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Architecture, emplacement mode of late-Variscan plutons and their relationships with post-collisional phases: examples from Sarrabus igneous massif (SE Sardinia, Italy).
No full textSardinia is a southern transect of the Variscan Belt intruded by many post-collisional coalescent igneous
complexes forming the Sardinia-Corsica batholith. The Sardinian portion of this batholith grew during
two main magmatic peaks, clustered at about 305 Ma (Old Magmatic Peak, OMP) and at 285 Ma (Young
Magmatic Peak, YMP); plutons intruding different parts of the Variscan basement show different geological
styles in terms of emplacement style and mantle/crust contribution. The Sàrrabus igneous massif (400 km2) is
a multi-pulse, composite intrusive complex, occurring in the frontal part of the orogenic wedge in SE Sardinia.
It records a complex evolutive history, consisting of several intrusive sequences. The coalescing intrusion
are roughly elongated WNW, with sharp sub-vertical contacts. Schematically, the Sàrrabus igneous massif
consists of a southern part dominated by granodioritic up to monzogranitic rocks related to the OMP, and a
northern part made up of leucogranitic rocks referred to the YMP. A continuous contribution of mantle pulses
is documented mostly in the OMP. Early mantle-derived products are gabbrotonalites exposed close to the
northern contacts with the host basement; these mafic intrusives occur as a homogeneous sills or masses
dismembered by YMP leucogranites. A further mafic pulse consists of disrupted sub-vertical, syn-plutonic,
gabbroic dikes associated with quartz-diorites, which are well exposed along the southern Sàrrabus coastline.
These dismembered dykes, scattered within the granodiorite with a general WNW trend. The mafic activity
evolved towards diffuse diking (mainly spessartites), which resulted in several NNW trending dike swarms
that crosscut the OMP intrusives with cool, sharp contact. Spessartites are the latest episodes referable to the
OMP; they are frequently associated to metaluminous and garnet-bearing peraluminous felsic dikes and stocks.
A subsequent generation of olivine plagioclase -phyric mafic dikes with tholeiitic signature crosscut the YMP.
The resulting scenario suggests a northward growth of Sàrrabus igneous massif, accompanied by (1) bimodal
character of this magmatism; (2) increasing contribution of crustal melts and a progressive decrease of mantle/
crust interactions; (3) progressive shallower emplacement conditions. The late NS trending dyke swarm, which
emplaced in dilational jogs accounts for a NS σ1 stress field affecting the entire southern Sardinia lithosphere
during Permian time. Conversely, the emplacement of the OMS intrusions and the related dismembered
mafic bodies and dykes were controlled by a possible WNW transtensional kinematics. On a larger scale, this
variability of stress field, joined to crustal inhomogeneity, could account for different mechanisms of magma
ascent and decompression melting that result in different rock associations and petrological signatures
STRUCTURAL-GEOLOGICAL SURVEY OF AN ECLOGITIZED CHAOTIC COMPLEX: THE RIFFELBERG -GARTEN UNIT IN THE BREUIL DELL (ZERMATT-SAAS ZONE, ITALIAN WESTERN ALPS)
No full textThe Riffelberg-Garten Unit (RGU) is a tectono-stratigraphic unit, belonging to the Zermatt-Saas Zone (ZSZ), characterized by a chaotic mixture of metasediments, metabasites and serpentinites
(Bearth, 1967; Dal Piaz & Ernst, 1978; Campari et al., 2004). In particular the RGU is composed by meter to cm-sized clasts of eclogites, glaucophanites, marbles, and serpentinites within a
heterogenous matrix of micaschists, marbles and calcschists. This unit mainly occurs in the Valais and in upper Aosta Valley, and its originally complex lithostratigraphy is further complicated by
polyphase deformation generated during Alpine subduction, collision, and the subsequent exhumation. Such a complexity makes the origin of this mélange still debated. The multiscale structural
analysis was performed over an area of 12km2 in the upper Valtournanche valley (Breuil) and revealed the occurrence of four superposed groups of ductile structures. The new structural map at
1:5000 scale has been integrated by form surface maps performed at more detailed scales (1:100, 1:50, 1:200). Microstructural and petrologic investigations show that the first two groups of
structures, D1 and D2, developed under eclogite facies conditions, while D3 and D4 developed under decreasing P and T during the progressive RGU exhumation. New quantitative PT estimates
suggest that the thermal regime associated with the development of D1 and D2 structures is compatible with a cold subduction, as the one already inferred for ZSZ. On the contrary the T/P ratio
characterizing D3 and D4 results to be higher, indicating that the exhumation occurred in a mature collisional setting
U-Pb detrital zircon ages from Gorgoglione Flysch sandstones (Southern Apennines, Italy): inferences on source area
No full textLA-ICP-MS U-Pb ages were collected on detrital zircons from one sample of sandstone belonging to the
Gorgoglione Flysch (GF) outcropping in Southern Apennines (Basilicata Region, Italy).
The Gorgoglione Flysch represents a sedimentary siliciclastic succession having ≈1500 m thickness
consisting of coarse-medium grained turbidites with mudstone layers. The deposition age of detritus was
Langhian-Serravallian in a wedge-top basin belonging to the Southern Apennine Foreland Basin System
(e.g. Lentini et al., 2002). GF sandstones show immature mineralogical composition and textural features. The
composition varies from arkoses to lithic arkoses with some abundance of micas; the texture shows widespread
siliciclastic and calcareous matrix and scarce cementation.
The provenance studies on GF sandstones based on quantitative modal analysis, indicated a crystalline
basement formed by continental crust rocks located in the eastern sectors of the Alpine Chain (Critelli &
Loiacono, 1988). The prevalent granitoids and low grade metamorphic rocks occur in the crystalline basement
as testified by nature of lithic fragments in GF sandstones.
The detrital zircon radiometric dating through U-Pb spot analyses, tend to establish the ages of the source
rocks supplying the sedimentation basin in Langhian-Serravallian times.
The age data collected on nine detrital zircons selected by one sample of sandstone reveal twelve ages
ranging from Neoproterozoic to Triassic ages and four Oligocene-Aquitanian ages. The oldest age (669±25 Ma)
was measured on homogeneous luminescent zircon probably derived from metamorphites; a meaningful
Carboniferous-Permian age cluster (n=10) ranging from 319±13 Ma to 262±4 Ma seem connected to zircons
showing oscillatory magmatic zoning linked to granitoid and to recrystallized zircons in metamorphic
conditions; one Triassic age (247±6 Ma) was measured on broken crystal whereas four sub-concordant ages
(25±1 Ma to 23±9 Ma) are shown by two euhedral zircon crystals with regular oscillatory magmatic zoning.
The preliminary dating of detrital zircons from GF sandstones seem to indicate a provenance of detritus
from Hercynian magmatic and metamorphic rocks forming the Alpine chain but the presence of a younger
magmatic component suggested that even igneous rocks connected to Oligocene magmatic activity were
present in the source area
The Triassic sills of the Costabella Crest (Moena, TN-Italy) in comparison with coeval Dolomitic magmatites
No full textThe trigger of the Triassic magmatism in the Eastern Alps (about 235 Ma) is still highly debated, and both extensional and compressional theories are invoked. The first is mainly supported by the related extensional geologic structures, while the second family of theories is supported by the chemistry of the better exposed lithotypes and the high sedimentation rate, typical of a back-arc environment, whose arc is supposed to be located east or south of the Adria Plate. We support a not orogenic genesis for the dolomitic Triassic magmatism due to the presence of coeval magmatic products showing not orogenic features, by the position of such magmatic province during Triassic times (edge of the Intra Pangea Dextral Shear; IPDS) and by the sedimentation rate which appears comparable with that of the North America Atlantic coast located along the IPDS. It is interesting to notice that the IPDS, which probably begun to move in early Permian, started its extensional movement 235 My ago. In this work we mainly attempt to evaluate possible interaction of the magmatic products with the carbonate (host rocks) through the study of the sills located in the Costabella Crest (Moena, TN Italy), and with the comparison with other dolomitic Triassic products, then, to give a small contribute about the geodynamic discussion.Generally, the samples show ipoialine to strong porphyric textures and a variable grade of alteration mainly due to disequilibrium between olivine and the melts in the magmatic chamber. In the Total Alkali Silica diagram the sills fall in the alkaline field (from basanite to tefriphonolite), but this partially contrasts with their paragenesis. Indeed, among the phenocrystals the plagioclase appears very abundant and show a bimodal composition (labradorite and anorthite). Carbonates can be present with primary textures to suggest the presence of small amount of carbonatic melts in the magma chamber possibly explaining the isotopic features found in the dolomitic flows where a strong isotopic Sr variability is associated to small Pb and Nd isotopic ones. Apart the strong interaction with the host rocks and the post-emplacement alterations, three groups with different La/Yb ratio can be recognized suggesting a heterogenic source. Finally, to evaluate the supposed subduction-related chemical features, as the negative Nb anomaly, the Triassic samples have been compared with other not arc related magmatic products placed along the IPDS of the Central Atlantic Magmatic Province emplaced at the TJ boundary. Despite the very different grade of alkalinity, locally their incompatible element pattern shows strong similitudes that we relate to past subductions
Geological Map of Forenza Town Area (prov. of Potenza), 1:15.000 scale. External Sector of Southern Apennines
No full text
UAV assisted geological mapping: application to stratigraphy and structural survey
No full textFollowing previous researches and experiences (Casella et al., 2017; Martinez et al, 2017; Nieminski et al. 2017), some experimental tests were carried out during Digital Geological Survey (Geological Sciences MSc.) and Geomatics (Applied Information technology BSc) courses at Urbino University. During the last year field activities students and researchers tested the use of UAV (unmanned aerial vehicle) both commercial (DJI Phantom 3) and in-house built machine.
Because of the reliability, we choose to perform our survey tests using the commercial one.After having digital field mapped an Apennines area where the Miocene turbidite Marnoso Arenacea Formation crops out (Marche- Tuscany border), we choose to fly on top of two already tape measured stratigraphic sections. After some flight we were able to built orthophotos and DEM with points clouds (using Agisoft Photoscan) that could be imported in QGIS 3.0 where we measured the stratigraphic columns, highlighting bedding and key strata. As pros of tape measurement is the direct contact with bedding allowing more accurate observations. In the other side, as cons, the unsafe measurement on vertical cliffs (performed with climbing techniques) can be avoided with reliable remote measurements without noticeable deviations.Moreover we tried to build a 3D geological model of a quite complex triangle zone associated to a main thrust. The UAV flew manually controlled along a creek where the deformed and faulted beds crop out. The very detailed points cloud allowed to draw and build an interpretative model
“Sassi”, the old town of Matera in southern Italy: a potential urban geopark in the European Capital of Culture 2019
No full textA new Megaslide in the Bradano Foredeep area (Southern Apennines, Ionian Sea).
No full textAlong convergent margins, mass-transport represents an important mechanism for sediment distribution within sedimentary basins and, especially if related to seismic activity, it can generate tsunamis. This is also the case of the Gulf of Taranto where mass movements of different size and age are already known. However, a detailed quantitative analysis of geometry, origin, triggering mechanism and final age of their emplacement has not been fully accomplished.
In this study, the submerged portion of the Southern Apennine collisional belt within the Bradano foredeep is investigated. A composite data-set including seismic reflection profiles, exploration wells and seafloor morphology, allowed definition of new large-size Mass Transport Deposit, named the “Bradano Basento Mega Slide” (BBMS) and containing a younger slide mass (BBMS1). The BBMS forms a lens 31 by 19.5 km wide, corresponding to an area of ~396 km2 A rough depth-conversion allow to estimate a maximum thickness of about ~600 m and a volume of ~130 km3. The run-out distance is estimated up to few hundreds of meters.
These estimates are conservative, since BBMS and BBMS1 likely have an onshore extension, not imaged by our marine data. This is the largest MTD complex described in the Gulf of Taranto. The BBMS and BBMS1 remobilized toward the SE Middle-Late Pleistocene-Holocene clay/silty-clay deposits. Based on stratigraphic correlations, carried out using well-logs and the ages of correlative deposits onshore, it was emplaced in Late Pleistocene and predated the LGM.
Several lines of evidence, including the fact that the BBMS gliding surface appears to have been controlled by main tectonic structures in the area, suggest that the most likely trigger mechanism for the emplacement of the MTDs is seismic shaking. Thus, it is suggested that BBMS and BBMS1 should be considered paleoseismological markers of large magnitude earthquakes in the Bradano Foredeep basin. The discovery of BBMS and BBMS1 might be useful to complete the onshore paleo-seismological record and may contribute to clarify the paleo-seismological behavior of this geologically complex area.
The discovery of this new megaslide suggests the need for a re-evaluation of the potential for large
earthquakes and tsunamis and in general for a reliable geological hazard assessment along the coast of the Gulf of Taranto, a heavily populated area, site of many industrial infrastructures
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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