The structural geometry and geological history of Archean rocks at Kenora, north-western Ontario—a proposed type area for the Kenoran Orogeny

1981 ◽  
Vol 18 (6) ◽  
pp. 1075-1091 ◽  
Author(s):  
Charles F. Gower ◽  
Paul M. Clifford
Keyword(s):  
Structural Level ◽  
Geological History ◽  
Structural Geometry ◽  
Type Area ◽  
Igneous Origin ◽  
Isotopic Studies ◽  
Facies Metamorphism ◽  
Major Fault ◽  
History Of ◽  
North Western

The Kenora area, at the south margin of the English River Subprovince, consists of polydeformed gneisses intruded by granitoid plutons, some of which are also deformed. The gneisses are mainly tonalites of igneous origin, but contain remnants of an earlier, dominantly mafic, supracrustal sequence and severely deformed pegmatites.Within the gneissosity are intrafolial F1 folds subsequently refolded by tight-to-open F2 folds. Major F2 folds can be delineated from the geometry and distribution of minor F2 structures. During deformation the area was subjected to upper amphibolite facies metamorphism (650–750 °C, 4–7 kbar (400–700 MPa)) with K-feldspar megacrysts and garnet developed in the deeper levels. Major F2 folds are refolded in a rim synform (F3), which developed synchronously with the emplacement of the Dalles granodiorite, an event that also created a plunge culmination uplifting part of the deeper K-feldspar megacryst – garnet structural level. Cumulative apparent dextral displacement of 6 km in two periods of movement, related partly to the emplacement of the Dalles granodiorite, is suggested for a major fault 1.5 km north of, and parallel to, the English River – Wabigoon Subprovince interface. Open, upright F4 folds caused buckling of dioritic dikes and pegmatites. Later deformation involved minor faulting and joint development.Rb–Sr isotopic studies indicate that this geological history took place within about 150 Ma with most activity over by 2600 Ma. It is proposed that this should be selected as the type area for the Kenoran Orogeny.

Geochemistry and geochronology of the gneisses east of the Southern Rocky Mountain Trench, near Valemount, British Columbia

1985 ◽  
Vol 22 (7) ◽  
pp. 980-991
Author(s):  
V. E. Chamberlain ◽  
R. St J. Lambert ◽  
J. G. Holland
Keyword(s):  
Rocky Mountain ◽  
Tholeiitic Basalt ◽  
Geochemical Data ◽  
Geological History ◽  
Calc Alkaline ◽  
Geochronological Data ◽  
Alkaline Granite ◽  
Facies Metamorphism ◽  
Major Fault ◽  
Southern Rocky Mountain

Petrographic, geochemical, and geochronological data are presented on the gneisses of the Bulldog Creek block, the Mount Blackman block, and the Hugh Allan Creek block, which lie to the east of the Southern Rocky Mountain Trench (SRMT) south of Valemount, British Columbia.Petrographical and geochemical data, especially immobile-trace-element ratios (Nb: Y, Ti: Zr), and CaO versus Y and AFM plots are used to deduce the probable origins and protoliths of the gneisses. The Mount Blackman block consists of a psammitic paragneiss, probably derived from an immature arkosic sedimentary protolith, intruded by sills of tholeiitic basalt, now amphibolites. The Bulldog Creek block consists of felsic orthogneisses of calc-alkaline affinity, which are structurally concordant with mafic orthogneisses of possible tholeiitic basalt parentage. The Hugh Allan Creek block consists of a felsic orthogneiss with a probable alkaline granite protolith.Rb–Sr, and some U–Pb analyses show that each block has experienced a separate geological history. The Mount Blackman block psammitic paragneisses are the only analysed gneisses east of SRMT with a probable Archean Rb–Sr model crustal residence age. U–Pb analyses on zircons from these gneisses give a 1950 Ma minimum source rock age, and Rb–Sr whole-rock analyses suggest a 1860 ± 50 Ma age for amphibolite-facies metamorphism of both paragneisses and amphibolites. The Bulldog Creek block gneisses have a metamorphic age of at least 640 Ma, but their Rb–Sr systematics have been extensively disturbed, possibly during Mesozoic retrogressive metamorphism. The Hugh Allan Creek block gneisses have a Rb–Sr model crustal residence age of ~900 Ma and a metamorphic age of 805 ± 11 Ma. It is not possible to correlate any of these lithologies or events across the SRMT with the Malton block, and it is concluded that the SRMT is the site of a major fault or faults at this latitude.

LATE QUATERNARY GEOLOGICAL HISTORY OF RIO GRANGE DO SUL COASTAL PLAIN, SOUTHERN BRAZIL

2000 ◽  
Vol 30 (3) ◽  
pp. 474-476 ◽  
Author(s):  
LUIZ JOSÉ TOMAZELLI ◽  
SÉRGIO REBELLO DILLENBURG ◽  
JORGE ALBERTO VILLWOCK
Keyword(s):  
Coastal Plain ◽  
Late Quaternary ◽  
Geological History ◽  
Southern Brazil ◽  
History Of

Distribution, systematics and nomenclature of the three taxa of Common Stonechats (Aves, Passeriformes, Muscicapidae, Saxicola) that breed in the Caucasian region

2020 ◽  
Vol 29 (1) ◽  
pp. 33-57
Author(s):  
V.M. Loskot ◽  
G.B. Bakhtadze
Keyword(s):  
Geographic Distribution ◽  
Habitat Preferences ◽  
Junior Synonym ◽  
Type Locality ◽  
Diagnostic Features ◽  
Western Turkey ◽  
Geographical Variations ◽  
History Of ◽  
The Individual ◽  
North Western

Geographic distribution and habitat preferences of Saxicola rubicola rubicola (Linnaeus, 1766), S. maurus variegatus (S.G. Gmelin, 1774), and S. m. armenicus (Stegman, 1935) inhabiting the Caucasian Isthmus and adjacent areas are described in detail. We examined the individual, sexual, age, seasonal and geographical variations of seven main diagnostic features of both plumage and morphometrics (exactly, the length of wing and tail) using 381 skin specimens. Substantially improved diagnoses of S. m. variegatus and S. m. armenicus are provided. After a thorough examination of the materials and history of the expedition of Samuel Gmelin in 1768–1774, and his description of Parus variegatus, it was concluded that the type locality of this taxon was the vicinity of Shamakhi in Azerbaijan not Enzeli in North-Western Turkey. It is also shown the fallacy of the recently proposed attribution of the holotype of the northern subspecies S. m. variegatus to the southern taxon S. m. armenicus and synonymisation of these names, as well as the replacement of the name S. m. variegatus by its junior synonym S. m. hemrichii Ehrenberg, 1833 for the northern subspecies.

Geoinformation Mapping Through the Types of Geological and Geomorphological Structure of the Katun Valley (Altay Mountains) Based on Morphometric Indicators

2018 ◽  
Vol 938 (8) ◽  
pp. 38-43
Author(s):  
S.A. Kotler ◽  
I.D. Zolnikov ◽  
D.V. Pchelnikov
Keyword(s):  
Morphometric Parameters ◽  
Morphometric Parameter ◽  
Geological History ◽  
Mountain Rivers ◽  
Quaternary Period ◽  
Modern Variety ◽  
Altay Mountains ◽  
History Of

The types of geological and geomorphological structure of the Katun valley are distinguished in the work. For this, a method of geoinformation mapping using morphometric indicators of the valley’s width and meandering of the channel was developed. The morphometric parameter of the valley’s width was calculated as the total area of terraces. As the morphometric parameters of the channel’s meandering, the angles of the river segments’ deviation relative to each other were calculated. Conjugated analysis of these morphometric indicators enabled identifying 18 morphotypes. These morphotypes according to the geological and geomorphological structure of the valley were combined into 4 classes. Separation of the Katun valley in certain classes and morphotypes is due to the different geological history of these sites during the Quaternary period. The most important reasons predetermining the modern variety of geological and geomorphological types of the valley are neotectonic movements and exogenous phenomena (glaciers, dam lakes, landslides, etc.) naturally localized in the space from the upstream of the river to its exit into the foothills. The developed method can be applied for quantitative morphometric classification of the mountain rivers’ valleys in other regions.

BORON ISOTOPES AS TRACERS OF THE TECTONIC ORIGIN AND GEOLOGICAL HISTORY OF SERPENTINITES IN SUBDUCTION AND SUTURE ZONES

2016 ◽  
Author(s):  
Celine Martin ◽  
◽  
George E. Harlow ◽  
George E. Harlow ◽  
George E. Harlow ◽  
...  
Keyword(s):  
Boron Isotopes ◽  
Geological History ◽  
History Of ◽  
Tectonic Origin

Beyond Wallace: a new lineage of Chrysorthenches (Lepidoptera: Yponomeutoidea: Glyphipterigidae) reveals a journey tracking its host-plants, Podocarpus (Pinopsida: Podocarpaceae)

2020 ◽  
Vol 190 (2) ◽  
pp. 709-736
Author(s):  
Jae-Cheon Sohn ◽  
Shigeki Kobayashi ◽  
Yutaka Yoshiyasu
Keyword(s):  
Maximum Likelihood ◽  
East Asia ◽  
Host Plants ◽  
Morphological Characters ◽  
Species Group ◽  
Geological History ◽  
Dna Barcodes ◽  
History Of ◽  
Species Groups ◽  
Maximum Likelihood Phylogeny

Abstract A northward trans-Wallacean radiation is demonstrated for Chrysorthenches, a member of the Orthenches group. Here we review Chrysorthenches and allied genera resulting in a generic transfer of Diathryptica callibrya to Chrysorthenches and two new congeners: C. muraseaeSohn & Kobayashisp. nov. from Japan and C. smaragdinaSohnsp. nov. from Thailand. We review morphological characters of Chrysorthenches and allied genera, and find polyphyly of Diathryptica and the association of the Orthenches-group with Glyphipterigidae. These findings were supported in a maximum likelihood phylogeny of DNA barcodes from ten yponomeutoids. We analysed 30 morphological characters for 12 species of Chrysorthenches, plus one outgroup, via a cladistic approach. The resulting cladogram redefined two pre-existing Chrysorthenches species-groups and identified one novel lineage: the C. callibrya species-group. We review the host associations between Chrysorthenches and Podocarpaceae, based on mapping the working phylogenies. Our review suggests that ancestral Chrysorthenches colonized Podocarpus and later shifted to other podocarp genera. Biogeographical patterns of Chrysorthenches show that they evolved long after the Podocarpaceae radiation. Disjunctive trans-Wallacean distribution of the C. callibrya species-group is possibly related to the tracking of their host-plants and the complicated geological history of the island-arc system connecting Australia and East Asia.

scholarly journals The geological history of the Lake Rudolf Basin, Kenya colony

1939 ◽  
Vol 229 (560) ◽  
pp. 219-274 ◽  
Keyword(s):  
Rift Valley ◽  
Public Works ◽  
General Description ◽  
Geological History ◽  
East African ◽  
The Public ◽  
Geographical Society ◽  
History Of ◽  
African Rift ◽  
At Home

The Lake Rudolf Rift Valley Expedition was designed to carry out many different lines of investigation in the Lake Rudolf Basin. One of the chief of these was a study of the geological history of that part of the East African Rift Valley. The expedition was assisted financially by The Royal Society, The Geological Society of London, The Royal Geographical Society, The Percy Sladen Trustees and the Geographical and Geological Sections of the British Association. A general description of the activities of the Expedition was given in a paper read before the Royal Geographical Society (Fuchs 1935). Owing to the tragic loss of two members of the expedition, Dr W. S. Dyson and Mr W. R. H. Martin, two fruitless months were spent searching for them. Consequently a great amount of the work planned for the east side of the lake had to be abandoned. Nevertheless, the considerable distance travelled within the 50,000 sq. miles of the Rudolf Basin has enabled me to make out the chief events of its geological history. I am very much indebted to all those who assisted us in the field and at home, in particular to the Kenya Government, the Officers of the King’s African Rifles, and Mr H. L. Sikes of the Public Works Department; I would also like to thank Mr A. M. Champion, Provincial Commissioner of Turkana, who wholeheartedly assisted us in every way possible both in the field and at home, for he has placed at my disposal his own excellent topographical maps and his extensive observations on the geology of the area. I am also deeply indebted to Professor O. T. Jones, Mr Henry Woods and Mr W. Campbell Smith for their criticisms. Mr Campbell Smith has also given me provisional identifications of the rocks.

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