Structural tests of diapir hypotheses in Archean crust of Ontario

Schwerdtner, W. M.

doi:10.1139/e90-035

Cited by 37 publications

(22 citation statements)

References 19 publications

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“…There are very few studies of the geometry of collapsed salt diapir stems (diapir tracks) that an ascending diapir would leave in its wake (see also account of unsuccessful hunt for igneous examples by Schwerdtner, 1990). An exposed salt diapir track discussed by Jackson et al (1998) has been reinterpreted as an astrobleme (Kriens et al, 1999 and Dunbar (2000), however, report the distribution of faults implied by this model, but the primary seismic data and mapping are unreleased.…”

Section: Passive Diapirism In Fluid Overburdenmentioning

confidence: 99%

Implications of passive salt diapir kinematics for reservoir segmentation by radial and concentric faults

Stewart

2006

Marine and Petroleum Geology

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Section: Passive Diapirism In Fluid Overburdenmentioning

confidence: 99%

Implications of passive salt diapir kinematics for reservoir segmentation by radial and concentric faults

Stewart

2006

Marine and Petroleum Geology

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“…Other arguments against the possibility of magmatic diapiric upwellings in the crust involve field observations (Schwerdtner 1990), consideration of the relative ascent velocities compared with crystallization rates, the lack of the expected crustal structures (e.g. Clemens & Mawer 1992) or spacing between plutons using volumetric data for the emplaced magmas (Vigneresse 1995b).…”

Section: Arguments Against Granitic Diapir•mmentioning

confidence: 99%

Granitic magma ascent and emplacement: neither diapirism nor neutral buoyancy

Vigneresse

Clemens

2000

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Abstract:It is probable that granitic magma ascent does not result from the intrinsic properties of the magmas. Within the uppermost crust, neither the reduced viscosity nor the density contrast between magma and surroundings are themselves sufficient to induce either low-inertia flow (diapirism) or fracture-induced magma propagation (dyking). Igneous diapirism is intrinsically restricted to the lower, ductile crust. Dyking is therefore the most probable ascent mechanism for granitic magmas that reach shallow crustal levels. A neutral buoyancy level in the crust, at which magma ascent should stall, is never observed. This,is demonstrated by coeval emplacement of magmas with different compositions and densities, and the negative gravity anomalies measured over many granitic plutons. We suggest that deformation, through strain partitioning, is necessary to magma ascent. Pluton formation is controlled by local structures and rock types rather than by intrinsic magma properties. As a result of its intermittent character, deformation (both local and regional) induces magma pulses, and this may have important consequences for the chemical homogeneity of intruded magmas.Ascent of granitic (leucogranitic to tonalitic) magma in the continental lithosphere is the most potent means of mass transfer and chemical segregation between the lower and upper crust. Granitic magmatism contributes to crustal recycling and, to a lesser extent, continental growth. In rapidly accreted crust, granitic rocks can occupy up to one-third of the volume of the middle crust (Meissner 1986). Together with shear zones, they are the most conspicuous effects of plate convergence and collision in orogenic zones. Consequently, they are a key element in understanding the evolution of Earth's mechanical workings.As most felsic magmas are emplaced in a liquid, or near-liquid state, at temperatures over 800~ a major heat source must be involved in their genesis. The existence of such a heat source also has consequences for the deformation regime of the crust. Commonly, a large temperature rise in the lithosphere will also increase the capacity of crustal material to respond to stress (by deformation). Such a thermal anomaly will contribute to the dissipation of energy and thus buffer the temperature effects. The stress regime will be imposed externally by the tectonic processes operating at the time. As a reaction to a significant increase in crustal heat flow, the rheological capacity of rocks to sustain stresses decreases, and this activates deformation. Therefore, most departures from a 'normal' heat distribution in the lithosphere will trigger deformation (e.g. formation of extensional rift zones, or shear zones in convergent situations).

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“…Finally, some authors consider that all the craton supracrustal rocks belong to a single unit whose deformation is linked to one long-lived 'Dharwar orogeny' (Drury et al 1984, Pichamuthu & Srinivasan 1984, Naha et al 1986, Srinivasan 1988.…”

Section: Sargurjdharwar Controversymentioning

confidence: 99%

“…It should be noted that systematic surveys of strain fields (variations in the local characteristics of the finite strain) are still few in number, but that they are particularly pertinent to deal with this question (Schwerdtner 1990, Choukroune et al 1995.…”

Section: Introductionmentioning

confidence: 99%

Strain patterns, décollement and incipient sagducted greenstone terrains in the Archaean Dharwar craton (south India)

Chardon

Cartigny

Jayananda

1996

Journal of Structural Geology

138

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Abstract-The Archaean Dharwar craton is characterized by two greenstone successions: the > 3 Ga Sargur Group and the 3.0-2.5 Ga Dharwar Supergroup. Examples of both successions are described from the region of Jayachamarajapura where they are also distinguished by different tectonic patterns. The younger greenstones have undergone only minor deformation and are only slightly metamorphosed and so provide a good case study of the relative behavior of greenstones in relation to their granite-gneiss country rocks. A detailed structural analysis indicates two strain fields associated with two deformational episodes: Dr and Dz. The Dr episode produced domeand-basin structures and affected merely the older greenstones and the gneisses. The mapped strain field is compatible with the hypothesis that it is associated with the development of diapiric-type gravitational instabilities. The Dz episode affects only the younger greenstone belt, which has the overall geometry of a complex syncline. It is discordant over a complex of gneisses and older greenstones that was deformed during the Dr episode. The base of the discordant cover sequence is tectonized and constitutes a dtcollement surface. Kinematic criteria at this surface have opposite sense and converge towards the belt axis. These structural features are interpreted in terms of progressive deformation compatible with the incipient development of a sagducting trough.These results are consistent with those obtained from other parts of the craton, where the tectonic evolution appears to reflect mainly relative vertical displacements facilitated by the reheating of continental crust during two major Archaean tectonometamorphic episodes.

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Structural tests of diapir hypotheses in Archean crust of Ontario

Cited by 37 publications

References 19 publications

Implications of passive salt diapir kinematics for reservoir segmentation by radial and concentric faults

Implications of passive salt diapir kinematics for reservoir segmentation by radial and concentric faults

Granitic magma ascent and emplacement: neither diapirism nor neutral buoyancy

Strain patterns, décollement and incipient sagducted greenstone terrains in the Archaean Dharwar craton (south India)

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