A geomathematic investigation of syntexis in a Gabbroic formation

Mathematical methods were employed in an investigation of syntexis in the Gabbro di Sondalo, a mafic igneous formation in the Central Alps (Italy). A set of 100 specimens was selected according to sampling criteria and analyzed by X-ray fluorescence for eight elements; Q-mode and R-mode factor analysis then was applied to these data. Results of the computations indicate that the general trend of differentiation is related to the syntexis of gneissic wall rocks (Gneiss del Monte Tonale) in the mafic melt. Ca and Mg are abundant in the gabbro, and Si and K in the gneiss; the independent variation trend of Fe and Ti may be related to a differentiation episode due to a magmatic phase. Spatial representation of multivariate data on differentiation also was performed on the main elements and a picture of the trend of syntexis was mapped.     

The North Tyrrhenian–Northern Apennines post-collisional system: constraints for a geodynamic model

The North Tyrrhenian–Northern Apennines post-collisional system (NTAS) has been analysed on the basis of marine reflection profiles and bibliographic sources with the aim of providing an up-to-date geotectonic and evolutive framework consistent with structural data. The continental rifting began to affect the most internal (western) side of the system in the middle (?)-upper Miocene, while the most external (eastern) zones were touched by rifting only in Pleistocene times. The birth and development of extensive, asymmetric basins took place with a progressive speeding up of rifting towards the external sectors. A diachronous, regionally extended and eastward rejuvenating unconformity, recognizable within the Neogene–Quaternary basins, marks the passage from the syn-rift to the post-rift tectonic regime. While the first is everywhere dominated by extension, the second one produces vertical movements. Reflection terminations related to this unconformity are interpreted in terms of vertical tectonic component. Three zones that experienced different post-rift vertical movements are thus recognized in the NTAS: subsidence in the North Tyrrhenian deep water region; tectonic stability or alternation of moderate subsidence and uplift in the continental shelf and western Tuscany, strong uplift in eastern Tuscany. The updated structural data demonstrate that the NTAS upper crust is crosscut by both Tyrrhenian-dipping and Apennine-dipping low-angle detachment planes, above which the upper crustal blocks rotated and experienced extensional transport along two opposite directions: to the west and to the east, respectively. The coexistence of opposite-dipping crustal surfaces bears two fundamental implications for the NTAS geodynamics. First it stresses the importance of the anti-Apennine transfer faults, since they separate crustal blocks of opposite extension polarity. Secondly, it testifies that the extension tectonics not only re-utilized former crustal thrust planes, but also gave origin to new significant E- and NE-dipping detachment planes. Plan and crossview geometries of faults, together with considerations on the role of the metamorphic core complexes, point to an interpretation of the NTAS structure that is more consistent with the ‘anastomosing shear’ model rather than the 'simple shear' or the ‘delamination’ ones.     

Piperno from Campi Flegrei: a relevant stone in the historical and monumental heritage of Naples (Italy)

This paper reports novel data concerning the volcanic formation of the Piperno, a stone that has been used for a long time in the monumental architecture of Naples and the Campanian region (Southern Italy). A careful field survey of the outcrops or underground sites so far accessible allowed us to draw a lithostratigraphic reconstruction of the formation and enabled the recognition of the three main layers exploited in past centuries and which provided dimension stones for architectural and structural purposes. Petrophysical and mineralogical characterization also enabled us to discriminate the same layers previously identified. Different scoriae/matrix ratio, scoriae dimension and welding degree are the most peculiar features of these horizons. The combination of these three parameters, even though they did not affect the use of Piperno as dimension stone, somehow determined its variable susceptibility to the weathering agents. However, a linear relationship between the exposure time and the decay of the stone itself, at a parity of weathering intensity, was not observed. This assumption was proved by verifying that the specific layers of the volcanic sequence controlled the weathering degree of Piperno from monuments disregarding their age of emplacement.     

The sulfur flow fields of the Fossa di Vulcano

Sulfur flow deposits at the Fossa di Vulcano fumarole field (Italy) are dominated by thermal erosion features. These are characteristic of sulfur flows at this location, where most flows are emplaced in a combusting mode such that all flow sulfur is melted and consumed during the emplacement event. Further, thermal erosion during emplacement results in pits and channels that mark the passage of the combusting flow. These thermal erosion pits and channels are typically littered with non-combusted silicate blocks, show overhanging rims and an absence of sulfur. If activity remains confined to a source fumarole basin, then sulfur lake activity will result. Combustion of such a feature leaves thermally eroded pits, typically a few tens of centimeters to a few meters wide and long, and a few tens of centimeters deep. However, the increase in sulfur volume during melting and erosion of pit walls mean that overflow and breaching is common. This leads to capture of new sulfur encrusted fumarole basins and flow extension. Flow extension away from the lake results in thermal erosion channels as much as 1.7 m wide, 0.6 m deep and 23.5 m long. Flow direction is dictated by slope, cinder ejection and sources of new sulfur, thus flows are capable of moving down, across and/or up slope if that is the dominant source of new sulfur. We estimate that sulfur flow activity has combusted 2,000–5,000 m³, or 4,000–10,000 tons, of sulfur at Vulcano. Only one noncombusted unit could be found during seven fumarole-fieldwide surveys during 1998–2003; this was 7.3 m long and 0.3 m wide, and had a viscosity of 0.1–40 Pa s. This viscosity is consistent with emplacement temperatures of 165–180°C, which are lower than sulfurs combustion temperature. At Vulcano the commonality of thermal erosion features over noncombusted sulfur flow units indicates that combusting emplacement has been the main mode of flow emplacement at this volcano. The common occurrence of combustion is also evident from reference to the same phenomenon by Déodat de Dolomieu in 1783.Editorial responsibility: M. Carroll     

The lack of thermical equilibrium as a consequence on the universe expansion

The time-asymmetry of the universe is essentially produced by its low-entropy, unstable states. Using quantitative arguments Paul Davies has demonstrated that the expansion of the universe coupled with nuclear reaction within the stars may produce a decrease in entropy, thereby explaining its low entropy states. This idea is implemented in a qualitative way in a simple homogeneous model. Some rough coincidence with observational data is found.     

Proper motion measurements of umbral and penumbral structure

Horizontal proper motions of penumbral structure and umbral dots have been measured from a 17-min-long time series of sunspot images by numerical techniques. In the penumbra, inflows are seen to occur predominantly in the inner region, with an average velocity of 290 m s^–1. Penumbral outflows take place mostly in the outer part, where they reach velocities as high as 1.5 km s^–1, with an average velocity of 500 m s^–1. In the umbra, proper motions of 28 bright dots have been measured with an accuracy better than 50 m s^–1. The mean velocity of the umbral dots is 210 m s^–1. Most of the umbral dots display the well-known inward motion away from the peripheral umbra.     

The Cretaceous megabreccias of the Gargano Promontory (Apulia, southern Italy): their stratigraphic and genetic meaning in the evolutionary framework of the Apulia Carbonate Platform

Huge megabreccias occur at the eastern margin of the Cretaceous Apulia Carbonate Platform (Gargano Promontory, southern Italy). Their stratigraphic and genetic meaning are controversial in the debated geological evolution of the Apulia Platform. New stratigraphic analyses have revealed that three distinct megabreccia levels occur within the coarse debrites that were previously interpreted to be the result of repeated collapses of a scalloped platform margin during the late Albian–Cenomanian. Each level has peculiar chronostratigraphic distribution, geometry, composition and genetic features. They are the Posta Manganaro Megabreccias (late early Aptian to late Albian pp. ), Monte S. Angelo Megabreccias (early–middle Cenomanian) and Belvedere di Ruggiano Megabreccias (middle Turonian). These deposits overlie regional, tectonically enhanced unconformities of late early Aptian, late Albian and late Cenomanian age. These megabreccias, which were formed, respectively, during drowning, prograding and exposure events of the Apulia Platform, reflect important turning points in its Cretaceous geodynamic evolution.     

The current tectonic motion of the Northern Andes along the Algeciras Fault System in SW Colombia

Riedel, synthetic and antithetic type faults, principal displacement zones (PDZ), pull-apart basins (such as lazy-S shaped releasing bend, extensive and rhomboidal shaped and releasing sidestep basins) and minor folds located oblique to the main trace of the Algeciras Fault System (AFS) are interpreted from Landsat TM 5 images and geological mapping. These tectonic features are affecting Quaternary deposits and are related to major historical earthquakes and recent registered seismic events, indicating neotectonic activity of the structure.The AFS is classified as a right lateral wrench complex structure, with an important vertical component in which sedimentary cover and basement rocks are involved. In addition, the system represents a simple shear caused by the oblique convergence between the Nazca Plate and the northern Andes. The transpressive boundary in SW Colombia was previously located along the Eastern Frontal Fault System. However, this paper shows that the AFS constitutes the actual boundary of the current transpressive regime along the Northern Andes, which begins at the Gulf of Guayaquil in Ecuador and continues into Colombia and Venezuela.