Flood basalts, dike swarms and sub-crustal flow

1968 ◽  
Vol 5 (1) ◽  
pp. 93-96 ◽  
Author(s):  
Paul M. Clifford
Keyword(s):  
Unsteady Motion ◽  
Canadian Shield ◽  
Published Data ◽  
Flood Basalts ◽  
Crustal Movements ◽  
Geologic Time ◽  
Dike Swarms ◽  
Convective Cells

A review of published data on flood basalts and diabase dike swarms suggests that they are related in origin, typically being developed in zones of crustal tension induced by sub-crustal flow. Perhaps, therefore, these basaltic effusions may be used to map convective cells in the mantle for various periods during geologic time. The inferred pattern of sub-crustal movements, particularly for the southern continents, is seen to be complicated, both temporarily and spatially, and is strongly suggestive of unsteady motion. Dikes of the Canadian Shield permit inferences about the site of convective cells back to 2150 million years.

Tuzo Wilson and the acceptance of pre-Mesozoic continental drift

2014 ◽  
Vol 51 (3) ◽  
pp. 197-207 ◽  
Author(s):  
Paul F. Hoffman
Keyword(s):  
Continental Drift ◽  
Early Experience ◽  
Canadian Shield ◽  
Sea Floor ◽  
Geologic Time ◽  
Sea Floor Spreading ◽  
Continental Accretion

Tuzo Wilson’s well-known pre-1961 opposition to continental drift stemmed from his early experience as a geologist in the Appalachians and the Canadian Shield, which convinced him that orogenesis did not change drastically over geologic time. Conversely, Taylor (in 1910) and Wegener (in 1912) hypothesized that continental drift began in Cenozoic or Mesozoic time. Between 1949 and 1960, Tuzo Wilson with Adrian Scheidegger developed a quasi-uniformitarian model of progressive continental accretion around fixed Archean nuclei. Tuzo abruptly jettisoned this model in 1961 when, under pressure from paleomagnetic evidence for continental drift and a nascent concept of sea-floor spreading, he finally entertained the possibility of pre-Mesozoic as well as younger continental drift. He immediately found it a superior fit to Appalachian and Shield geology, while his uniformitarian conviction remained intact. Tuzo had blinded himself to the evidence for continental drift so long as he confined it to Taylor or Wegener’s conception. In continental drift operating continuously over geologic time, he found a theory he could eagerly accept.

Isotope and trace-element geochemistry of Proterozoic Natkusiak flood basalts from the northwestern Canadian Shield

1995 ◽  
Vol 120 (1-2) ◽  
pp. 15-25 ◽  
Author(s):  
C. Dupuy ◽  
A. Michard ◽  
J. Dostal ◽  
D. Dautel ◽  
W.R.A. Baragar
Keyword(s):  
Trace Element ◽  
Canadian Shield ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Flood Basalts

Standing Stock and Production of Fish in a Cascading Lake System on the Canadian Shield

1985 ◽  
Vol 42 (7) ◽  
pp. 1315-1320 ◽  
Author(s):  
John R. M. Kelso
Keyword(s):  
Standing Stock ◽  
Canadian Shield ◽  
Published Data ◽  
Fish Biomass ◽  
Fish Production ◽  
Large Fish ◽  
Lake Depth ◽  
Lake System ◽  
Total Fish ◽  
Shield Lakes

To examine factors influencing fish biomass and production, I carried out a multiple mark and recapture program in a cascading lake system on the Canadian Shield. Standing stock and production were determined for all "large" fish (vulnerable to the gear in use) in the system. Total fish biomass (range 5.2–24.8 kg∙ha−1) decreased with progression downstream and with increasing depth. Production ranged from approximately 2.2 to 6.6 kg∙ha−1∙yr−1 and operated in a manner identical to standing stock. Salmonid flesh production, however, formed a greater proportion to overall fish production in the downstream, less productive lakes. Biomass was strongly influenced by lake depth in this watershed, and this was confirmed by examination of other published data for fish biomass and production in Shield lakes.

The chemical evolution of the Canadian Shield

1968 ◽  
Vol 5 (5) ◽  
pp. 1247-1252 ◽  
Author(s):  
W. F. Fahrig ◽  
K. E. Eade
Keyword(s):  
Chemical Evolution ◽  
Sedimentary Basins ◽  
Crystalline Rocks ◽  
Canadian Shield ◽  
Progressive Change ◽  
Chemical Zoning ◽  
Crystalline Crust ◽  
Secondary Result ◽  
Dike Swarms ◽  
Proterozoic Age

Archean surface crystalline rocks of the Canadian Shield differ chemically from those of Proterozoic age. The younger rocks are higher in K2O, TiO2, U, and Th and lower in Na2O, Cr, Ni, and possibly MgO and CaO. This may be a secondary result of vertical chemical zoning of the crust as a result of metamorphism accompanied by anatectic melting. The erosion of a zoned crust would result in the enrichment of elements such as K, Na, Si, U, and Th in younger sedimentary basins. The crystalline crust subsequently evolved from the sediments of these basins would be enriched in these elements relative to older rocks exposed as a result of erosion. The secular chemical evolution of the shield may also reflect a progressive, though irregular, shift in the composition of new sial being added to the crust. Evidence for this progressive change is found in the increase in the abundance of potassium of successive dike swarms that were feeders of new sial to the upper part of the crust.

An assessment of the relative roles of crust and mantle in magma genesis: an elemental approach

1984 ◽  
Vol 310 (1514) ◽  
pp. 549-590 ◽  
Keyword(s):  
Subduction Zones ◽  
Published Data ◽  
Flood Basalts ◽  
Continental Flood Basalts ◽  
Ocean Island Basalts ◽  
Mid Ocean Ridge ◽  
Source Mantle ◽  
Mantle Reservoir ◽  
Mafic Magmas ◽  
Ocean Ridge

The elemental compositions of terrestrial igneous rocks are reviewed with special emphasis on those elements that partition strongly into the liquids in mafic and ultramafic systems. Published data are supplemented by 79 new major- and trace-element analyses. The magmatism of ocean basins is considered in terms of a model that has the following main features: (i) density layering in the sub-lithospheric upper mantle, so that the more fertile source of ocean-island basalts (o.i.b.) underlies the less fertile source of mid-ocean ridge basalts (m.o.r.b.); (ii) the genesis of all mantle-derived magmas restricted to very small degrees of partial fusion; (iii) genesis of m.o.r.b. source mantle as residuum from the loss of a melt fraction (forming o.i.b. magmas and lithospheric veins) from o.i.b.-source mantle; (iv) subduction of o.i.b;- veined lithosphere, with a thin veneer of m.o.r.b. and sediments, to the 670 km seismic discontinuity, followed by re-heating of these components and their buoyant upwelling into the o.i.b.-source reservoir; (v) very little chemical communication across the 670 km discontinuity. All continental anorogenic magmatism (distant from subduction zones in space and time) seems to be related ultimately to the o.i.b.-source mantle reservoir, which therefore must extend beneath the lithospheric roots of continents. The minor sodic-alkalic magmatism of continents is effectively identical in composition to o.i.b. Some continental flood basalts are similar but the majority contain minor contamination (rarely more than 15%) from fusible sialic rocks. Although substantial amounts of sediments appear to be subducted, only a small proportion of them seems to re-appear in the products of island-arc and Cordilleran magmatism. Much larger sediment fractions enter the sparse ultrapotassic magmatism that occurs far behind some subcontinental subduction zones and also characteristically follows the subduction related magmatism of collisional orogenies. The remaining subducted sediments finally pass into the o.i.b.-mantle source reservoir. It is well established that, during and immediately after collisional orogeny, the fusion of sialic crust contributes substantially (or even occasionally exclusively) to batholithic magmatism. Nevertheless, the elemental variation in such magmas implies that the role of fractional crystallization in their genesis has tended to be underestimated in recent years. Mantle-derived mafic to ultramafic magmas appear to be directly or indirectly (as heat sources) involved at deep crustal levels in the parentage of most batholithic intermediate and acid magams. These mantle-derived liquids are subduction-related before continental collisions and then change to o.i.b., several million years after subduction ceases. Enhanced subduction of terrigenous sediments during the final stages of ocean closure leads to the large subducted sialic fractions which re-emerge in the ultrapotassic mafic magmas that characteristically appear immediately after a continental collision.

Regional variation in paleomagnetic polarity of the Matachewan dyke swarm related to the Kapuskasing Structural Zone, Ontario

1990 ◽  
Vol 27 (2) ◽  
pp. 200-211 ◽  
Author(s):  
M. P. Bates ◽  
H. C. Halls
Keyword(s):  
Lower Crust ◽  
Regional Variation ◽  
Canadian Shield ◽  
Dyke Swarm ◽  
Published Data ◽  
Superior Province ◽  
The North ◽  
Paleomagnetic Pole ◽  
Abitibi Subprovince

The 2.45 Ga Matachewan dykes from the Abitibi Subprovince of the Canadian Shield yield a mean paleomagnetic pole of 42°N, 58°E (α95 = 3°; N (sites) = 36), which is a composite of new and previously published data. Domains of paleomagnetic polarity are defined: an area of dykes predominantly of reversed magnetization in the Abitibi Subprovince contrasts with an area of exclusively normal dykes to the north. The polarity domains are separated by faults related to the 1.95 Ga uplift and exposure of the lower crust in the Kapuskasing Structural Zone and therefore reflect Hudsonian age tectonics in the Archean Superior Province.

scholarly journals Eocene Origin of Owens Valley, California

Geosciences ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 194 ◽  
Author(s):  
Francis J. Sousa
Keyword(s):  
Boundary Conditions ◽  
Tectonic Activity ◽  
Published Data ◽  
Owens Valley ◽  
White Mountains ◽  
Major Phase ◽  
Geologic Time ◽  
Temperature Modeling ◽  
Initial And Boundary Conditions

Bedrock (U-Th)/He data reveal an Eocene exhumation difference greater than four kilometers athwart Owens Valley, California near the Alabama Hills. This difference is localized at the eastern fault-bound edge of the valley between the Owens Valley Fault and the Inyo-White Mountains Fault. Time-temperature modeling of published data reveal a major phase of tectonic activity from 55 to 50 Ma that was of a magnitude equivalent to the total modern bedrock relief of Owens Valley. Exhumation was likely accommodated by one or both of the Owens Valley and Inyo-White Mountains faults, requiring an Eocene structural origin of Owens Valley 30 to 40 million years earlier than previously estimated. This analysis highlights the importance of constraining the initial and boundary conditions of geologic models and exemplifies that this task becomes increasingly difficult deeper in geologic time.

Influence of nascent polypeptide positive charges on translation dynamics

2020 ◽  
Vol 477 (15) ◽  
pp. 2921-2934
Author(s):  
Rodrigo D. Requião ◽  
Géssica C. Barros ◽  
Tatiana Domitrovic ◽  
Fernando L. Palhano
Keyword(s):  
Mrna Decay ◽  
Translation Termination ◽  
Published Data ◽  
Translation Efficiency ◽  
Amino Acid Residues ◽  
High Concentration ◽  
Strong Argument ◽  
Translation Arrest ◽  
Exit Tunnel ◽  
Positively Charged

Protein segments with a high concentration of positively charged amino acid residues are often used in reporter constructs designed to activate ribosomal mRNA/protein decay pathways, such as those involving nonstop mRNA decay (NSD), no-go mRNA decay (NGD) and the ribosome quality control (RQC) complex. It has been proposed that the electrostatic interaction of the positively charged nascent peptide with the negatively charged ribosomal exit tunnel leads to translation arrest. When stalled long enough, the translation process is terminated with the degradation of the transcript and an incomplete protein. Although early experiments made a strong argument for this mechanism, other features associated with positively charged reporters, such as codon bias and mRNA and protein structure, have emerged as potent inducers of ribosome stalling. We carefully reviewed the published data on the protein and mRNA expression of artificial constructs with diverse compositions as assessed in different organisms. We concluded that, although polybasic sequences generally lead to lower translation efficiency, it appears that an aggravating factor, such as a nonoptimal codon composition, is necessary to cause translation termination events.

Metallic prions

2004 ◽  
Vol 71 ◽  
pp. 193-202 ◽  
Author(s):  
David R Brown
Keyword(s):  
Prion Protein ◽  
Binding Capacity ◽  
Normal Function ◽  
Transmissible Spongiform Encephalopathies ◽  
Published Data ◽  
Normal Brain ◽  
Copper Binding ◽  
Loss Of Function ◽  
Spongiform Encephalopathies ◽  
The Brain

Prion diseases, also referred to as transmissible spongiform encephalopathies, are characterized by the deposition of an abnormal isoform of the prion protein in the brain. However, this aggregated, fibrillar, amyloid protein, termed PrPSc, is an altered conformer of a normal brain glycoprotein, PrPc. Understanding the nature of the normal cellular isoform of the prion protein is considered essential to understanding the conversion process that generates PrPSc. To this end much work has focused on elucidation of the normal function and activity of PrPc. Substantial evidence supports the notion that PrPc is a copper-binding protein. In conversion to the abnormal isoform, this Cu-binding activity is lost. Instead, there are some suggestions that the protein might bind other metals such as Mn or Zn. PrPc functions currently under investigation include the possibility that the protein is involved in signal transduction, cell adhesion, Cu transport and resistance to oxidative stress. Of these possibilities, only a role in Cu transport and its action as an antioxidant take into consideration PrPc's Cu-binding capacity. There are also more published data supporting these two functions. There is strong evidence that during the course of prion disease, there is a loss of function of the prion protein. This manifests as a change in metal balance in the brain and other organs and substantial oxidative damage throughout the brain. Thus prions and metals have become tightly linked in the quest to understand the nature of transmissible spongiform encephalopathies.

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