Sedimentology, Stratigraphy, and Crustal Evolution of the Archean Greenstone Belt near Sioux Lookout, Ontario

1973 ◽  
Vol 10 (6) ◽  
pp. 817-845 ◽  
Author(s):  
Colin C. Turner ◽  
Roger G. Walker
Keyword(s):  
Greenstone Belt ◽  
Large Scale ◽  
Depositional Environment ◽  
Final Section ◽  
Volcanic Rocks ◽  
Alluvial Fan ◽  
Facies Associations ◽  
Feature Based ◽  
Archean Greenstone Belt ◽  
Coastal Deposits

In the Archean greenstone belt at Sioux Lookout, N.W. Ontario, a lowermost belt of volcanic rocks is unconformably overlain by sediments of the Abram Group. Our mapping has subdivided the Abram Group into three formations. The lowest (Ament Bay Formation) consists of interbedded conglomerates and sandstones. The sandstones contain large-scale cross-stratification, and the conglomerates and sandstones both lack graded bedding. The depositional environment was a subaerial alluvial fan—this is the first description of such a feature based upon modern sedimentological work in Archean rocks. The Daredevil Formation conformably overlies the Ament Bay Formation, and is composed of felsic and basic tuffs, and some interbedded turbidites. The uppermost (Little Vermilion) Formation is composed entirely of turbidites.The petrography of the sand, and large clasts, in the Ament Bay Formation indicates derivation from a dominantly granodioritic terrain. Some granodiorite boulders contain greenstone xenoliths, implying intrusion of the granodiorite after formation of the lowermost belt of volcanic rocks.In a final section of the paper, we define two Archean facies associations—a Resedimented association containing turbidites, pebbly mudstones, resedimented conglomerates, and basinal black argillites; and a Continental association, containing alluvial fan deposits, and possible coastal deposits from South Africa and Australia. The facies sequence in the Sioux Lookout belt is Continental followed by Resedimented facies, the reverse of the normal geosynclinal flysch (resedimented) → molasse (continental) sequence.

Facies architecture of fluviatile deposits of the Jurassic-Cretaceous Bertangga Formation, Peninsular Malaysia

2020 ◽  
Vol 298 (2) ◽  
pp. 177-195
Author(s):  
Hassan Baioumy ◽  
Chong Jing Ting ◽  
Sherif Farouk ◽  
Khaled Al-Kahtany
Keyword(s):  
Depositional Environment ◽  
Facies Analysis ◽  
Flow Direction ◽  
Volcanic Rocks ◽  
Peninsular Malaysia ◽  
Carbonaceous Shale ◽  
Point Bar ◽  
Facies Associations ◽  
Crevasse Splay ◽  
Floodplain Sediments

Bertangga Formation is a part of the Jurassic-Cretaceous non-marine sequences in Thailand and Malaysia. However, its facies analysis and depositional model have not been investigated in detail. Eleven lithofacies have been described in the Bertangga Formation and combined five facies associations including channel, point bar, floodplain, crevasse splay and swamp facies associations. Channel deposits are stacked bodies of fining upward sequences with prevalent erosional bases, formed by vertical aggradation and avulsion of channels. Point bar sands comprise cross bedded sandstone bodies formed in upper flow regime and possible lateral accretion surfaces. Crevasse splay deposits form sheets of fine-to-medium-grained sandstone. Floodplain sediments are composed of motteled grey mudstone. Swamp depositional environment is characterized by an association of coal, carbonaceous shale and siltstone. Facies analysis allows reconstruction of the depositional environment of the Bertangga Formation as a meandering fluvial system. Facies association also shows the increasingly distal and fine-grained trend from west to east of the studied area, which suggests possible eastward paleo-flow direction of the river. The existence of kaolinite in all samples indicates weathering of felsic rocks under acidic conditions. In the same time, the presence of smectite in the eastern part of the study area may suggest a contribution of mafic and/or volcanic rocks to the source of sediments in this area.

U–Pb zircon ages of volcanism and plutonism in the Mishibishu greenstone belt near Wawa, Ontario

1990 ◽  
Vol 27 (5) ◽  
pp. 649-656 ◽  
Author(s):  
A. Turek ◽  
R. Keller ◽  
W. R. Van Schmus
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Superior Province ◽  
Calc Alkaline ◽  
Metasedimentary Rocks ◽  
Metavolcanic Rocks ◽  
Volcanic Pile ◽  
Archean Greenstone Belt

The Mishibishu greenstone belt, located 40 km west of Wawa, is a typical Archean greenstone belt and is probably an extension of the Michipicoten belt. This belt is composed of basic to felsic metavolcanic rocks of tholeiitic to calc-alkaline affinity and of metasedimentary rocks ranging from conglomerate to argillite. Granitoids, diorites, and gabbros intrude and embay supracrustal rocks as internal and external plutons.Six U–Pb zircon ages have been obtained on rocks in this area. The oldest is 2721 ± 4 Ma for the Jostle Lake tonalite. The bulk of the volcanic rocks formed by 2696 ± 17 Ma, which is the age of the Chimney Point porphyry at the top of the volcanic pile. The Pilot Harbour granite has a similar age of 2693 ± 7 Ma. The age of the Tee Lake tonalite is 2673 ± 12 Ma, and the age of the Iron. Lake gabbro is 2671 ± 4 Ma. The youngest age for volcanics in this part of the Superior Province is 2677 ± 7 Ma, obtained from, the David Lakes pyroclastic breccia. these ages agree with those reported for the adjacent Michipicoten and Gamitagama belts.

Development of sedimentary basins in the Archean Abitibi belt, Canada: an overview

1992 ◽  
Vol 29 (10) ◽  
pp. 2249-2265 ◽  
Author(s):  
W. Mueller ◽  
J. A. Donaldson
Keyword(s):  
Shallow Water ◽  
Large Scale ◽  
Volcanic Rocks ◽  
Sedimentary Basins ◽  
Sedimentary Facies ◽  
Volcanic Zone ◽  
Sedimentary Cycles ◽  
Southern Volcanic Zone ◽  
Facies Associations ◽  
Sedimentary Cycle

Sedimentation in the Archean Abitibi greenstone belt occurred during four depositional episodes: (i) sedimentary cycle 1, 2730–2720 Ma; (ii) sedimentary cycle 2, 2715–2705 Ma; (iii) sedimentary cycle 3, 2700–2687 Ma; and (iv) sedimentary cycle 4, 2685–2675 Ma. Records of the first two sedimentary cycles are preserved in basins within the northern volcanic zone, whereas basins formed during the latter two sedimentary cycles are located within the southern volcanic zone of the Abitibi belt. Sedimentary cycles 1 and 3 represent deep-water facies, as indicated by turbidites, resedimented conglomerates, pelagic sediments, and ubiquitous iron-formations; subaerial deposits have not been identified. In contrast, sedimentary cycles 2 and 4 show a prevalence of fluvial to shallow-water marine and (or) lacustrine deposits. Tectono-magmatic influence on sedimentation during cycles 2 and 4 is documented by (i) the presence of numerous unconformities underlain by plutonic and volcanic rocks; (ii) locally voluminous shoshonitic and calc-alkaline volcanic rocks; (iii) abundance of plutonic detritus; (iv) rapid vertical and lateral facies changes; and (v) repetition of successions of large-scale (50–250 m thick) alluvial and shallow-water deposits. Sedimentary cycle 1 represents incipient arc basins dominated by volcaniclastic debris, whereas cycle 2 reflects unroofing of arc volcanoes down to the plutonic roots. The sedimentary basins of cycle 3 have been tentatively interpreted as basins connecting arc terranes, within which small extensional cycle 4 basins of the successor or pull-apart type developed. The sedimentary facies associations, the tectono-magmatic influence on sedimentation, the chronological basin evolution, and overall southward younging of the basins invite comparison with modern island arcs formed by plate-tectonic processes.

Late Archaean clastic sedimentary rocks (Shamvaian Group) of the Zimbabwe craton: first observations from the Bindura-Shamva greenstone belt

2002 ◽  
Vol 39 (11) ◽  
pp. 1689-1708 ◽  
Author(s):  
A Hofmann ◽  
PH GM Dirks ◽  
H A Jelsma
Keyword(s):  
Greenstone Belt ◽  
Sedimentary Rocks ◽  
Sedimentary Facies ◽  
Shear Zones ◽  
Alluvial Fan ◽  
Sediment Supply ◽  
Turbidity Currents ◽  
Late Archaean ◽  
Facies Associations ◽  
Felsic Volcanic

The ~2.65 Ga old Shamvaian Group sedimentary rocks occur as a folded succession in the central part of the Bindura–Shamva greenstone belt of Zimbabwe. The strata comprise distinct, shear zone-bounded tectonostratigraphic units which may be stratigraphically arranged as follows. The lower part of the succession is represented by a transgressive, fining-upward sequence of alluvial fan conglomerate, overlain by fluvial braid-plain pebbly sandstone and marine shoreface sandstone. Detritus was derived from a mid-Archaean granitoid-gneiss terrain situated to the east. Sediment supply and subsidence rate must have been high. Shallow shelf sedimentation was followed by deep-water (sub-wave base) deposition by turbidity currents, giving rise to a thick succession of fine to coarse clastic material. The turbidite deposits were locally overlain by shallow-marine sandstone and fluvial to alluvial fan conglomerate. An upward increase in the abundance of intermediate and felsic volcanic clasts suggests an increase in the proximity of a volcanic terrain, such as a volcanic arc. Deposition was followed by layer-parallel shearing during thrust belt-style tectonism. Major shear zones developed preferentially along the contact between shallow- and deep-marine facies associations. Basin initiation may have been related to extensional tectonics, possibly on rifted continental crust, whereas later stages of basin history were characterized by compression, suggesting a foreland or fore-arc basin setting. Sedimentary facies, stratigraphy, and facies distribution are remarkably similar to some late Archaean sedimentary sequences of the Superior Province in Canada.

Rubidium–strontium ages from the Oxford Lake – Knee Lake greenstone belt, northern Manitoba

1980 ◽  
Vol 17 (5) ◽  
pp. 560-568 ◽  
Author(s):  
G. S. Clark ◽  
S.-P. Cheung
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Superior Province ◽  
Granitic Intrusion ◽  
Greenstone Belts ◽  
Archean Greenstone Belts

Rb–Sr whole-rock ages have been determined for rocks from the Oxford Lake – Knee Lake – Gods Lake greenstone belt, in the Superior Province of northeastern Manitoba.The age of the Magill Lake Pluton is 2455 ± 35 Ma (λ87Rb = 1.42 × 10−11 yr−1), with an initial 87Sr/86Sr ratio of 0.7078 ± 0.0043. This granitic stock intrudes the Oxford Lake Group, so it is post-tectonic and probably related to the second, weaker stage of metamorphism.The age of the Bayly Lake Pluton is 2424 ± 74 Ma, with an initial 87Sr/86Sr ratio of 0.7029 ± 0.0001. This granodioritic batholith complex does not intrude the Oxford Lake Group. It is syn-tectonic and metamorphosed.The age of volcanic rocks of the Hayes River Group, from Goose Lake (30 km south of Gods Lake Narrows), is 2680 ± 125 Ma, with an initial 87Sr/86Sr ratio of 0.7014 ± 0.0009.The age for the Magill Lake and Bayly Lake Plutons can be interpreted as the minimum ages of granitic intrusion in the area.The age for the Hayes River Group volcanic rocks is consistent with Rb–Sr ages of volcanic rocks from other Archean greenstone belts within the northwestern Superior Province.

Two key switches in regional stress field during multi-stage deformation in the Carboniferous−Triassic southernmost Altaids (Beishan, NW China): Response to orocline-related roll-back processes

2021 ◽  
Author(s):  
Zhonghua Tian ◽  
Wenjiao Xiao ◽  
Brian F. Windley ◽  
Peng Huang ◽  
Ji’en Zhang ◽  
...  
Keyword(s):  
Stress Field ◽  
Large Scale ◽  
Electron Backscatter Diffraction ◽  
Volcanic Rocks ◽  
Structural Deformation ◽  
Regional Stress ◽  
Regional Stress Field ◽  
Multi Stage ◽  
Beishan Orogenic Collage ◽  
Roll Back

The orogenic architecture of the Altaids of Central Asia was created by multiple large-scale slab roll-back and oroclinal bending. However, no regional structural deformation related to roll-back processes has been described. In this paper, we report a structural study of the Beishan orogenic collage in the southernmost Altaids, which is located in the southern wing of the Tuva-Mongol Orocline. Our new field mapping and structural analysis integrated with an electron backscatter diffraction study, paleontology, U-Pb dating, 39Ar-40Ar dating, together with published isotopic ages enables us to construct a detailed deformation-time sequence: During D1 times many thrusts were propagated northwards. In D2 there was ductile sinistral shearing at 336−326 Ma. In D3 times there was top-to-W/WNW ductile thrusting at 303−289 Ma. Two phases of folding were defined as D4 and D5. Three stages of extensional events (E1−E3) separately occurred during D1−D5. Two switches of the regional stress field were identified in the Carboniferous to Early Permian (D1-E1-D2-D3-E2) and Late Permian to Early Triassic (D4-E3-D5). These two switches in the stress field were associated with formation of bimodal volcanic rocks, and an extensional interarc basin with deposition of Permian-Triassic sediments, which can be related to two stages of roll-back of the subduction zone on the Paleo-Asian oceanic margin. We demonstrate for the first time that two key stress field switches were responses to the formation of the Tuva-Mongol Orocline.

Tholeiitic volcanic rocks of the late Archean Blake River Group, southern Abitibi greenstone belt: origin and geodynamic implications

1992 ◽  
Vol 29 (7) ◽  
pp. 1448-1458 ◽  
Author(s):  
M. R. Laflèche ◽  
C. Dupuy ◽  
J. Dostal
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Incompatible Trace Element ◽  
Progressive Change ◽  
Abitibi Greenstone Belt ◽  
Mid Ocean Ridge ◽  
Compositional Variations ◽  
Arc Setting ◽  
Back Arc ◽  
Ocean Ridge

The late Archean Blake River Group volcanic sequence forms the uppermost part of the southern Abitibi greenstone belt in Quebec. The group is mainly composed of mid-ocean-ridge basalt (MORB)-like tholeiites that show a progressive change of several incompatible trace element ratios (e.g., Nb/Th, Nb/Ta, La/Yb, and Zr/Y) during differentiation. The compositional variations are inferred to be the result of fractional crystallization coupled with mixing–contamination of tholeiites by calc-alkaline magma which produced the mafic–intermediate lavas intercalated with the tholeiites in the uppermost part of the sequence. The MORB-like tholeiites were probably emplaced in a back-arc setting.

scholarly journals Syntax Role for Neural Semantic Role Labeling

2021 ◽  
pp. 1-48
Author(s):  
Zuchao Li ◽  
Hai Zhao ◽  
Shexia He ◽  
Jiaxun Cai
Keyword(s):  
Argument Structure ◽  
Large Scale ◽  
Language Models ◽  
Semantic Role ◽  
Semantic Role Labeling ◽  
Empirical Survey ◽  
Learning Framework ◽  
Syntactic Information ◽  
Feature Based ◽  
Predicate Argument Structure

Abstract Semantic role labeling (SRL) is dedicated to recognizing the semantic predicate-argument structure of a sentence. Previous studies in terms of traditional models have shown syntactic information can make remarkable contributions to SRL performance; however, the necessity of syntactic information was challenged by a few recent neural SRL studies that demonstrate impressive performance without syntactic backbones and suggest that syntax information becomes much less important for neural semantic role labeling, especially when paired with recent deep neural network and large-scale pre-trained language models. Despite this notion, the neural SRL field still lacks a systematic and full investigation on the relevance of syntactic information in SRL, for both dependency and both monolingual and multilingual settings. This paper intends to quantify the importance of syntactic information for neural SRL in the deep learning framework. We introduce three typical SRL frameworks (baselines), sequence-based, tree-based, and graph-based, which are accompanied by two categories of exploiting syntactic information: syntax pruningbased and syntax feature-based. Experiments are conducted on the CoNLL-2005, 2009, and 2012 benchmarks for all languages available, and results show that neural SRL models can still benefit from syntactic information under certain conditions. Furthermore, we show the quantitative significance of syntax to neural SRL models together with a thorough empirical survey using existing models.

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