<p>Raw materials are essential for the sustainable development of modern so... more <p>Raw materials are essential for the sustainable development of modern societies. Access to and cost-effectiveness of mineral raw materials are critical to the smooth functioning of the EU economy. The growing demand for raw materials raises increasing concerns about mineral resources. Feldspars along with quartz, the main components of granitoid rocks, are widely used in ceramic and glass industry. The need to meet the demands of the ceramic industry has stimulated research and development of new ceramic flows in granite complexes.</p><p>Italy is the world’s second-largest feldspar producer (22% of total) and the world biggest importer (22% of global world trades) (European Commission). Since the strong demand is rapidly depleting the proven reserves in EU Member States, the EU ceramics sector is increasingly dependent on feldspar imports from Turkey. Thus, it is necessary to find additional sources of feldspar or to further increase inter-continental transport. At present, Buddusò-Alà dei Sardi (Sardinia-Italy) is the most important granite production area in Italy. However, granite mining activities cause serious environmental problems. Feldspar production and trade generate large amounts of pollutant and greenhouse gas emissions, due either to the energy consumption of mining activities or the transport of the finished product from the exporting countries. The areas where quarries are active suffer from landscape degradation, due to incomplete compliance or non-compliance with quarry recovery plans, considering that opening new quarries is cheaper than moving large amounts of waste. Finally, granite mining accounts for huge amounts of soil consumption, as it requires large areas in which the quarry waste accumulates.</p><p>The LIFE REGS II project (LIFE19 ENV/IT/000373 LIFE REGS II) aims at demonstrating an innovative and economically-viable extraction technology to produce feldspars, of the same quality to those obtained from virgin raw material, using granite scraps. This will reduce demand for feldspar from environmentally-damaging granite mining operations as well as to minimize the soil consumption and to boost the awareness about the importance of recycling granite scraps.</p><p>To this respect, samples of the granite scraps accumulated in 18 landfills located in the Buddusò-Alà dei Sardi granite quarries have been analyzed for their mineral texture and composition. Modal variability of the main mineral constituents (quartz+plagioclase±potassium-feldspar+biotite/chlorite) allowed to distinguish three main groups characterized by different ratios of feldspars/mafic phases with the exception of samples from a specific landfill that display an increase in the plagioclase at the expense of potassium-feldspar+quartz along with an increase in epidote at the expense of biotite/chlorite.</p><p>Texturally potassium-feldspar occasionally occurs as microcline perthite while plagioclase is always affected by extensive alteration resulting in a variety of textural intergrowths of neoformed minerals. Such features are reflected in the inter/intra-crystalline compositional variations in terms of feldspar end-members and in the type of the alteration products. This provides the elements for a first estimate of the technological properties of felsdpars, allowing to recognize the material stored in the 18 landfills qualitatively better for commercial purpose, and to experimentally identify the most effective methods of physical treatments to enrich and extract feldspars useful for industrial uses.</p>
<p>Assessing the nature and evolution of the Sub-Continental Lithospheric M... more <p>Assessing the nature and evolution of the Sub-Continental Lithospheric Mantle (SCLM) is crucial to understand the dynamics of Earth’s interior and the global scale tectono-magmatic processes. The study of ultramafic xenoliths brought to the surface in specific context, such as northern Victoria Land (Antarctica), is a key to investigate how the SCLM bear witness of large-scale geodynamic episodes. Indeed, the Antarctica lithosphere was involved into three main tectono-magmatic episodes since Paleozoic, i.e. the 550-110 Ma Ross subduction, the Jurassic (~182 Ma) Ferrar magmatism and the Cenozoic alkaline magmatism responsible for the opening of the West Antarctic Rift System (WARS).</p><p>In this study, a review of the petrological and geochemical features of >200 mantle-derived and cumulate xenoliths brought to the surface at Baker Rocks, Greene Point, Handler Ridge, Harrow Peaks, Browning Pass and Mount Overlord enabled us to reconstruct the main depletion and enrichment processes that took place in the Antarctica SCLM. Strong depletion is recorded by Greene Point lherzolites and harzburgites (18-21%), which likely began melting in the garnet facies and terminated in the spinel facies (Perinelli et al. 2006), whereas mild melt extraction in the spinel stability field was hypothesized at Baker Rocks and Handler Ridge (12-16% and 7-13% melting, respectively). The onset of the Jurassic Ferrar large magmatic event is testified by both the refertilisation in Greene Point-Baker Rocks peridotites and the appearance of cumulate orthopyroxenites/olivine-websterites at Harrow Peaks and Baker Rocks. Late enrichment process/es took place in concomitance with the Cenozoic alkaline magmatism of the WARS, resulting in both cryptic and modal metasomatism and overprinting earlier chemical modifications. This metasomatism was particularly effective at Baker Rocks, as shown by the increase of clinopyroxene abundance, its trace element enrichment and the formation of amphibole disseminated and in veins. Clinopyroxene composition in Cenozoic cumulate rocks matches the enrichment path observed in the peridotites, supporting the link between the last metasomatic process and the recent alkaline magmatism.</p><p>Among mantle xenoliths populations, Greene Point record the highest T-P (870-1059 °C; 0.8-1.6 GPa) and the least oxidized conditions (fO<sub>2</sub> down to -2/-3 ΔFMQ). Cumulate rocks yield the highest fO<sub>2</sub> (up to +1.5 ΔFMQ), at T varying between 900 and 1150°C, approximating the conditions of crystallizing melts. No discrepancies in fO<sub>2</sub> emerged between amphibole-bearing and amphibole-free peridotites, ruling out a strict correlation between amphibole stability, H<sub>2</sub>O activity and fO<sub>2</sub>. Nevertheless, the alkaline metasomatic event, which led to amphibole formation, caused a remarkable increase in the H<sub>2</sub>O content of the system. In fact, anhydrous peridotites preserve bulk H<sub>2</sub>O contents ≤128 ppm, while lherzolites with disseminated amphibole and hornblendites have H<sub>2</sub>O contents as up to 354-1120 ppm and 1.42 wt%, respectively.</p><p> </p><p>Perinelli, C., et al. 2006. Geochemical and O-isotope constraints on the evolution of lithospheric mantle in the Ross Sea rift area (Antarctica). Contributions to Mineralogy and Petrology, 151(3), 245-266.</p>
Equilibrium crystallization experiments were carried out on two primitive basaltic rocks (APR16: ... more Equilibrium crystallization experiments were carried out on two primitive basaltic rocks (APR16: Na 2 O+K 2 O=4.40 wt.%; CM42: Na 2 O+K 2 O=2.59 wt.%) with the aim to investigate the amphibole stability in the differentiation processes at deep crustal level, of primitive alkaline (APR16) and calc-alkaline (CM42) magmas. The experiments were performed with different initial H 2 O contents (0-5 wt.%), at pressure of 800 MPa, in a temperatures range of 975-1225°C. For the explored conditions the amphibole crystallization is limited for both compositions, to H 2 O in the melt >7wt.%, while the temperature of amphibole occurrence is lower in the alkaline composition (< 1050°C in APR16 and ≥1050°C in CM42). Moreover, amphibole crystallization seems to be influenced by the Na 2 O/K 2 O ratio rather than the absolute Na 2 O content in the melt. This is evident when experimental results on the APR16 and CM42 are compared with experimental data obtained from a primitive ultrapotassic c...
In the framework of the spatial-temporal distribution and compositional variability of Plio-Quate... more In the framework of the spatial-temporal distribution and compositional variability of Plio-Quaternary magmatic products emplaced in the Tyrrhenian and surrounding regions, the magmatism of he Western Pontine Islands (WPI -Ponza, Zannone, Palmarola) is still matter of debate,due to the complex geological setting in which the islands formed. The magmatism of WPI offers the opportunity to investigate the origin of calcalkaline and alkaline-peralkaline magmas. in a complex basin undergoing extension within an overall collisional geodynamic setting. Previous studies defined that: 1) Pliocene volcanic episodes are represented by silica-rich, high-K calcalkaline volcanic units at Ponza and Zannone islands; 2) Pleistocene volcanic episodes are represented by intermediate to highly evolved (K-trachytes to peralkaline trachytes and rhyolites) shoshonitic rocks cropping out in SE Ponza and Palmarola islands. According to Conte & Dolfi (2002) the magmatism of WPI was related to magmas similar ...
Abgarm ultramafic complex is a part of the Esfandagheh-Hajiabad coloured melange belt located in ... more Abgarm ultramafic complex is a part of the Esfandagheh-Hajiabad coloured melange belt located in the south east of Iranian segment of Alpine-Himalayan orogenic belt. The complex has faulted contacts with flysch type sediments of upper cretaceous ophiolite melange complex. Harzburgite is the dominant lithotype, dunites and lherzolites also occur in lesser extents. Some dunites contain massive chromitite pods or bands. The chemistry of minerals of harzburgite samples reflects the depleted nature of these rocks and indicates that the Abgarm mantle experienced a melt extraction less than 30%. Geothermo-barometric estimates indicate that the harzburgitic Abgarm mantle have been initially equilibrated at temperatures between 809-923°C and then at 613-725 °C, in a range of pressures of 1.1 and 2.3 GPa. Moreover, fO2 calculation gives a redox state that is in a range of 0.7 log bar units above the fayalite–magnetite–quartz buffer FMQ (log = 0.1 ÷ 0.7 log-bar units). Tectonomagmatic discrim...
Volcanic eruptions are shallow phenomena that represent the final stage of density- and viscosity... more Volcanic eruptions are shallow phenomena that represent the final stage of density- and viscosity- driven processes of melt migration from source rocks at upper mantle depths. In this experimental study, we investigated the effect of pressure (0.7–7.0 GPa) and temperature (1335–2000 °C) on the viscosity and the atomic melt structure of a synthetic anhydrous primitive alkaline basalt, an analogue of the pre-eruptive magma that likely feeds the Campi Flegrei Volcanic District at present day. Obtained viscosities (0.5–3.0 Pa s), mobility (0.1–0.4 g cm3 Pa−1 s−1) and ascent velocity (1.5–6.0 m yr−1) are presented to support geochemical and geophysical observations of Campi Flegrei as a critical volcanic district currently undergoing gradual magma recharge at depth.
Equilibrium crystallization experiments were carried out on two primitive basaltic rocks (APR16: ... more Equilibrium crystallization experiments were carried out on two primitive basaltic rocks (APR16: Na 2 O+K 2 O=4.40 wt.%; CM42: Na 2 O+K 2 O=2.59 wt.%) with the aim to investigate the amphibole stability in the differentiation processes at deep crustal level, of primitive alkaline (APR16) and calc-alkaline (CM42) magmas. The experiments were performed with different initial H 2 O contents (0-5 wt.%), at pressure of 800 MPa, in a temperatures range of 975-1225°C. For the explored conditions the amphibole crystallization is limited for both compositions, to H 2 O in the melt >7wt.%, while the temperature of amphibole occurrence is lower in the alkaline composition (< 1050°C in APR16 and ≥1050°C in CM42). Moreover, amphibole crystallization seems to be influenced by the Na 2 O/K 2 O ratio rather than the absolute Na 2 O content in the melt. This is evident when experimental results on the APR16 and CM42 are compared with experimental data obtained from a primitive ultrapotassic c...
Abstract Leucititic rocks, K-foiditic in composition are volumetrically important in the Colli Al... more Abstract Leucititic rocks, K-foiditic in composition are volumetrically important in the Colli Albani (also known as Alban Hills) volcanic district (Central Italy) especially during the most explosive phases of activity (>200 km3). The Colli Albani tephra in distal (>500 km) deposits indicates that K-foiditic magma chambers fed large explosive eruptions (i.e., tens of km3 of pyroclastic rocks). Major oxides, trace elements and Raman spectra were measured on the glasses and minerals occurring in the K-foiditic scoria clasts of the ~530 kyr-old Tufo del Palatino, erupted in the Colli Albani volcanic district. The Colli Albani pre-eruptive magmatic system is characterized by the aH2O 200 °C) and the K-foiditic melt shows low viscosity (104Pa·s at 1000 °C). Actually, the low melt viscosity, that increases the growth rate, and the large temperature interval of crystallization are intrinsic factors that increase the release of the latent heat of crystallization from the phonotephritic parental magma. Extrinsic factors enhancing the assimilation process efficiency are the thickness (>4 km) and the depth (down to 5–7 km) of the carbonate substrate in the Colli Albani volcanic district.
Present-day Sant'Antioco Island (SW-Sardinia, Italy) hosted one of the southernmost, and youn... more Present-day Sant'Antioco Island (SW-Sardinia, Italy) hosted one of the southernmost, and youngest, subduction-related, Cenozoic magmatic events of western Sardinia. A high-alumina basalt-andesite rock association, the focus of this paper, crops out in the southern portion of the island and represents the mafic end-member of volcanism developed during Miocene. Basaltic andesites and andesites are the dominant rock-types, while basalts and dacites are occasional. Minero-petrographic and geochemical characteristics reveal:i)a clear calc-alkaline signature for these rocks, in spite of high FeO*/MgO ratios that mimic a tholeiitic affinity; ii) a magma evolution mainly controlled by fractional crystallization and iii) some degree of crustal assimilation. Phase relationships and compositions, mass balance calculations and T, P, X, estimates consistently indicate that fractional crystallization occurred at low pressure (P=100-400 MPa), under different P(H2O) conditions, which explain th...
... Experimental constraints on evolution of leucite-basanite magma at 1 and 10 4 GPa: implicati... more ... Experimental constraints on evolution of leucite-basanite magma at 1 and 10 4 GPa: implications for parental compositions of Roman high-potassium magmas. Aida Maria Conte 1 ,* , Daniela Dolfi 2 , Mario Gaeta 3 , Valeria Misiti 4 , Silvio Mollo 2 ,4 and Cristina Perinelli 5. ...
Abstract Leucititic rocks, K-foiditic in composition are volumetrically important in the Colli Al... more Abstract Leucititic rocks, K-foiditic in composition are volumetrically important in the Colli Albani (also known as Alban Hills) volcanic district (Central Italy) especially during the most explosive phases of activity (>200 km3). The Colli Albani tephra in distal (>500 km) deposits indicates that K-foiditic magma chambers fed large explosive eruptions (i.e., tens of km3 of pyroclastic rocks). Major oxides, trace elements and Raman spectra were measured on the glasses and minerals occurring in the K-foiditic scoria clasts of the ~530 kyr-old Tufo del Palatino, erupted in the Colli Albani volcanic district. The Colli Albani pre-eruptive magmatic system is characterized by the aH2O 200 °C) and the K-foiditic melt shows low viscosity (104Pa·s at 1000 °C). Actually, the low melt viscosity, that increases the growth rate, and the large temperature interval of crystallization are intrinsic factors that increase the release of the latent heat of crystallization from the phonotephritic parental magma. Extrinsic factors enhancing the assimilation process efficiency are the thickness (>4 km) and the depth (down to 5–7 km) of the carbonate substrate in the Colli Albani volcanic district.
Volcanic eruptions are shallow phenomena that represent the final stage of density- and viscosity... more Volcanic eruptions are shallow phenomena that represent the final stage of density- and viscosity- driven processes of melt migration from source rocks at upper mantle depths. In this experimental study, we investigated the effect of pressure (0.7–7.0 GPa) and temperature (1335–2000 °C) on the viscosity and the atomic melt structure of a synthetic anhydrous primitive alkaline basalt, an analogue of the pre-eruptive magma that likely feeds the Campi Flegrei Volcanic District at present day. Obtained viscosities (0.5–3.0 Pa s), mobility (0.1–0.4 g cm3 Pa−1 s−1) and ascent velocity (1.5–6.0 m yr−1) are presented to support geochemical and geophysical observations of Campi Flegrei as a critical volcanic district currently undergoing gradual magma recharge at depth.
The crystal chemistry of Cr-spinels included in spinel peridotite mantle xenoliths from Baker Roc... more The crystal chemistry of Cr-spinels included in spinel peridotite mantle xenoliths from Baker Rocks and Greene Point (northern Victoria Land, Antarctica) has been studied by single-crystal 2+ substitution and pertain to the Mg-rich portion of the spinel sensu stricto-chromite join. The two groups of samples, Baker Rocks (BR) and Greene Point (GP), show distinct degree of cation order with the inversion parameter ranging from 0.17 to 0.20 for BR spinels and from 0.06 to 0.13 for GP crystals. Closure temperatures, computed by a geothermometer based on the Al+ Al+Mg intracrystalline exchange, range from 883 to 911 °C for BR spinels and from 592 to 675 °C for GP spinels. We show that this difference is due 3+ in GP spinels that enabled a faster kinetics of the intracrystalline cation ordering reaction, allowing the GP spinels to reach a higher degree of cation ordering and then lower closure temperatures.
Journal of Volcanology and Geothermal Research, 2016
Abstract The Pontine Islands form a volcanic archipelago in the Tyrrhenian Sea. It consists of tw... more Abstract The Pontine Islands form a volcanic archipelago in the Tyrrhenian Sea. It consists of two edifices, the islands of Ponza, Palmarola and Zannone and the islands of Ventotene and Santo Stefano, respectively. The Archipelago developed during two main volcanic cycles in the Plio-Pleistocene: 1) the Pliocene episode erupted subalkaline, silica-rich volcanic units, which constitute the dominant products in the western edifice (Ponza and Zannone Islands); 2) the Pleistocene episode erupted more alkaline products, represented by evolved rocks (trachytes to peralkaline rhyolites) in the islands of Ponza and Palmarola and by basic to intermediate rocks in the eastern edifice (Ventotene and Santo Stefano Islands). In this paper we present new geochemical and petrological data from submarine rock samples collected in two oceanographic cruises and a scuba diving survey. The main result is the recovery of relatively undifferentiated lithotypes that provide further insights on the magmatic spectrum existing in the Pontine Archipelago, allowing modelling of the whole suite of rocks by fractional crystallization processes. New major and trace element data and thermodynamic constrains (by the software PELE) indicate the existence of three distinct evolutionary trends corresponding to a HK calcalkaline series in the Pliocene, followed by a transitional and then by a shoshonite series in the Pleistocene. In particular, the transitional series, so far overlooked in the literature, is required in order to explain the genesis of several peralkaline felsic rocks recognized in the Archipelago. On the whole, the new geochemical data i) confirm the orogenic signature of the suites, ii) allow to rule out an anatectic origin for both subalkaline and peralkaline rhyolites and iii) indicate highly heterogeneous mantle sources, due to crustal components variously recycled in the mantle via subduction.
&amp;lt;p&amp;gt;Raw materials are essential for the sustainable development of modern so... more &amp;lt;p&amp;gt;Raw materials are essential for the sustainable development of modern societies. Access to and cost-effectiveness of mineral raw materials are critical to the smooth functioning of the EU economy. The growing demand for raw materials raises increasing concerns about mineral resources. Feldspars along with quartz, the main components of granitoid rocks, are widely used in ceramic and glass industry. The need to meet the demands of the ceramic industry has stimulated research and development of new ceramic flows in granite complexes.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Italy is the world&amp;amp;#8217;s second-largest feldspar producer (22% of total) and the world biggest importer (22% of global world trades) (European Commission). Since the strong demand is rapidly depleting the proven reserves in EU Member States, the EU ceramics sector is increasingly dependent on feldspar imports from Turkey. Thus, it is necessary to find additional sources of feldspar or to further increase inter-continental transport. At present, Budduso&amp;amp;#768;-Ala&amp;amp;#768; dei Sardi (Sardinia-Italy) is the most important granite production area in Italy. However, granite mining activities cause serious environmental problems. Feldspar production and trade generate large amounts of pollutant and greenhouse gas emissions, due either to the energy consumption of mining activities or the transport of the finished product from the exporting countries. The areas where quarries are active suffer from landscape degradation, due to incomplete compliance or non-compliance with quarry recovery plans, considering that opening new quarries is cheaper than moving large amounts of waste. Finally, granite mining accounts for huge amounts of soil consumption, as it requires large areas in which the quarry waste accumulates.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The LIFE REGS II project (LIFE19 ENV/IT/000373 LIFE REGS II) aims at demonstrating an innovative and economically-viable extraction technology to produce feldspars, of the same quality to those obtained from virgin raw material, using granite scraps. This will reduce demand for feldspar from environmentally-damaging granite mining operations as well as to minimize the soil consumption and to boost the awareness about the importance of recycling granite scraps.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;To this respect, samples of the granite scraps accumulated in 18 landfills located in the Buddus&amp;amp;#242;-Al&amp;amp;#224; dei Sardi granite quarries have been analyzed for their mineral texture and composition. Modal variability of the main mineral constituents (quartz+plagioclase&amp;amp;#177;potassium-feldspar+biotite/chlorite) allowed to distinguish three main groups characterized by different ratios of feldspars/mafic phases with the exception of samples from a specific landfill that display an increase in the plagioclase at the expense of potassium-feldspar+quartz along with an increase in epidote at the expense of biotite/chlorite.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Texturally potassium-feldspar occasionally occurs as microcline perthite while plagioclase is always affected by extensive alteration resulting in a variety of textural intergrowths of neoformed minerals. Such features are reflected in the inter/intra-crystalline compositional variations in terms of feldspar end-members and in the type of the alteration products. This provides the elements for a first estimate of the technological properties of felsdpars, allowing to recognize the material stored in the 18 landfills qualitatively better for commercial purpose, and to experimentally identify the most effective methods of physical treatments to enrich and extract feldspars useful for industrial uses.&amp;lt;/p&amp;gt;
&amp;lt;p&amp;gt;Assessing the nature and evolution of the Sub-Continental Lithospheric M... more &amp;lt;p&amp;gt;Assessing the nature and evolution of the Sub-Continental Lithospheric Mantle (SCLM) is crucial to understand the dynamics of Earth&amp;amp;#8217;s interior and the global scale tectono-magmatic processes. The study of ultramafic xenoliths brought to the surface in specific context, such as northern Victoria Land (Antarctica), is a key to investigate how the SCLM bear witness of large-scale geodynamic episodes. Indeed, the Antarctica lithosphere was involved into three main tectono-magmatic episodes since Paleozoic, i.e. the 550-110 Ma Ross subduction, the Jurassic (~182 Ma) Ferrar magmatism and the Cenozoic alkaline magmatism responsible for the opening of the West Antarctic Rift System (WARS).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In this study, a review of the petrological and geochemical features of &amp;gt;200 mantle-derived and cumulate xenoliths brought to the surface at Baker Rocks, Greene Point, Handler Ridge, Harrow Peaks, Browning Pass and Mount Overlord enabled us to reconstruct the main depletion and enrichment processes that took place in the Antarctica SCLM. Strong depletion is recorded by Greene Point lherzolites and harzburgites (18-21%), which likely began melting in the garnet facies and terminated in the spinel facies (Perinelli et al. 2006), whereas mild melt extraction in the spinel stability field was hypothesized at Baker Rocks and Handler Ridge (12-16% and 7-13% melting, respectively). The onset of the Jurassic Ferrar large magmatic event is testified by both the refertilisation in Greene Point-Baker Rocks peridotites and the appearance of cumulate orthopyroxenites/olivine-websterites at Harrow Peaks and Baker Rocks. Late enrichment process/es took place in concomitance with the Cenozoic alkaline magmatism of the WARS, resulting in both cryptic and modal metasomatism and overprinting earlier chemical modifications. This metasomatism was particularly effective at Baker Rocks, as shown by the increase of clinopyroxene abundance, its trace element enrichment and the formation of amphibole disseminated and in veins. Clinopyroxene composition in Cenozoic cumulate rocks matches the enrichment path observed in the peridotites, supporting the link between the last metasomatic process and the recent alkaline magmatism.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Among mantle xenoliths populations, Greene Point record the highest T-P (870-1059 &amp;amp;#176;C; 0.8-1.6 GPa) and the least oxidized conditions (fO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; down to -2/-3 &amp;amp;#916;FMQ). Cumulate rocks yield the highest fO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; (up to +1.5 &amp;amp;#916;FMQ), at T varying between 900 and 1150&amp;amp;#176;C, approximating the conditions of crystallizing melts. No discrepancies in fO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; emerged between amphibole-bearing and amphibole-free peridotites, ruling out a strict correlation between amphibole stability, H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O activity and fO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;. Nevertheless, the alkaline metasomatic event, which led to amphibole formation, caused a remarkable increase in the H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O content of the system. In fact, anhydrous peridotites preserve bulk H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O contents &amp;amp;#8804;128 ppm, while lherzolites with disseminated amphibole and hornblendites have H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O contents as up to 354-1120 ppm and 1.42 wt%, respectively.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Perinelli, C., et al. 2006. Geochemical and O-isotope constraints on the evolution of lithospheric mantle in the Ross Sea rift area (Antarctica). Contributions to Mineralogy and Petrology, 151(3), 245-266.&amp;lt;/p&amp;gt;
Equilibrium crystallization experiments were carried out on two primitive basaltic rocks (APR16: ... more Equilibrium crystallization experiments were carried out on two primitive basaltic rocks (APR16: Na 2 O+K 2 O=4.40 wt.%; CM42: Na 2 O+K 2 O=2.59 wt.%) with the aim to investigate the amphibole stability in the differentiation processes at deep crustal level, of primitive alkaline (APR16) and calc-alkaline (CM42) magmas. The experiments were performed with different initial H 2 O contents (0-5 wt.%), at pressure of 800 MPa, in a temperatures range of 975-1225°C. For the explored conditions the amphibole crystallization is limited for both compositions, to H 2 O in the melt >7wt.%, while the temperature of amphibole occurrence is lower in the alkaline composition (< 1050°C in APR16 and ≥1050°C in CM42). Moreover, amphibole crystallization seems to be influenced by the Na 2 O/K 2 O ratio rather than the absolute Na 2 O content in the melt. This is evident when experimental results on the APR16 and CM42 are compared with experimental data obtained from a primitive ultrapotassic c...
In the framework of the spatial-temporal distribution and compositional variability of Plio-Quate... more In the framework of the spatial-temporal distribution and compositional variability of Plio-Quaternary magmatic products emplaced in the Tyrrhenian and surrounding regions, the magmatism of he Western Pontine Islands (WPI -Ponza, Zannone, Palmarola) is still matter of debate,due to the complex geological setting in which the islands formed. The magmatism of WPI offers the opportunity to investigate the origin of calcalkaline and alkaline-peralkaline magmas. in a complex basin undergoing extension within an overall collisional geodynamic setting. Previous studies defined that: 1) Pliocene volcanic episodes are represented by silica-rich, high-K calcalkaline volcanic units at Ponza and Zannone islands; 2) Pleistocene volcanic episodes are represented by intermediate to highly evolved (K-trachytes to peralkaline trachytes and rhyolites) shoshonitic rocks cropping out in SE Ponza and Palmarola islands. According to Conte & Dolfi (2002) the magmatism of WPI was related to magmas similar ...
Abgarm ultramafic complex is a part of the Esfandagheh-Hajiabad coloured melange belt located in ... more Abgarm ultramafic complex is a part of the Esfandagheh-Hajiabad coloured melange belt located in the south east of Iranian segment of Alpine-Himalayan orogenic belt. The complex has faulted contacts with flysch type sediments of upper cretaceous ophiolite melange complex. Harzburgite is the dominant lithotype, dunites and lherzolites also occur in lesser extents. Some dunites contain massive chromitite pods or bands. The chemistry of minerals of harzburgite samples reflects the depleted nature of these rocks and indicates that the Abgarm mantle experienced a melt extraction less than 30%. Geothermo-barometric estimates indicate that the harzburgitic Abgarm mantle have been initially equilibrated at temperatures between 809-923°C and then at 613-725 °C, in a range of pressures of 1.1 and 2.3 GPa. Moreover, fO2 calculation gives a redox state that is in a range of 0.7 log bar units above the fayalite–magnetite–quartz buffer FMQ (log = 0.1 ÷ 0.7 log-bar units). Tectonomagmatic discrim...
Volcanic eruptions are shallow phenomena that represent the final stage of density- and viscosity... more Volcanic eruptions are shallow phenomena that represent the final stage of density- and viscosity- driven processes of melt migration from source rocks at upper mantle depths. In this experimental study, we investigated the effect of pressure (0.7–7.0 GPa) and temperature (1335–2000 °C) on the viscosity and the atomic melt structure of a synthetic anhydrous primitive alkaline basalt, an analogue of the pre-eruptive magma that likely feeds the Campi Flegrei Volcanic District at present day. Obtained viscosities (0.5–3.0 Pa s), mobility (0.1–0.4 g cm3 Pa−1 s−1) and ascent velocity (1.5–6.0 m yr−1) are presented to support geochemical and geophysical observations of Campi Flegrei as a critical volcanic district currently undergoing gradual magma recharge at depth.
Equilibrium crystallization experiments were carried out on two primitive basaltic rocks (APR16: ... more Equilibrium crystallization experiments were carried out on two primitive basaltic rocks (APR16: Na 2 O+K 2 O=4.40 wt.%; CM42: Na 2 O+K 2 O=2.59 wt.%) with the aim to investigate the amphibole stability in the differentiation processes at deep crustal level, of primitive alkaline (APR16) and calc-alkaline (CM42) magmas. The experiments were performed with different initial H 2 O contents (0-5 wt.%), at pressure of 800 MPa, in a temperatures range of 975-1225°C. For the explored conditions the amphibole crystallization is limited for both compositions, to H 2 O in the melt >7wt.%, while the temperature of amphibole occurrence is lower in the alkaline composition (< 1050°C in APR16 and ≥1050°C in CM42). Moreover, amphibole crystallization seems to be influenced by the Na 2 O/K 2 O ratio rather than the absolute Na 2 O content in the melt. This is evident when experimental results on the APR16 and CM42 are compared with experimental data obtained from a primitive ultrapotassic c...
Abstract Leucititic rocks, K-foiditic in composition are volumetrically important in the Colli Al... more Abstract Leucititic rocks, K-foiditic in composition are volumetrically important in the Colli Albani (also known as Alban Hills) volcanic district (Central Italy) especially during the most explosive phases of activity (>200 km3). The Colli Albani tephra in distal (>500 km) deposits indicates that K-foiditic magma chambers fed large explosive eruptions (i.e., tens of km3 of pyroclastic rocks). Major oxides, trace elements and Raman spectra were measured on the glasses and minerals occurring in the K-foiditic scoria clasts of the ~530 kyr-old Tufo del Palatino, erupted in the Colli Albani volcanic district. The Colli Albani pre-eruptive magmatic system is characterized by the aH2O 200 °C) and the K-foiditic melt shows low viscosity (104Pa·s at 1000 °C). Actually, the low melt viscosity, that increases the growth rate, and the large temperature interval of crystallization are intrinsic factors that increase the release of the latent heat of crystallization from the phonotephritic parental magma. Extrinsic factors enhancing the assimilation process efficiency are the thickness (>4 km) and the depth (down to 5–7 km) of the carbonate substrate in the Colli Albani volcanic district.
Present-day Sant'Antioco Island (SW-Sardinia, Italy) hosted one of the southernmost, and youn... more Present-day Sant'Antioco Island (SW-Sardinia, Italy) hosted one of the southernmost, and youngest, subduction-related, Cenozoic magmatic events of western Sardinia. A high-alumina basalt-andesite rock association, the focus of this paper, crops out in the southern portion of the island and represents the mafic end-member of volcanism developed during Miocene. Basaltic andesites and andesites are the dominant rock-types, while basalts and dacites are occasional. Minero-petrographic and geochemical characteristics reveal:i)a clear calc-alkaline signature for these rocks, in spite of high FeO*/MgO ratios that mimic a tholeiitic affinity; ii) a magma evolution mainly controlled by fractional crystallization and iii) some degree of crustal assimilation. Phase relationships and compositions, mass balance calculations and T, P, X, estimates consistently indicate that fractional crystallization occurred at low pressure (P=100-400 MPa), under different P(H2O) conditions, which explain th...
... Experimental constraints on evolution of leucite-basanite magma at 1 and 10 4 GPa: implicati... more ... Experimental constraints on evolution of leucite-basanite magma at 1 and 10 4 GPa: implications for parental compositions of Roman high-potassium magmas. Aida Maria Conte 1 ,* , Daniela Dolfi 2 , Mario Gaeta 3 , Valeria Misiti 4 , Silvio Mollo 2 ,4 and Cristina Perinelli 5. ...
Abstract Leucititic rocks, K-foiditic in composition are volumetrically important in the Colli Al... more Abstract Leucititic rocks, K-foiditic in composition are volumetrically important in the Colli Albani (also known as Alban Hills) volcanic district (Central Italy) especially during the most explosive phases of activity (>200 km3). The Colli Albani tephra in distal (>500 km) deposits indicates that K-foiditic magma chambers fed large explosive eruptions (i.e., tens of km3 of pyroclastic rocks). Major oxides, trace elements and Raman spectra were measured on the glasses and minerals occurring in the K-foiditic scoria clasts of the ~530 kyr-old Tufo del Palatino, erupted in the Colli Albani volcanic district. The Colli Albani pre-eruptive magmatic system is characterized by the aH2O 200 °C) and the K-foiditic melt shows low viscosity (104Pa·s at 1000 °C). Actually, the low melt viscosity, that increases the growth rate, and the large temperature interval of crystallization are intrinsic factors that increase the release of the latent heat of crystallization from the phonotephritic parental magma. Extrinsic factors enhancing the assimilation process efficiency are the thickness (>4 km) and the depth (down to 5–7 km) of the carbonate substrate in the Colli Albani volcanic district.
Volcanic eruptions are shallow phenomena that represent the final stage of density- and viscosity... more Volcanic eruptions are shallow phenomena that represent the final stage of density- and viscosity- driven processes of melt migration from source rocks at upper mantle depths. In this experimental study, we investigated the effect of pressure (0.7–7.0 GPa) and temperature (1335–2000 °C) on the viscosity and the atomic melt structure of a synthetic anhydrous primitive alkaline basalt, an analogue of the pre-eruptive magma that likely feeds the Campi Flegrei Volcanic District at present day. Obtained viscosities (0.5–3.0 Pa s), mobility (0.1–0.4 g cm3 Pa−1 s−1) and ascent velocity (1.5–6.0 m yr−1) are presented to support geochemical and geophysical observations of Campi Flegrei as a critical volcanic district currently undergoing gradual magma recharge at depth.
The crystal chemistry of Cr-spinels included in spinel peridotite mantle xenoliths from Baker Roc... more The crystal chemistry of Cr-spinels included in spinel peridotite mantle xenoliths from Baker Rocks and Greene Point (northern Victoria Land, Antarctica) has been studied by single-crystal 2+ substitution and pertain to the Mg-rich portion of the spinel sensu stricto-chromite join. The two groups of samples, Baker Rocks (BR) and Greene Point (GP), show distinct degree of cation order with the inversion parameter ranging from 0.17 to 0.20 for BR spinels and from 0.06 to 0.13 for GP crystals. Closure temperatures, computed by a geothermometer based on the Al+ Al+Mg intracrystalline exchange, range from 883 to 911 °C for BR spinels and from 592 to 675 °C for GP spinels. We show that this difference is due 3+ in GP spinels that enabled a faster kinetics of the intracrystalline cation ordering reaction, allowing the GP spinels to reach a higher degree of cation ordering and then lower closure temperatures.
Journal of Volcanology and Geothermal Research, 2016
Abstract The Pontine Islands form a volcanic archipelago in the Tyrrhenian Sea. It consists of tw... more Abstract The Pontine Islands form a volcanic archipelago in the Tyrrhenian Sea. It consists of two edifices, the islands of Ponza, Palmarola and Zannone and the islands of Ventotene and Santo Stefano, respectively. The Archipelago developed during two main volcanic cycles in the Plio-Pleistocene: 1) the Pliocene episode erupted subalkaline, silica-rich volcanic units, which constitute the dominant products in the western edifice (Ponza and Zannone Islands); 2) the Pleistocene episode erupted more alkaline products, represented by evolved rocks (trachytes to peralkaline rhyolites) in the islands of Ponza and Palmarola and by basic to intermediate rocks in the eastern edifice (Ventotene and Santo Stefano Islands). In this paper we present new geochemical and petrological data from submarine rock samples collected in two oceanographic cruises and a scuba diving survey. The main result is the recovery of relatively undifferentiated lithotypes that provide further insights on the magmatic spectrum existing in the Pontine Archipelago, allowing modelling of the whole suite of rocks by fractional crystallization processes. New major and trace element data and thermodynamic constrains (by the software PELE) indicate the existence of three distinct evolutionary trends corresponding to a HK calcalkaline series in the Pliocene, followed by a transitional and then by a shoshonite series in the Pleistocene. In particular, the transitional series, so far overlooked in the literature, is required in order to explain the genesis of several peralkaline felsic rocks recognized in the Archipelago. On the whole, the new geochemical data i) confirm the orogenic signature of the suites, ii) allow to rule out an anatectic origin for both subalkaline and peralkaline rhyolites and iii) indicate highly heterogeneous mantle sources, due to crustal components variously recycled in the mantle via subduction.
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