1,721,188 research outputs found
Kirschsteinite in the Capo di Bove melilite leucitite lava (cecilite), Alban Hills, Italy
No full textShoshonite and sub-alkaline magmas from an ultrapotassic volcano: Sr-Nd-Pb isotope data on the Roccamonfina volcanic rocks, Roman Magmatic Province, Southern Italy
No full textThe Roccamonfina Volcano is characterised by a two stage volcanic activity, divided by volcano-
tectonic collapses. Ultrapotassic leucite-bearing rocks are confined in the pre-caldera stage and display
geochemical characteristics very similar to those of other volcanoes of the Roman Province. Shoshonitic
rocks have been poured out from cinder cones and domes both within the caldera and on the external flanks
of the pre-caldera Roccamonfina volcano. On the basis of new trace element and Sr-Nd-Pb isotope data,
Roccamonfina shoshonitic rocks show differences with respect to shoshonites from Northern Roman
Province, and recall closely those of the Neapolitan volcanoes. Eventually, in the very last phases of
volcanic activity, sub-alkaline magmas are found both as enclaves in trachytic domes, and as final lavas
vented by a fracture within the Monte Santa Croce dome. Ultrapotassic rocks that built up the pre-caldera
composite volcano are plagioclase-bearing leucitites and, similarly to other Roman Provinces volcanoes, have by high levels of incompatible trace elements with an orogenic signature having troughs at Ba, Ta, Nb,
Ta, and Ti, and peaks at Cs, K, Th, U, and Pb. Initial values of 87Sr/86Sr range from 0.709261 to 0.709987,
of 143Nd/144Nd range from 0.512134 to 512195, of 206Pb/204Pb range from 18.788 to 18.851, of
207Pb/204Pb range from 15.685 to 15.701, and of 208Pb/204Pb range from 39.048 to 39.076. Shoshonites
show a larger differentiation degree but, as a whole, lower levels of incompatible trace elements with similar
pattern of incompatible trace element contents with respect to earlier ultrapotassic leucite-bearing rocks. On
the other hand, shoshonitic rocks have Sr, Nd, and Pb isotopes consistently different than pre-caldera
ultrapotassic leucite-bearing rocks. 87Sr/86Sr ranges from 0.706604 to 0.708332, 143Nd/144Nd ranges
from 0.512179 to 0.512382, 206Pb/204Pb ranges from 18.838 to 19.153, 207Pb/204Pb ranges from 15.661
to 15.694, and 208Pb/204Pb ranges from 38.999 to 39.212. High-K calc-alkaline samples have intermediate
isotopic values between ultrapotassic plagioclase leucitites and shoshonites, but the lowest levels of
incompatible trace element contents. The genesis of this uncommon association is investigated in details. It
is argued that ultrapotassic magmas have been generated in a modified lithospheric mantle after crustal-
derived metasomatism. Interaction between metasomatic agent and lithospheric upper mantle produced a
low-melting metasomatised veined network. Pure partial melting of vein mineralogy produced pre-caldera
leucite-bearing ultrapotassic magmas. Leucite-free magmas have been generated further melting, at higher
temperature, of the same meltasomatic mantle previously depleted by the ectraction of ultrapotassic rocks.
We suggest that a key role in this second episode of melting is played by little but significant addition of
astenospheric upper mantle material from foreland mantle, flowing through the corner of the Ionian present
day subducted slab during its roll-bac
The Tyrrhenian margin geological setting: from the Apennine orogeny to the K-rich volcanism
No full textWe present an up-to-date review of the existing data on the evolution of the Apennine–
Tyrrhenian basin system and of the tectonic models developed to interpret the complex evolution of
magmatism and volcanism along the Tyrrhenian margins of peninsular Italy from Miocene to
the Present. The Tyrrhenian margin volcanic belt lies within a back-arc basin located on top of
the NW-dipping Adriatic–Ionian slab, active along the convergent boundary between the Africa
and Eurasia plates. It is characterized by significant crustal thinning, high thermal flow and huge
production of mantle fluids. Seismic activity is very low and clusters in geothermal and volcanic
areas. The structural architecture of the extensional Tyrrhenian margin is mainly controlled by
NW–SE oriented normal faults, which are presently active along the Apennine water shade.
This volcanism can be divided on the basis of time–space and petrographic criteria into four
different provinces: the Corsica Magmatic Province, the Tuscan Magmatic Province, the Roman
Magmatic Province and the Lucanian Magmatic Province. Inside each of these magmatic
regions, igneous rocks with different petrochemical affinities are found in the same timespan
beside the main magmatic association. The structural control over the Roman Magmatic Province
volcano locations and spacing can be divided into two main components: the geometry of
the mantle source, which defines the general trend of the volcanic chain, and the structure of the
crust, which defines zones of preferential permeability to magmatic fluids. On a crustal scale,
the localization of volcanoes is ubiquitously related to cross-cutting NW-trending and NE-trending
transverse extensional structures. Volcanoes of the Tyrrhenian margin show a variety of morphologies
and eruption styles. In particular, Middle–Upper Pleistocene volcanoes of the Roman
Magmatic Province display both effusive and explosive activity. Highly explosive volcanoes
have erupted several intermediate- to large-volume ignimbrites and are characterized by large,
polyphased calderas and vast ignimbrite plateaus. Volcanoes characterized by intermittent effusive
and explosive activity have formed stratovolcanoes and also erupted intermediate-volume
ignimbrites that generally formed small summit collapse composite calderas
The Tyrrhenian margin geological setting: from the Apennine orogeny to the K-rich volcanism
No full textWe present an up-to-date review of the existing data on the evolution of the Apennine –
Tyrrhenian basin system and of the tectonic models developed to interpret the complex evolution of
magmatism and volcanism along the Tyrrhenian margins of peninsular Italy from Miocene to
the Present. The Tyrrhenian margin volcanic belt lies within a back-arc basin located on top of
the NW-dipping Adriatic – Ionian slab, active along the convergent boundary between the Africa
and Eurasia plates. It is characterized by significant crustal thinning, high thermal flow and huge
production of mantle fluids. Seismic activity is very low and clusters in geothermal and volcanic
areas. The structural architecture of the extensional Tyrrhenian margin is mainly controlled by
NW – SE oriented normal faults, which are presently active along the Apennine water shade.
This volcanism can be divided on the basis of time – space and petrographic criteria into four
different provinces: the Corsica Magmatic Province, the Tuscan Magmatic Province, the Roman
Magmatic Province and the Lucanian Magmatic Province. Inside each of these magmatic
regions, igneous rocks with different petrochemical affinities are found in the same timespan
beside the main magmatic association. The structural control over the Roman Magmatic Province
volcano locations and spacing can be divided into two main components: the geometry of
the mantle source, which defines the general trend of the volcanic chain, and the structure of the
crust, which defines zones of preferential permeability to magmatic fluids. On a crustal scale,
the localization of volcanoes is ubiquitously related to cross-cutting NW-trending and NE-trending
transverse extensional structures. Volcanoes of the Tyrrhenian margin show a variety of mor-
phologies and eruption styles. In particular, Middle – Upper Pleistocene volcanoes of the Roman
Magmatic Province display both effusive and explosive activity. Highly explosive volcanoes
have erupted several intermediate- to large-volume ignimbrites and are characterized by large,
polyphased calderas and vast ignimbrite plateaus. Volcanoes characterized by intermittent effusive
and explosive activity have formed stratovolcanoes and also erupted intermediate-volume
ignimbrites that generally formed small summit collapse composite calderas
Mo and stable U isotopes as tracers for subduction components in the Quaternary West-Mediterrean potassic and ultrapotassic magmatism
No full textThe central-western Mediterranean is one of the most important areas on Earth for studying subduction-related potassic and ultrapotassic magmatism. In a very restricted area, leucite-free (lamproite) and leucite-bearing (kamafugite, leucitite, and plagioleucitite) ultrapotassic rocks have been emplaced and are associated with shoshonites and high-K calc-alkaline volcanic rocks.
Despite their alkaline characteristics, the least evolved Italian ultrapotassic rocks associated with destructive plate margins invariably show a strong depletion of Nb and Ta along with the highest levels of incompatible trace elements ever seen in any volcanic arc. These characteristics are thought to be derived through the recycling of sediments via subduction within the mantle wedge, and their extreme trace element enrichments make them unique for understanding the roles of different subduction-related metasomatic agents (e.g. silico-clastic vs carbonate). In fact, the variable compositions of the sedimentary materials, subducted along the Adriatic slab and transported into the overlying mantle forming a vein network, could explain the distinct geochemical signature of each Italian magmatic region (Avanzinelli et al., 2009).
We propose to investigate this issue considering two stable isotopic systematics that are perceptive to redox condition-related isotopic fractionation. We measured Mo and stable U isotopes with the high-resolution MC-ICP-MS (Neptune), using a double-spike technique, on selected volcanic rocks from three Italian magmatic provinces and representative samples of subducting sediments.
Molybdenum has seven stable isotopes, which have been shown to fractionate during the incorporation into oceanic sediments. Under oxic conditions, Mo adsorbs to particles into the sediment, particularly when Fe-Mn oxides are present, producing lighter isotopic composition (δ98Mo/95Mo), whilst is quantitatively removed in anoxic conditions, leaving sediments with a heavier isotopic signature. The recently observed variability in natural 238U/235U values (different from the widely used “consensus” value of 137.88) due to isotopic fractionation during the redox transition between the U(IV) and U(VI) oxidation states, produces as well as Mo isotopes, a lighter isotopic composition (δ238U/235U) in oxic sediments compared to a heavier composition in anoxic sediments. We interpret those results in order to recognize the U and Mo isotopic signature of sediments, with different lithology and chemical composition, recorded into the selected volcanic rocks, and to set new constraints on the metasomatic agents responsible for the transition from silica oversaturated lamproite-like to strongly silica undersaturated HKS magmas
Oligo-Miocene A-type granites and granophyres from Yemen: isotopic and trace-element constraints bearing on their genesis
No full textOligo-Miocene A-type granites and granophyres from Yemen were emplaced during the early stages of lithospheric break-up and thinning prior to the onset of rifting and sea-floor spreading of the Red Sea. New trace element data together with Sr isotope are reported in the present paper. The Yemen granites and granophyres have high alkali (7-11 wt.%), high field strength element, and Zn contents along with low Sr and Ba contents. They are characterised by high FeOtot/MgO, Ga/Al values. The initial Sr isotope values range from 0.704 to 0.721, Y/Nb, Yb/Ta, and Ce/Nb values are similar to those of Yemen Trap Series basalts and clustered to the field of OIB. These trace element ratios argue against the origin of the Yemen granites and granophyres by crustal anatexis processes, and provide evidence for a genetic link with coeval basalts of the Yemen Trap Series. Furthermore, two groups of high silica magmas can be recognised, which are characterised by Nb/Y values of ∼ 1 (Low Nb/Y Granites) and ∼ 2 (High Nb/Y Granite). The overall geochemical characteristics of the Yemen granites and granophyres, along with their Sr isotope composition, support an origin for the Low Nb/Y and High Nb/Y Granites by a two-stage Assimilation and Fractional Crystallisation process (AFC) commencing from two types of the Yemen Trap Series basalts with slightly different within-plate signature. Each of the two AFC stages could be occurred in distinct magma reservoirs located in the lower (Step I) and middle-upper crust (Step II
Petrology, mineralogy and isotopes in olivine mela-nephelinites, basanites and carbonatites from Uwaynat region, south east Libya: inferences on their genesis
No full textIn the Uwaynat region, there are hundreds of volcanic plugs, dykes and lava flows, ranging in composition from carbonatites to olivine mela-nephelinites, alkali-basalts and minor phonolites and trachytes. Olivine mela-nephelinites, basanites and alkali basalts are the most abundant rock types. These rocks are from ring complexes and mafic plugs located between the Uwaynat Inlier and the Al Kufrah basin, in the Libyan desert. These volcanic rocks range from 28.2 to 26.7 Ma in age. Olivine mela-nephelinites and basanites are characterised by extremely high titania (up to 6 wt.%) and incompatible trace elements contents. Minor ferro-carbonatites are also present and they are also characterised by high content of titania and related high field strength elements and higher content in incompatible trace and rare earth elements than olivine mela-nephelinites and basanites. No large variations in the initial Sr and Nd isotope compositions are observed. This may suggest none or very little contribution of crustal rocks-magma interaction. A similar isotopic signature for the source of olivine mela-nephelinites and ferro-carbonatites is inferred. Olivine mela-nephelinites and basanites are not genetically related to each other by fractionation but they represent primitive magmas generated by different degrees of partial melting of a metasomatised upper mantle source. Incompatible trace elements in olivine mela-nephelinites may be modelled with small degrees of partial melting of such a source. Close relationships are also observed with the slightly older volcanic rocks from Gilf Gebir (SW Egypt), suggesting that Uwaynat magmatism is possibly related to a northeastward migration of the African plate above an intracontinental hot spot
Crystal chemistry of clinopyroxene from alkaline undersaturated rocks of the Monte Vulture Volcano, Italy.
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