Petrology of the Archean Pontiac and Kewagama sediments and implications for the stratigraphy of the southern Abitibi belt

1984 ◽  
Vol 21 (11) ◽  
pp. 1305-1314 ◽  
Author(s):  
Jean Lajoie ◽  
John Ludden
Keyword(s):  
Earth Element ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Igneous Rocks ◽  
Present Position ◽  
The West ◽  
Abitibi Greenstone Belt ◽  
Sedimentary Sequences ◽  
Bed Thickness ◽  
Water Facies

We present an interpretation of the petrology of two Archean sedimentary groups in the southeastern portion of the Abitibi greenstone belt: (1) the Pontiac sediments, which represent an assemblage of quartz-rich sandstones, and (2) the Kewagama sediments, which are quartz poor and rich in volcanic fragments. The Pontiac sediments display a north–south decrease in bed thickness, sand/shale ratio, and grain size, suggesting derivation from a northern source relative to their present position. Petrographic and rare earth element (REE) analysis indicates that three provenances contributed to the Pontiac: (1) a mature craton, (2) light/heavy REE fractionated igneous rocks probably of tonalite–trondhjemite composition, and (3) ultramafic–mafic volcanics.In contrast to the Pontiac sediments, the Kewagama sediments were derived from acid to mafic volcanic rocks (ratio of 3:1), with minor contributions from plutonic rocks and from graded sedimentary rocks (possibly the Pontiac). The REE data indicate a source fractionated in light/heavy REE relative to the adjacent Blake River Group volcanic rocks, and it is suggested that a suitable source may be the upper Skead volcanics 60 km to the west or a volcanic assemblage similar to the upper Skead that has been eroded from a location above the Blake River Group.The Pontiac Group has characteristics similar to Phanerozoic sedimentary sequences that have accumulated at a passive continental margin, whilst the Kewagama sediments were derived from uplifted volcamc terrane.Our study indicates that the Pontiac Group is stratigraphically below the Blake River Group and that it is not a lateral deep-water facies of the Timiskaming Group. In addition, we consider the possibility that the Kewagama is younger than the Pontiac.

The Pontiac problem, Quebec–Ontario, in the light of gravity data

1987 ◽  
Vol 24 (9) ◽  
pp. 1916-1919 ◽  
Author(s):  
J. Kalliokoski
Keyword(s):  
Gravity Anomaly ◽  
Greenstone Belt ◽  
Gravity Data ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Iron Formation ◽  
Bouguer Gravity ◽  
The West ◽  
Abitibi Greenstone Belt ◽  
Uplifted Block

A belt of Archean quartzose metasedimentary gneisses with minor mafic volcanic rocks (the Pontiac Group) lies south of the Blake River and older Archean mafic volcanic rocks of the Abitibi Greenstone Belt, and is separated from them by the Larder Lake – Cadillac Break. To the west of the Pontiac Group, on strike, is the Archean Larder Lake Group of turbidite conglomerate, argillite, limestone, and iron formation with abundant mafic flows and intrusions. These strata also lie south of the Larder Lake – Cadillac Break and south of the Blake River and older Archean mafic volcanic rocks. The western contact between the Pontiac and Larder Lake groups is covered by a narrow north–south strip of Proterozoic Cobalt sedimentary rocks. On the basis of gravity work that compares the Bouguer gravity anomaly gradient across the Cadillac Break with that across the west margin of the Pontiac Group, it is proposed that the Larder Lake and Pontiac groups are separated by a north–south fault and that the Pontiac Group represents a lithologically distinct uplifted block. The Pontiac block may be an Archean terrane.

IV.—Notes on the Arenig Rocks near Aberdaron, Carnarvonshire

1902 ◽  
Vol 9 (3) ◽  
pp. 118-122 ◽  
Author(s):  
Charles A. Matley
Keyword(s):  
Sedimentary Rocks ◽  
Igneous Rocks ◽  
The West

The geology of the Lleyn peninsula has from time to time attracted the attention of geologists, and several workers have added much to our knowledge of this district; but their researches have been mainly confined to (1) the strip of ancient rocks (usually assigned to the pre-Cambrian) in the west between Porth Dinlleyn and Bardsey Island, and (2) the igneous rocks lying in the Ordovician ground which occupies the eastern and larger portion of the peninsula. Thus the Ordovician sedimentary rocks have largely escaped attention, a result probably also due to their monotony, to the rarity of fossiliferous localities, and to the great extent to which the beds are concealed beneath accumulations of drift.

The Ordovician volcanics of the Elmtree–Belledune inlier and their relationship to volcanics of the northern Miramichi Highlands, New Brunswick

1992 ◽  
Vol 29 (7) ◽  
pp. 1430-1447 ◽  
Author(s):  
J. A. Winchester ◽  
C. R. van Staal ◽  
J. P. Langton
Keyword(s):  
New Brunswick ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Late Ordovician ◽  
Igneous Rocks ◽  
Volcanic Arc ◽  
Middle Ordovician ◽  
Marginal Basin ◽  
Tectonic Mélange ◽  
Back Arc

An investigation of the geology and chemistry of the basic igneous rocks in the Elmtree and Belledune inliers in northern New Brunswick shows that the bulk of the Middle Ordovician rocks of the ophiolitic Fournier Group are best interpreted as the products of volcanism and sedimentation in an extensive ensimatic back-arc basin southeast of a volcanic arc. The oceanic back-arc-basin igneous rocks form the basement to renewed arc-related basaltic volcanism in late Middle to Late Ordovician time. The Fournier Group is separated from the structurally-underlying, shale-dominated Elmtree Formation of the Tetagouche Group by an extensive tectonic melange, which incorporates lenses of serpentinite, mafic volcanic rocks, and sedimentary rocks of both the Tetagouche and Fournier groups. The mafic volcanic rocks in the Elmtree Formation correlate best with those intercalated with the lithologically similar sediments of the Llandeilian–Caradocian Boucher Brook Formation in the northern Miramichi Highlands. The melange and the present structural amalgamation of the Tetagouche and Fournier groups result from closure of the marginal basin by northward-directed subduction at the end of the Ordovician. Most mafic suites in the Elmtree and Belledune inliers can be chemically correlated with similar suites in the northern Miramichi Highlands, showing that the two areas are not separated by a terrane boundary.

ARCHAEAN SEDIMENTARY ROCKS OF NORTH SPIRIT LAKE AREA, NORTHWESTERN ONTARIO

1965 ◽  
Vol 2 (6) ◽  
pp. 622-647 ◽  
Author(s):  
J. A. Donaldson ◽  
G. D. Jackson
Keyword(s):  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Sole Source ◽  
Lake Area ◽  
Red Lake ◽  
Sedimentary Sequences ◽  
The North ◽  
Northwestern Ontario ◽  
History Of ◽  
Granitoid Rocks

Archaean sedimentary rocks of the North Spirit Lake area show little evidence of having been derived predominantly from associated Archaean volcanic rocks. Instead, compositions of the sediments reflect significant sedimentary and (or) granitoid provenance. A remarkably high content of clastic quartz in thick units of sandstone and conglomerate suggests either reworking of older quartzose sediments, or reduction of the labile constituents in quartz-rich granitoid rocks through prolonged weathering and rigorous transport. Observations for other sedimentary sequences in the region between Red Lake and Lansdowne House suggest that the North Spirit sediments are not unique in the Superior Province. Quartzose sandstones commonly are regarded as atypical of the Archaean, but such rocks arc abundant in northwestern Ontario. Frameworks of many Archaean greywackes actually are richer in quartz than typical greywackes from numerous Proterozoic and Phanerozoic sequences.The concept of rapidly rising volcanic arcs as the sole source of Archaean sedimentary detritus is rejected for the North Spirit area. The volcanies, rather than representing relicts of protocontinents, probably record events removed from initial volcanism in the history of the earth by one or more orogenic cycles. Major unconformities may therefore exist not only between sedimentary and volcanic units, but also between these units and older granitoid rocks.

The Phanerozoic cover sequences preserved as xenoliths in the kimberlite of eastern Sierra Leone

1983 ◽  
Vol 120 (1) ◽  
pp. 67-71 ◽  
Author(s):  
F. H. Hubbard
Keyword(s):  
Sierra Leone ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
West African ◽  
The West ◽  
West African Craton ◽  
Marine Transgression ◽  
Surface Rock ◽  
Lower Palaeozoic ◽  
Magmatic Event

SummarySedimentary and volcanic rocks, now unrepresented in surface exposure, occur as xenoliths in the kimberlite of the Koidu District of eastern Sierra Leone. The sedimentary rocks prove, on micropalaeontological evidence, to have Lower Palaeozoic stratigraphic age. An eastern extension of the Ordovician/Silurian marine transgression on to the Leo Uplift of the West African Craton of some 200 km is indicated. The volcanic rocks may belong to the same cycle of surface rock generation or relate to the younger, widespread, Triassic magmatic event.

scholarly journals Chemical alteration and preservation of sedimentary/organic nitrogen isotope signatures in a 2.7 Ga seafloor volcanic sequence

2017 ◽  
Vol 18 (3) ◽  
pp. 235-250 ◽  
Author(s):  
L. D. Anderson ◽  
G. E. Bebout ◽  
M. R. M. Izawa ◽  
N. J. Bridge ◽  
N. R. Banerjee
Keyword(s):  
Organic Nitrogen ◽  
Volcanic Rocks ◽  
Nitrogen Isotope ◽  
Igneous Rocks ◽  
Biogeochemical Processes ◽  
Potential Utility ◽  
Rock Interaction ◽  
Late Archaean ◽  
Abitibi Greenstone Belt ◽  
And Shifts

AbstractMassive to lobate volcanic flows and brecciated hyaloclastite units in the Abitibi greenstone belt allow investigation of Late Archæan seafloor alteration and associated incorporation into these rocks of nitrogen (N) biogeochemical signatures. In this suite (the Blake River Group), hyaloclastite units containing putative microbial ichnofossils are particularly enriched in large-ion lithophile elements (K, Rb, Ba, Cs), B, and Li, consistent with their having experienced the greatest fluid–rock interaction during subseafloor hydrothermal alteration. Similarly, silicate-δ18O and δ15N values for samples from the hyaloclastites show the greatest shifts from plausible magmatic values. The chemical and isotopic patterns in these tholeiitic igneous rocks greatly resemble those in modern altered seafloor basalts, consistent with the preservation of an Archæan seafloor alteration signature. The N enrichments and shifts in δ15N appear to reflect stabilization of illite and interaction with fluids carrying sedimentary/organic signatures. Enrichments of N (and the δ15N of this N) in altered glass volcanic rocks on Earth's modern and ancient seafloor point to the potential utility of N for tracing past and present biogeochemical processes in similar rocks at/near the Mars surface.

scholarly journals Not simply volcanoes – The Geoheritage of the Cretaceous System in the Land of the Extinct Volcanoes Geopark, West Sudetes (SW Poland)

2021 ◽  
pp. 3-22
Author(s):  
Piotr Migoń ◽  
Edyta Pijet-Migoń
Keyword(s):  
Large Scale ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
The Other ◽  
The West ◽  
Qualitative And Quantitative ◽  
Deformation Structures ◽  
Volcanic Geoheritage ◽  
West Sudetes ◽  
Sw Poland

Volcanic geoheritage is emphasized as the main asset and distinctive characteristic of the Land of Extinct Volcanoes Geopark in the West Sudetes (SW Poland). However, the geoheritage values of the region are not limited to the legacy of ancient volcanism but include various other elements. This paper explores the contribution of geosites that expose sedimentary rocks of Cretaceous age and landforms developed upon these rocks. Six localities from the Geopark area, included in the comprehensive regional inventory of geosites, are presented. They represent natural and man-made sandstone outcrops and show, among others, lithological variations, small- and large-scale post-sedimentary deformation structures, landforms arising from differential weathering (rock shelters, honeycombs), boulder fields and a sandstone xenolith in volcanic rocks. Next, five localities from outside the Geopark, but still within the Pogórze Kaczawskie region, are described. Qualitative and quantitative evaluation of both groups is attempted, and the results show that, in general, geosites within the Geopark rank higher. However at least two from the other group also have significant geotourist potential. Finally, a brief comparative analysis with other parts of the Sudetes, where Cretaceous sedimentary rocks occur, is offered.

Geochemical and isotopic characteristics of Early Silurian clastic sequences in Antigonish Highlands, Nova Scotia, Canada: constraints on the accretion of Avalonia in the Appalachian – Caledonlde Orogen

1996 ◽  
Vol 33 (3) ◽  
pp. 379-388 ◽  
Author(s):  
J. Brendan Murphy ◽  
J. Duncan Keppie ◽  
Mary Pat Cude ◽  
Jarda Dostal ◽  
John W. F. Waldron
Keyword(s):  
Nova Scotia ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Structural Data ◽  
Strike Slip ◽  
Late Ordovician ◽  
Igneous Rocks ◽  
Oblique Collision ◽  
Isotopic Signatures ◽  
Clastic Sedimentary

Avalonia is a terrane that accreted to Laurentia–Baltica during the development of the Appalachian–Caledonide Orogen. Interpretations of the timing of accretion have been constrained by comparing faunal affinities, overstep sequences, age and kinematics of inferred accretionary deformational events, and controversial paleomagnetic data. We show that the time of accretion of Avalonia may also be constrained by contrasts in the geochemical and isotopic signatures of its igneous rocks (which reflect the characteristics of the underlying continental basement and mantle) and sedimentary rocks (which reflect provenance). Early Silurian clastic sedimentary rocks of the Beechill Cove Formation, Antigonish Highlands, Nova Scotia, were deposited on Avalonian crust. The formation predominantly consists of approximately 80 m of siltstones and shales deposited in a nearshore environment and derived from the northeast. Their age is constrained by paleontological data and by directly underlying Late Ordovician – Early Silurian bimodal volcanic rocks that have typically Avalonian geochemical signatures. In comparison with typical Avalonian rocks, the Beechill Cove sediments are characterized by high SiO2, Ce/Yb, and initial 87Sr/86Sr, low Fe2O3, MgO, and TiO2, and strongly negative εNd(ur). These characteristics cannot be attributed to erosion of underlying Avalonian basement or coeval volcanic rocks and are consistent with derivation via significant transport from radiogenically enriched continental crust. εNd data are typical of Grenvillian basement compositions and suggest that the Beechill Cove sedimentary rocks were derived from an adjacent landmass with Grenvillian crust. The data, in conjunction with paleocontinental reconstructions and recent geochronological and structural data from the northern Appalachians, suggest that the Caledonide orogenic belt is the most likely source. Deposition of the Beechill Cove Formation is inferred to have occurred in an intracontinental basin associated with strike-slip tectonics during the oblique collision of the Avalon with Laurentia–Baltica.

Lithostratigraphy of the Palaeoproterozoic Hekpoort Formation (Pretoria Group, Transvaal Supergroup), South Africa

2020 ◽  
Vol 123 (4) ◽  
pp. 655-668
Author(s):  
N. Lenhardt ◽  
W. Altermann ◽  
F. Humbert ◽  
M. de Kock
Keyword(s):  
South Africa ◽  
Bushveld Complex ◽  
Sedimentary Rocks ◽  
Type Locality ◽  
Large Igneous Province ◽  
Braided River ◽  
River Systems ◽  
The West ◽  
Igneous Province ◽  
Transvaal Supergroup

Abstract The Palaeoproterozoic Hekpoort Formation of the Pretoria Group is a lava-dominated unit that has a basin-wide extent throughout the Transvaal sub-basin of South Africa. Additional correlative units may be present in the Kanye sub-basin of Botswana. The key characteristic of the formation is its general geochemical uniformity. Volcaniclastic and other sedimentary rocks are relatively rare throughout the succession but may be dominant in some locations. Hekpoort Formation outcrops are sporadic throughout the basin and mostly occur in the form of gentle hills and valleys, mainly encircling Archaean domes and the Palaeoproterozoic Bushveld Complex (BC). The unit is exposed in the western Pretoria Group basin, sitting unconformably either on the Timeball Hill Formation or Boshoek Formation, which is lenticular there, and on top of the Boshoek Formation in the east of the basin. The unit is unconformably overlain by the Dwaalheuwel Formation. The type-locality for the Hekpoort Formation is the Hekpoort farm (504 IQ Hekpoort), ca. 60 km to the west-southwest of Pretoria. However, no stratotype has ever been proposed. A lectostratotype, i.e., the Mooikloof area in Pretoria East, that can be enhanced by two reference stratotypes are proposed herein. The Hekpoort Formation was deposited in a cratonic subaerial setting, forming a large igneous province (LIP) in which short-termed localised ponds and small braided river systems existed. It therefore forms one of the major Palaeoproterozoic magmatic events on the Kaapvaal Craton.

KERCH STRAIT IN KAMYSH-BURUN SPIT AREA: HIGH-RESOLUTION SEISMOACOUSTIC APPROACH

2018 ◽  
Author(s):  
В. Зинько ◽  
V. Zin'ko ◽  
А. Зверев ◽  
A. Zverev ◽  
М. Федин ◽  
...  
Keyword(s):  
High Resolution ◽  
Fracture Zone ◽  
Sedimentary Cover ◽  
Sedimentary Rocks ◽  
The West ◽  
Early Generation ◽  
The Third ◽  
Azov Sea ◽  
Kerch Strait ◽  
Made In

The seismoacoustical investigations was made in the western part of the Kerch strait (Azov sea) near Kamysh-Burun spit. The fracture zone with dislocated sedimentary rocks layers and buried erosional surface was revealed to the west of spit. Three seismofacial units was revealed to the east of spit. The first unit was modern sedimentary cover. The second ones has cross-bedding features and was, probably, the part of early generation of Kamysh-Burun spit, which lied to the east of its modern position. The lower border of the second unit is the erosional surface supposed of phanagorian age. The third unit is screened by acoustic shedows in large part.

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