The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
C. Ruppel - One of the best experts on this subject based on the ideXlab platform.
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Extensional processes in Continental Lithosphere
Journal of Geophysical Research, 1995Co-Authors: C. RuppelAbstract:Since Vening-Meinesz's realization that the East African Rift represented an extensional, not compressional, feature and since the widespread acceptance of plate tectonics two decades later, research on the nature and causes of extensional tectonism within Continental Lithosphere has intensified. Among the manifestations of extensional processes affecting Continental Lithosphere are passive margins (Atlantic margin), discrete intraContinental rift zones (East African Rift), diffuse rifts (Basin and Range Province), strike-slip dominated rifts (Dead Sea Rift), and rifts in zones of regional compression (Tibetan grabens). Although no two rift zones are alike, Continental rifts can generally be characterized by normal faulting with subsidiary strike-slip faulting, lithospheric thinning which outpaces crustal stretching; varying amounts of alkaline magmatism, heat flow that is locally elevated near faults and magmatic centers, and crust that has experienced magmatic underplating and some amount of magmatic intrusion. Most aspects of rift related deformation can;be explained in terms of three parameters: (1) lithospheric and (sometimes) asthenospheric thermal structure, (2) lithospheric (particularly crustal) theology, and (3) temporal factors such as the absolute age, timing, and rate of extension. The interaction of these physical parameters determines the eventual outcome of rifting (failure or progression to complete Continental breakup), the patterns of subsidence and uplift, and the mode of extensional deformation. Modes of rifting (the Lithosphere's mechanical response to extensional stress) can be broadly, divided into pure shear, simple shear, and lower crustal flow mechanisms. In a general sense, these categories of rift mechanisms can account for observations at rifted margins, in the Basin and Range Province, and at metamorphic core complexes respectively. The mechanisms of Continental Lithosphere rifting (the effects) are here distinguished from the processes which actually drive extension (the causes). Following the terminology of previous authors; the causal processes are categorized as either passive or active: Passive processes originate at plate boundaries or in response to convective drag on the base of the Lithosphere, while active processes are seated in the sublithospheric mantle and typically involve the interaction of mantle plumes and the lithospheric plates. A peculiar set of factors, including the local stress state, the retreat of a subducting plate, and convective instability of thickened crustal roots, may drive extension in compressional settings like Tibet. In the future, rifting studies are likely to focus on further clarification of the active and passive rifting terminology, better constraints on deformation rates and lithospheric theology and thermal structure, along-axis segmentation of rifts, and the analogies and differences between rifting on Earth and nearby planets.
Othmar Muntener - One of the best experts on this subject based on the ideXlab platform.
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thinning mechanisms of heterogeneous Continental Lithosphere
Earth and Planetary Science Letters, 2019Co-Authors: Benoit Petri, Garry D. Karner, Thibault Duretz, Geoffroy Mohn, Stefan M Schmalholz, Othmar MuntenerAbstract:Abstract The mechanisms responsible for the formation of extremely thinned Continental crust ( P 0 ) vs. depth diagrams of crustal to lithospheric sections, to quantify rift-related modifications on inherited lithostatic pressure gradients. Two field examples from the Alpine Tethys margins in the Eastern and Southern Alps (SE Switzerland and N Italy) were selected to characterize: (1) the pre-rift architecture of the Continental Lithosphere; (2) the localization of rift-related deformation in distinct portions of the Lithosphere; and (3) the interaction between pre-existing heterogeneities of the Lithosphere and rift-related structures. These observations are compared with high-resolution, two-dimensional thermo-mechanical numerical models. The design of the models takes into account pre-existing mechanical heterogeneities representing the initial pre-rift architecture of the Continental Lithosphere. Extensional structures consist of high-angle and low-angle normal faults, anastomosing shear-zones and decoupling horizons. Such structures accommodate the lateral extraction of mechanically stronger levels derived from the middle to lower crust. As a result, the extremely thinned Continental crust in Tethyan passive margins represents the juxtaposition and amalgamation of distinct strong levels of the crust separated by major extensional structures identified by sharp pressure gradients. Future work should determine the applicability of these results to other present-day and fossil rifted margins.
Louis Moresi - One of the best experts on this subject based on the ideXlab platform.
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the structural evolution of the deep Continental Lithosphere
Tectonophysics, 2017Co-Authors: C M Cooper, Meghan S Miller, Louis MoresiAbstract:Abstract Continental Lithosphere houses the oldest and thickest regions of the Earth's surface. Locked within this deep and ancient rock record lies invaluable information about the dynamics that has shaped and continue to shape the planet. Much of that history has been dominated by the forces of plate tectonics which has repeatedly assembled super continents together and torn them apart - the Wilson Cycle. While the younger regions of Continental Lithosphere have been subject to deformation driven by plate tectonics, it is less clear whether the ancient, stable cores formed and evolved from similar processes. New insight into Continental formation and evolution has come from remarkable views of deeper lithospheric structure using enhanced seismic imaging techniques and the increase in large volumes of broadband data. Some of the most compelling observations are that the Continental Lithosphere has a broad range in thicknesses ( 300 km), has complex internal structure, and that the thickest portion appears to be riddled with seismic discontinuities at depths between ~ 80 and ~ 130 km. These internal structural features have been interpreted as remnants of lithospheric formation during Earth's early history. If they are remnants, then we can attempt to investigate the structure present in the deep Lithosphere to piece together information about early Earth dynamics much as is done closer to the surface. This would help delineate between the differing models describing the dynamics of craton formation, particularly whether they formed in the era of modern plate tectonics, a transitional mobile-lid tectonic regime, or are the last fragments of an early, stagnant-lid planet. Our review paper (re)introduces readers to the conceptual definitions of the Lithosphere and the complex nature of the upper boundary layer, then moves on to discuss techniques and recent seismological observations of the Continental Lithosphere. We then review geodynamic models and hypotheses for the formation of the Continental Lithosphere through time and implications for the formation and preservation of deep structure. These are contrasted with the dynamical picture of modern day Continental growth during lateral accretion of juvenile crust with reference to examples from the Australian Tasmanides and the Alaskan accretionary margin.
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The thermal structure of stable Continental Lithosphere within a dynamic mantle
Earth and Planetary Science Letters, 2004Co-Authors: C M Cooper, Adrian Lenardic, Louis MoresiAbstract:Abstract The thermal structure of stable Continental Lithosphere is determined by (1) the concentration and distribution of heat sources within the crust and (2) the amount of heat input from the convecting mantle. The self-consistent coupling of these two factors has not been included in thermal models of stable Lithosphere to date. We conducted two suites of numerical simulations (one with variable crustal heat production and the other with a chemically distinct cratonic root) to explore the thermal coupling between stable Continental Lithosphere and the convecting mantle. The distribution of heat producing elements within the crustal column was found to play a significant role in determining the local thermal structure of the Continental Lithosphere. Concentrating heat producing elements in the lower crust lead to a thinner thermal Lithosphere. Mantle heat flux into the base of stable continents was low relative to surface heat flux and did not vary significantly within the simulations regardless of the presence or absence of a thick cratonic root. A suite of simulations with variable root thickness indicated that although cratonic roots have a weak effect on surface heat flow patterns, relative to crustal heat source variations, they do have a pronounced effect on deeper thermal structure. Roots stabilized temporal variations of deep Continental geotherms and were required to generate a thick thermal Lithosphere. The ratio of thermal to chemical lithospheric thickness was found to decrease toward unity with increasing root thickness and thick cratonic roots limited small-scale mantle convection beneath themselves.
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How long can diamonds remain stable in the Continental Lithosphere
Earth and Planetary Science Letters, 2003Co-Authors: Craig O'neill, Louis MoresiAbstract:Abstract Do Archean ages obtained for diamonds from many of the world’s cratons constitute a strong constraint on the thermal state of the Archean Continental Lithosphere? The apparent longevity of diamonds obtained from cratonic kimberlites [Boyd et al., Nature 315 (1985) 387–389; Richardson et al., Nature 310 (1984) 198–202] has been used to infer the physical and chemical isolation of cratonic roots from the convecting mantle since 3 Ga. This would also provide an extremely strong constraint on the thermal history of the lithospheric mantle – requiring low temperatures at depth for its entire history. Recent evidence suggests, however, that the published ‘diamond’ ages may not represent the ages of the diamonds themselves, but significantly pre-date them [Shimizu and Sobolev, Nature 375 (1995) 308–311; Spetsius et al., Earth Planet. Sci. Lett. 199 (2002) 111–126]. We use a particle-in-cell finite element code to model the thermal stability of the Continental Lithosphere in a convecting mantle. The Continental crust modulates the thermal conditions of the underlying mantle Lithosphere, increasing the depth of the thermal boundary layer beneath the continent and providing a mechanism for stabilizing the sub-Continental thermal field. If diamonds have survived in cratonic roots since the Archean, the conditions necessary for diamond stability must have existed in the Archean Continental Lithosphere, and those conditions must have remained relatively unperturbed for ∼3 Gyr [Boyd et al., Nature 315 (1985) 387–389]. Here, the longevity of the diamond stability field is explored for systems with chemically distinct Continental crust and a strongly temperature-dependent mantle viscosity. Such models frequently produce the temperature conditions needed to form diamonds within the Archean Lithosphere, but the temperature fluctuations experienced within the modeled mantle Lithosphere are generally able to destroy these diamonds within 1 Gyr. Increasing the distance to active margins has only a marginal effect on the longevity of the diamond stability field. Convectively stable cratonic roots extend the lifetime of the diamond stability field in those regions. However, while the residence time of diamonds approaches the order of magnitude required (284–852 Myr), extremely fortuitous mantle conditions are required to explain Archean diamonds.
Thibault Duretz - One of the best experts on this subject based on the ideXlab platform.
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thinning mechanisms of heterogeneous Continental Lithosphere
Earth and Planetary Science Letters, 2019Co-Authors: Benoit Petri, Garry D. Karner, Thibault Duretz, Geoffroy Mohn, Stefan M Schmalholz, Othmar MuntenerAbstract:Abstract The mechanisms responsible for the formation of extremely thinned Continental crust ( P 0 ) vs. depth diagrams of crustal to lithospheric sections, to quantify rift-related modifications on inherited lithostatic pressure gradients. Two field examples from the Alpine Tethys margins in the Eastern and Southern Alps (SE Switzerland and N Italy) were selected to characterize: (1) the pre-rift architecture of the Continental Lithosphere; (2) the localization of rift-related deformation in distinct portions of the Lithosphere; and (3) the interaction between pre-existing heterogeneities of the Lithosphere and rift-related structures. These observations are compared with high-resolution, two-dimensional thermo-mechanical numerical models. The design of the models takes into account pre-existing mechanical heterogeneities representing the initial pre-rift architecture of the Continental Lithosphere. Extensional structures consist of high-angle and low-angle normal faults, anastomosing shear-zones and decoupling horizons. Such structures accommodate the lateral extraction of mechanically stronger levels derived from the middle to lower crust. As a result, the extremely thinned Continental crust in Tethyan passive margins represents the juxtaposition and amalgamation of distinct strong levels of the crust separated by major extensional structures identified by sharp pressure gradients. Future work should determine the applicability of these results to other present-day and fossil rifted margins.
Guilhem Barruol - One of the best experts on this subject based on the ideXlab platform.
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Rheological heterogeneity, mechanical anisotropy and deformation of the Continental Lithosphere
Tectonophysics, 1998Co-Authors: Alain Vauchez, Andréa Tommasi, Guilhem BarruolAbstract:Abstract This paper aims to present an overview on the influence of rheological heterogeneity and mechanical anisotropy on the deformation of continents. After briefly recapping the concept of rheological stratification of the Lithosphere, we discuss two specific issues: (1) as supported by a growing body of geophysical and geological observations, crust/mantle mechanical coupling is usually efficient, especially beneath major transcurrent faults which probably crosscut the Lithosphere and root within the sublithospheric mantle; and (2) in most geodynamic environments, mechanical properties of the mantle govern the tectonic behaviour of the Lithosphere. Lateral rheological heterogeneity of the Continental Lithosphere may result from various sources, with variations in geothermal gradient being the principal one. The oldest domains of continents, the cratonic nuclei, are characterized by a relatively cold, thick, and consequently stiff Lithosphere. On the other hand, rifting may also modify the thermal structure of the Lithosphere. Depending on the relative stretching of the crust and upper mantle, a stiff or a weak heterogeneity may develop. Observations from rift domains suggest that rifting usually results in a larger thinning of the lithospheric mantle than of the crust, and therefore tends to generate a weak heterogeneity. Numerical models show that during Continental collision, the presence of both stiff and weak rheological heterogeneities significantly influences the large-scale deformation of the Continental Lithosphere. They especially favour the development of lithospheric-scale strike-slip faults, which allow strain to be transferred between the heterogeneities. An heterogeneous strain partition occurs: cratons largely escape deformation, and strain tends to localize within or at the boundary of the rift basins provided compressional deformation starts before the thermal heterogeneity induced by rifting are compensated. Seismic and electrical conductivity anisotropies consistently point towards the existence of a coherent fabric in the lithospheric mantle beneath Continental domains. Analysis of naturally deformed peridotites, experimental deformations and numerical simulations suggest that this fabric is developed during orogenic events and subsequently frozen in the lithospheric mantle. Because the mechanical properties of single-crystal olivine are anisotropic, i.e. dependent on the orientation of the applied forces relative to the dominant slip systems, a pervasive fabric frozen in the mantle may induce a significant mechanical anisotropy of the whole lithospheric mantle. It is suggested that this mechanical anisotropy is the source of the so-called tectonic inheritance, i.e. the systematic reactivation of ancient tectonic directions; it may especially explain preferential rift propagation and Continental break-up along pre-existing orogenic belts. Thus, the deformation of continents during orogenic events results from a trade-off between tectonic forces applied at plate boundaries, plate geometry, and the intrinsic properties (rheological heterogeneity and mechanical anisotropy) of the Continental plates.
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Rheological heterogeneity, mechanical anisotropy and deformation of the Continental Lithosphere
Tectonophysics, 1998Co-Authors: Alain Vauchez, Andréa Tommasi, Guilhem BarruolAbstract:International audienceThis paper aims to present an overview on the influence of rheological heterogeneity and mechanical anisotropy on the deformation of continents. After briefly recapping the concept of rheological stratification of the Lithosphere, we discuss two specific issues: (1) as supported by a growing body of geophysical and geological observations, crust=mantle mechanical coupling is usually efficient, especially beneath major transcurrent faults which probably crosscut the Lithosphere and root within the sublithospheric mantle; and (2) in most geodynamic environments, mechanical properties of the mantle govern the tectonic behaviour of the Lithosphere. Lateral rheological heterogeneity of the Continental Lithosphere may result from various sources, with variations in geothermal gradient being the principal one. The oldest domains of continents, the cratonic nuclei, are characterized by a relatively cold, thick, and consequently stiff Lithosphere. On the other hand, rifting may also modify the thermal structure of the Lithosphere. Depending on the relative stretching of the crust and upper mantle, a stiff or a weak heterogeneity may develop. Observations from rift domains suggest that rifting usually results in a larger thinning of the lithospheric mantle than of the crust, and therefore tends to generate a weak heterogeneity. Numerical models show that during Continental collision, the presence of both stiff and weak rheological heterogeneities significantly influences the large-scale deformation of the Continental Lithosphere. They especially favour the development of lithospheric-scale strike-slip faults, which allow strain to be transferred between the heterogeneities. An heterogeneous strain partition occurs: cratons largely escape deformation, and strain tends to localize within or at the boundary of the rift basins provided compressional deformation starts before the thermal heterogeneity induced by rifting are compensated. Seismic and electrical conductivity anisotropies consistently point towards the existence of a coherent fabric in the lithospheric mantle beneath Continental domains. Analysis of naturally deformed peridotites, experimental deformations and numerical simulations suggest that this fabric is developed during orogenic events and subsequently frozen in the lithospheric mantle. Because the mechanical properties of single-crystal olivine are anisotropic, i.e. dependent on the orientation of the applied forces relative to the dominant slip systems, a pervasive fabric frozen in the mantle may induce a significant mechanical anisotropy of the whole lithospheric mantle. It is suggested that this mechanical anisotropy is the source of the so-called tectonic inheritance, i.e. the systematic reactivation of ancient tectonic directions; it may especially explain preferential rift propagation and Continental break-up along pre-existing orogenic belts. Thus, the deformation of continents during orogenic events results from a trade-off between tectonic forces applied at plate boundaries, plate geometry, and the intrinsic properties (rheological heterogeneity and mechanical anisotropy) of the Continental plates