102,562 research outputs found
Heavy mineral ditribution in Late Quaternary sediments of the Southern Aegean Sea: Implication for provenance and sediment dispersal in a sedimentary basin at active margins
No full textThe Southern Aegean Sea (Sea of Crete) is a present day forearc basin in a dynamic tectonic setting that includes Quaternary calc-alkaline volcanism (Cyclades) on the northern margin; vertical uplift on the southern trench-ward margin forming the Hellenic Arc ofPaleozoic to Miocene alpine deformed rocks; and extensional tectonics affecting the whole Aegean area. Extension in the forearc basin has created a series of basin ponds separated by structural highs that limit sediment transport by bottom currents. Heavy mineral associations along the Crete and Rhodes coasts and in turbidite deposits from the Southern Aegean Sea were subjected to Q-mode factor analysis, which offers the advantage of denning a small number of end members by variable combinations of different minerals. Four heavy mineral suites along Crete and Rhodes coasts (one from the volcanic arc, three from different terranes exposed on the Hellenic Arc), and five from the Southern Aegean Sea (one from the volcanic margin and four from different parts of the Hellenic Arc) were identified. The mineralogical composition of sands from the different basins varies significantly, reflecting the composition of the nearby source areas. Heavy mineral analysis allowed a more detailed identification of source terranes than did light mineral analysis of the same sediments (Saccani 1987)
Petrological and tectono-magmatic significance of ophiolitic basalts from the Elba Island within the Alpine Corsica-Northern Apennine system
No full textTwo distinct ophiolitic units, which represent remnants of the Jurassic Ligurian-Piedmont Ocean, crop out in the Elba Island. They are the Monte Strega unit in central-eastern Elba and the Punta Polveraia-Fetovaia unit in western Elba. Ophiolitic rocks from the Monte Strega unit are commonly affected by ocean floor metamorphism, whereas those from the Punta Polveraia-Fetovaia unit are affected to various extent by thermo-metamorphism associated with the Late Miocene Monte Capanne monzogranitic intrusion. Both ophiolitic units include pillow lavas and dykes with compositions ranging from basalt to basaltic andesite, Fe-basalt, and Fe-basaltic andesite. Basaltic rocks from these distinct ophiolitic units show no chemical differences, apart those due to fractional crystallization processes. They display a clear tholeiitic nature with low Nb/Y ratios and relatively high TiO2, P2O5, Zr, and Y contents. They generally display flat N-MORB normalized high field strength element patterns, which are similar to those of N-MORB. Chondrite-normalized rare earth element patterns show light REE / middle REE (LREE/MREE) depletion and marked heavy (H-) REE fractionation with respect to MREE. This HREE/MREE depletion indicates a garnet signature of their mantle sources. Accordingly, they can be classified as garnet-influenced MORB (G-MORB), based on Th, Nb, Ce, Dy, and Yb systematics. We suggest that the Elba Island ophiolitic basalts were generated at magma starved, slow-spreading mid-ocean ridge. REE, Th, and Nb partial melting modelling show that the compositions of the relatively primitive Elba Island ophiolitic basalts are compatible with partial melting of a depleted MORB mantle (DMM) source bearing garnet-pyroxenite relics. Hygromagmatophile element ratios suggest that basalts from both ophiolitic units were originated from chemically very similar mantle sources. A comparison with basalts and metabasalts from Alpine Corsica and northern Apennine ophiolitic units shows that the composition of the inferred mantle source for the Elba Island basalts is similar to that of some Lower Schistes Lustrés metabasalts of Alpine Corsica ophiolites, and some basalts from the Internal Ligurian units of northern Apennine. In contrast, it slightly differs from those of other ophiolitic units of Alpine Corsica and northern Apennine. The chemical differences observed between basalts and metabasalts from different Ligurian-Piedmont ophiolitic units were likely associated with different partial melting degrees of either DMM source or garnet-pyroxenite relics and/or different mixing proportions of melts derived from them, as well as to different compositions of garnet-pyroxenite relics
Potential mineral resources in historically dismissed volcanogenic massive sulfide (VMS) deposits of the Emilia Romagna region (Italy): petrological and geochemical study for Critical Raw Materials (CRMs) exploration and exploitation
No full textThe last update on the Critical Raw Materials Act (2023) drawn up by the European Union identified
54 Critical Raw Materials (CRMs), i.e., minerals, elements, or materials that are fundamental to supply for
technology and strategic for the green transition, but subjected to fickle supply, e.g., for the fragile geopolitical
contest (Kiss et al., 2023). This led many European countries, including Italy, to focus on the metal recovery
from dismissed mines, mine wastes, and landfills to accomplish the circular economy politics. Italy has
more than 100 historically dismissed mining sites just in the North, and, among them, the ones in the Emilia
Romagna region are now under investigation for the various volcanogenic massive sulfide (VMS) deposits
(Zaccarini & Garuti, 2008). These are a type of metal sulfide ore deposits that occur as a result of underwater
volcanic eruptions, associated with hydrothermal events in submarine environments, and are divided based
on ore composition (Cu, Cu-Zn, Cu-Zn-Pb group) and environment formation (Cyprus, Kuroko, Besshi, as
mentioned by Zaccarini & Garuti, 2008). In the Emilia Romagna region, these deposits occur as pods within
small bodies of ophiolitic basalts cropping out as olistoliths in the Northern Apennine External Ligurian units
and owe their origin to the metal-rich hydrothermal circulation which developed quartz-sulfide veins when
mixed with seawater through a fissures network (Saccani, 2015; Kiss et al., 2023). These ophiolites represent
Jurassic Alpine Tethys oceanic crust fragments obducted in the continental crust (Zaccarini & Garuti, 2008).
The stratigraphy of the area is characterized by sequences of pillow lavas associated with serpentine and gabbro
breccias, radiolarian cherts, limestones, and abundant serpentinized subcontinental mantle peridotites (Kiss et
al., 2023). Basalts, then, show Ocean Continent Transition Zone (OCTZ) chemical features with transitionalMORB affinity and a garnet signature (Dyn/Yb0: 1.2-1.4, Saccani, 2015), in agreement with Cyprus-type
VMS deposits (Zaccarini & Garuti, 2008). Major and trace elements bulk rock geochemical analyses were
performed in a group of basalts of the Boccassuolo ophiolite and compared with the previous results (e.g.,
Barrie & Hannington, 1999; Zaccarini & Garuti, 2008; Kiss et al., 2023): the VMS deposits in the Emilia
Romagna region belong to the Cu and Cu-Zn types (Cu up to 5818 ppm, 200 times Upper Continental Crust,
UCC, composition; Zn up to 7941 ppm, 118*UCC), low to very low Pb contents (< 1 ppm, max. 0.42*UCC).
These preliminary results provide the first relevant geochemical information to map trace metal enrichment
distribution in the main rocks of the area. Radiogenic (Sr-Nd-Pb) and stable (S-C) isotopic analyses, as well as
mineralogical and in-situ analyses, will provide additional information on the enrichment and distribution of
VMS deposits in the Region.
Barrie C.T. & Hannington M.D. (1999) - Classification of Volcanic-Associated Massive Sulfide Deposits Based on
Host-Rock Composition. In: Barrie C.T. & Hannington M.D. (Eds), Volcanic-Associated Massive Sulfide Deposits:
Processes and Examples in Modern and Ancient Settings, Rev. Econ. Geol., 8, 2-10.
Kiss G.B. et al. (2023) - Tracing the Source of Hydrothermal Fluid in Ophiolite-Related Volcanogenic Massive Sulfide
Deposits: A Case Study from the Italian Northern Apennines. Minerals, 13, 8.
Saccani E. (2015) - A new method of discriminating different types of post-Archean ophiolitic basalts and their
tectonic significance using Th-Nb and Ce-Dy-Yb systematics. Geosci. Front., 6, 481-501, https://doi.org/10.1016/j.
gsf.2014.03.006.
Zaccarini F. & Garuti G. (2008) - Mineralogy and chemical composition of VMS deposits. Mineral. Petrol., 94, 61-83,
https://doi.org/10.1007/s00710-008-0010-9
Più splendon le carte. Manoscritti, libri, documenti, biblioteche: Dante "dal tempo all'etterno"
No full textMostra di manoscritti e libri danteschi organizzata presso la Biblioteca Reale di Torino dal 16 giugno al 31 luglio 201
Petrology and tectonic setting of Corsica ophiolitic basalt and comparison with those of the Northern Apennine: Implication for the geological evolution of the Corsica-Apennine orogenic system
No full textBoth Alpine Corsica and Northern Apennine represent a key area for the study of the ophiolites originated in the Piedmont-Ligurian oceanic basin. In fact, the coexistence in the Alpine Corsica of Ligurian-type ophiolitic units (characterized by absent or modest metamorphic imprinting) and Piedmont-type units (with HP/LT metamorphism) is of particular interest for the reconstruction of the genesis of this oceanic sector, as well as of its consumption during the early orogenic phases.
Many of the Corsica ophiolitic units have been object of recent structural-stratigraphic and petrologic studies. The Balagne, Nebbio, Pineto, and Rio Magno units display typical Ligurian-type features, whereas the Schistes Lustrès, the Inzecca units, and several units of the Castagniccia have typical Piedmont-type features. The S. Angelo di Tenda unit singularly display greenschistes facies metamorphism, thus differing from all the other Corsica ophiolites. This unit could be comparable to the less metamorphosed Inzecca unit.
The petrological data of Corsica ophiolitic basalts indicate a T-MORB affinity for the Balagne-Nebbio unit and N-MORB affinity for all other ophiolitic units. Ophiolitic basalts of both the Tyrrhenian area (e.g. Elba I.) and Internal Ligurides of the Northern Apennine (e.g. Vara unit) show N-MORB affinity. Ophiolites represented in olistoliths and olistostromes in turbidites from the Northern Apennine display both N-MORB (mainly in Tuscany) and T-MORB (mainly in the Liguria-Parmesan Apennine) affinities. Recent petrological studies have shown that Corsica ophiolitic basalts show geochemical differences, probably related to differences in their mantle sources. The T-MORBs derived from mantle sources variably enriched by plume components probably related to the magmatic activity associated with the continental break-up. The S. Angelo di Tenda and some Pineto basalts display a little but definite enrichment by a plume component. The Schistes Lustrès, Rio Magno, and some Pineto basalts derived from pure sub-oceanic lithosphere without any influence of plume components.
The ophiolitic successions of the Balagne are characterized by the occurrence of siliciclastic sediments and breccias, which are interlayered in all the rocks of the succession, from basalts to Cretaceous deposits (Toccone breccias), whereas the ophiolitic successions of the Schistes Lustrès (e.g., Inzecca unit) display general features, which are very similar to those of the Internal Liguride ophiolites.
These characteristics led many authors to interpret the Balagne ophiolites (in the western side) and the Liguria-Parmesan ophiolites (in the eastern side) as the initial oceanic products, and therefore as the two opposite margins of the Ligurian ocean. By contrast, the other ophiolitic units of the Corsica and those of the Vara unit (Northern Apennine) represent products formed during the steady-state oceanic phase.
The distribution of the ages of the basalts (obtained from biostratigraphical data on radiolarites), as well as of associated gabbroic and plagiogranitic rocks (obtained from absolute datings) show that the older ages of basalts are found in the eastern Ligurian ophiolites. The absolute datings on gabbros of the External Ligurides, as well as of the Voltri Group are estimated at about 180 Ma. By contrast, in the Balagne biostratigraphic data and absolute datings on plagiogranites indicate relatively younger ages (160-150 Ma).
The integration of the various stratigraphic, tectonic, and petrological data obtained from Corsica and Northern Apennine ophiolites, as well as their significance for the dynamics of oceanic opening, the spreading phases, and the spatial-temporal evolution of the Ligurian ocean will be discussed. Finally, the several geodynamic models of oceanic consumption up to day proposed in literature will be discussed in order to examine which model can better satisfies the new data from Corsica ophiolites
Sulfur isotopic signature of subduction-unrelated and subduction-related ophiolitic rocks
No full textSulfur (S) is one of the key volatiles in Earth’s chemical cycles as it affects biological, climate, ore-deposits, and redox processes. It is known that
S stored in the crust is recycled into the mantle at subduction zones. However, some aspects of the S cycle in the deep Earth such as S speciation, flux, isotope composition and fractionation processes still remain unclear. The study of ophiolites could provide information about contents and isotopic
features of S in subduction-unrelated and subduction-related geodynamic settings. In this work we compiled a global dataset of both subduction-unrelated and subduction-related ophiolitic basalts, and we measured their whole rock S contents and the relative S isotopic ratio (34S/32S) using an elemental analyzer coupled with a mass spectrometer (EA-IRMS). The
considered samples are Mid-Ocean Ridge Basalts (MORBs) from Corsica, Romania, Albania, and North Macedonia; ii) Island Arc Tholeiites (IAT)
from Albania and Greece; iii) Calc-Alkaline Basalts (CAB) from Greece, Romania, North Macedonia, and Iran already constrained from a petrological and geochemical point of view by different studies (Moberly et al., 2006; Saccani et al., 2011; Brombin et al., 2022). In the studied basalts, the S contents range from 200 and 300 ppm. Despite the different areas of provenance, for most of the samples the S isotopic signatures are similar in rocks having similar geochemical affinity. The average S isotopic ratios are –0.7‰, +5.8, and +7.4‰, for MORBs, IATs, and CABs, respectively. It is evident that only MORBs preserved the typical S signature of the Earth
mantle (i.e., from –2‰ to 0‰). The subduction related magmatic rocks (i.e., IATs and CABs) show positive S isotopic values, probably due to the contamination of i) enriched-34S subducting sediments in the magma sources or ii) fluids released by serpentinized rocks of the slab, which
typically have comparatively more positive S signature.
In summary, this work allowed the definition of: i) the S isotope compositions in both subduction-unrelated and subduction-related magmatic rocks; ii) the possible causes which modify the original S signature (e.g., contamination by subducting sediments). Research like this are therefore essential to unravel the global S cycle.
REFERENCES
Dilek Y., Furnes H., 2014. Ophiolites and Their origins. Elements, 10: 93-100.
Moberly, R., Ishii, T., Garcia, M.O., Ross, K., Artita, K., 2006. Enriched, transitional, and normal mid-ocean-ridge basalt glass, ODP Leg 203. In Schultz, A., Orcutt, J.A., and Davies, T.A. (Eds.), Proc. ODP, Sci. Results, 203, 1–36
Saccani E., Beccaluva L., Photiades A., Zeda O., 2011. Petrogenesis and tectono-magmatic significance of basalts and mantle peridotites from the Albanian–Greek ophiolites and subophiolitic mélanges. New constraints for the Triassic–Jurassic evolution of the Neo-Tethys in the Dinaride sector. Lithos, 124: 227-242.
Brombin V., Barbero E., Saccani E., Precisvalle N., Lepitkova S., Milevski I., Ristovski I., Milcov I., Dimov G., Bianchini G., 2022. Subduction signature of the Vardar ophiolite of North Macedonia: new constraints from geochemical
and stable isotope data. Ofioliti, 47: 85-102
The pathologist and the clinical oncologist: new effective partnership in assessing tumor prognosis.
No full textPrognostic indicators in primary breast cancer. Indian Journal of Cancer Chemotherapy, II: 1-8, 1989
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