1,721,926 research outputs found
Evidence for Triassic contractional tectonics in the Northern Dolomites (Southern Alps, Italy)
No full textThe occurrence of Middle Triassic extensional and strike-slip tectonics has been widely recognized in the Do-lomites and is supported by stratigraphic evidence. Contrarily, the recognition of Triassic contractional tectonic structures is less straightforward because such structures were heavily superimposed by Neogene Alpine shortening.In this work we provide a detailed analysis of a top-class outcrop displaying a syn-sedimentary Middle Triassic extensional fault that displaces a coeval sedimentary me acute accent lange containing an olistholith of Lower Triassic rocks, characterized by Triassic contractional structures (folds, axial plane cleavage, joints, local thrust faults orna-mented with slickenfibers and associated with forced folds).In particular, integrating geological field mapping and structural analyses, structural analyses on a 3D virtual outcrop model and microstructural analyses, we demonstrate that: 1) the orientation of tectonic structures in the olistholith is at odd with that of regional structures, implying that deformation occurred prior to deposition of the melange; 2) folds and small-scale thrusts in the olistholith developed in lithified rocks, pointing to the existence of Middle Triassic fold and thrust tectonics. In summary, the tectonic structures in the analyzed olistholith represent an outstanding, possibly unique, example of fully preserved, practically frozen, Middle Triassic contractional structures
On the increasing size of the orogens moving from the Alps to the Himalayas in the frame of the net rotation of the lithosphere
No full textThe tectonic equator represents the great circle of the non-random mainstream of plate motions and it is inclined about 30° relative to the geographic equator. Divergence or convergence rates among plates are in average faster along the tectonic equator and they tend to decrease toward the polar areas. Moving from Western Europe to eastern Asia, the mainstream is roughly oriented southwest northeast. Here we show how this pattern may have played a role in determining the dimension of the Alpine-Himalayas orogenic belt, which is increasing in size and thickness moving from west-northwest to east-southeast, i.e., moving from high-latitude to low-latitude of the tectonic mainstream of plates. The Alps are in average 200–250 km wide, whereas the Himalayas are regularly > 1000 km wide. Moreover, due to the “westerly” polarization of the lithospheric mainstream relative to the mantle, either the net-rotation or the westward drift of the lithosphere, the subduction zones can be differentiated into two types, 1) increasing or 2) decreasing the lithospheric thickness. The Alpine-Himalayas system pertains to type 1 and it may represent a prototype of the continental lithosphere growth since the Archean. The increasing size of the orogens moving from the Alps to the Himalayas is presently concentrated in the northern hemisphere of the tectonic mainstream because subduction type 2 dominated the western margin of the Pacific ocean, hence preventing continental growth in the southern hemisphere in that longitude range. Therefore, the largest growth of continental crust and mantle lithosphere should have occurred along the tectonic equator, but only where type 1 subduction was generated
West-dipping subductions develop along the back-thrust belts of former East-dipping subductions
No full textConstitutive p63 expression in airway basal cells. A molecular target in diffuse lung diseases
No full textFrom Mesozoic rifting to Apennine orogeny: The Gran Sasso range (Italy)
No full textThe Apennines are a low-temperature accretionary prism generated by the west-directed subduction of the Adriatic–Ionian plate, whose structural origin is still to be fully understood. The highest and best-exposed segment of the Apennines, the Gran Sasso range is here documented to unravel the tectonic history of the northern tip of Gondwana. It is located along a NE-verging salient of thrust sheets decoupling the sedimentary cover of the subducting Adriatic lithosphere. Field mapping and structural analysis along the E–W trending left-lateral transpressive segment of the salient highlight the interplay of the inheritedMesozoic passive margin stratigraphic and tectonic framework with the Neogene contraction. The rheological differences between the massive carbonate platform and the well-bedded turbiditic and pelagic limestones determined along-strike undulations of the thrusts geometries and fold styles during shortening. Heterogeneities are due to inherited syn- and post rift Mesozoic tectonics. The Gran Sasso overturned anticline shows a backlimb anomalously tilted toward the foreland and we infer this dip as being related to a deeper back-thrust of a triangle zone. The pinching out of the foredeep sequence on the growth anticline forelimb dates the contractional phases of the region to the late Messinian. From the late Pliocene to Present, the area has been uplifted and extended about 2 km by oblique normal faults cross-cutting the accretionary prism. Some of them are seismically active, as shown by the 2009 Mw 6.3 L'Aquila earthquake
Asymmetric ocean basins
No full textWhile the superficial expression of oceanic ridges is generally symmetric, their deeper roots may be asymmetric. Based on a surface wave tomographic, we construct a global cross section parallel to the tectonic equator. VS indicate a difference between the western and eastern flanks of the three major oceanic rift basins. In general, the western limbs have a faster velocity and thicker lithosphere relative to the eastern or northeastern one, whereas the upper asthenosphere is faster in the eastern limb than in the western limb. We interpret the difference between the two flanks as the combination of mantle depletion along the oceanic rifts and of the westward migration of the ridges and the lithosphere relative to the mantle. The low-velocity layer in the upper asthenosphere is assumed to represent the decoupling between the lithosphere and the underlying mantle. These results could be explained in the frame of the westward drift of the lithosphere relative to the underlying mantle
Tubular adenoma of choroid plexus: a case report.
No full textA case of choroid plexus neoplasm histologically composed of tubular structures lined by a layer of cuboidal epithelium is reported. The neoplasm was located in the fourth ventricle of a 26-year-old man. The intense positivity for antisera anti-vimentin, anti-cytokeratin, anti-EMA and anti-S100 protein exhibited by these cells was consistent with choroid plexus origin. The patient is alive and in good health 5 years after surgery. The lesion represents a benign choroid plexus neoplasm not previously reported. The name "tubular adenoma of choroid plexus" is suggested for this variant
Normal faulting vs regional subsidence and sedimentation rate
No full textNormal faults occur in a variety of geodynamic environments, both in subsiding and uplifting areas. Normal faults may have slip rates faster or slower than regional subsidence or uplift rates. The total subsidence may be defined as the sum of the hangingwall subsidence generated by the normal fault and the regional subsidence or uplift rate. Positive total subsidence obviously increases the accommodation space (e.g. passive margins and back-arc basins), in contrast with negative total subsidence (e.g. orogens). Where the hangingwall subsidence rate is faster than the sedimentation rate in case of both positive and negative total subsidence, the facies and thickness of the syntectonic stratigraphic package may vary from the hangingwall to the footwall. A hangingwall subsidence rate slower than sedimentation rate only results in a larger thickness of the strata growing in the hangingwall, with no facies changes and no morphological step at the surface. The isostatic footwall uplift is also proportional to the amount and density of the sediments filling the half-graben and therefore it should be more significant when the hangingwall subsidence rate is higher than sedimentation rate
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