A fault-bounded outlier of Archean clastic rocks near Thunder Bay, Ontario

1988 ◽  
Vol 25 (1) ◽  
pp. 152-157
Author(s):  
M. M. Kehlenbeck
Keyword(s):  
Sedimentary Sequence ◽  
Clastic Rocks ◽  
Basin Structure ◽  
Thunder Bay ◽  
Crenulation Cleavage ◽  
Metavolcanic Rocks ◽  
Internal Disruption ◽  
Clastic Sedimentary

A fault-bounded clastic sedimentary sequence occurs as an outlier in contact with a terrane of Archean metavolcanic rocks. In addition to a regional penetrative fabric, the rocks of the clastic sequence possess a crenulation cleavage that is axial planar to a set of minor, north-plunging folds. Abundant faulting of the clastic rocks has resulted in significant internal disruption of the sequence as a whole and suggests it is a down-faulted block of a basin structure.

Geochronology of detrital zircons from the Elzevir and Frontenac terranes, Central Metasedimentary Belt, Grenville Province, Ontario

1993 ◽  
Vol 30 (3) ◽  
pp. 465-473 ◽  
Author(s):  
E. Anne Sager-Kinsman ◽  
R. R. Parrish
Keyword(s):  
Detrital Zircons ◽  
Time Interval ◽  
Adirondack Mountains ◽  
Sedimentary Sequence ◽  
Grenville Province ◽  
Clastic Rocks ◽  
Metavolcanic Rocks ◽  
Group A ◽  
Clastic Sedimentary ◽  
Detrital Zircon Ages

The Central Metasedimentary Belt (CMB) of the Grenville Province contains metasedimentary sequences belonging to a number of distinct tectono-stratigraphic terranes whose depositional ages are poorly known. This study provides information on not only the provenance, but also the maximum age of clastic rocks in two of these terranes, the Elzevir Terrane on the northwest and the Frontenac Terrane to its southeast, adjacent to the Adirondack Mountains of New York.The Flinton Group, a component of the Elzevir Terrane, is a distinctive, mostly clastic, sedimentary sequence that unconformably overlies igneous and metavolcanic rocks of the main part of Elzevir Terrane of the CMB. Analyzed zircons from quartzose metasediments of the Flinton Group are 0–2% discordant and range in age from 1150 to 1335 Ma, with older rounded grains at 1461 ± 5 and 1877 ± 3 Ma. The quartzite was therefore deposited after ca. 1150 Ma, indicating that the Flinton Group is more than 100 Ma younger than the intrusion of the underlying Elzevir batholith. We speculate that 1150–1180 Ma zircons within the Flinton Group were derived from plutons in the Frontenac Terrane to the southeast, implying that the Elzevir and Frontenac terranes were contiguous during Flinton Group deposition. Subsequent metamorphism of the Flinton Group occured between 1150 and 1080 Ma.The high-grade Frontenac Terrane of the CMB lies southeast of Elzevir Terrane, and contains marble associated with pelitic gneiss and quartzite, as well as granitic intrusive rocks; it resembles a metamorphosed continental margin sedimentary sequence. U–Pb analyses of zircons from quartzites from two different localities are generally less than 5% discordant, but show stronger evidence for Grenvillian Pb loss than zircons from the Flinton Group. 207Pb/206Pb ages range from 1493 to 2580 Ma, with one analysis (2% discordant) at 1306 ± 16 Ma, another at 3185 ± 3 Ma, and a cluster of ages between 1745 and 1892 Ma. Detrital zircon ages are, for the most part, distinctly older than in the Flinton Group. The age of this quartzite sequence is tentatively regarded as less than ca. 1300 Ma (based on one grain), but is certainly less than 1500 Ma. It could therefore have been deposited during the same time interval as the 1.2–1.3 Ga metasedimentary and metavolcanic rocks of the Elzevir Terrane. Although Frontenac Terrane experienced metamorphism along with Elzevir Terrane around 1.1 Ga, the principle metamorphic culmination in the Frontenac occurred prior to 1170 Ma.

scholarly journals PHYSICAL-MECHANICAL PROPERTIES OF METAVOLCANIC ROCKS OF THE MOUNTAIN CRIMEA

2018 ◽  
Vol 13 (4-5) ◽  
pp. 36-51
Author(s):  
J. V. Frolova ◽  
V. V. Ladygin ◽  
E. M. Spiridonov ◽  
G. N. Ovsyannikov
Keyword(s):  
Mechanical Properties ◽  
Magnetic Susceptibility ◽  
Volcanic Rocks ◽  
Low Grade ◽  
Secondary Mineral ◽  
Grade Metamorphism ◽  
Clastic Rocks ◽  
Metavolcanic Rocks ◽  
Physical Density ◽  
Characteristic Values

The article considers the petrogenetic features of the volcanogenic rocks of the Middle Jurassic age of the Mountain Crimea and analyzes their influence on physical (density, porosity, water absorption, and magnetic susceptibility) and physical-mechanical properties (strength, modulus of elasticity, and Poisson's ratio). Among volcanogenic strata there are subvolcanic, effusive and volcanogenic-clastic rocks. All volcanic rocks were altered under the influence of the regional low-grade metamorphism of the zeolite and prehnite-pumpellyite facies, which resulted in a greenstone appearance. Among the secondary mineral the most common are albite, chlorite, quartz, adularia, sericite, calcite, pumpellyite, prenite, zeolites, epidote, sphene, and clay minerals. It is shown that low-grade metamorphism is characterized by heterogenious transformations: there are both slightly modified, practically fresh differences, and fully altered rocks. Tuffs are usually altered to a greater extent than effusive and subvolcanic rocks. In general, effusive and volcanogenic-clastic rocks differ markedly in their physicalmechanical properties, which is due to the peculiarities of their formation: the former are substantially more dense and stronger, less porous and compressible. However, these differences are leveled as a result of intensive changes in mineral composition and porosity in the process of low-grade metamorphism. The most characteristic values of metavolcanite properties were revealed. It is shown that among all studied parameters, the magnetic susceptibility most clearly correlates with the degree of rocks alteration.

scholarly journals Prelithification and synlithification tectonic foliation development in a clastic sedimentary sequence

Geology ◽  
2016 ◽  
Vol 44 (4) ◽  
pp. 291-294 ◽  
Author(s):  
Patrick A. Meere ◽  
Kieran F. Mulchrone ◽  
Dave J. McCarthy ◽  
Martin J. Timmerman ◽  
John F. Dewey
Keyword(s):  
Sedimentary Sequence ◽  
Clastic Sedimentary

Recently exposed vegetation reveals Holocene changes in the extent of the Quelccaya Ice Cap, Peru

2009 ◽  
Vol 72 (2) ◽  
pp. 157-163 ◽  
Author(s):  
Aron M. Buffen ◽  
Lonnie G. Thompson ◽  
Ellen Mosley-Thompson ◽  
Kyung In Huh
Keyword(s):  
Radiocarbon Dating ◽  
Sedimentary Sequence ◽  
Western Margin ◽  
The Past ◽  
Ice Cap ◽  
Plant Samples ◽  
Clastic Sedimentary ◽  
Quelccaya Ice Cap ◽  
Vegetation Samples

AbstractRadiocarbon dating of well-preserved, in-place vegetation exposed by the retreating Quelccaya Ice Cap of southeastern Peru constrains the last time the ice cap's extent was smaller than at present. Seventeen plant samples from two sites along the central western margin collectively date to 4700 and 5100 cal yr BP and strongly indicate that current ice cap retreat is unprecedented over the past ∼ 5 millennia. Seventeen vegetation samples interbedded in a nearby clastic sedimentary sequence suggest ice-free conditions at this site from ∼ 5200 to at least ∼ 7000 cal yr BP, and place minimum constraint on early- to mid-Holocene ice cap extent.

scholarly journals Conodont biostratigraphy and depositional history of the Darriwilian (Middle Ordovician) Pygodus serra Zone, western Argentina

2019 ◽  
Vol 46 (2) ◽  
pp. 336
Author(s):  
Susana Heredia ◽  
Ana Mestre ◽  
Cintia Kaufmann ◽  
Tatiana Soria
Keyword(s):  
Variable Amount ◽  
Depositional History ◽  
Middle Ordovician ◽  
Clastic Rocks ◽  
Stratigraphic Record ◽  
Conodont Zone ◽  
History Of ◽  
San Rafael ◽  
Clastic Sedimentary ◽  
Almost All

The stratigraphic record of the Pygodus serra conodont Zone in the Cuyania terrane of western Argentina is discussed in this contribution. Three well-known sections were sampled in Precordillera and the San Rafael Block. The studied successions are composed mainly by clastic rocks with variable amount of carbonate. The lower part of Ponón Trehué Formation of the San Rafael Block and the La Cantera Formation of the Eastern Precordillera are composed of conglomerate and represent the input of coarse clastic deposits to the Cuyania basin. The Los Azules Formation, in Los Amarillitos section of the Central Precordillera, has a massive sandstone bed with carbonate nodules in a section largely of black shale. Key conodonts recovered from these sections indicate a correlation to the E. robustus and E. lindstroemi subzones of the Pygodus serra Zone of the upper Darriwillian Stage (Middle Ordovician Series). The species in the Ponón Trehué Formation are almost all the same as those in the Precordillera sections. Correlation of the clastic sedimentary successions between the three sections indicates that vertical facies changes were not controlled by eustasy. More likely, they were controlled by differential tectonic subsidence.

Structural cross sections based on a gravity survey of parts of the Quetico and Wawa subprovinces near Thunder Bay, Ontario

1990 ◽  
Vol 27 (2) ◽  
pp. 187-199 ◽  
Author(s):  
M. M. Kehlenbeck ◽  
S. P. Cheadle
Keyword(s):  
Cross Sections ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Gravity Models ◽  
Low Grade ◽  
Thunder Bay ◽  
Metavolcanic Rocks ◽  
Dimensional Gravity ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

In this study, gravity data from 350 new gravity stations are combined with those from 50 previously surveyed stations in a detailed Bouguer anomaly map of a portion of the Quetico and Wawa subprovinces north and west of Thunder Bay, Ontario.In general, high gravity values characterize the southern and southwestern part of the area where metavolcanic rocks of the Wawa subprovince dominate. Much of the Quetico subprovince forms a broad gravitational low, reflecting extensive exposures of gneisses, schists, and migmatites. Well-defined gravity lows are associated with several granitic intrusive bodies.Three- and [Formula: see text]-dimensional gravity models of subsurface configuration of the density contrasts, representative of major rock units, indicate a trough-like structure for the metavolcanic rocks of the Wawa subprovince. This trough-like structure is flanked by a domical feature in the granitoid rocks to the south. North of the metavolcanic rocks, a succession of low-grade greywackes and slates occupies a basinal structure. These structures form the principal subsurface elements of the Wawa subprovince in this area.The gneisses, schists, and migmatites of the Quetico subprovince form a thick, southward-dipping, wedge-shaped structure that may extend under the structures of the Wawa subprovince. This wedge-shaped structure is underlain by a model unit of greater density representative of mafic gneisses and amphibolites. The denser substratum is modelled with local abrupt changes in dip corresponding in position with the Quetico and Hawkeye Lake faults.

The transition from dyke to sill in the Otish Mountains, Quebec; relations to host-rock characteristics

1987 ◽  
Vol 24 (1) ◽  
pp. 110-116 ◽  
Author(s):  
E. H. Chown ◽  
Guy Archambault
Keyword(s):  
Host Rock ◽  
Sedimentary Basin ◽  
Superior Province ◽  
Sedimentary Sequence ◽  
Grenville Province ◽  
Clastic Rocks ◽  
The North ◽  
Dyke Swarms ◽  
East West

The Otish gabbro sills intrude Aphebian clastic rocks lying uncanformably on the Archean rocks of the Superior Province close to its juncture with the Grenville Province. The sills are undated but by inference may be ca. 1750 Ma. Two dyke swarms are known in the vicinity, the 1950 Ma, northwest-trending Mistassini dykes and a northeast-trending swarm of unknown age extending 600 km from Senneterre to the Otish Mountains and possibly another 300 km to the northeast. The trends of feeder dykes to the Otish sills are physically compatible with the dominant northeast dykes, which are therefore considered to be the feeders and should be called the Otish dykes.The Otish sills appear to be a unique occurrence along the 900 km dyke trend, possibly, but not entirely because of the chances of preservation. The general form of the Otish sill complex is a triangle bounded on the north by the east–west lip of the sedimentary basin, on the southwest by a northwest-trending Otish feeder dyke, and on the southeast by the underlying northeast feeder dykes. These dykes segment the sills into a series of four or five separate intrusive complexes, small in the northwest and becoming larger to the southeast. The regular inclination of tension fractures in the basal chilled margin of the sills suggests a crude pattern of flow from the feeder dykes inward to the centre of the sheets.Interpretation of the sedimentary sequence indicates that the Otish clastics were deposited higher on the paleoslope than the Mistassini carbonates. Although few dykes intrude the deeper basin, the magma rose and formed sills within the higher sequence. This variation may be explained by the different mechanical character of the two types of cover rock controlling the dyke behaviour. The relatively plasto-viscous Mistassini carbonate–shale sequence resisted the formation of tension fractures, whereas the brittle elastics opened easily, allowing the magma to rise into the stratified sequence, forming the sill complexes.

scholarly journals The northern termination of the Cache Creek terrane in Yukon: Middle Triassic arc activity and Jurassic–Cretaceous structural imbrication

2020 ◽  
Vol 57 (2) ◽  
pp. 227-248
Author(s):  
Luke Bickerton ◽  
Maurice Colpron ◽  
H. Daniel Gibson ◽  
Derek Thorkelson ◽  
James L. Crowley
Keyword(s):  
Lower Jurassic ◽  
Coarse Grained ◽  
Second Phase ◽  
Clastic Rocks ◽  
South Central ◽  
Metavolcanic Rocks ◽  
Two Samples ◽  
Intrusive Rocks ◽  
Siliciclastic Rocks ◽  
Back Arc

The northernmost part of the Cache Creek terrane lies in south-central Yukon and comprises metavolcanic rocks, hemipelagic chert and shale, newly identified volcaniclastic and clastic rocks (Michie formation, informal), pyroxenite and gabbro intrusive rocks with an arc to back-arc geochemical signature, as well as tectonized and serpentinized ultramafic rocks. The proximally sourced Michie formation yielded zircon from two samples with unimodal peaks at 245.85 ± 0.07 and 244.64 ± 0.08 Ma. These dates are likely close to the depositional ages and compare favourably with those from the Kutcho assemblage of northern British Columbia. The Michie formation is exposed along the northwestern flank of Mount Michie and represents singular detrital input from a nearby eroding island-arc. The Cache Creek terrane rocks are imbricated with epiclastic and carbonate rocks of the Stikinia and Lower Jurassic siliciclastic rocks of the synorogenic Whitehorse trough. This imbrication records two compressional deformation phases in the region: (1) an initial phase of west-verging thrusting along the Judas Mountain fault that placed the Cache Creek terrane rocks over the arc and basinal rocks of Stikinia and Whitehorse trough; and (2) a second phase of east-verging thrusting along the Mount Michie fault that repositioned rocks of Stikinia and the Whitehorse trough structurally above those of the Cache Creek terrane. Deformation in the centre of the study area was followed by emplacement of a coarse-grained syenite that yielded 40Ar/39Ar biotite and muscovite cooling ages of 165–160 Ma.

Pleistocene echinoid (Echinodermata) fauna from southeast Jamaica

1994 ◽  
Vol 68 (2) ◽  
pp. 351-358 ◽  
Author(s):  
Stephen K. Donovan ◽  
Harold L. Dixon ◽  
Ron K. Pickerill ◽  
Eamon N. Doyle
Keyword(s):  
Sedimentary Sequence ◽  
Upper Pleistocene ◽  
Lower Pleistocene ◽  
The Caribbean ◽  
Clastic Sedimentary

A previously undocumented echinoid fauna occurs in the terrigenous clastic sedimentary sequence of the Old Pera Beds (Lower Pleistocene) and the overlying Port Morant Formation (Upper Pleistocene) at Old Pera, parish of St. Thomas, southeast Jamaica. The fauna is comprised of complete tests (particularly from two horizons in the Port Morant Formation), test fragments, and radioles, and includes: Cidaris (Tretocidaris) bartletti (A. Agassiz); Eucidaris tribuloides (Lamarck); diadematoid indet. gen. and sp.; Echinometra viridis A. Agassiz; Echinometra? sp.; Clypeaster rosaceus (Linné); a juvenile C. subdepressus? (Gray); mellitid indet. gen. and sp.; clypeasteroid sp.; Schizaster doederleini Chesher; Meoma ventricosa (Lamarck); and irregular indet. gen. and sp. Schizaster doederleini is still extant in the Caribbean, but is not known to live in Jamaican waters. Schizaster doederleini and Meoma ventricosa are the first nominal spatangoids to be reported from the Jamaican Pleistocene.

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