Occurrences and Origin of the Ophiolites of Southern Quebec, Northern Appalachians

1975 ◽  
Vol 12 (3) ◽  
pp. 443-455 ◽  
Author(s):  
Roger Laurent
Keyword(s):  
Country Rock ◽  
Volcanic Rocks ◽  
Spreading Ridge ◽  
Middle Ordovician ◽  
Early Ordovician ◽  
Basaltic Rocks ◽  
Stratigraphic Position ◽  
Thrust Sheets ◽  
Ultramafic Cumulate ◽  
Sheeted Dike Complex

The ophiolites of southern Quebec are thrust sheets. Prior to their folding with the country-rock. they were emplaced as solid masses into the thick metasedimentary and metavolcanic geosynclinal prism of Notre Dame Trough, in Early Ordovician time. The occurrence of the ophiolites is controlled by their structural and stratigraphic position. Complete ophiolites occur as stratified sheets lying structurally above the Cambrian Caldwell Group, and they are overlain by a mélange assumed to be of Early Ordovician age. Dismembered ophiolites consist of peridotite sheets and lenses which may have been attached originally to the basal peridotite of the larger stratified sheets; they are tectonically intruded into Cambrian rocks.The stratified sheets have a simple, regularly-layered structure with no well developed sheeted-dike complex. Other feature s include a thin upper unit of gabbroic and basaltic rocks with a relatively thick ultramafic cumulate at the base and a thicker lower unit of Alpine peridotite. There is apparently no transition zone between the upper and lower units. All these features suggest that the ophiolites of southern Quebec represent possible fragments of an oceanic crust formed on a rapidly spreading ridge. It is assumed that they have been emplaced on the Early Ordovician continental margin by obduction and contemporaneously with the development of a subduction zone, which may have caused the magmatism that generated the adamellitic granites intruded into the ophiolitic complexes, and the calcalkatline volcanic rocks of the Lower to Middle Ordovician Ascot and Weedon Groups.

Volcanism on the passive margin of Laurentia: an early Paleozoic analogue of Cretaceous volcanism on the northeastern American margin

1988 ◽  
Vol 25 (11) ◽  
pp. 1824-1833 ◽  
Author(s):  
Stephen Kumarapeli ◽  
Karen St. Seymour ◽  
Hillar Pintson ◽  
Elizabeth Hasselgren
Keyword(s):  
Volcanic Rocks ◽  
Passive Margin ◽  
Fracture Zones ◽  
Transform Faults ◽  
Middle Ordovician ◽  
Early Ordovician ◽  
Basaltic Rocks ◽  
Sedimentary Sequences ◽  
Late Cambrian ◽  
Cretaceous Volcanism

Allochthonous masses of basaltic lava flows and related tuffs are present in several localities in an approximately 30 km long segment of the western margin of the Granby Nappe, in southeastern Quebec. They occur either as numerous small blocks in the Drummondville wildflysch related to the nappe or as larger masses intercalated with sedimentary sequences of limestone and shale of probable Late Cambrian to Early Ordovician age. These latter occurrences and the associated sedimentary units form "island-like" areas within lithologies of the Granby Nappe consisting of Cambrian sediments that accumulated on the continental rise. Their overall characteristics suggest that they represent slabs derived from the shelf margin of Laurentia and incorporated into the cratonward-moving nappes during the Middle Ordovician Taconian Orogeny.The volcanic rocks are mainly transitional but include some alkali olivine basalts. There are some indications that their affinities are to basaltic rocks of seamount chains localized along leaky transform faults. The segment of the continental margin from which the volcanic rocks were derived originated in the latest Precambian times, by rifting involving a rift–rift–rift (RRR) triple junction. Thus, it was a likely location for deep-seated transverse fracture zones linked to ridge-to-ridge transform faults of Iapetus. Therefore, the best explanation of the volcanism is that it was localized along such fracture zones. This episode of Late Cambrian – Early Ordovician volcanism related to the Iapetus cycle is probably analogous to the recently documented Early Cretaceous volcanism related to the Atlantic cycle on the northeastern American margin.

Autochthonous and allochthonous rocks in the Pistolet Bay area in northernmost Newfoundland

1968 ◽  
Vol 5 (3) ◽  
pp. 501-513 ◽  
Author(s):  
M. F. Tuke
Keyword(s):  
Lower Cambrian ◽  
Volcanic Rocks ◽  
The Other ◽  
North Central ◽  
Middle Ordovician ◽  
Early Ordovician ◽  
Bay Area

Rocks outcropping in the northernmost part of the island of Newfoundland belong to two sequences, which are partly contemporaneous and very different in lithology. One sequence consists of Lower Cambrian sandstones and Lower and Middle Ordovician carbonates and shales. The other sequence consists of graywackes, volcanic rocks, and ultrabasic intrusions, which are, in part, early Ordovician. This latter sequence is interpreted as allochthonous because it is underlain by major low-angle faults and because of its strong facies contrast with the first sequence. The allochthonous rocks occur in three separate klippen.The trend of slickensides, attitude of folds, and deflection of beds at fault surfaces all indicate that movement along the low-angle faults that underlie the klippen was to the northwest. The klippen probably originated from an area 60 km to the southeast, which is on strike with similar rocks in north-central Newfoundland.It is suggested that the klippen moved by gravity sliding in late Middle Ordovician time.

A revision of the stratigraphic nomenclature of the Cambrian–Ordovician strata of the Philipsburg tectonic slice, southern Quebec

2007 ◽  
Vol 44 (12) ◽  
pp. 1775-1790 ◽  
Author(s):  
O Salad Hersi ◽  
G S Nowlan ◽  
D Lavoie
Keyword(s):  
Middle Ordovician ◽  
Upper Cambrian ◽  
Early Ordovician ◽  
Late Cambrian ◽  
Lower Ordovician ◽  
Stratigraphic Position ◽  
Stratigraphic Nomenclature ◽  
Unconformable Contact ◽  
Tectonic Slice ◽  
Upper Boundary

The Philipsburg tectonic slice is bounded to the west by a northeast–southwest-trending thrust fault (Logan’s Line) and preserves 10 formations of Middle (?) to Late Cambrian (Milton, Rock River, and Strites Pond formations), Early Ordovician (Wallace Creek, Morgan Corner, Hastings Creek, and Naylor Ledge formations), and early Middle Ordovician (Luke Hill, Solomons Corner, and Corey formations) age. The strata were previously assigned to the Philipsburg Group. Early correlations between the Philipsburg succession and coeval strata of the St. Lawrence Platform were mainly based on sparse macrofauna and inferred stratigraphic position. Unconformities at the Cambrian–Ordovician and Early Ordovician – Middle Ordovician boundaries occurring in autochthonous St. Lawrence Platform and the allochthonous Philipsburg succession (Philipsburg tectonic slice) highlight new stratigraphic interpretations between the inner-shelf (St. Lawrence Platform) and the outer-shelf (Philipsburg) successions. The succession in the Philipsburg tectonic slice is divided into three new groups. The Middle (?) to Upper Cambrian Missisquoi Group (new) includes the Milton, Rock River, and Strites Pond formations. The upper boundary of the Missisquoi Group is defined by the upper unconformable contact between the Upper Cambrian Strites Pond Formation and overlying Lower Ordovician Wallace Creek Formation. The Missisquoi Group correlates with the Potsdam Group of the St. Lawrence Platform. The Lower Ordovician School House Hill Group (new) includes the Wallace Creek, Morgan Corner, Hastings Creek, and Naylor Ledge formations. The upper boundary of this group is marked by a regionally extensive unconformity at the top of the Naylor Ledge Formation and correlates with the younger Beekmantown-topping unconformity. The School House Hill Group is correlative with the lower to upper part of the Beekmantown Group (Theresa Formation and the Ogdensburg Member of the Beauharnois Formation) of the St. Lawrence Platform. The Middle Ordovician Fox Hill Group (new) consists of the Luke Hill, Solomons Corner, and Corey formations. This group correlates with the uppermost part of the Beekmantown Group (Huntingdon Member of the Beauharnois Formation and the Carillon Formation).

scholarly journals Formation of the rear slope of the island arc of Chingiz Kaledonid ridge in eastern Kazakhstan

2019 ◽  
pp. 72-80
Author(s):  
S. G. Samygin
Keyword(s):  
Volcanic Activity ◽  
Volcanic Rocks ◽  
Island Arc ◽  
Middle Ordovician ◽  
Upper Cambrian ◽  
Early Ordovician ◽  
Landslide Processes ◽  
Mass Frontier ◽  
Eastern Kazakhstan

Process of formation of the island-arc rear slope is considered on the example of the Upper Cambrian–Middle Ordovician arc found in the Chingiz ridge in eastern Kazakhstan. Its occurrence is shown at the end of volcanic activity in the island-arc structure, beginning at the end of the early Arenig (from the end of the Flos century of the Early Ordovician) with tephroturbidites appearance. After the cessation of volcanism, two sedimentation cycles were distinguished in the sedimentary section of the slope in the middle Ordovician: (1) transgressive when the island arc submerged, (2) and regressive when the Chingiz arc began to build up at the beginning of the Llanwyrn (Darrivilian) century. The sedimentation was repeatedly accompanied by landslide processes, which ended in the middle of llanvirna (darrivilia) with the disruption of tectonic-gravity plate composed of Upper Cambrian volcanic rocks with limestone in the sole, resulting in the formation of coarsely fragmented mixtite at the allochthonous mass frontier, the further sedimentation on the rear slope stopped. Keywords: the island-arc; rear slope; sedimentation cycles; landslide processes

Palaeozoic within-plate volcanic rocks in Nova Scotia (Canada) reinterpreted: isotopic constraints on magmatic source and palaeocontinental reconstructions

1997 ◽  
Vol 134 (4) ◽  
pp. 425-447 ◽  
Author(s):  
J. D. KEPPIE ◽  
J. DOSTAL ◽  
J. B. MURPHY ◽  
B. L. COUSENS
Keyword(s):  
Nova Scotia ◽  
Active Faults ◽  
Volcanic Rocks ◽  
Geochemical Data ◽  
Isotopic Data ◽  
Middle Ordovician ◽  
Early Ordovician ◽  
Late Proterozoic ◽  
Regional Tectonic ◽  
Felsic Volcanic

Palaeozoic volcanism in the Avalon Terrane of northern Nova Scotia occurred during three time intervals: Cambrian–early Ordovician, late Ordovician–early Silurian and middle–late Devonian. In the Meguma Terrane of southern Nova Scotia, Palaeozoic volcanism is limited to the middle Ordovician. Geochemical data show that most of these volcanic rocks are bimodal, within-plate suites. Initial εNd signatures range from +5.4 to −1.9 in the rhyolites and +6.8 to +2.7 in the basalts, a difference attributable to the absence or presence, respectively, of a significant crustal component. The data and regional tectonic settings of the Avalon and Meguma terranes suggest that the volcanism was generated in three different within-plate settings: (1) Cambrian–early Ordovician volcanism related to thermal decay of late Proterozoic arc magmatism during transtensional deformation; (2) middle Ordovician–early Silurian volcanism during sinistral telescoping between Laurentia and Gondwana where extensional bends in the Appalachians produced rifting; and (3) Devonian volcanism resulting from lithospheric delamination during dextral transpression and telescoping. In each setting, active faults served as conduits for the magmas. Nd isotopic data indicate that the source of the Palaeozoic felsic volcanic rocks is isotopically indistinguishable beneath southern and northern Nova Scotia and did not substantially change with time. This crustal source appears to have separated from the mantle during the Proterozoic, a conclusion consistent with the hypothesis that the Palaeozoic rocks in Nova Scotia were deposited upon a late Proterozoic oceanic–cratonic volcanic arc terrane. The Nd data, when combined with published faunal, palaeomagnetic and U–Pb isotopic data, suggest that the Avalon Terrane was peripheral to Gondwana off northwestern South America during Neoproterozoic and early Palaeozoic times.

Geochemical and isotopic (Nd, O) data from Ordovician felsic plutonic and volcanic rocks of the Miramichi Highlands: petrogenetic and metallogenic implications for the Bathurst Mining Camp

1998 ◽  
Vol 35 (3) ◽  
pp. 237-252 ◽  
Author(s):  
Joseph B Whalen ◽  
Neil Rogers ◽  
Cees R van Staal ◽  
Frederick J Longstaffe ◽  
George A Jenner ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Middle Ordovician ◽  
Basaltic Rocks ◽  
Volcanogenic Massive Sulphide ◽  
Vms Deposits ◽  
Bathurst Mining Camp ◽  
Felsic Volcanic ◽  
Back Arc ◽  
T Values ◽  
Felsic Volcanic Rocks

Middle Ordovician felsic magmatism contemporaneous with Bathurst Camp Pb-Zn volcanogenic massive sulphide(VMS) deposits consists of strongly altered volcanic to subvolcanic rocks, belonging to the Tetagouche Group, and relativelyunaltered granitoid plutons, which are divided into northern, central, and southern groups within the Miramichi Highlands.Calc-alkalic felsic volcanic rocks and northern plus central plutons have EpsilonNd(T) values ranging from -8.2 to -1.9 and -4.0 to +0.3, respectively. They exhibit within-plate-type volcanic and transitional I- to A-type granite geochemical characteristics.Granitoid rock Delta18O values range from +8.0 to +10.1‰. Published granitoid rock Pb isotopic compositions overlapunpublished galena data from Bathurst VMS deposits. Field, geochemical, and isotopic evidence indicate that these volcanicand granitoids rocks are consanguineous and mainly derived from Proterozoic orolder infracrustal sources. Alkalic felsic volcanic rocks, and associated alkaline basaltic rocks, are more juvenile (EpsilonNd(T) = +3.2 to +4.2) and were possibly derivedfrom slightly enriched mantle sources. Southern plutons exhibit continental arc-type features. The felsic magmatism and VMS deposits likely formed in an Okinawa-type back-arc basin developed from rifting the Early Ordovician Popelogan continentalarc, of which the southern plutons are remnants. Correlations between pluton groups and volcanic formations indicate that felsic magmatism was erupted through and onto the Miramichi Group. As most felsic volcanic formations lack plutonicequivalents, the Tetagouche Group probably does not represent disrupted slices of an originally conformable stratigraphic section. This supports a model in which thrust slices juxtapose remnants of volcanic centres erupted at different locationswithin a back-arc basin.

Ordovician gabbro-tonalite-trondhjemite complex and associated volcanic rocks in the paleozoic suture between Urals and Kazakhstan

2019 ◽  
Vol 485 (2) ◽  
pp. 202-206
Author(s):  
А. V. Ryazantsev
Keyword(s):  
Volcanic Rocks ◽  
The Urals ◽  
Middle Ordovician ◽  
Early Ordovician ◽  
Plutonic Complex

This paper reports new data on the Early Ordovician age established for granitoids of the gabbro-tonalite-trond- hjemite complex in the Denisovka ophiolite zone (suture) on the boundary between the Paleozoic structures (Paleozoides) of the Urals and Kazakhstan. The ages of 482.6 ± 3.6 Ma and 486.2 ± 6.7 Ma were established by the U/Pb method (SHRIMP II) on the age data for zircon extracted from granitoids. The plutonic complex associates with the Early-Middle Ordovician effusive complex, composed of a series of rocks differentiated from basalts to rhyolites. The volcano-plutonic association was formed in the supra-subduction settings, as is evidenced by the composition of the rocks.

Age, chemistry, and tectonic setting of Miramichi terrane (Early Paleozoic) volcanic rocks, eastern and east-central Maine, USA

2021 ◽  
Vol 57 ◽  
pp. 239-273
Author(s):  
Allan Ludman ◽  
Christopher McFarlane ◽  
Amber T.H. Whittaker
Keyword(s):  
New Brunswick ◽  
Subduction Zone ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Calc Alkaline ◽  
East Central ◽  
Arc Volcanism ◽  
Middle Ordovician ◽  
Volcanic Suite ◽  
Back Arc

Volcanic rocks in the Miramichi inlier in Maine occur in two areas separated by the Bottle Lake plutonic complex: the Danforth segment (Stetson Mountain Formation) north of the complex and Greenfield segment to the south (Olamon Stream Formation). Both suites are dominantly pyroclastic, with abundant andesite, dacite, and rhyolite tuffs and subordinate lavas, breccias, and agglomerates. Rare basaltic tuffs and a small area of basaltic tuffs, agglomerates, and lavas are restricted to the Greenfield segment. U–Pb zircon geochronology dates Greenfield segment volcanism at ca. 469 Ma, the Floian–Dapingian boundary between the Lower and Middle Ordovician. Chemical analyses reveal a calc-alkaline suite erupted in a continental volcanic arc, either the Meductic or earliest Balmoral phase of Popelogan arc activity. The Maine Miramichi volcanic rocks are most likely correlative with the Meductic Group volcanic suite in west-central New Brunswick. Orogen-parallel lithologic and chemical variations from New Brunswick to east-central Maine may result from eruptions at different volcanic centers. The bimodal Poplar Mountain volcanic suite at the Maine–New Brunswick border is 10–20 myr younger than the Miramichi volcanic rocks and more likely an early phase of back-arc basin rifting than a late-stage Meductic phase event. Coeval calc-alkaline arc volcanism in the Miramichi, Weeksboro–Lunksoos Lake, and Munsungun Cambrian–Ordovician inliers in Maine is not consistent with tectonic models involving northwestward migration of arc volcanism. This >150 km span cannot be explained by a single east-facing subduction zone, suggesting more than one subduction zone/arc complex in the region.

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.

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