Search results for "Transition zone"
showing 10 items of 32 documents
Four- and five-phase peridotites from a continental rift system: evidence for upper mantle uplift and cooling at the Ross Sea margin (Antarctica)
1992
Upper mantle plagioclase+spinel- and spinel-peridotite xenoliths occur in basanitic and tephritic lavas of the 2.7 my to Recent Mt. Melbourne Volcanic Field (Antarctica). This field belongs to the Cenozoic McMurdo volcanic group which is located between the deep western trough of the Ross Sea rift system and the uplifted rift shoulder of the Transantarctic Mountains. Our samples cover the transition zone between rift and shoulder. We examined texture and composition of plagioclase+spinel and normal spinel peridotites and determined temperatures and pressures of formation using the internally consistent Ca-ol/cpx and 2px-thermobarometer of Kohler and Brey (1990) and Brey and Kohler (1990). D…
Tectono-stratigraphic modelling of the North Sicily continental margin (southern Tyrrhenian Sea).
2004
A two-dimensional numerical modelling that simulate the kinematic and thermal response of the lithosphere to thinning was used for the quantitative reconstruction of the late Neogene to Recent times tectonic and stratigraphic evolution of the North Sicily continental margin (southern Tyrrhenian Sea). The numerical study of the evolution of the North Sicily margin builds on the crustal image and kinematic interpretation of the margin obtained by Pepe et al. [Tectonics 19 (2000) 241] on the basis of seismic data and gravity modelling. Tectonic modeling indicate that different segments of the margin were undergoing different vertical movements, which are mainly expression of the rifting and th…
Genetic structure in the Mediterranean seagrass Posidonia oceanica: disentangling past vicariance events from contemporary patterns of gene flow
2010
The Mediterranean Sea is a two-basin system, with the boundary zone restricted to the Strait of Sicily and the narrow Strait of Messina. Two main population groups are recognized in the Mediterranean endemic seagrass Posidonia oceanica, corresponding to the Western and the Eastern basins. To address the nature of the East-West cleavage in P. oceanica, the main aims of this study were: (i) to define the genetic structure within the potential contact zone (i.e. the Strait of Sicily) and clarify the extent of gene flow between the two population groups, and (ii) to investigate the role of present water circulation patterns vs. past evolutionary events on the observed genetic pattern. To achiev…
Hyper-extended rifted margin in the Tyrrhenian Sea, upper plate of the Ionian subduction zone
2011
The Tyrrhenian Sea is a Miocene to Present back-arc basin developed in the upper plate of the Ionian subduction zone. Refraction seismic data indicate that the central sector of the Marsili Basin is a zone of thin crust ∼7 km thick compatible with its oceanic origin (Steinmetz et al., 1983). Conventional models rather define a Continent-Ocean Transition (COT) with normal oceanic crust (i.e. Finetti et al., 2005). This does not seem to be the case for the whole Tyrrhenian Basin. Serpentinized peridotites, emplaced during Pliocene, have been drilled at ODP Site 651 (Sartori et al. 2004). The W Calabria segment of the Tyrrhenian continental margin is peculiar as seismic data has excluded the p…
On the thermodynamics of listric faults
2004
We investigate a novel fully coupled thermal-mechanical numerical model of the crust in order to trace the physics of interaction of its brittle and ductile layers. In a unified approach these layers develop in a natural transition as a function of the state variables pressure, deviatoric stress, temperature and strain-rate. We find that the main storage of elastic energy lies in the domain where brittle and ductile strain-rates overlap so that shear zones are attracted to this zone of maximum energy dissipation. This dissipation appears as a local heat source (shear heating). The brittle-ductile transition zone evolves through extreme weakening by thermo-mechanical feedback. The physics of…
A Transition Zone Complex Regulates Mammalian Ciliogenesis and Ciliary Membrane Composition
2011
Mutations in genes encoding ciliary components cause ciliopathies, but how many of these mutations disrupt ciliary function is unclear. We investigated Tectonic1 (Tctn1), a regulator of mouse Hedgehog signaling, and found that it is essential for ciliogenesis in some, but not all, tissues. Cell types that do not require Tctn1 for ciliogenesis require it to localize select membrane-associated proteins to the cilium, including Arl13b, AC3, Smoothened and Pkd2. Tctn1 forms a complex with multiple ciliopathy proteins associated with Meckel (MKS) and Joubert (JBTS) syndromes, including Mks1, Tmem216, Tmem67, Cep290, B9d1, Tctn2, and Cc2d2a. Components of the Tectonic ciliopathy complex colocaliz…
Resolution Dependence of the Tropopause Inversion Layer in an Idealized Model for Upper-Tropospheric Anticyclones
2009
Abstract This note investigates the dependence of the extratropical tropopause inversion layer (TIL) on numerical resolution in an idealized modeling framework. Axisymmetric upper-tropospheric anticyclones are constructed by specifying potential vorticity (PV) and solving the nonlinear PV-inversion problem. The PV distribution has a smooth but near-discontinuous change of PV across the tropopause in a transition zone with vertical depth δ. For fixed δ the strength of the TIL changes with changing resolution until the transition zone is resolved by a fairly large number of grid points. The quality-controlled numerical solutions are used to study the behavior for δ → 0. This limit can lead to…
Structure, evolution, and dynamics of the Norwegian-Greenland Sea in the Blue Road Geotraverse area
1981
The orogeny of the Scandinavian and Greenland Caledonides is shortly reviewed, and a structural sketch map of the Scandinavian Caledonide part of the Geotraverse is presented. Post-Caledonian rifting episodes prior to the formation of the North Atlantic Ocean are briefly discussed, as well as the opening of the northern North Atlantic Ocean and its spreading rates. Computations of density models carried out on the basis of the Simplex-Algorithm which allows a least-squares solution under certain constraints show clearly a Moho-depression beneath the Caledonides and a comparatively thick oceanic crust in the Norwegian Sea. The transition zone oceanic continental crust has a complex structure…
Slab-triggered wet upwellings produce large volumes of melt: Insights into the destruction of the North China Craton
2018
Abstract Cratons have remained stable for billions of years, despite of ongoing mantle convection and plate tectonics. The North China Craton (NCC), however, is abnormal, as it has experienced a destruction event during the Mesozoic and Cenozoic which was accompanied by extensive magmatism. Several lines of evidence suggest that the (Paleo-)Pacific plate played an important role in this event. Yet, the geodynamic link between subduction and craton destruction remains poorly understood, and it is unclear why there is no systematic spatial and temporal variation of magmatism related to subduction. Here, we perform 2-D petrological-thermomechanical simulations to investigate the influence of s…
A regional-scale discontinuity in western Sicily revealed by a multidisciplinary approach: A new piece for understanding the geodynamic puzzle of the…
2015
The results of an integrated stratigraphic, structural, geophysical, and geochemical study reveal the presence of a crustal discontinuity in western Sicily that, at present, runs roughly N-S along a band from San Vito Lo Capo to Sciacca (SVCS). The boundary between the two zones of this discontinuity is nearly orthogonal to the main thrust propagation of the Sicilian thrust-and-fold belt. The different Permian to Tertiary sedimentary evolution recorded by the two zones appears related to this discontinuity, with thick carbonate platforms in the western sector facing deep-water successions in the eastern one. The presence of Upper Triassic reefs, huge megabreccias bodies, and widespread subm…