1,721,161 research outputs found
Tectonic Blocks in Northern Victoria Land (antarctica): Geological and Structural Constraints by Satellite Lineament Domain Analysis
No full textFlank cones at Mount Etna volcano: Do they have a power-law distribution?
No full textMount Etna is currently characterised by intense effusive and explosive activity of its summit vents, whereas 319 non-active Holocene flank cones are spread across its flanks at altitudes of between 2990 and 475 m. In volcanic areas the relationships between fracture occurrence and cone growth/location are well established. With this in mind, the spatial distribution of the Mount Etna flank cones was analysed in order to make some inferences about the fracture systems that feed the cones. The positions of the flank cones were acquired by the use of a digital elevation model of the volcano with a geometric resolution of 10x10 m. Spatial distribution of the cones was analysed through counting-box and sand-box methods, checking for fractal or multifractal behaviours. The four data sets analysed consist of the whole number of parasitic cones (319), and cones located on the NE (50), south (143) and west (61) rifts, respectively. The cones have a non-trivial power-law distribution. The sand-box method gave the best results with a fractal exponent D-f for all cones of 1.41+/-0.02 over the length range 0.2-10 km. The same analysis was performed on the other data sets: South Rift (1.42+/-0.02); West Rift (1.39+/-0.02); and NE Rift (1.43+/-0.02), The cones do not have a multifractal distribution, as suggested also by the strong similarity between fractal exponents of the different data sets. Data suggest a strong control over flank cone distribution by fracture length and density. These two characteristics are, in turn, expressions of highly connected fractures activated as magma feeders by the volcano's present stress field. We interpret the rifts as inherited structures that represent preferential sites of fracture connectivity
Contribution to Geothermal Survey by spectral analysis of TM Landsat satellite data in Mt. Melbourne Area, Northern Victoria Land (Antarctica)
No full textSpatial distribution of cones snd satellite-detected lineaments in the Pali Aike Volcanic Field (southernmost Patagonia): insights into the tectonic setting of a Neogene rift system
No full textHydrofracturing-related sill and dyke emplacementat shallow crustal levels: The eastern Elba Dyke Complex, Italy
No full textAn example of sheet-like intrusion emplacement at very shallow crustal levels
on Elba Island, Italy, is described. The Eastern Elba Dyke Complex (EEDC) consists of
decimetre- to metre-thick sheeted aplites emplaced within intensely folded low-grade metamorphic
rocks. Field data indicate that sill and dyke emplacement was controlled by mechanical
discontinuities, represented by fractures in the host rocks, and was strongly favoured by
magma overpressure. The occurrence of angular fragments of host rocks in the dyke border
zones and the branching of sills testify to hydraulic fracturing. Analysis of the spatial distribution
and geometry of EEDC sills and dykes provides clues on fluid pressure conditions
and the stress state at the time of magma emplacement, as well as on the depth of
emplacement. The calculated stress ratio and driving pressure ratio were used to estimate a
magma overpressure of 6–54 MPa at the time of emplacement of the EEDC at a depth of
about 2 km
Crustal segmentation of the Transantarctic Mountains rift shoulder along the David Glacier Lineament, Victoria Land (Antarctica).
No full textPaleontological evidence for Late Cambrian in the Arburese area, SW Sardinia
No full textNew palynological investigations allowed a better definition of the age of terrigenous deposits of the Monte Fonnesu tectonic Unit, exposed in the Arburese area (SW Sardinia). The section investigated consists of a coarsening upwards positive sequence, up to 10 m thick, that is made up of quartz-arenitic sandstones and light gray quartzite beds (0.5 m thick), interbedded with thin beds of black shale. In the lower part of the section, two quartzitic levels are rich in lingulid (brachiopods) shell fragments. This is the first report of macrofossils from the Monte Fonnesu Unit. Samples collected for palynological analyses in the black shale at the base and at the top of the lowest quartzitic level yielded a Late Cambrian acritarch microflora that can be correlated with the Peltura trilobite Superzone. The Late Cambrian age assigned to the lower part of the sequence allows us to define more precisely the age of Mt. Fonnesu sandstone, which in consequence is bracketed between the Late Cambrian and the Early Ordovician
Interactions between low-angle normal faults and plutonism in the upper crust: Insights from the island of Elba, Italy: Comment
No full textThe interplay between magmatism and tectonics is pivotal for deciphering the tectonic and geodynamic evolution of mountain belts. In the northern Apennines - northern Tyrrhenian Sea orogenic system large amounts of magma were emplaced at shallow crustal levels since the middle-late Miocene to recent (e.g. Serri et al., 1993; Rosenbaum et al., 2008). In this sector of the Apennine chain the mutual relationships between magmatism and tectonics are still a matter of debate (e.g., Rossetti et al., 1999; Acocella and Rossetti, 2002; Musumeci et al., 2005; 2008; Rosenbaum et al., 2008). Elba Island, located in the Tyrrhenian Sea about 30 km west of the inner portion of the chain, is a key area where tectonics - magmatism relationships can be studied
Sills and dikes emplacement at shallow crustal levels:the role of hydrofracturing and host rock mechanical discontinuity (eastern Elba Island, Italy)
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