12 research outputs found
Reappraisal of the magma-rich versus magma-poor rifted margin archetypes
Abstract Rifted margins are commonly defined as magma-poor or magma-rich archetypes based on their morphology. We re-examine the prevailing model inferred from this classification that magma-rich margins have excess decompression melting at lithospheric breakup compared with steady-state seafloor spreading, while magma-poor margins have inhibited melting. We investigate the magmatic budget related to lithospheric breakup along two high-resolution long-offset deep reflection seismic profiles across the SE Indian (magma-poor) and Uruguayan (magma-rich) rifted margins. Resolving the magmatic budget is difficult and several interpretations can explain our seismic observations, implying different mechanisms to achieve lithospheric breakup and melt production for each archetype. We show that the Uruguayan and other magma-rich margins may indeed involve excess decompression melting compared with steady-state seafloor spreading but could also be explained by a gradual increase with an early onset relative to crustal breakup. A late onset of decompression melting relative to crustal breakup enables mantle exhumation characteristic of magma-poor margin archetypes (e.g. SE India). Despite different volumes of magmatism, the mechanisms suggested at lithospheric breakup are comparable between both archetypes. Considerations on the timing of decompression melting onset relative to crustal thinning may be more important than the magmatic budget to understand the evolution and variability of rifted margins.</jats:p
Evolution morpho-tectonique et magmatique polyphasée des marges ultra-distales pauvres en magma : la transition océan-continent fossile de l'Err et de la Platta (SE Suisse) et comparaison avec des analogues actuels
The aim of this study is to investigate the morpho-structural and magmatic evolution of magma-poor distal rifted margins, as well as their reactivation. This study is focused on the fossil distal margins of the Alpine Tethys. The study of the reactivation of these domains, (Err and Platta, Switzerland) shows that alpine thrusts principally reworked former rift structures. The Err nappe can be restored as a hyper-extended domain characterized by a system of detachment faults with a complex architecture evolving in-sequence and leads to the continental crust separation and the exhumation of mantle. The Platta nappe corresponds to a subcontinental exhumed mantle domain associated to an increase of syn-tectonic magmatic additions oceanwards. The distal domain is interpreted as the relic of a dome-shaped structure capped by a detachment fault and crosscut by latter normal faults facilitating the emplacement of basalts and fluid circulations. The approach developed in this thesis enabled a better understanding of one distal and ultra-distal magma-poor rifted margin, as well as to discuss processes related to the formation and reactivation of plate boundaries.Cette thĂšse a pour but dâĂ©tudier lâĂ©volution morpho-structurale et magmatique des marges distales pauvres en magma ainsi que leur rĂ©activation. Cette Ă©tude est focalisĂ©e sur les marges fossiles distales de la TĂ©thys Alpine. LâĂ©tude de la rĂ©activation de ces domaines (lâErr et la Platta, Suisse) montre que les chevauchements alpins rĂ©activent principalement dâanciennes structures de rift. LâErr peut ainsi ĂȘtre restaurĂ©e et correspond Ă un ancien domaine de croute hyper-amincie caractĂ©risĂ© par un systĂšme de failles de dĂ©tachement qui Ă©volue en sĂ©quence et conduit Ă la rupture continentale et Ă lâexhumation du manteau. La Platta correspond Ă un domaine de manteau sous continental exhumĂ© associĂ© Ă une augmentation des additions magmatiques syn-tectoniques dans les parties distales. Ce domaine est interprĂ©tĂ© comme la relique dâune structure en dĂŽme coiffĂ©e par une faille de dĂ©tachement et recoupĂ©e par des failles normales favorisant la mise en place de magma et de fluides. Lâapproche utilisĂ©e a permis de mieux contraindre lâarchitecture dâune marge distale pauvre en magma et de discuter les processus de formation et de la rĂ©activation des limites de plaque
Morpho-tectono-magmatic evolution and reactivation of ultra-distal magma-poor rifted margins : the fossil Err-Platta Ocean-Continent-Transition (SE Switzerland) and comparison to present-day analogues
Cette thĂšse a pour but dâĂ©tudier lâĂ©volution morpho-structurale et magmatique des marges distales pauvres en magma ainsi que leur rĂ©activation. Cette Ă©tude est focalisĂ©e sur les marges fossiles distales de la TĂ©thys Alpine. LâĂ©tude de la rĂ©activation de ces domaines (lâErr et la Platta, Suisse) montre que les chevauchements alpins rĂ©activent principalement dâanciennes structures de rift. LâErr peut ainsi ĂȘtre restaurĂ©e et correspond Ă un ancien domaine de croute hyper-amincie caractĂ©risĂ© par un systĂšme de failles de dĂ©tachement qui Ă©volue en sĂ©quence et conduit Ă la rupture continentale et Ă lâexhumation du manteau. La Platta correspond Ă un domaine de manteau sous continental exhumĂ© associĂ© Ă une augmentation des additions magmatiques syn-tectoniques dans les parties distales. Ce domaine est interprĂ©tĂ© comme la relique dâune structure en dĂŽme coiffĂ©e par une faille de dĂ©tachement et recoupĂ©e par des failles normales favorisant la mise en place de magma et de fluides. Lâapproche utilisĂ©e a permis de mieux contraindre lâarchitecture dâune marge distale pauvre en magma et de discuter les processus de formation et de la rĂ©activation des limites de plaque.The aim of this study is to investigate the morpho-structural and magmatic evolution of magma-poor distal rifted margins, as well as their reactivation. This study is focused on the fossil distal margins of the Alpine Tethys. The study of the reactivation of these domains, (Err and Platta, Switzerland) shows that alpine thrusts principally reworked former rift structures. The Err nappe can be restored as a hyper-extended domain characterized by a system of detachment faults with a complex architecture evolving in-sequence and leads to the continental crust separation and the exhumation of mantle. The Platta nappe corresponds to a subcontinental exhumed mantle domain associated to an increase of syn-tectonic magmatic additions oceanwards. The distal domain is interpreted as the relic of a dome-shaped structure capped by a detachment fault and crosscut by latter normal faults facilitating the emplacement of basalts and fluid circulations. The approach developed in this thesis enabled a better understanding of one distal and ultra-distal magma-poor rifted margin, as well as to discuss processes related to the formation and reactivation of plate boundaries
Morpho-tectono-magmatic evolution and reactivation of ultra-distal magma-poor rifted margins : the fossil Err-Platta Ocean-Continent-Transition (SE Switzerland) and comparison to present-day analogues
Cette thĂšse a pour but dâĂ©tudier lâĂ©volution morpho-structurale et magmatique des marges distales pauvres en magma ainsi que leur rĂ©activation. Cette Ă©tude est focalisĂ©e sur les marges fossiles distales de la TĂ©thys Alpine. LâĂ©tude de la rĂ©activation de ces domaines (lâErr et la Platta, Suisse) montre que les chevauchements alpins rĂ©activent principalement dâanciennes structures de rift. LâErr peut ainsi ĂȘtre restaurĂ©e et correspond Ă un ancien domaine de croute hyper-amincie caractĂ©risĂ© par un systĂšme de failles de dĂ©tachement qui Ă©volue en sĂ©quence et conduit Ă la rupture continentale et Ă lâexhumation du manteau. La Platta correspond Ă un domaine de manteau sous continental exhumĂ© associĂ© Ă une augmentation des additions magmatiques syn-tectoniques dans les parties distales. Ce domaine est interprĂ©tĂ© comme la relique dâune structure en dĂŽme coiffĂ©e par une faille de dĂ©tachement et recoupĂ©e par des failles normales favorisant la mise en place de magma et de fluides. Lâapproche utilisĂ©e a permis de mieux contraindre lâarchitecture dâune marge distale pauvre en magma et de discuter les processus de formation et de la rĂ©activation des limites de plaque.The aim of this study is to investigate the morpho-structural and magmatic evolution of magma-poor distal rifted margins, as well as their reactivation. This study is focused on the fossil distal margins of the Alpine Tethys. The study of the reactivation of these domains, (Err and Platta, Switzerland) shows that alpine thrusts principally reworked former rift structures. The Err nappe can be restored as a hyper-extended domain characterized by a system of detachment faults with a complex architecture evolving in-sequence and leads to the continental crust separation and the exhumation of mantle. The Platta nappe corresponds to a subcontinental exhumed mantle domain associated to an increase of syn-tectonic magmatic additions oceanwards. The distal domain is interpreted as the relic of a dome-shaped structure capped by a detachment fault and crosscut by latter normal faults facilitating the emplacement of basalts and fluid circulations. The approach developed in this thesis enabled a better understanding of one distal and ultra-distal magma-poor rifted margin, as well as to discuss processes related to the formation and reactivation of plate boundaries
Defining diagnostic criteria to describe the role of rift inheritance in collisional orogens: the case of the Err-Platta nappes (Switzerland)
International audienc
The tectono-magmatic and subsidence evolution during lithospheric breakup in a salt-rich rifted margin: Insights from a 3D seismic survey from southern Gabon
International audienc
Carbonatation chaude en relation spatiale et gĂ©nĂ©tique avec la mise en place de basaltes durant lâexhumation mantellique TĂ©thysienne enregistrĂ©e dans la nappe de la Platta, Alpes Suisses
International audienceLes transitions ocĂ©an-continent (OCT) sont reconnues comme des environnements propices Ă la formation et au piĂ©geage dâhydrocarbures. Ainsi lors des derniĂšres dĂ©cennies, de nombreuses Ă©tudes ont Ă©tĂ© entreprises Ă travers lâacquisition de donnĂ©es de sismique rĂ©flexion, de modĂ©lisation numĂ©rique et analogique ou encore lâĂ©tude dâanalogues de terrain. Une importante dĂ©couverte a Ă©tĂ© la reconnaissance de roches mantelliques exhumĂ©es par des dĂ©tachements dans les parties les plus distales de certaines marges. Ces structures ressemblent Ă celles imagĂ©es le long des rides ocĂ©aniques au niveau des Oceanic Core Complex. Ces structures tectoniques focalisent des circulations de fluides rĂ©agissant avec de larges volumes de roches mafiques (systĂšmes hydrothermaux) et ultramafiques (serpentinisation, ophicalcitisation) et aboutissent notamment Ă des minĂ©ralisations spĂ©cifiques (sites de Rainbow, Lost-City, TAG sur la dorsale atlantique). Dans la nappe de la Platta (Canton des Grisons, Suisse), les serpentinites sont affectĂ©es par une carbonatation importante (ophicalcites) en relation spatiale avec un dĂ©tachement Jurassique associĂ© avec la formation de lâocĂ©an tĂ©thysien. Dans ce travail nous caractĂ©risons dâabord dâun point de vue structural les relations entre les circulations fluides gĂ©nĂ©ratrices dâophicalcites et le fonctionnement du dĂ©tachement, en suite de quoi nous caractĂ©risons par une approche pĂ©tro-gĂ©ochimique, notamment en isotopes stables, les sources des fluides impliquĂ©es et les conditions de leur circulation. La carbonatation affecte les basaltes au toit du dĂ©tachement ainsi que les serpentinites sous-jacentes sur quelques dizaines de mĂštres. Les compositions isotopiques des veines calcitiques recoupant les basaltes autant que les serpentinites sont homogĂšnes Ă la fois en ÎŽ18O (autour de 16%o) et ÎŽ13C (0-1%o). Ces donnĂ©es sont compatibles avec un seul Ă©vĂ©nement de carbonatation. Le fluide est dĂ©rivĂ© de lâeau de mer, et gĂ©nĂšre la carbonatation Ă des tempĂ©ratures entre 90 et 105 C. La circulation des fluides est associĂ©e Ă lâavĂšnement du magmatisme basaltique, dont : i) les Ă©panchements ont fourni la charge lithostatique requise pour la rĂ©activation de ce segment du dĂ©tachement ; ii) la chaleur a dĂ©clenchĂ© lâadvection de fluides, en particulier, Ă lâinterface basalte-serpentinite. Le systĂšme de la Platta reprĂ©sente un " end-member " des processus de carbonatation hydrothermaux en relation avec le magmatisme dans un contexte dâexhumation mantellique
Birth of an oceanic spreading center at a magma-poor rift system
Abstract Oceanic crust is continuously created at mid-oceanic ridges and seafloor spreading represents one of the main processes of plate tectonics. However, if oceanic crust architecture, composition and formation at present-day oceanic ridges are largely described, the processes governing the birth of a spreading center remain enigmatic. Understanding the transition between inherited continental and new oceanic domains is a prerequisite to constrain one of the last major unsolved problems of plate tectonics, namely the formation of a stable divergent plate boundary. In this paper, we present newly released high-resolution seismic reflection profiles that image the complete transition from unambiguous continental to oceanic crusts in the Gulf of Guinea. Based on these high-resolution seismic sections we show that onset of oceanic seafloor spreading is associated with the formation of a hybrid crust in which thinned continental crust and/or exhumed mantle is sandwiched between magmatic intrusive and extrusive bodies. This crust results from a polyphase evolution showing a gradual transition from tectonic-driven to magmatic-driven processes. The results presented in this paper provide a characterization of the domain in which lithospheric breakup occurs and enable to define the processes controlling formation of a new plate boundary
The syn-rift stratigraphic record across a fossil hyper-extended rifted margin: the example of the northwestern Adriatic margin exposed in the Central Alps
International audienceTo understand the overall spatial and temporal evolution and resulting sedimentary stacking patterns within an evolving hyper-extended rift system, we investigated the Austroalpine and Upper Penninic nappes in the Central Alps. These nappes preserve pristine remnants of the northwestern Adriatic rifted margin showing the transition from stretched and hyper- extended continental crust to exhumed mantle of a sediment-starved, magma-poor rifted margin. Our paper reviews sedi- mentological and structural data that enable us to determine a general chrono-tectono-stratigraphic framework for the syn-rift succession of the margin. The detailed study of the facies distribution within the different rift domains, including proximal, necking, hyper-extended, and exhumed mantle domains, allow us to identify syn- and post-tectonic sedimentary packages. The correlation of these sedimentary packages between the rift domains is based on the identification of basin-wide cor- relative stratigraphic intervals linked to global or basin-wide Jurassic events: (1) the Early Toarcian Oceanic Anoxic Event; (2) an Early Bajocian bio-siliceous event; and (3) the onset of Tithonian carbonate-dominated sedimentation. Using these timelines, we could recognize the oceanward propagation of the syn-tectonic package from the proximal to the exhumed mantle domains as a function of time. A key observation is that syn-tectonic packages can be compartmentalized into four tectonic system tracts across the margin. Each system tract and their associated bounding surfaces record the stratigraphic evolution and change in deformation mode related to distinct and successive syn-rift phases that correspond to the stretching (~ 10My), necking (~ 6My), hyper-extension (~ 15My), and mantle exhumation (~ 18My) phases
Reappraisal of the magma-rich versus magma-poor rifted margin archetypes
International audienc