Structural tests of diapir hypotheses in Archean crust of Ontario

1990 ◽  
Vol 27 (3) ◽  
pp. 387-402 ◽  
Author(s):  
W. M. Schwerdtner
Keyword(s):  
Solid State ◽  
Horizontal Displacement ◽  
Gneiss Dome ◽  
Gneiss Domes ◽  
Archean Crust ◽  
Structural Tests ◽  
Greenstone Belts ◽  
Ductile Shear

Detailed structural maps of two granitoid complexes in the Wabigoon Subprovince are used to test three diapir hypotheses advanced in earlier papers. The gneiss masses of, and individual domes within, the complexes fail the test for solid-state diapirism. The gneiss domes also fail the test for tensile bending caused by hypothetical magmatic diapirs in the subsurface. An oval pluton located near the best-exposed gneiss dome proves to be a synformal sheet rather than a funnel-shaped magmatic diapir. This pluton could be a syenite–diorite phacolith emplaced into a concordant zone of dilation during the late upright folding of the gneiss mass about horizontal axes. Earlier tight folds were probably recumbent and south verging and, like the gneissosity, generated in a ductile shear regime with subhorizontal glide planes. These observations have important implications for Archean tectonics, especially the relative horizontal displacement of large greenstone masses (potentially allochthonous greenstone belts).

On the origin of Early Proterozoic gneiss domes and metamorphic nodes, northern Michigan

1996 ◽  
Vol 33 (7) ◽  
pp. 1053-1053 ◽  
Author(s):  
David Schneider ◽  
Daniel Holm ◽  
Daniel Lux
Keyword(s):  
Gravity Anomaly ◽  
Gneiss Dome ◽  
Near Surface ◽  
Dome Formation ◽  
Crustal Shortening ◽  
Gneiss Domes ◽  
History Of ◽  
The Republic ◽  
Different Origins ◽  
Northern Michigan

Biotite 40αr/39αr cooling ages from medium-pressure (500–600 MPa) rocks in the Watersmeet district, northern Michigan, suggest significant cooling–uplift and concomitant deformation during gneiss dome formation at~1755 Ma, well after the close of the 1870–1830 Ma Penokean orogeny. However, an 1822 Ma hornblende plateau date indicates that the isograds surrounding the dome are Penokean in age. We attribute gneiss dome formation and doming of Penokean-aged isograds to an episode of orogenic collapse superimposed on an earlier history of crustal shortening. This contrasts with the compressional origin for gneiss domes preserved in the low-pressure (200–300 MPa) Republic district. The different origins may reflect the fact that collapse was localized along the overthickened region of the orogenic belt. In contrast to the Watersmeet area, hornblende and biotite 40Ar/39Ar ages obtained from the Republic area are 1720–1680 Ma. Given the relatively shallow depth of this region, it is unlikely that temperatures remained above 500 °C for over 100 Ma following collision. We interpret these ages to reflect a major thermal event that may have been responsible for formation of the Republic metamorphic node. This interpretation is supported by the recent identification of an ~1730 Ma pluton that is likely the cause of a large, near-surface, negative gravity anomaly coincident with the node, and by the fact that the metamorphic node crosscuts Penokean structures.

La zonation structurale des dômes gneissiques. Un exemple : le massif de Saint-Malo (Massif armoricain, France)

1977 ◽  
Vol 14 (8) ◽  
pp. 1697-1707 ◽  
Author(s):  
Jean-Pierre Brun
Keyword(s):  
Structural Analysis ◽  
Dynamic Model ◽  
Experimental Models ◽  
Gneiss Dome ◽  
Gneiss Domes

The Saint-Malo massif provides an example of a gneiss dome with a migmatitic core. The results of a structural analysis are used to describe a structural zonation around the migmatitic core, and a dynamic model of the massif is proposed. A comparison of these results with experimental models of gneiss domes shows that this zonation is the product of diapirism.

Early Archean crust of the Middle Dnepr and Azov domains, Ukrainian Shield--evidence from ages of detrital zircons in Mesoarchean greenstone belts

2010 ◽  
Vol 310 (10) ◽  
pp. 1595-1622 ◽  
Author(s):  
E. Bibikova ◽  
S. Claesson ◽  
A. Fedotova ◽  
G. Artemenko ◽  
L. Ilyinsky
Keyword(s):  
Detrital Zircons ◽  
Ukrainian Shield ◽  
Archean Crust ◽  
Greenstone Belts

Patterns of total and incremental strain in subsiding troughs: experimental centrifuged. models of inter-diapir synclines

1983 ◽  
Vol 20 (12) ◽  
pp. 1843-1861 ◽  
Author(s):  
J. M. Dixon ◽  
J. M. Summers
Keyword(s):  
Surface Deformation ◽  
Main Body ◽  
Gneiss Domes ◽  
Strain Pattern ◽  
Vertical Extension ◽  
Greenstone Belts ◽  
Vertical Gravity ◽  
Incremental Strain ◽  
Archean Greenstone Belts ◽  
Model Structures

The experimental technique of centrifuge modelling has been used to elucidate patterns of total strain and progressive deformation associated with troughs that form by gravitational subsidence of a dense cover into a less dense basement. Model structures are analogous to synclines found between mantled gneiss domes, and the models provide data with which to test the hypothesis that Archean greenstone belts are products of vertical gravity tectonics.Experimental results include the following. (1) Strain within the main body of subsiding belts is dominated by strong horizontal contraction and vertical extension. In natural structures this strain pattern would produce vertical foliation and steeply plunging mineral lineation. (2) Within cover units near trough margins the flattening plane trends parallel with or at a low angle to the cover–basement interface at all levels in the trough. (3) Patterns of strain within subsiding troughs, at least as expressed in surface deformation, reflect the geometry of the cover–basement interface at depth. Flow within the cover units converges towards points of maximum trough subsidence to produce local vertical constrictive strain. Deformation above trough saddles is characterized by vertical flattening strain. (4) Horizontal shortening within a subsiding, stratified cover sequence produces early folds with horizontal axes and steep axial surfaces. Where the stratified sequence forms a relatively low-density unit within the cover, folds and thrusts verge consistently away from the trough axis. Continued subsidence and horizontal contraction tend to rotate initially shallowly dipping structures into steeply dipping attitudes.

Relationships between granite-gneiss terrains, greenstone belts and granulite belts in the archean crust of Lapland (Fennoscandia)

1980 ◽  
Vol 69 (3) ◽  
pp. 648-658 ◽  
Author(s):  
P. Barbey ◽  
J. Convert ◽  
H. Martin ◽  
B. Moreau ◽  
R. Capdevila ◽  
...  
Keyword(s):  
Granite Gneiss ◽  
Archean Crust ◽  
Greenstone Belts

Structure of the Lac Nominingue – Mont-Laurier region, Central Metasedimentary Belt, Quebec Grenville Province

2001 ◽  
Vol 38 (5) ◽  
pp. 787-802
Author(s):  
L B Harris ◽  
B Rivard ◽  
L Corriveau
Keyword(s):  
Regional Scale ◽  
Shear Zones ◽  
Granulite Facies ◽  
Crustal Thickening ◽  
Gneiss Dome ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Ductile Shear Zones ◽  
Ductile Shear ◽  
East West

The Lac Nominingue – Mont-Laurier region of the Central Metasedimentary Belt, Grenville Province of Quebec, comprises the granulite-facies Bondy gneiss complex (core of the Bondy gneiss dome) and overlying Sourd group metasedimentary rocks. A metamorphic foliation – transposed compositional layering (S1; host to peak-pressure parageneses) has been folded by isoclinal folds (F2 and F3) crosscut by leucosomes that host peak-temperature assemblages. The orthopyroxene isograd cuts obliquely across F3 folds, indicating that 1.20–1.18 Ga granulite-facies metamorphism post-dated D3. D3 structures are cut by ductile shear zones and boudinaged in D4 and are folded by regional-scale, open, upright north–south folds (F5). Folds with shallowly dipping axial surfaces (F6) are subsequently developed in the Sourd group. F5 (and probably F6) developed prior to intrusion of the ca. 1165 Ma Chevreuil suite. In the Nominingue–Chénéville deformation zone (NCDZ) east of the Bondy gneiss dome, Chevreuil intrusions contain north-striking magmatic and tectonic foliations. These, along with host gneisses and metasedimentary rocks, are displaced by conjugate ductile shear zones (northeast dextral and south-southeast sinistral) and north-northeast-striking thrusts. Late open folds (F8) with east-northeast-striking axial surfaces produce dome and basin interference patterns. F2 to F5 folds may have formed during either subhorizontal, east–west contraction or east–west extension resulting from orogenic collapse or convective lithospheric thinning following crustal thickening during terrane assembly in the Elzevirian orogeny. Structures in the NCDZ imply ESE–WNW contraction and NNE–SSW (orogen-parallel) extension in D7 syn- to post-intrusion of the Chevreuil suite. F8 folds imply a late, Grenvillian SSE–NNW contraction.

Preparation of Thin Cadmium Telluride Samples for Electron Microscope Studies

1974 ◽  
Vol 32 ◽  
pp. 548-549
Author(s):  
T. J. Magee ◽  
J. Peng ◽  
J. Bean
Keyword(s):  
Electron Microscope ◽  
Sulfuric Acid ◽  
Solid State ◽  
Sample Preparation ◽  
Cadmium Telluride ◽  
Potassium Dichromate ◽  
Optical Components ◽  
The Past ◽  
Solid State Devices

Cadmium telluride has become increasingly important in a number of technological applications, particularly in the area of laser-optical components and solid state devices, Microstructural characterizations of the material have in the past been somewhat limited because of the lack of suitable sample preparation and thinning techniques. Utilizing a modified jet thinning apparatus and a potassium dichromate-sulfuric acid thinning solution, a procedure has now been developed for obtaining thin contamination-free samples for TEM examination.

The Collagenic Molecular Structural Unit of Solid State Complexes

1971 ◽  
Vol 29 ◽  
pp. 478-479
Author(s):  
Kenneth M. Richter ◽  
John A. Schilling
Keyword(s):  
Molecular Weight ◽  
Solid State ◽  
Structural Unit ◽  
X Ray Diffraction ◽  
X Ray ◽  
Naoh Treatment

The structural unit of solid state collagen complexes has been reported by Porter and Vanamee via EM and by Cowan, North and Randall via x-ray diffraction to be an ellipsoidal unit of 210-270 A. length by 50-100 A. diameter. It subsequently was independently demonstrated by us in dog tendon, dermis, and induced complexes. Its detailed morphologic, dimensional and molecular weight (MW) aspects have now been determined. It is pear-shaped in long profile with m diameters of 57 and 108 A. and m length of 263 A. (Fig. 1, tendon, KMnO4 fixation, Na-tungstate; Fig. 2a, schematic of unit in long, C, and x-sectional profiles of its thin, xB, and bulbous, xA portions; Fig. 2b, tendon essentially unmodified by ether and 0.4 N NaOH treatment, Na-tungstate). The unit consists of a uniquely coild cable, c, of ṁ 22.9 A. diameter and length of 2580-3316 A. The cable consists of three 2nd-strands, s, each of m 10.6 A.

Structure-property relations of liquid crystalline polymers

1987 ◽  
Vol 45 ◽  
pp. 460-463
Author(s):  
Linda C. Sawyer
Keyword(s):  
Solid State ◽  
Liquid Crystalline ◽  
Structural Model ◽  
Crystalline Polymer ◽  
Liquid Crystalline Polymers ◽  
Mechanical Anisotropy ◽  
Structure Property ◽  
Preparation Methods ◽  
Crystalline Polymers ◽  
Extended Chain

Recent liquid crystalline polymer (LCP) research has sought to define structure-property relationships of these complex new materials. The two major types of LCPs, thermotropic and lyotropic LCPs, both exhibit effects of process history on the microstructure frozen into the solid state. The high mechanical anisotropy of the molecules favors formation of complex structures. Microscopy has been used to develop an understanding of these microstructures and to describe them in a fundamental structural model. Preparation methods used include microtomy, etching, fracture and sonication for study by optical and electron microscopy techniques, which have been described for polymers. The model accounts for the macrostructures and microstructures observed in highly oriented fibers and films.Rod-like liquid crystalline polymers produce oriented materials because they have extended chain structures in the solid state. These polymers have found application as high modulus fibers and films with unique properties due to the formation of ordered solutions (lyotropic) or melts (thermotropic) which transform easily into highly oriented, extended chain structures in the solid state.

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