Seismic anisotropy, structures and geodynamics of continents Shear-wave splitting in the Appalachians and the Pyrenees: importance of the inherited tectonic fabric of the lithosphere

International audienceSplitting of teleseismic shear waves has been measured in the Appalachians (eastern USA) and the Pyrenees (western Europe) using data recorded by permanent and portable stations. From a comparison of the results, it appears that an interpretation of the recorded seismic anisotropy in terms of geodynamics is not straightforward. Successive geodynamic events have generated structures that may have resulted in a similar pattern of mantle flow and that therefore may have contributed in the development of the recorded anisotropy. Combining geological and geophysical arguments, it appears that the mantle anisotropy measured across the Appalachians and the Pyrenees may not be systematically Appalachian or Pyrenean in age but may be mainly due to a lithospheric structure formed during earlier major tectonic events, i.e. the Grenvillian and the Hercynian orogenies, respectively. We suggest that during major episodes of continent assembly, a pervasive tectonic fabric is developed in the lithospheric mantle. In the subsequent evolution of the continent, this fabric may induce a significant mechanical anisotropy that will drastically influence the mechanical behaviour of the Iithosphere when submitted to new tectonic events

Why do continents break-up parallel to ancient orogenic belts?

International audienceThe frequently observed parallelism between rifts and the pre­ existing orogenic fabric of continents suggests that the inherited tectonic fabric of the lithosphere influences the rupture of continents. We propose that the existence of a pervasive fabric in the lithospheric mantle induces an anisotropie strength in the lithosphere, that guides the propagation of continental rifts. Subcrustal mantle mechanical anisotropy is supported by (i) the anisotropie strength of olivine, (ii) an ubiquitous tectonic fabric in exposed mantle rocks, and (iii) measurements of seismic and electrical anisotropy. During major episodes of continent Rifting parallel to orogenic belts Ocean-opening through rifting and continent break-up is frequently related to the occurrence ofhotspots. There is, howevcr, a discrepancy between hot­ spots acting as pin point sources of heat and the linear extent of rifts over thou­ sands ofkilometres. Moreover rifts tend to parallel pre-existing orogenic fab

An integrated study of microstructural, geochemical, and seismic properties of the lithospheric mantle above the Kerguelen plume (Indian Ocean)

International audiencePeridotite xenoliths brought up to the surface by the volcanism of the Kerguelen Islands represent a mantle that has been affected by a high degree of partial melting followed by intense melt percolation above the Kerguelen plume. These xenoliths are therefore particularly suitable to investigate effects of melt-rock interaction on crystallographic fabrics (lattice-preferred orientation (LPO)) of peridotite minerals and on the LPO-induced seismic properties of peridotites above a mantle plume. We have studied a suite of 16 ultramafic samples representative of different degrees of partial melting and magma-rock interaction among which the protogranular harzburgites are the least metasomatised xenoliths and dunites are the ultimate stage of metasomatism. Olivine LPO is characterized by high concentration of [010] axes perpendicular to the foliation and [100] axes close to the lineation or distributed in the foliation plane in harzburgites, whereas the high concentration of [100] axes is parallel to the lineation and [010] axes is perpendicular to the assumed foliation in dunites. Olivine LPO in harzburgites is interpreted as being due to a deformation regime in axial compression or transpression. The fabric strength of olivine decreases progressively from protogranular to poikilitic harzburgites and finally to dunites, for which it remains nevertheless significant (J index 3.8). Seismic properties calculated from LPO of minerals indicate that metasomatism at higher melt/rock ratio lowers the P wave velocities. The most significant difference between harzburgites and dunites corresponds to the distribution of S wave anisotropy. Harzburgites display the maximum of anisotropy within the foliation plane and the minimum of anisotropy perpendicular to the foliation plane, whereas the lowest anisotropy is parallel to the lineation for dunites. These modifications of seismic properties as a result of metasomatic processes may induce seismic heterogeneities in the mantle above the Kerguelen plume. In addition, assuming a lithospheric mantle primarily harzburgitic and structured with a horizontal foliation, the seismic properties calculated for the Kerguelen xenoliths reconcile the rather high anisotropy evidenced by the horizontally propagating surface waves with the apparent isotropy revealed by the absence of splitting of vertically propagating teleseismic SKS waves recorded by the GEOSCOPE Kerguelen station

Evolução Cinemática das Porções Internas do Cinturão Dom Feliciano, Região de Piratini, RS

Dois episódios cinemáticos afetando rochas da associação de arco magmático precoce (AAM I) do Cinturão Dom Feliciano foram reconhecidos na área de Piratini: um fluxo tectônico mais antigo de orientação NW-SE seguido por um fluxo de orientação NE-SW. O fluxo tectônico precoce transversal ao alongamento do cinturão é registrado por zonas de cisalhamento sub-horizontais e subverticais. O fluxo tangencial é caracterizado por deformação de alta temperatura no estado sólido afetando gnaisses dioríticos da associação de arco magmático precoce. Estruturas de escala microscópica dessa deformação foram em grande parte obliteradas por migmatização e/ou injeções graníticas sin- a tardi-tectônicas. Os padrões de fluxo, tanto o de deformação no estado sólido quanto o magmático, sugerem movimento do bloco superior para NW. A zona de cisalhamento transcorrente NW-SE é caracterizada por uma movimentação levogira sob condições metamórficas da fácies anfibolito afetando gnaisses granodioríticos da AAM I. A trama resultante foi parcialmente rearranjada por crescimento estático da maioria dos minerais que foram subsequentemente recristalizados durante reativação dessas zonas de cisalhamento sob condições decrescentes de temperatura. A deformação tardia é caracterizada por fluxo paralelo ao orógeno (NE-SW) em (i) uma zona de cisalhamento transcorrente de escala regional associado com um expressivo magmatismo sincinemático, e (ii) ao longo de diversas zonas de cisalhamento discretas e subordinadas, retrabalhando as rochas ígneas pré-existente. Indicadores cinemáticos consistentes, nas zonas de cisalhamento discretas de pequena escala, sugerem sentido de cisalhamento dextrogiro. Essa deformação desenvolvida sob condições metamórficas retrogressivas da fácies anfibolito superior a xisto verde inferior foi provavelmente controlada pelo resfriamento dos granitoides sincinemáticos

The Paradoxes of Democracy and the Rule of Law

The promise of modernization after the Second World War was that economic growth, equality, the rule of law and democracy would proceed together. In many ways, this has happened. Yet many of the promises of social progress developed after WWII have been undermined by internal tensions within the democratic project, as well as by social and economic trends. While stating the challenges that these trends have posed for democratic institutions and actors, we also look at the responses (both proposals and practices) that have emerged in order to address those challenges. In doing this, we note that the very conception of democracy as liberal democracy (based on delegation and majority voting) is under stress as neoliberalism has attacked those very intermediary institutions (parties, unions, voluntary associations) that had been at the basis of the development of the welfare state and democratic capitalism. We start by noting the growth in inequality, which means that formal democracy is shaped by uneven power resources as concentration of wealth provides advantages in the capacity to influence public decision making with mutual convertibility of economic and political resources. The spiral of inequality and corporate political power is reflected in a growing legitimacy crisis in old and new democracies. Liberalism, which promised the separation between the state and the market, has evolved into neoliberalism, , based on the domination of the corporation, exacerbated by privatization and de-regulation. This has raised private profit criteria about considerations of the broader public good and in many cases encouraged corruption. The ensuing inefficiency and lack of transparency foster institutional mistrust, with perverse effects. Challenges are also related to the fact that democracy has been mainly defined in a national mode, with the demos identified as the nation. Economic rescaling produced by global capitalism has however a produced both de-territorialization and re-territorialization, which requires a (yet unachieved) rethinking of the basis for democracy but also of welfare and its foundation in both identities and institutions. In the North and (with different characteristics) in the South of the globe, movement of capital and of people pose challenges of national pluralism and its constitutional recognition, questioning key concepts such as the definition of political community and popular sovereignty and the . relationship between human rights and citizenship. Citizenship is more appropriately considered as related not to fixed institutions but rather as ‘acts of citizenships’ requiring subjectivity and agency and more inclusive conceptions. The main actors in democratic development have been affected by these challenges. Political parties are an important element in democracy but they have become an interest in their own right. A crisis of representation has emerged from growing social detachment of political parties from social cleavages as well as of elected representatives from the citizens. This had most dramatic effects on the Left, when left-wing parties have supported neoliberal reforms. Relying on expertise for the development of progressive policies is not a solution given the non-accountable power of science as well as the increasing challenges of privatization of knowledge-making, opacity of knowledge production and persistence of fundamental class imbalances in access to knowledge. Participatory channels of access to institutions have been opened to ‘ordinary citizens’ but, within neoliberalism, they are often based on individualist conceptions and do not address fundamental issues of inequalities. While citizens often call for direct participation, existing experiments rarely empower the citizens. While the judiciary has been seen as a surrogate for democratic participation for marginalized minority groups, its capacity for rights enforcement is limited by the expansion (in particular at international level) of a lex mercatoria as well as the use of courts in order to protect economic freedom from democratic dynamics. The rule of law has also been subverted by unequal access to the law and by the influence of money while the judiciary also has its own particular interests and corporate lawyers assume a brokerage function in globalized markets. On the other hand, in the control of political dissent, the state, rather than being weakened from globalization, increases its reach and power. The ‘war on terror’ has been used to challenge the rule of law by states of emergency as well as authoritarian drifts with attempts at imposing a permanent ‘state of exception’. On the other hand, progressive social movements have addressed growing inequalities and democratic crises by developing alternative visions of democracy, stressing participation over delegation and deliberation over majoritarian decision-making. Participatory and deliberative conceptions have been prefigured as well as elaborated in recent waves of protests. The consolidation of oppositional actors, however, faces challenges in the fragmentation of the potential social bases, the need to build a new collective identity as well as to establish channels of access to power. This has resulted from, but also triggered, the reduction in citizens’ entitlements and the weakening of the social contract upon which social progress depends

Perspectives on Europeanization of National Judiciaries: Old and New Questions

The aim of this article is to bring together different legal, political science and sociological perspectives addressing the problem of Europeanization of national judiciaries. In that sense, this article provides an overview of several old aspects regarding the way and extent national courts/judges adapted to their role of European judges. Next to that, it is looked into the manner of and reasons behind judges’ involvement in the process of EU legal integration, whereby a new research agenda is offered. For that purpose, new questions are raised and different empirical aspects are discussed concerning, for instance, courts compliance with EU law, the relevance of national judges’ individual profiles (knowledge, attitudes and values) but also the role of institutions (networks) and legal systems in the process of Europeanization of judges

Tectono-stratigraphic evolution and crustal architecture of the Orphan Basin during North Atlantic rifting

The Orphan Basin is located in the deep offshore of the Newfoundland margin, and it is bounded by the continental shelf to the west, the Grand Banks to the south, and the continental blocks of Orphan Knoll and Flemish Cap to the east. The Orphan Basin formed in Mesozoic time during the opening of the North Atlantic Ocean between eastern Canada and western Iberia–Europe. This work, based on well data and regional seismic reflection profiles across the basin, indicates that the continental crust was affected by several extensional episodes between the Jurassic and the Early Cretaceous, separated by events of uplift and erosion. The preserved tectono-stratigraphic sequences in the basin reveal that deformation initiated in the eastern part of the Orphan Basin in the Jurassic and spread towards the west in the Early Cretaceous, resulting in numerous rift structures filled with a Jurassic–Lower Cretaceous syn-rift succession and overlain by thick Upper Cretaceous to Cenozoic post-rift sediments. The seismic data show an extremely thinned crust (4–16 km thick) underneath the eastern and western parts of the Orphan Basin, forming two sub-basins separated by a wide structural high with a relatively thick crust (17 km thick). Quantifying the crustal architecture in the basin highlights the large discrepancy between brittle extension localized in the upper crust and the overall crustal thinning. This suggests that continental deformation in the Orphan Basin involved, in addition to the documented Jurassic and Early Cretaceous rifting, an earlier brittle rift phase which is unidentifiable in seismic data and a depth-dependent thinning of the crust driven by localized lower crust ductile flow