocline and the South Mayo Terrane as a remnant of an early Ordovician arc and fore arc which in mid-Ordovician times became a back arc/marginal basin to northwest subduction. The Lake District-Wexford Terrane is part of an arc to southeast subduction under Gondwanaland whose activity climaxed in the mid-Ordovician. The Central Terrane is interpreted as a Silurian overstep assemblage which blankets the junction between Laurentian- and Gondwanaland-derived oceanic terranes, and therefore Iapetus is regarded as an Ordovician ocean which closed prior to the Silurian. The model suggests that at the end of the Silurian, a clockwise-rotating Gondwanaland, having carried Laurentia into collision with Baltica, broke free and created a major sinistral strike-slip zone which disrupted the Ordovician palaeogeography in the British Isles/North American sector of Iapetus.

New echinoderms from the Early Ordovician of west Texas

1994 ◽  
Vol 68 (2) ◽  
pp. 324-338 ◽  
Author(s):  
James Sprinkle ◽  
Gregory P. Wahlman
Keyword(s):  
North America ◽  
El Paso ◽  
Middle Ordovician ◽  
Early Ordovician ◽  
West Texas ◽  
Lower Ordovician ◽  
Single Well ◽  
Thecal Plate ◽  
Stem Segments

Four specimens of blastozoan and crinozoan echinoderms are described from the Lower Ordovician El Paso Group in the southern Franklin Mountains just north of El Paso, west Texas.Cuniculocystis flowerin. gen. and sp., based on two partial specimens, appears to be a typical rhombiferan in most of its morphologic features except that it lacks pectinirhombs and instead has covered epispires (otherwise known only from Middle Ordovician eocrinoids) opening on most of the thecal plate sutures. The covered epispires inCuniculocystisindicate that some early rhombiferans had alternate respiratory structures and had not yet standardized on pectinirhombs, a feature previously used as diagnostic for the class Rhombifera.Bockia?elpasoensisn. sp. is a new eocrinoid based on one poorly preserved specimen that has a small ellipsoidal theca and unbranched brachioles attached to a flat-topped spoutlike summit. It is the earliest known questionable representative of this genus and the only one that has been described from North America.Elpasocrinus radiatusn. gen. and sp. is an early cladid inadunate crinoid based on a single well-preserved calyx. It fits into a lineage of early cladids leading to the dendrocrinids and toCarabocrinus.Several additional separate plates, stem segments, and a holdfast of these and other echinoderms are also described.

Mid-Ordovician subduction, obduction, and eduction in western Newfoundland; an eclogite problem

2021 ◽  
Author(s):  
J.F. Dewey ◽  
J.F. Casey
Keyword(s):  
Subduction Zone ◽  
Shear Zone ◽  
Continental Margin ◽  
Amphibolite Facies ◽  
Island Arcs ◽  
Early Ordovician ◽  
The North ◽  
Shelf Slope ◽  
Major Strike ◽  
Laurentian Margin

Abstract. The narrow, short-lived Taconic-Grampian Orogen occurs along the north-western margin of the Appalachian-Caledonian Belt from, at least, Alabama to Scotland, a result of the collision of a series of early Ordovician oceanic island arcs with the rifted margin of Laurentia. The present distribution of Taconian-Grampian ophiolites is unlikely to represent a single fore-arc from Alabama to Scotland colliding at the same time with the continental margin along its whole length; more likely is that there were several Ordovician arcs with separate ophiolites. The collision suture is at the thrust base of obducted fore-arc ophiolite complexes, and obduction distance was about two hundred kilometres. Footwalls to the ophiolites are, sequentially towards the continent, continental margin rift sediments and volcanics and overlying rise sediments, continental shelf slope carbonates, and sediments of foreland flexural basins. The regionally-flat obduction thrust complex between the ophiolite and the rifted Laurentian margin is the collision suture between arc and continent. A particular problem in drawing tectonic profiles across the Taconic-Grampian Zone is several orogen-parallel major strike-slip faults, both sinistral and dextral, of unknown displacements, which may juxtapose portions of different segments. In western Newfoundland, most of the Grenville basement beneath the Fleur-de-Lys metamorphic complex (Neoproterozoic to early Ordovician meta-sediments) was eclogitised during the Taconic Orogeny and separated by a massive shear zone from the overlying Fleur-de-Lys, which was metamorphosed at the same time but in the amphibolite facies. The shear zone continued either to a distal intracontinental “subduction zone” or to the main, sub-fore-arc, subduction zone beneath which the basement slipped down to depths of up to seventy kilometres at the same time as the ophiolite sheet and its previously-subcreted metamorphic sole were being obducted above. Subsequently, the eclogitised basement was returned to contact with the amphibolite-facies cover by extensional detachment eduction, possibly enhanced by subduction channel flow, which may have been caused by slab break-off and extension during subduction polarity flip. Although the basal ophiolite obduction thrust complex and the Fleur-de-Lys-basement subduction-eduction surfaces must have been initially gently-dipping to sub-horizontal, they were folded and broken by thrusts during late Taconian, late Ordovician Salinic-Mayoian, and Acadian shortening.

scholarly journals The stratigraphy, correlation, provenance and palaeogeography of the Skiddaw Group (Ordovician) in the English Lake District

1995 ◽  
Vol 132 (2) ◽  
pp. 185-211 ◽  
Author(s):  
A. H. Cooper ◽  
A. W. A. Rushton ◽  
S. G. Molyneux ◽  
R. A. Hughes ◽  
R. M. Moore ◽  
...  
Keyword(s):  
Lake District ◽  
Volcanic Material ◽  
Early Ordovician ◽  
Isle Of Man ◽  
Lower Ordovician ◽  
Continental Arc ◽  
English Lake District

AbstractA new lithostratigraphy is presented for the Skiddaw Group (lower Ordovician) of the English Lake District. Two stratigraphical belts are described. Five formations are defined in the Northern Fells Belt, ranging in age from Tremadoc to early Llanvirn. They are all mudstone or sandstone dominated, of turbidite origin; in ascending order they are named the Bitter Beck, Watch Hill, Hope Beck, Loweswater and Kirk Stile formations. Two formations are defined in the Central Fells Belt, ranging in age from late Arenig to Llanvirn. These are the Buttermere Formation – a major olistostrome deposit – overlain by the Tarn Moor Formation, consisting of turbidite mudstones with volcaniclastic turbidite sandstone beds. A revised graptolite and new acritarch biostratigraphy for the Skiddaw Group is presented with eight graptolite biozones and thirteen acritarch assemblages and sub-assemblages. The provenance of the group is assessed from detailed petrographical and geochemical work. This suggests derivation, in the early Ordovician, largely from an old inactive continental arc terrane lying to the southeast, with the appearance of juvenile volcanic material in the Llanvirn. Comparisons and correlations of the Skiddaw Group are made with the Isle of Man and eastern Ireland.

A new early Ordovician Didymograptid, and its bearing on the correlation of the Skiddaw Group of England with the Tøyen Shale of Scandinavia

1991 ◽  
Vol 128 (4) ◽  
pp. 335-343 ◽  
Author(s):  
J. Maletz ◽  
A. W. A. Rushton ◽  
K. Lindholm
Keyword(s):  
Short Range ◽  
Lake District ◽  
Early Ordovician ◽  
Lower Ordovician ◽  
English Lake District

AbstractDidymograptus (s.l.) rigoletto sp.nov. is a distinctive species in the balticus group of didymograptids occurring in the Tøyen Shale (Lower Ordovician). In three localities in Sweden it has a short range near the top of the range of Tetragraptus phyllograptoides, and it occurs at about the same level at localities in the Oslo region, Norway; at most of these localities it occurs within the range of Tetragraptus of the approximatus group. Its presence in the Skiddaw Group of the English Lake District indicates the occurrence there of the basal Arenig (sensu lato), equivalent to the T. phyllograptoides Biozone of Scandinavia and the T. approximatus Biozone (= Lancefieldian 3) of the Australasian succession.

Age and origin of the Boil Mountain ophiolite and Chain Lakes massif, Maine: implications for the Penobscottian orogeny

1997 ◽  
Vol 34 (5) ◽  
pp. 646-654 ◽  
Author(s):  
T. M. Kusky ◽  
J. S. Chow ◽  
S. A. Bowring
Keyword(s):  
North America ◽  
Late Ordovician ◽  
Ophiolite Complex ◽  
Middle Ordovician ◽  
Iapetus Ocean ◽  
Lower Ordovician ◽  
Mid Ocean Ridge ◽  
Back Arc ◽  
Ocean Ridge ◽  
Age Constraints

The Boil Mountain ophiolite complex of west-central Maine is widely interpreted to mark the Lower Ordovician Penobscottian suture between the Dunnage, Chain Lakes, and Gander terranes. The ophiolite consists of two distinct volcanic groups, including a lower island-arc tholeiite sequence and an upper mid-ocean-ridge basalt sequence. A new Middle Ordovician 477 ± 1 Ma U–Pb age on a tonalite sill that intrudes the lower volcanic–gabbroic sequence is younger than other ca. 500 Ma age constraints for the ophiolite and represents a maximum age for the ophiolite prior to final emplacement over gneissic rocks of the Chain Lakes massif. A comparison of ages and paleogeography of the Boil Mountain ophiolite with ophiolitic sequences in Quebec and Newfoundland indicates that the Taconian and Penobscottian orogenies and ophiolite obduction occurred simultaneously, although on different margins of the Iapetus Ocean. The Taconian ophiolite sequences were obducted onto the Appalachian margin of Laurentia during its collision with the Notre Dame – Bronson Hill belt in the Middle Ordovician, whereas the Boil Mountain ophiolite was obducted onto the Gander margin of Gondwana during its collision with the Exploits subzone – Penobscot arc of the Dunnage terrane in the Lower – Middle Ordovician. We suggest that the lower volcanic–gabbroic sequence of the Boil Mountain ophiolite represents the fore-arc ophiolitic basement to the Penobscot arc. Middle Ordovician rifting of the Penobscottian orogenic collage on the Gander margin formed a new volcanic sequence (Popelogan arc) in front of a growing back-arc basin, and erupted the upper tholeiitic sequence of the Boil Mountain ophiolite in a back-arc-basin setting. The tonalité sill formed during this event by partial melting of the lower volcanic–gabbroic sequence. Spreading in this back-arc basin (Tetagouche basin) brought a fragment of the Gander margin (Chain Lakes massif), along with an allochthonous ophiolitic cover (Boil Mountain complex) across Iapetus, where it collided with the Taconic modified margin of North America in the Late Ordovician and was then intruded by the Ashgillian Attean pluton.

A new Lower Ordovician (Arenig) faunule from the Coy Pond Complex, central Newfoundland, and a refined understanding of the closure of the Iapetus Ocean

1992 ◽  
Vol 29 (9) ◽  
pp. 2046-2057 ◽  
Author(s):  
S. Henry Williams ◽  
W. Douglas Boyce ◽  
Stephen P. Colman-Sadd
Keyword(s):  
North America ◽  
First Record ◽  
Ophiolite Complex ◽  
Early Ordovician ◽  
South Central ◽  
Iapetus Ocean ◽  
Lower Ordovician ◽  
Age Limit ◽  
Southern Upland

A newly discovered fossiliferous horizon within sediments belonging to the Coy Pond Complex of the Exploits Subzone in central Newfoundland yields the graptolite Undulograptus austrodentatus s.l. and cyclopygid trilobite Cyclopyge grandis brevirhachis. This late Arenig faunule constrains the upper age limit of the ophiolite complex and is the first record of an Early Ordovician cyclopygid trilobite in North America. This is consistent with a paleogeographic affinity for south-central Newfoundland with the northern oceanic margin of Avalonia in a peri-Gondwanan position during the Early Ordovician and contrasts with coeval shelly and graptolitic faunas from the Notre Dame Subzone of central Newfoundland, which show marked Laurentian affinities. The Exploits Subzone is generally considered equivalent to the region of Scotland lying south of the Southern Upland Fault. The Newfoundland discovery, which is supported by faunal data from elsewhere in Newfoundland and in Ireland, suggests that the region around the Southern Upland Fault, rather than the Solway Firth, represents the location of the "Iapetus suture" in Britain in Lower Ordovician rocks.

The palaeogeographic position of the Lake District in the early Ordovician

1989 ◽  
Vol 126 (1) ◽  
pp. 9-17 ◽  
Author(s):  
R. A. Fortey ◽  
R. M. Owens ◽  
A. W. A. Rushton
Keyword(s):  
North America ◽  
Lake District ◽  
The South ◽  
Early Ordovician ◽  
Iapetus Ocean ◽  
First Time

AbstractThe early Ordovician was a time of maximum continental separation and hence a time when faunal evidence can be used to assess palaeogeography in a critical way. We summarize the known trilobite occurrences (18 genera) from the Arenig–Llanvirn of the Lake District, and record some genera for the first time. Maps of the distribution of some of these forms are given. All genera except Cyclopyge were confined to the Gondwana continent at the time, and some are known from many localities; and two species are widespread in England, Wales, France, Iberia and Bohemia. The fauna is entirely distinct from those of Scandinavia and North America. All the palaeontological evidence points to the Lake District being adjacent to Ordovician Gondwana. In the earlier Ordovician it is not reasonable to suggest that the Iapetus Ocean lay to the south of the Lake District as did Allen (1987).

On the non-existence of a Cadomian basement in southern France (Pyrenees, Montagne Noire): implications for the significance of the pre-Variscan (pre-Upper Ordovician) series

2004 ◽  
Vol 175 (6) ◽  
pp. 643-655 ◽  
Author(s):  
Bernard Laumonier ◽  
Albert Autran ◽  
Pierre Barbey ◽  
Alain Cheilletz ◽  
Thierry Baudin ◽  
...  
Keyword(s):  
Lower Cambrian ◽  
Classical Model ◽  
Black Shales ◽  
High Grade ◽  
Upper Ordovician ◽  
Lower Paleozoic ◽  
Early Ordovician ◽  
Lower Ordovician ◽  
Montagne Noire ◽  
Back Arc

Abstract The deepest Hercynian metamorphic terrains in the Pyrenees and in the nearby Montagne Noire are made up of medium-grade orthogneisses and micaschists, and of high-grade, often granulitic, paragneisses. The existence of a granitic-metamorphic Cadomian basement and of its sedimentary Lower Paleozoic cover was advocated from the following main arguments: (i) a supposed unconformity of the Lower Cambrian Canaveilles Group (the lower part of the Paleozoic series) upon both granitic and metamorphic complexes; (ii) a ca. 580 Ma U-Pb age for the metagranitic Canigou gneisses. A SE to NW transgression of the Cambrian cover and huge Variscan recumbent (“penninic”) folds completed this classical model. However, recent U-Pb dating provided a ca. 474 Ma, early Ordovician (Arenigian) age for the me-tagranites, whereas the Vendian age (581 ± 10 Ma) of the base of the Canaveilles Group was confirmed [Cocherie et al., 2005]. In fact, these granites are laccoliths intruded at different levels of the Vendian-Lower Cambrian series. So the Cadomian granitic basement model must be discarded. In a new model, developed in the Pyrenees and which applies to the Montagne Noire where the orthogneisses appear to be Lower Ordovician intrusives too, there are neither transgression of the Paleozoic nor very large Hercynian recumbent folds. The pre-Variscan (pre-Upper Ordovician) series must be divided in two groups: (i) at the top, the Jujols Group, mainly early to late Cambrian, that belongs to a Cambrian-Ordovician sedimentary and magmatic cycle ; the early Ordovician granites pertain to this cycle; (ii) at the base, the Canaveilles Group of the Pyrenees and the la Salvetat-St-Pons series of the Montagne Noire, Vendian (to earliest Cambrian?), are similar to the Upper Alcudian series of Central Iberia. The Canaveilles Group is a shale-greywacke series with rhyodacitic volcanics, thick carbonates, black shales, etc. The newly defined olistostromic and carbonated, up to 150 m thick Tregurà Formation forms the base of the Jujols Group, which rests more or less conformably on the Canaveilles Group. The high-grade paragneisses which in some massifs underlie the Canaveilles and Jujols low- to medium grade metasediments are now considered to be an equivalent of the Canaveilles Group with a higher Variscan metamorphic grade; they are not derived from metamorphic Precambrian rocks. So, there is no visible Cadomian metamorphic (or even sedimentary) basement in the Pyrenees. However, because of its age, the Canaveilles Group belongs to the end of the Cadomian cycle and was deposited in a subsident basin, probably a back-arc basin which developed in the Cadomian, active-transform N-Gondwanian margin of this time. The presence of Cadomian-Panafrican (ca. 600 Ma) zircon cores in early Ordovician granites and Vendian volcanics implies the anatexis of a thick (> 15 km?) syn-Cadomian series, to be compared to the very thick Lower Alcudian series of Central Iberia, which underlies the Upper Alcudian series. Nd isotopic compositions of Neoproterozoic and Cambrian-Ordovician sediments and magmatites, as elsewhere in Europe, yield Paleoproterozoic (ca. 2 Ga) model-ages. From the very rare occurrences of rocks of this age in W-Europe, it can be envisionned that the thick Pyrenean Cadomian series lies on a Paleoproterozoic metamorphic basement. But, if such a basement does exist, it must be “hidden”, as well as the lower part of the Neoproterozoic series, in the Variscan restitic granulites of the present (Variscan) lower crust. So a large part of the pre-Variscan crust was made of volcano-sedimentary Cadomian series, explaining the “fertile” characteristics of this crust which has been able to produce the voluminous Lower Ordovician and, later, Upper Carboniferous granitoids.

Paleomagnetic reexamination of the Lower Ordovician Wabana and Bell Island Groups of the Avalon Peninsula of Newfoundland

1982 ◽  
Vol 19 (5) ◽  
pp. 1055-1069 ◽  
Author(s):  
K. L. Buchan ◽  
J. P. Hodych
Keyword(s):  
North America ◽  
Early Paleozoic ◽  
Magnetization Direction ◽  
Early Ordovician ◽  
End Point ◽  
Iapetus Ocean ◽  
Lower Ordovician ◽  
Avalon Peninsula

The Wabana and Bell Island Groups of the Avalon Peninsula of Newfoundland contain oolitic hematite beds of Early Ordovician age, dipping ~11° north-northwest. Twenty-one oolitic hematite samples from nine sites were thermally demagnetized in 10 or 11 steps to 660 or 680 °C. At 450 °C, 15 samples from six sites define a stable magnetization direction (D = 21.2°, I = −12.5°, k = 137, α95 = 5.7°) with respect to bedding. The remaining six samples failed to attain the stable end-point, five of them because of growth of much "magnetite," which probably resulted from breakdown of siderite during thermal demagnetization.The paleopole for the Wabana – Bell Island Groups lies at 33°N 102°E (dm = 5.8°, dp = 3.0°). It is compared with other early Paleozoic paleopoles from cratonic North America and the Avalon zone, and its significance for the Iapetus Ocean is discussed.

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