1,721,166 research outputs found
Non-traditional isotope tracers (238U/235U and 98Mo/95Mo) of subduction processes in the Central-Mediterranean magmatism.
No full textNon-traditional isotope systems such as Mo and 238U/235U are
notably fractionated by redox-related processes on the Earth’s
surface. Such distinctive signatures may be carried into the mantle
wedge via subduction and provide valuable tracers of components
involved in magma genesis. Thus we measured Mo isotopes and
238U/235U on a suite of central-western Mediterranean calc-alkaline
to ultra-potassic rocks (both silica-oversaturated and under-saturated).
The studied rocks are associated with destructive plate
margins, showing strong depletions in Nb and Ta, highly radiogenic
Sr isotopes and most notably extreme enrichment in incompatible
trace elements with respect to other volcanic arcs. These features
have been long related to recycling of sedimentary material of
different compositions into their mantle sources, making these
rocks particularly suitable to investigate the role and nature of
recycled sediments in subduction related magmatism. The data
show an extremely wide spread of 98Mo/95Mo values, especially for
the silica under-saturated products, that is significantly larger than
any volcanic rocks suites reported so far. Smaller variations have
been measured for 238U/235U. We discuss the isotope compo
sition of the studied volcanic rocks and possible sedimentary end-
members with the aim of constraining the lithology of the recycled sediments as well the
mechanism of element transport from the slab to the mantle (i.e.
fluids vs. melts)
Constraining slab recycling under Vesusius volcano from combined U-series and non-traditional stable isotope (Mo, 238U/235U) data.
No full textThe fate of deeply subducted oceanic crust and overlying
sediments is of great importance for its role in the generation
of magmas in subduction-related geodynamic settings. Italian volcanoes, and Vesuvius in particular, are good laboratories to
investigate these processes due to their strong enrichment in K
and incompatible trace element that requires a significant
amount of sediment material recycled into the mantle.
Volcanic rocks from Vesuvius display ubiquitous 238U excesses
(up to 27%), a feature that is unusual in such enriched
subduction-related magmas. In addition they have among the
highest (231Pa/235U) and (226Ra/230Th) reported for arc rocks.
These characteristics require a recent addition of a high-U
component to the mantle beneath the Italy. In order to
constrain the origin and nature of this slab-related component
we present new data on non-traditional stable isotopes (Mo,
238U/235U) on both volcanic rocks and possible sedimentary
end-members. Non-traditional isotope systems such as Mo and
238U/235U are sensitive to redox-related isotopic fractionation
on the Earth’s surface, hence they may provide key
information on the type of material recycled from the
subducting slab to the mantle wedge.
The combined use of these different isotope systematics
will provide a wider picture of the mechanism and timescales
of the processes occurring from slab subduction to magmas
generation and ascent above subduction zones
The role of carbon from recycled sediments in the origin of ultrapotassic igneous rocks in the Central Mediterranean
Full text linkThe Central Mediterranean region is one of the most important areas on Earth for studying subduction-related potassic and ultrapotassic magmatism, derived from partial melting of the metasomatised lithospheric mantle wedge. In this region, leucite-free (i.e., lamproite) and leucite-bearing (i.e., kamafugite, leucitite, and plagioleucitite) ultrapotassic rocks closely occur, in a time-related progression, linked to the evolution of both the mantle source and the regional tectonic regime. Time- and space-related magmatism migration followed the roll-back of the subducting slab and the anticlockwise drift of the Italian Peninsula. Leucite-free silica-rich lamproites are restricted to the early stage of magmatism and are associated with ultrapotassic shoshonites and high-K calc-alkaline volcanic rocks. Leucite-bearing (i.e., Roman Province) rocks are erupted consistently later than lamproite-like and associated shoshonitic rocks, with post-leucititic volcanism occurring in the late stage of volcanic activity with eruption of alkali-basaltic to latitic and trachytic rocks, often after major caldera-forming events. Present-day ultrapotassic volcanism is restricted to the Neapolitan area. Central Mediterranean potassic and ultrapotassic rocks are extremely enriched in incompatible trace elements with variable fractionation of Ta, Nb, and Ti in comparison to Th and large ion lithophile elements (LILE). They are also variably enriched in radiogenic Sr and Pb and unradiogenic Nd. The main geochemical and isotopic signatures are consistent with sediment recycling within the mantle wedge via subduction. A twofold metasomatism, induced by the recycle of pelitic sediments and dehydration of lawsonite-bearing schists generates the early metasomatic events that enriched the mantle wedge from which leucite-free ultrapotassic rocks (i.e., lamproite) were generated. Recycling of carbonate-rich pelites played an important role in the shift to silica-undersaturated ultrapotassic rocks (kalsilite- and leucite-bearing) of the classic ‘Roman province’
New <sup>40</sup>Ar-<sup>39</sup>Ar dating and revision of the geochronology of the Monte Amiata Volcano, Central Italy
No full textThe duration of the Mt. Amiata volcanic activity is still a matter of debate, in spite of the presence of several geochronological data in the literature. We performed new 40Ar-39Ar dating on the sanidinegroundmass pairs of the upper stratigraphic units: Dome and massive Lava flows Complex (DLC) and Olivine Latitic final Lavas (OLF). The aim was twofold: to check the reliability of sanidine ages as geochronometer in these products, questioned in the literature, and to better define the chronology of the late activity of this volcano. Ages obtained on coexisting sanidine and groundmass of the Dome and massive Lava flows Complex (DLC) samples overlap within errors, demonstrating that sanidine crystals recorded reliable emplacement ages in these rocks. The Olivine Latite final lavas (OLF) display a different scenario, where the groundmass has an age younger than that of the sanidine, which is xenocrystic and, evidently, retains inherited Ar. Preferred ages for analysed DLC samples are comprised between 301 and 294 ka, an interval of time too short to resolve the ages of the four dome samples taken into account. The Ermeta lava is about 60 ka younger. We propose that the majority of Mt. Amiata volcanic rocks were emplaced in a narrow interval of time, whilst a temporal gap, which needs more detailed constraints, exists with at least one of the Olivine Latite final lavas (OLF)
Gelogical map of the Monte Amiata region (Southern Tuscany, Italy). 1:50.000 scale.
No full textThis paper and the associated 1:50,000 geological map are devoted to describe the geological features of the Monte Amiata region. The tectono-stratigraphic setting of Monte Amiata region includes, from bottom to top, 1) the pre-Neogene stack of tectonic units, made up of Tuscan, Sub-Ligurian and Ligurian Tectonic Units, 2) the Neogene sedimentary deposits and 3) the Plei -stocene Radicofani and Monte Amiata volcanoes. The pre-Neogene stack of tectonic units includes, from bottom to top, the Tuscan Nappe, belonging to the Tuscan Domain, and Canetolo Tectonic Unit, belonging to the Sub-Ligurian Domain. These tectonic units, regarded as representative of the thinned continental margin of the Adria plate, are topped by the Santa Fiora and Ophiolitic Tectonic Units, interpreted as remnants of the Ligure-Piemontese oceanic basin and its transition to the Adria continental margin. All the tectonic units of the pre-Neogene stack have been affected by folds and thrusts originated during the convergence related to the Europe-Africa motion during the Middle Eocene-Early Miocene. Subsequently, these tectonic units were affected by a widespread reduction of thickness of their successions due to low-angle normal faulting related to the Middle Miocene extensional tectonics. The Neogene sedimentary deposits unconformably overlie the pre-Neogene stack of tectonic units. They consist of Upper Miocene to Pliocene continental and marine sediments, filling the Cinigiano-Baccinello, Velona, and Siena-Radicofani basins, adopting an informal hierarchy of different stratigraphic units where the first order units are synthems. The Pleistocene Radicofani and Monte Amiata volcanoes are made up by high-K basaltic andesitic to shoshonitic volcanic rocks and by trachydacitic to trachytic and olivine-latitic volcanic rocks, respectively. The geological mapping has provided evidences of a complex tectonic setting resulting from a long-lived history shifting from Cretaceous to Early Miocene compressive events to Middle Miocene extensional tectonics and Late Miocene-Pleistocene contractional and extensional events during which the Pleistocene magmatic activity occurred. In this regard, the Monte Amiata region can be regarded as a key area where the final result of a 200 Ma long geological history of the Northern Apennines is exposed
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
Conservation of 87Sr/86Sr During Wine-Making of White Wines: A Geochemical Fingerprint of Geographical Provenance and Quality Production
Full text linkConservation of 87Sr/86Sr isotopic ratios during the winemaking processes of 'Red' wines to validate their use as geographic tracer
Full text link87Sr/86Sr has been determined in wines, musts grape juices, soils and rocks from six selected vineyards of 'Cesanese' wine area. Cesanese is a monocultivar wine from a small region characterised by different geologic substrata, a key locality to test the influence of both substratum and winemaking procedure on the 87Sr/86Sr of wines. Experimental work has been performed on wines from different vintage years to check possible seasonal variations. The data reveal that 87Sr/86Sr does not change through time, to validate the selection of wineries performed, and in addition no isotopic variations are observed during winemaking. Indeed, no significant isotopic variations have been observed in musts and wines. These findings reinforce the hypothesis that the isotopic signature of wines is strongly related to the bioavailable fraction of the soil rather than to its bulk. The data corroborate the possibility that Sr-isotopes of high-quality wines can be used as a reliable tool for fingerprinting wine geographic provenance
Petrogenesis of Mediterranean lamproites and associated rocks: the role of overprinted metasomatic events in the postcollisional lithospheric upper mantle
Full text linkHigh-MgO lamproite and lamproite-like (i.e. lamprophyric) ultrapotassic rocks are recurrent in the Mediterranean and surrounding regions. They are associated in space and time with ultrapotassic shoshonites and high-K calc-alkaline rocks. This magmatism is linked with the geodynamic evolution of the westernmost sector of the Alpine–Himalayan collisional margin, which followed the closure of the Tethys Ocean. Subduc- tion-related lamproites, lamprophyres, shoshonites and high-K calc-alkaline suites were emplaced in the Medi- terranean region in the form of shallow level intrusions (e.g. plugs, dykes and laccoliths) and small volume lava flows, with very subordinate pyroclastic rocks, starting from the Oligocene, in the Western Alps (northern Italy), through the Late Miocene in Corsica (southern France) and in Murcia-Almeria (southeastern Spain), to the Plio- Pleistocene in Southern Tuscany and Northern Latium (central Italy), in the Balkan peninsula (Serbia and Mac- edonia) and in the Western Anatolia (Turkey). The ultrapotassic rocks are mostly lamprophyric, but olivine latitic lavas with a clear lamproitic affinity are also found, as well as dacitic to trachytic differentiated products. Lamp- roite-like rocks range from slightly silica under-saturated to silica over-saturated composition, have relatively low Al2O3, CaO and Na2O contents, resulting in plagioclase-free parageneses, and consist of abundant K-feldspar, phlogopite, diopsidic clinopyroxene and highly forsteritic olivine. Leucite is generally absent, and it is rarely found only in the groundmasses of Spanish lamproites. Mediterranean lamproites and associated rocks share an extreme enrichment in many incompatible trace elements and depletion in High Field Strength Elements and high, and positively correlated Th/La and Sm/La ratios. They have radiogenic Sr and unradiogenic Nd iso- tope compositions, high 207Pb over 206Pb and high time-integrated 232Th/238U. Their composition requires an originally depleted lithospheric mantle source metasomatized by at least two different agents: (1) a high Th/ La and Sm/La (i.e. SALATHO) component deriving from lawsonite-bearing, ancient crustal domains likely hosted in mélanges formed during the diachronous collision of the northward drifting continental slivers from Gondwana; (2) a K-rich component derived from a recent subduction and recycling of siliciclastic sediments. These metasomatic melts produced a lithospheric mantle source characterized by network of felsic and phlogo- pite-rich veins, respectively. Geothermal readjustment during post-collisional events induced progressive melt- ing of the different types of veins and the surrounding peridotite generating the entire compositional spectrum of the observed magmas. In this complex scenario, orogenic Mediterranean lamproites represent rocks that charac- terize areas that were affected by multiple Wilson cycles, as observed in the Alpine–Himalayan Realm
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