Continental lithosphere strength: the critical role of lower crustal deformation

Kusznir, Nick; Park, R. G.

doi:10.1144/gsl.sp.1986.024.01.09

Cited by 81 publications

(57 citation statements)

References 17 publications

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“…at depths within 12-15 km. These conditions cannot correspond to the steadystate ductile -brittle transition in a melt-devoid crust, where the rheology is likely controlled by quartz as the softer mineral phase (Handy, 1990), hence a ductile -brittle transition at about 350 8C (Kusznir and Park, 1986). Nevertheless, a transient brittle behaviour may result from the magmatic overpressure driven by magma squeezing at a deeper level (Williams et al, 1995).…”

Section: The Gapmentioning

confidence: 99%

Syntectonic granite emplacement at different structural levels: the Closepet granite, South India

Moyen

Nédélec

Martin

et al. 2003

Journal of Structural Geology

110

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The Closepet granite, in South India, is a large (400 km long but only 30 km wide), elongate, Late Archaean granitic body. Structural levels from deep crust to upper levels crop out, as evidenced by a shallowing of paleo-depths from north to south all along the Closepet granite. This allows the study of the emplacement of the same granitic body at various crustal levels. Four zones have been identified: a root zone, where magmas are collected in active shear zones; a transfer zone, featuring large-scale magma ascent and crystal -liquid partitioning in the granitic 'mush'; a 'gap', where the mush was filtered, allowing only the liquids to rise; shallow intrusions, filled with this liquid.The Closepet granite was emplaced syntectonically. Field work and anisotropy of magnetic susceptibility allowed documentation of steep foliations with subhorizontal lineations, both in the root and transfer zones and in the shallow intrusions. Remote sensing evidenced a network of shear zones bounding the Closepet granite. In the porphyritic root and transfer zones, magmas cooled slowly, thus developing strong fabrics during large-scale dextral shearing. Ascent of residual liquids amidst the crystallizing solid framework was not recorded in the fabrics. However, these liquids were channelised through the gap and infilled the homogeneous shallow intrusions, where rapid cooling only permitted the development of feint, although wholly consistent, fabrics. q

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Section: The Gapmentioning

confidence: 99%

Syntectonic granite emplacement at different structural levels: the Closepet granite, South India

Moyen

Nédélec

Martin

et al. 2003

Journal of Structural Geology

110

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“…The mechanical strength, in turn, depends on lithospheric structure, composition, geothermal gradient, volatile content, as well as on the rates of the applied processes (e.g., Watts and Burov, 2003;Freed et al, 2012). Where the lower continental crust is quartzo-feldspathic or with elevated geotherms, extensional stress is accommodated by creep rather than by faulting, and the lower crust deforms aseismically (e.g., Sibson, 1982;Kusznir and Park, 1986;Chen and Molnar, 1983;Wells and Coppersmith, 1994;Niemi et al, 2004) (e.g., Fig. 1B).…”

Section: Along-axis Segmentationmentioning

confidence: 99%

The time scales of continental rifting: Implications for global processes

Ebinger

Wijk

Keir

2013

The Web of Geological Sciences: Advances, Impacts, and Interactions

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The rifting cycle initiates with stress buildup, release as earthquakes and/or magma intrusions/eruptions, and visco-elastic rebound, multiple episodes of which combine to produce the observed, time-averaged rift zone architecture. The aim of our synthesis of current research initiatives into continental rifting-to-rupture processes is to quantify the time and length scales of faulting and magmatism that produce the time-averaged rift structures imaged in failed rifts and passive margins worldwide. We compare and contrast seismic and geodetic strain patterns during discrete, intense rifting episodes in magmatic and amagmatic sectors of the East African rift zone that span early-to late-stage rifting. We also examine the longer term rifting cycle and its relation to changing far-fi eld extension directions with examples from the Rio Grande rift zone and other cratonic rifts. Over time periods of millions of years, periods of rotating regional stress fi elds are marked by a lull in magmatic activity and a temporary halt to tectonic rift opening. Admittedly, rifting cycle comparisons are biased by the short time scale of global seismic and geodetic measurements, which span a small fraction of the 10 2 -10 5 year rifting cycle. Within rift sectors with upper crustal magma chambers beneath the central rift valley (e.g., Main Ethiopian, Afar, and Eastern or Gregory rifts) seismic energy release accounts for a small fraction of the deformation; most of the strain is accommodated by magma intrusion and slowslip. Magma intrusion processes appear to decrease the time period between rifting episodes, effectively accelerating the rift to rupture process. Thus, the inter-seismic period in rift zones with crustal magma reservoirs is strongly dependent upon the

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“…In an analog rheological reasoning for continental crust, the occurrence of a mid-crustal transition zone in which crustal rocks change from a brittle to a ductile deformation mode has been proposed (e.g., [13]). At temperatures higher than 300^450 ‡C (depending on the composition, strain rate and geotherm), normally corresponding to lower crustal levels, rocks attain such a low viscosity that can actually creep-£ow [12].…”

Section: Ductile Lower Crustal Zonementioning

confidence: 99%

Mechanical (de-)coupling of the lithosphere in the Valencia Trough (NW Mediterranean): what does it mean?

Gaspar‐Escribano

Voorde

Roca

et al. 2003

Earth and Planetary Science Letters

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We study the mechanics of lithospheric decoupling in continental extensional basins in relation to the distribution of (non-)competent mechanical layers within the lithosphere and the position of the isostatic compensation level. We specifically address the different modes of deformation taking place in crustal levels according to a self-consistent formulation of the concept of mechanical decoupling. Subsequently, we investigate the style of lithospheric decoupling in the Valencia Trough (NW Mediterranean), a prime example of a young continental rift basin. During its evolution, the lower crust (or at least part of it) acted as a weak, non-competent layer that eventually flowed laterally to accommodate deformation in the subcrustal lithosphere and overlying crust, which became mechanically decoupled. We use a numerical model to discern whether these two layers deformed fully independently (vertical decoupling), or maintaining a mechanical link (horizontal and partial decoupling). Results of our study, constrained by a high-quality database, exclude fully decoupled mode and favor isostatic compensation level in the asthenosphere. Interpretation of our results in light of geological and geophysical data suggests that the present Valencia Trough is best described by partial lithospheric decoupling. ß

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Continental lithosphere strength: the critical role of lower crustal deformation

Cited by 81 publications

References 17 publications

Syntectonic granite emplacement at different structural levels: the Closepet granite, South India

Syntectonic granite emplacement at different structural levels: the Closepet granite, South India

The time scales of continental rifting: Implications for global processes

Mechanical (de-)coupling of the lithosphere in the Valencia Trough (NW Mediterranean): what does it mean?

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