Age and implications of Early Ordovician (Arenig) plutonism in the type area of the Bay du Nord Group, Dunnage Zone, southern Newfoundland Appalachians

1994 ◽  
Vol 31 (2) ◽  
pp. 351-357 ◽  
Author(s):  
R. D. Tucker ◽  
S. J. O'Brien ◽  
B. H. O'Brien
Keyword(s):  
Precambrian Basement ◽  
Stratigraphic Sequence ◽  
East Central ◽  
Middle Ordovician ◽  
Metasedimentary Rocks ◽  
Group Type ◽  
Late Precambrian ◽  
Type Area ◽  
Granitoid Rocks ◽  
Basement Inlier

In south Newfoundland, an extensive tract of metamorphosed Ordovician metavolcanic, metasedimentary, and granitoid rocks (Bay du Nord Group) lies north of a late Precambrian basement inlier of peri-Gondwanan affinity, separated from the latter by Silurian rocks. In the Bay du Nord Group type area, the metavolcanic and metasedimentary rocks were ductilely sheared and locally fault imbricated with metagabbro prior to emplacement of the Baggs Hill Granite, herein dated at 477.6 ± 1.8 Ma. Some of the volcano-sedimentary strata within this succession, however, contain foliated clasts of Baggs Hill Granite, and these strata must comprise a younger stratigraphic sequence which, in this area, is thrust northwestward over the older rocks.The pre-477.6 ± 1.8 Ma tectonic interleaving of the Dunnage Zone gabbro and stratified rocks is significantly earlier than the Llandovery (early Salinic) recumbent folding and thrusting of Middle Ordovician Exploits Subzone rocks in the east-central Hermitage Flexure. In both areas, the Dunnage Zone rocks were inhomogeneously thickened and tectonically telescoped north of a rigid block of late Precambrian peri-Gondwanan basement. The emplacement of the Baggs Hill Granite is coeval with intrusion of similar Ordovician granite into ophiolites obducted southeastward onto the Gondwanan margin during Arenigian (Penobscot) orogenesis.

scholarly journals Geochronology and lithogeochemistry of granitoid rocks from the central part of the Central plutonic belt, New Brunswick, Canada: implications for Sn-W-Mo exploration

2016 ◽  
Vol 52 ◽  
pp. 125 ◽  
Author(s):  
Reginald A. Wilson ◽  
Sandra L. Kamo
Keyword(s):  
New Brunswick ◽  
Peraluminous Granite ◽  
Early Devonian ◽  
Middle Ordovician ◽  
Metasedimentary Rocks ◽  
Hydrothermal Processes ◽  
Average Abundance ◽  
Granitoid Rocks ◽  
Plutonic Belt ◽  
Plate Type

The central part of the Central plutonic belt in New Brunswick is underlain by numerous plutons of calc-alkaline, foliated and unfoliated granite that intrude Cambrian to Early Ordovician metasedimentary rocks. U-Pb (zircon) dating demonstrates that granites range in age from Middle Ordovician to Late Devonian, although most are late Silurian to Early Devonian. An age of 467 ± 7 Ma has been obtained on the foliated McKiel Lake Granite, whereas unfoliated intrusions yield ages of 423.2 ± 3.2 Ma (Bogan Brook Granodiorite), 420.7 +1.8/-2.0 Ma (Nashwaak Granite), 419.0 ± 0.5 Ma (Redstone Mountain Granite), 416.1 ± 0.5 Ma (Beadle Mountain Granite), 415.8 ± 0.3 Ma (Juniper Barren Granite), 409.7 ± 0.5 Ma (Lost Lake Granite), and 380.6 ± 0.3 Ma (Burnthill Granite). All plutons exhibit mixed arc-like and within-plate geochemical signatures, although the Redstone Mountain and Burnthill granites are dominantly of within-plate type. Trace element data reveal a close overall geochemical similarity between Ordovician and Silurian – Devonian plutons, indicating that all were generated by partial melting of the same crustal source. Late Silurian to Early Devonian plutons mainly comprise biotite and/or muscovite-bearing, peraluminous granite and are considered prospective for granophile-element mineralization. All plutons contain Sn well in excess of the granite global average abundance, and several contain average tin values comparable to productive stanniferous granites elsewhere. The Burnthill, Lost Lake, Beadle Mountain, and Nashwaak granites are geochemically most evolved and enriched in Sn and W. The Burnthill Granite in particular has experienced late-stage hydrothermal processes that have resulted in local enrichments of these elements.

Sm–Nd isotopic geochemistry of Precambrian to Paleozoic granitoid suites and the deep-crustal structure of the southeast margin of the Newfoundland Appalachians

1995 ◽  
Vol 32 (2) ◽  
pp. 224-245 ◽  
Author(s):  
Andrew Kerr ◽  
George A. Jenner ◽  
Brian J. Fryer
Keyword(s):  
Fault System ◽  
Mobile Belt ◽  
Simple Extension ◽  
Precambrian Basement ◽  
Zone Boundary ◽  
First Order ◽  
Metasedimentary Rocks ◽  
Late Precambrian ◽  
Deep Crustal Structure ◽  
Appalachian Orogen

In the Eastern Central Mobile Belt of the Newfoundland Appalachians, late Precambrian basement inliers have εNd from −3 to +2, but Cambro-Ordovician metasedimentary rocks have initial εNd below −7. This region is inferred to have an "inverted" crustal residence structure, which influenced subsequent Appalachian-cycle magmatism. Ordovician and Silurian granitoid suites have εNd of −8 to −2, bracketing both basement and cover, but peraluminous, "S-type" granites have the lowest εNd. Devonian granites have initial εNd values from −5 to +1, and low εNd is associated with peraluminous character. These Paleozoic granites show geographic trends, with lowest εNd values in areas where metasedimentary rocks are abundant. They are suggested to contain anatectic material from both Precambrian basement and metasedimentary cover, but some "I-type" suites probably also include a mantle-derived component. In the adjacent Avalon Zone, Precambrian plutonic suites mostly have εNd from +1 to +6, but there are negative εNd values (−8 to −4) in the westernmost Avalon Zone. Devonian plutonic suites mostly have εNd from +2 to +5. Thus, the Precambrian crust of the Avalon Zone is largely "juvenile," except at its westernmost edge. Contrasts across the Eastern Central Mobile Belt–Avalon Zone boundary, defined by the Dover–Hermitage Bay fault system, indicate a major, crustal-scale structure, and suggest an isotopically distinct "central block" beneath the central Appalachian Orogen, rather than a simple extension of "Avalonian" crust. Similar geographic–isotopic patterns have been reported in Nova Scotia and New Brunswick, suggesting that this pattern represents a first-order deep-crustal subdivision of the northern Appalachian Orogen.

Geology and age of the Precambrian basement in the Windsor, Chatham, and Sarnia area, southwestern Ontario

1982 ◽  
Vol 19 (8) ◽  
pp. 1627-1634 ◽  
Author(s):  
A. Turek ◽  
R. N. Robinson
Keyword(s):  
Oil And Gas ◽  
Precambrian Basement ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Gas Drilling ◽  
Arch System ◽  
Grenvillian Orogeny ◽  
Anomaly Map ◽  
Paleozoic Rocks ◽  
Basement Surface

Precambrian basement in the Windsor–Chatham–Sarnia area is covered by Paleozoic rocks that are up to 1300 m thick. The basement surface is characterized by a northeast–southwest arch system with a relief of about 350 m. Extensive oil and gas drilling has penetrated and sampled this basement, and an examination of core and chip samples from 133 holes and an assessment of the magnetic anomaly map of the area have been used to produce a lithologic map of the Precambrian basement. The predominant rocks are granite gneisses and syenite gneisses but also significant are gabbros, granodiorite gneisses, and metasedimentary rocks. The average foliation dips 50° and is inferred to have a northeasterly trend. The Precambrian basement has been regarded as part of the Grenville Province. An apparent Rb–Sr whole rock isochron, for predominantly meta-igneous rocks, yields an age of 1560 ± 140 Ma. This we interpret as pre-Grenvillian, surviving the later imprint of the Grenvillian Orogeny. Points excluded from the isochron register ages of 1830, 915, and 670 Ma, and can be interpreted as geologically meaningful.

Geochemistry of the Namurian Lismore Formation, northern mainland Nova Scotia: sedimentation and tectonic activity along the southern flank of the Maritimes Basin

1999 ◽  
Vol 36 (10) ◽  
pp. 1655-1669 ◽  
Author(s):  
Jacquelyn E Stevens ◽  
J Brendan Murphy ◽  
Fred W Chandler
Keyword(s):  
Nova Scotia ◽  
Tectonic Activity ◽  
Isotopic Data ◽  
Rock Fragments ◽  
Metasedimentary Rocks ◽  
Clastic Rocks ◽  
Granitoid Rocks ◽  
Maritimes Basin ◽  
Group B ◽  
Southern Flank

Geochemical and isotopic data from the clastic rocks of the Namurian Lismore Formation in mainland Nova Scotia identify key episodes of tectonic activity during the development of the Maritimes Basin in Atlantic Canada. The Lismore Formation forms part of the Mabou Group and is an upward-coarsening 2500 m thick fluvial sequence deposited in the Merigomish sub-basin along the southern flank of the Maritimes Basin. Based on stratigraphic evidence, the Lismore Formation can be divided into upper and lower members which reflect variations in depositional environment and paleoclimate. The geochemical and isotopic data may also be subdivided into two groupings that primarily reflect varying contributions from accessory phases, clay minerals, or rock fragments. This subdivision occurs 115 m above the base of the upper member. The data from the lower grouping (group A) show an important contribution from underlying Silurian rocks, with a relatively minor contribution from Late Devonian granitoid rocks from the adjacent Cobequid Highlands and possibly metasedimentary rocks from the Meguma Terrane to the south. The data from the upper grouping (group B) reveal a more important contribution from the Cobequid Highlands granitoid rocks. This variation in geochemistry is thought to constrain the age of renewed motion and uplift along the faults along the southern flank of the Maritimes Basin and, more generally, suggests that geochemical and isotopic data of continental clastic rocks may help constrain the age of tectonic events that influence deposition of basin-fill 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.

Ordovician echinoderms from the Tabas and Damghan regions, Iran: palaeobiogeographical implications

2005 ◽  
Vol 176 (3) ◽  
pp. 231-242 ◽  
Author(s):  
Bertrand Lefebvre ◽  
Mansooreh Ghobadipour ◽  
Elise Nardin
Keyword(s):  
South China ◽  
Central Iran ◽  
East Central ◽  
First Report ◽  
Middle Ordovician ◽  
Alborz Range ◽  
First Time

Abstract Two echinoderm assemblages are described in the Middle Ordovician of Iran (Darriwilian). The Simeh Kuh section (Damghan area, eastern Alborz range) has yielded a rich and diverse blastozoan fauna consisting of fistuliporite (Echinosphaerites, Heliocrinites) and dichoporite rhombiferans (cheirocrinids indet., hemicosmitids indet.), as well as aristocystitid (Sinocystis) and sphaeronitid diploporites (Glyptosphaerites, Tholocystis). Heliocrinites, cheirocrinids, hemicosmitids, Glyptosphaerites, and Tholocystis are reported for the first time in the Ordovician of Iran. A less diverse assemblage was collected in the Shirgesht section (Tabas area, Derenjal Mountains), and represents the first report of Ordovician echinoderms in east-central Iran. The Shirgesht fauna includes fistuliporite rhombiferans (Heliocrinites), aristocystitid and sphaeronitid diploporites. The new Iranian material documents some of the earliest known assemblages of diploporites and rhombiferans, and thus, brings important information on the radiation of these two major blastozoan classes. The two Iranian echinoderm faunas show relatively strong affinities with contemporary faunas from Baltica, the northern Gondwanan margin (e.g. Bohemia, Morocco), Sibumasu, and South China terranes. Aristocystitids suggest stronger links between Iran, and regions from the “Province à Amphorides” (northern Gondwanan margin, Sibumasu, South China). These observations support a palaeogeographical position of Iran at intermediate palaeolatitudes during the early Middle Ordovician, in the periphery of the northeastern Gondwanan margin.

On the position of the Variscan front in southern New Brunswick and its relation to Precambrian basement

1976 ◽  
Vol 13 (1) ◽  
pp. 194-196 ◽  
Author(s):  
N. Rast ◽  
K. L. Currie
Keyword(s):  
New Brunswick ◽  
Precambrian Basement ◽  
Precambrian Rocks ◽  
Late Precambrian ◽  
Mylonite Zone

The Variscan front is marked by a zone of cataclasis that generally follows an older and larger mylonite zone, but locally cuts across relatively undeformed Precambrian rocks. The older mylonite zone probably developed in Late Precambrian (Avalonian) time. Correlative Precambrian rocks extend across both the Variscan front, and the Bellisle fault to the northwest.

Rb–Sr whole-rock geochronology of the Gamitagama area, north central Ontario

1981 ◽  
Vol 18 (2) ◽  
pp. 323-329 ◽  
Author(s):  
A. Turek ◽  
T. E. Smith ◽  
C. H. Huang
Keyword(s):  
Greenstone Belt ◽  
Complex Terrain ◽  
Regional Metamorphism ◽  
Superior Province ◽  
The South ◽  
Stratigraphic Sequence ◽  
North Central ◽  
Metasedimentary Rocks ◽  
Area North ◽  
Radiometric Ages

The Gamitagama greenstone belt is situated to the south of the Archean Wawa belt of the Superior Province, and is about 50 km south of Wawa, Ontario. The Rb–Sr ages being reported here show that the metavolcanic and associated metasedimentary rocks are older than 2665 ± 45 Ma, which is a whole-rock isochron age of the pretectonic or syntectonic trondhjemitic plutons. The Gamitagama Lake complex, a calcalkalic differentiated and multiple diorite pluton, postdates the regional metamorphism and gives an age of 2645 ± 100 Ma. Potassic granitoid stocks, which are considered to be coeval with the Gamitagama Lake complex, define an isochron age of 2590 ± 80 Ma. The greenstone belt and associated intrusives are adjacent to the Southern batholith, a complex terrain of gneisses and migmatites, for which an isochron age of 2570 ± 90 Ma has been obtained. The radiometric ages reported here support the established stratigraphic sequence and prove that the rocks are Archean in age.

scholarly journals Hidden Archaean and Palaeoproterozoic crust in NW Ireland? Evidence from zircon Hf isotopic data from granitoid intrusions

2009 ◽  
Vol 146 (6) ◽  
pp. 903-916 ◽  
Author(s):  
M. J. FLOWERDEW ◽  
D. M. CHEW ◽  
J. S. DALY ◽  
I. L. MILLAR
Keyword(s):  
Source Region ◽  
Isotope Analysis ◽  
Isotopic Signature ◽  
Detrital Zircons ◽  
Metasedimentary Rocks ◽  
Deep Crust ◽  
Gneiss Complex ◽  
Granitoid Rocks ◽  
Granitoid Intrusions

AbstractThe presence of major crystalline basement provinces at depth in NW Ireland is inferred from in situ Hf isotope analysis of zircons from granitoid rocks that cut structurally overlying metasedimentary rocks. Granitoids in two of these units, the Slishwood Division and the Tyrone Central Inlier, contain complex zircons with core and rim structures. In both cases, cores have average ϵHf values that differ from the average ϵHf values of the rims at 470 Ma (the time of granitoid intrusion). The Hf data and similarity in U–Pb age between the inherited cores and detrital zircons from the host metasedimentary rocks suggests local contamination during intrusion rather than transport of the grains from the source region at depth. Rims from the Slishwood Division intrusions have average ϵHf470 values of −7.7, consistent with a derivation from juvenile Palaeoproterozoic crust, such as the Annagh Gneiss Complex or Rhinns Complex of NW Ireland, implying that the deep crust underlying the Slishwood Division is made of similar material. Rims from the Tyrone Central Inlier have extremely negative ϵHf470 values of approximately −39. This isotopic signature requires an Archaean source, suggesting rocks similar to the Lewisian Complex of Scotland, or sediment derived wholly from it, occurs at depth in NW Ireland.

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