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1.
Laurent Desmurs Othmar Müntener Gianreto Manatschal 《Contributions to Mineralogy and Petrology》2002,144(3):365-382
Exhumation of subcontinental mantle rocks and its exposure at the seafloor is known from different magma-poor passive continental margins. However, the transition from largely amagmatic passive rifting to seafloor spreading is still poorly documented. In this contribution we use MOR-type gabbroic and basaltic rocks to characterize the magmatism associated with the formation of an ancient ocean-continent transition preserved in the Platta nappe, eastern Switzerland. Gabbros form individual small intrusions into exhumed serpentinized subcontinental mantle rocks. Mineral and bulk-rock chemistry and simple modeling indicate that each gabbro body records different magmatic processes ranging from predominantly fractional crystallization to solidification without fractionation. Mg numbers and Ni contents of equilibrium olivine calculated from basalts and gabbros indicate that few mafic rocks are primary melts but most represent fractionated compositions ranging from T- to N-MORB. Whereas most mafic rocks may be explained by low to moderate degrees of melting of an N-MORB-type mantle, the source of some basalt is enriched in incompatible elements. This compositional variation seems to correlate with the spatial distribution of the mafic rocks within the ocean-continent transition whereby mafic rocks with T-MORB signatures occur close to the continental margin whereas N-MORB signatures are predominantly found oceanwards. As in an opening system time and space are closely linked, the chemical evolution of the mafic rocks along the ocean-continent transitions suggests continuous thinning of the subcontinental mantle and associated uplift of the underlying asthenosphere during the time between the crustal and the lithospheric breakup. 相似文献
2.
Although of different age, the undeformed Cretaceous Iberia/Newfoundland margins and the relics of the Jurassic Briançonnais/Adriatic margins preserved in the Alps document a similar spatial and temporal evolution of rifting suggesting that the evolution of both pairs of margins was controlled by the same processes. Rifting appears to depend strongly on the thermal history of the lithosphere, which controls the rheology and consequently also the structural evolution of the margin. The tectonic evolution of non-volcanic margins appears to be distinctly different from that of volcanic ones. 相似文献
3.
Tsvetomila Mateeva George A. Wolff Gianreto Manatschal Suzanne Picazo Nick J. Kusznir John Wheeler 《Swiss Journal of Geoscience》2017,110(2):457-478
Evidence from ultraslow spreading mid-ocean ridges and both fossil and present-day Ocean–Continent Transitions (OCT) demonstrates that mantle serpentinization resulting from the interaction of mantle rock and water during tectonic exhumation is widespread. Observations at white smokers in modern ocean settings suggest that methane produced by serpentinization can support methanotrophic bio-systems, which use methane as the only source of carbon. An important question is whether such bio-systems are more generally pervasive in their association with serpentinized mantle in the subsurface. In this study, we examined whether there is evidence for such a methanotrophic system in exhumed serpentinized mantle at a magma-poor rifted continental margin, by probing for characteristic biological markers in these and associated sedimentary rocks in the Totalp unit of SE Switzerland. This unit represents a remnant of the former OCT of the southern Alpine Tethyan margin and was chosen because of its mild Alpine tectonic and low-grade metamorphic overprint during Alpine orogeny, hence giving potential for the preservation of indigenous organic matter (OM). Totalp samples are characterized by low organic carbon contents of 11–647 ppm. The majority of the samples contain hydrocarbons in the form of n-alkanes in the range C17–C36. Some sediments contain isoprenoids, for example pristane and phytane and a suite of steranes that are consistent with a marine origin for the OM preserved in the rocks. Traces of marine planktonic and bacterial OM are preserved in the serpentinized mantle and overlying sediments of this ancient Tethyan OCT, but there is no evidence that the OM has been generated from methanotrophic bio-systems. 相似文献
4.
Nicolò Incerpi Luca Martire Gianreto Manatschal Stefano M. Bernasconi 《Swiss Journal of Geoscience》2017,110(2):439-456
This paper investigates hydrothermal fluid circulation in pre- and syn-tectonic sediments associated with detachments faults. The study area, located in the Err Nappe (SE-Switzerland), preserves a portion of the Adriatic distal margin. Two sites were studied in combining fieldwork, petrography, geochemistry and fluid inclusion analysis: the Piz Val Lunga and Fuorcla Cotschna areas. Both preserve relationships between a spectacularly exposed rift-related extensional detachment fault and its footwall and hangingwall that consist of extensional allochthons and syn- to post-tectonic sediments. These areas register a complex fluid flow history characterized by dolomitization, de-dolomitization, calcite cementation, dolomite and quartz veining and diffuse silicification. Meso- and micro-scale observations allow defining two steps in fluid evolution, which are related to Jurassic rift activity. A first carbonate-rich event occurred before the exhumation of the granitic basement, and this was followed by a second event marked by a change in the fluid towards a silica-dominated chemistry. Homogenization temperatures of fluid inclusions (average Th = 120?130 °C), negative δ18O values and a radiogenic 87Sr/86Sr signatures of carbonate minerals support the hypothesis that both the pre-tectonic rocks constituting the allochthons and the syn-tectonic sediments overlying the detachment fault were crossed by a flux of over-pressured hydrothermal fluids originating from seawater that penetrated into the basement through fault and fracture systems. Field relationships show that this fluid circulation started latest in middle Early Jurassic time, when fault activity migrated from the proximal to the future distal margin. We propose that it evolved chemically as a result of the involvement of the granitic basement forming the footwall of the extensional detachment system. Hydrothermal activity continued until the Middle/Late Jurassic, when tectonic activity shifted outwards leading to the exhumation of mantle rocks. This paper provides an original contribution to better understand the complex evolution of hyperextended continental rift domains and to constrain their thermal regimes. 相似文献
5.
Low-angle detachment faults are key to our understanding of the tectonic evolution of magma-poor rifted continental margins. In seismic images of present-day rifted margins the identification and interpretation of such features is, however, notoriously difficult and ambiguous. We address this problem by studying the structure and seismic response of such faults through a synoptic interpretation of petrophysical data and geological evidence from the distal segments of the present-day West Iberian and the ancient Tethyan margins. On the basis of the geologically well-constrained remnants of the Tethyan margins, which are spectacularly preserved and exposed in the Alps of Eastern Switzerland, vertical profiles at four key geological settings of a typical magma-poor rifted margin are constructed and their synthetic seismic responses are compared to the observed seismic data from corresponding locations in the present-day Iberian margin. The seismic structure of these profiles is considered as the sum of deterministic large-scale and the stochastic small-scale components. Both components are analyzed for all pertinent lithologies. The large-scale structures are derived from laboratory measurements on samples from both, the West Iberian and Tethyan margins, whereas the small-scale fluctuations are constrained predominantly on the basis of well-log data from the Iberian margin. Different realizations of the simulated stochastic small-scale velocity fluctuations illustrate the potential variability of impedance contrasts and its impact on the seismic response from lithological interfaces and fault structures. Our results indicate that the nature of the seismic response from low-angle detachment faults is largely determined through the fracture-healing behavior of the surrounding rocks. Geological evidence from the exposed fragments of the Tethyan margins indicate that fracture-healing is generally well developed in crustal lithologies, but largely absent in mantle lithologies. It is for this reason that low-angle, intra-crustal detachment faults tend to be seismically undetectable. Conversely, crust–mantle detachments have a complex and variable seismic response, depending on the nature of the damaged zone and on the frequency content of the seismic data. These model-based inferences are consistent with the available evidence from the present-day Iberian passive margin and thus open new perspectives for the interpretation of the corresponding seismic images. 相似文献
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7.
Emmanuel Masini Gianreto Manatschal Geoffroy Mohn Jean‐François Ghienne François Lafont 《Basin Research》2011,23(6):652-677
We describe the tectono‐sedimentary evolution of a Middle Jurassic, rift‐related supra‐detachment basin of the ancient Alpine Tethys margin exposed in the Central Alps (SE Switzerland). Based on pre‐Alpine restoration, we demonstrate that the rift basin developed over a detachment system that is traced over more than 40 km from thinned continental crust to exhumed mantle. The detachment faults are overlain by extensional allochthons consisting of upper crustal rocks and pre‐rift sediments up to several kilometres long and several hundreds of metres thick, compartmentalizing the distal margin into sub‐basins. We mapped and restored one of these sub‐basins, the Samedan Basin. It consists of a V‐shape geometry in map view, which is confined by extensional allochthons and floored by a detachment fault. It can be restored over a minimum distance of 11 km along and about 4 km perpendicular to the basin axis. Its sedimentary infill can be subdivided into basal (initial), intermediate (widening) and top (post‐tectonic) facies tracts. These tracts document (1) formation of the basin initially bounded by high‐angle faults and developing into low‐angle detachment faults, (2) widening of the basin and (3) migration of deformation further outboard. The basal facies tract is made of locally derived, poorly sorted gravity flow deposits that show a progressive change from hangingwall to footwall‐derived lithologies. Upsection the sediments develop into turbidity current deposits that show retrogradation (intermediate facies tract) and starvation of the sedimentary system (post‐tectonic facies tract). On the scale of the distal margin, the syn‐tectonic record documents a thinning‐ and fining‐upward sequence related to the back stepping of the tectonically derived sediment source, progressive starvation of the sedimentary system and migration of deformation resulting in exhumation and progressive delamination of the thinned crust during final rifting. This study provides valuable insights into the tectono‐sedimentary evolution and stratigraphic architecture of a supra‐detachment basin formed over hyper‐extended crust. 相似文献
8.
Emmanuel Masini Gianreto Manatschal Julie Tugend Geoffroy Mohn Jean-Marie Flament 《International Journal of Earth Sciences》2014,103(6):1569-1596
In this paper, we present a sedimentary and structural analysis that together with maps, sections and new Ar/Ar data enable to describe the tectono-sedimentary evolution of the Mauléon hyper-extended rift basin exposed in the W-Pyrenees. Hyper-extension processes that ultimately resulted in exhuming mantle rocks are the result of the subsequent development of two diachronous detachment systems related to two evolutional stages of rifting. An initial Late Aptian Early Albian crustal thinning phase is first recorded by the development of a crustal necking zone controlled by the north-vergent Southern Mauléon Detachment system. During a subsequent exhumation phase, active faulting migrates to the north with the emplacement of the Northern Mauléon detachment system that exhumed north section thinned continental crust and mantle rocks. This diachronous crustal thinning and exhumation processes are also recorded by the diachronous deposition of syn-tectonic sedimentary tracts above the two supra-detachment sub-basins. Syn-tectonic sedimentary tracts record the progressive exhumation of footwall rocks along detachment systems. Tectonic migration from the southern to the northern Mauléon Detachment system is recorded by the coeval deposition of “sag” deposits above the necking zone basin and of syn-tectonic tracts above exhumed rocks north section. Located on a hanging-wall situation related to the Mauléon hyper-extension structures, the Arzacq Basin also records a major crustal thinning phase as shown by its subsidence evolution so as by deep seismic images. The absence of major top-basement structures and its overall sag morphology suggest that crustal thinning processes occurred by decoupled extension of lower crustal levels contrasting with the Southern Mauléon Detachment system. Reconciling observations from the Mauléon and Arzacq Basins, we finally propose in this paper that they were the result of one and the same asymmetric crustal thinning and exhumation processes, where extension is accommodated into the upper crust in the Mauléon Basin (lower plate basin) and relayed in ductile lower crust below the Arzacq Basin (upper plate basin). 相似文献
9.
Petri B. Mohn G. Skrzypek E. Mateeva T. Galster F. Manatschal G. 《International Journal of Earth Sciences》2017,106(8):2873-2893
International Journal of Earth Sciences - The end of an orogenic cycle is commonly associated with a general extensional regime, widespread magmatism and complex metamorphic overprints. The... 相似文献
10.
Asymmetry or symmetry of magma‐poor rifted margins refers commonly to the crustal architecture and the occurrence or absence of large‐scale extensional detachment faults. While distal parts of magma‐poor rifted margins are often considered to be asymmetric, the observation of downlapping sedimentary sequences over exhumed mantle domains at conjugate margins suggests a symmetric evolution during mantle exhumation. On the basis of seismic observations along the Iberia–Newfoundland and Australia–Antarctica margins, we propose that their most distal parts show evidence for the development of multiple, out‐of‐sequence asymmetric detachment faults. We present evidence for cyclic delocalization and re‐localization of deformation, resulting in an apparent symmetry of the exhumed mantle domain. The interaction between out‐of‐sequence detachment systems and the successive rise of the asthenosphere may explain the observed transition from fault‐controlled to magma‐controlled strain accommodation and the transition to more symmetric and localized accretion associated with the formation of a stable spreading center. 相似文献