1,721,045 research outputs found
Strain partitioning in the axial NW Alps since the Oligocene
No full textThis work analyzes the postmetamorphic
evolution of the northwestern Alps thanks to a
multiscale field geology study integrated by fission
track analysis. It illustrates how the fission track
method, constraining throws along major faults and
age of mesoscale deformation, provides interpretation
keys to detangle complex structural data sets. Results
are discussed within the framework of the Alps-
Apennines knot and give new insights on strain
partitioning within transpressional orogenic belts. The
axial NW Alps acted since the late Oligocene as an
orogen-scale shear zone accommodating, in the Aosta
Valley, dextral strike slip coeval with forward
propagation of external thrusts. Within this
transcurrent belt, right-lateral deformation was
partitioned between the fast exhuming Western
Block and the already unroofed Eastern Block.
These blocks show contrasting structural characters.
The former is cut by first-order longitudinal structures
bounding major tectonostratigraphic units. The latter is
fragmented by complex patterns of lower-order faults
interpreted as subsidiary shears. The onset of
mesoscale extension, widespread in the Eastern
Block, is diachronous across the belt and migrated
through time toward the European foreland. Transition
from syncollisional shortening to orogen-scale
transcurrence observed in the NW Alps corresponds
to a regional strain field variation, documented in the
mid-Oligocene all around the Alps-Apennines knot,
which is possibly related to a change of the Adria
trajectory relative to Europe. Since the late Oligocene,
deformation associated with oblique plate convergence
was partitioned between strike slip in the axial belt and
thrusting in external areas. Most of the shortening was
accommodated in the Helvetic chains (10E02 km).
Deformation was limited elsewhere to an order of 10E01 km
Magnetotelluric survey at the Alps-Apennines boundary (Tertiary Piemonte Basin - north/western Italy)
No full text
Carta Geologica d'Italia alla scala 1:50.000 -Foglio 450 Sant'Angelo dei Lombardi. ISPRA, Servizio Geologico d'Italia
No full textThe Gran San Bernardo nappe in the Aosta valley (western Alps):a composite stack of distinct continental crust unit
No full textAbstract. – In the Aosta Valley, the Gran San Bernardo nappe, which comprises the basement sequences classically re- ferred to as Ruitor Massif and Zona Interna, appears to be a stack of distinct basement units with distinct lithological features and contrasting tectono-metamorphic evolution piled up during the Eocene. In the former Zona Interna, two dif- ferent units (Gran Nomenon and Leverogne) have been distinguished. The Gran Nomenon unit is a polymetamorphic basement unit, with a pre-Alpine epidote-amphibolite facies metamorphic imprint, intruded by granitoid rocks during the early Mississippian. It bears the evidence of a pervasive Alpine metamorphic overprint under greenschist facies conditions, and does not share common characters with any other basement sequence exposed in the Gran San Bernardo nappe. The Leverogne unit is a monometamorphic basement unit, with some analogies with the Mont Pourri basement sequence, intruded by granophyric rocks of Middle Cambrian age. It suffered epidote-blueschist and greenschist facies metamorphism during the Alpine orogenesis, and shows a deformation history partly different with respect to the Gran Nomenon unit. These units are bounded by tectonic melanges that represent Alpine shear zones, and have been juxtapo- sed under greenschist facies conditions during the late stages of exhumation of the belt. The Gran Nomenon unit, which does not show a significant HP/LT overprint, was probably not as deeply buried as the Leverogne and the Ruitor units during Alpine orogenesis
Revisiting the Lanzo peridotite (NW-Italy): ‘asthenospherization’ of ancient mantle lithosphere.
No full textIn this paper, we comipled previous investigations and summarized recent results to show that the Lanzo peridotite records a sequence of deep lithospheric igneous events that largely obliterated the previous subcontinental history. Field, microtextural and trace element data indicate the progressive evolution of an igneous system that forms above an upwelling asthenosphere, most probably during the transition from a rifted system to the establishement of an (ultra-) slow spreading ridge of the Piedmont Ligurian ocean. Pervasive porous flow of melt forming 'reactive' spinel peridotites followed by plagioclase peridotite is later replaced by focused porous flow, reflected by a sysstem of replacive harzburgite and dunites. Cooling of the Lanzo peridotite leads to the interstitial crystallization of clinopyroxene and plagioclase, and finally to the formation of gabbro dikes. Thus, the Lanzo peridotite may indicate the extension-driven 'asthenospherization' of lithospheric mantle is an important process in the development of embryonic ocean basins
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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