Cenozoic magmatism of north Victoria Land, Antarctica: an experimental study on the mantle source of a primary basanite from the McMurdo Volcanic Group

Volcanoes of the McMurdo Vocanic Group (MMVG) (Antarctica) dot the eastern shoulder of Ross Sea Rift System giving rise to alkaline transitional volcanic suites which in north Victoria Land are emplaced since Early Cenozoic. Geochemical geological, geophysical and geochronological data on Cenozoic volcanic activity in NVL suggest that the region is a site of passive astenospheric rise, rather than affected by a thermally active mantle plume. Furthermore the comparison of geochemical and isotopical data of basic lavas with those provided by mantle xenoliths they carry to the surface, document the compositional heterogeneity of sublithospheric mantle caused by the coupled action of partial melting and metasomatism. In particular the metasomatic episode is probably linked to the amagmatic extensional event that affected the West Antarctic Rift System in the Late Cretaceous. The astenospheric melts generated during this event, moving through the upper mantle, can have crystallized as veins or may have led to the formation of metasomatic minerals such as amphibole or phlogopite. In this scenario the mineralogical and chemical composition of sources responsible for Cenozoic magmatism, amphibole-bearing spinel-peridotite versus pyroxenite in the garnet stability field, it is still a matter of debate. To shed light on this argument a previous experimental study on a basanite of MMVG, representative of primary magma (Orlando et al., 2000) has been integrated with new experimental investigation on the same basanitic composition. The preliminary experiments were conducted to pressures of 1.0 - 2.0GPa in the presence of 0-1% of added water and indicate olivine on the liquidus at 1.0 GPa that is substitute by clinopyroxene at 2.0GPa. The addition of 1% of water induces a decrease of liquidus temperature of about 40°C shifting its value in the T range (1280-1310°C) the same that was inferred by melt inclusions hosted in the olivine phenocrysts of the studied basanit

Bollettino Sismico Italiano gennaio – aprile 2018

Nel primo quadrimestre 2018 si sono verificati in Italia cinque eventi di magnitudo superiore o uguale a 4.0, di cui nessuno di magnitudo superiore a 5.0. Due di essi, avvenuti il 4 (MW 4.0) e il 10 aprile (MW 4.6), hanno interessato la zona della sequenza dell’Italia centrale, in provincia di Macerata. Un terremoto di magnitudo MW 4.3 è avvenuto in provincia di Campobasso, il 25 aprile, ad una profondità di 29 km. Infine due terremoti profondi, avvenuti il 12 febbraio (ML 4.4, con profondità di 379 km) e il 7 marzo (ML 4.0, con profondità di 294 km), hanno interessato il Tirreno Meridionale, al largo della costa calabra.Istituto Nazionale di Geofisica e Vulcanologia - Dipartimento di Protezione CivilePublished4IT. Banche dat

Bollettino Sismico Italiano settembre – dicembre 2018

Gli analisti del BSI hanno revisionato tutti gli eventi di magnitudo M≥1.5, localizzati dal 1 settembre al 31 dicembre 2018. I parametri dei terremoti di magnitudo inferiore a tale soglia di revisione, sono quelli calcolati in tempo reale, nella sala di sorveglianza sismica di Roma.Istituto Nazionale di Geofisica e Vulcanologia - Dipartimento di Protezione CivilePublished4IT. Banche dat

Acqua, Magma Mia

Materiale divulgativo sul tema dei vulcani per ragazzi dai 4 ai 14 anniIstituto Poligrafico dello Stato S.P.A.Published1TM. Formazione2TM. Divulgazione Scientifica3TM. Comunicazione5TM. Informazione ed editori

Aria, Magma Mia

Materiale divulgativo sul tema dei vulcani per ragazzi dai 4 ai 14 anniIstituto Poligrafico dello Stato S.P.A.Published1TM. Formazione2TM. Divulgazione Scientifica3TM. Comunicazione5TM. Informazione ed editori

Terra, Magma Mia

Materiale divulgativo sul tema dei vulcani per ragazzi dai 4 ai 14 anniIstituto Poligrafico dello Stato S.P.A.Published1TM. Formazione2TM. Divulgazione Scientifica3TM. Comunicazione5TM. Informazione ed editori

Cenozoic magmatism of north Victoria Land, Antarctica: an experimental study on the mantle source of a primary basanite from the McMurdo Volcanic Group

Volcanoes of the McMurdo Vocanic Group (MMVG) (Antarctica) dot the eastern shoulder of Ross Sea Rift System giving rise to alkaline transitional volcanic suites which in north Victoria Land are emplaced since Early Cenozoic. Geochemical geological, geophysical and geochronological data on Cenozoic volcanic activity in NVL suggest that the region is a site of passive astenospheric rise, rather than affected by a thermally active mantle plume. Furthermore the comparison of geochemical and isotopical data of basic lavas with those provided by mantle xenoliths they carry to the surface, document the compositional heterogeneity of sublithospheric mantle caused by the coupled action of partial melting and metasomatism. In particular the metasomatic episode is probably linked to the amagmatic extensional event that affected the West Antarctic Rift System in the Late Cretaceous. The astenospheric melts generated during this event, moving through the upper mantle, can have crystallized as veins or may have led to the formation of metasomatic minerals such as amphibole or phlogopite. In this scenario the mineralogical and chemical composition of sources responsible for Cenozoic magmatism, amphibole-bearing spinel-peridotite versus pyroxenite in the garnet stability field, it is still a matter of debate. To shed light on this argument a previous experimental study on a basanite of MMVG, representative of primary magma (Orlando et al., 2000) has been integrated with new experimental investigation on the same basanitic composition. The preliminary experiments were conducted to pressures of 1.0 - 2.0GPa in the presence of 0-1% of added water and indicate olivine on the liquidus at 1.0 GPa that is substitute by clinopyroxene at 2.0GPa. The addition of 1% of water induces a decrease of liquidus temperature of about 40°C shifting its value in the T range (1280-1310°C) the same that was inferred by melt inclusions hosted in the olivine phenocrysts of the studied basanitePublishedVienna2.3. TTC - Laboratori di chimica e fisica delle rocceope

Reddish metagranites from the Gennargentu Igneous Complex (Sardinia, Italy) : insight into metasomatism induced by magma mingling

The mineralogy of thermometamorphic granites is relatively simple, making it possible to track the spatial distribution of chemical and mineralogical variations in these rocks and investigate the processes that underpin these metamorphic reactions. We have undertaken a detailed investigation of metagranites from the contact aureole that fringes a quartz diorite intrusion of Late Permian age, emplaced into Carboniferous peraluminous granites of the Gennargentu Igneous Complex (Sardinia, Italy). New data are presented including the petrography of metagranites within a 500 m zone adjacent to the quartz diorite intrusion, the compositions of minerals and bulk-rocks, and the oxygen isotope compositions of separated minerals. We have used these data to assess the mobility of elements, expressed as Δoxide, in the aureole, and the physical conditions of fluid-assisted thermometamorphism. Modal variations and the oscillatory zoning of plagioclase demonstrate that the shallow (P ≤200 MPa) quartz diorite intrusion was emplaced through a number of magmatic injections. The border zone of the quartz diorite intrusion presents evidence of two main processes: hybridization between andesite and rhyolite magmas and volatile saturation of the mingled magma. Modal differences in the contact zone with respect to the protolith (i.e. peraluminous granite), variations in mineral composition, temperature constraints and ΔK₂O, ΔNa₂O, ΔSiO₂ and ΔAl₂O₃ indicate that a relatively large volume of the host granite (up to 400 m from the contact) was metasomatized by high-temperature (650–350℃) fluids derived from the mingled zone of the quartz diorite intrusion. In detail, the metasomatic K₂O-rich fluid reacted with albite to form K-feldspar, and triggered the recrystallization of quartz and plagioclase to higher calcium concentrations. The progressive increase in the MgO/(MgO + FeO) of chlorite closer to the contact indicates that this phase also recrystallized. The iron released during chlorite recrystallization was buffered by hematite formation in the pores of metasomatic K-feldspar. The Gennargentu metagranites provide evidence that metasomatic fluids can play a major role in driving metamorphic reactions in contact aureoles. For instance, the expected increase of Ca in plagioclase owing to thermal equilibration was not achieved in the high-T zone of the aureole because of fluid-assisted removal of cations. We conclude that caution should be taken when interpreting the processes that underpin contact metamorphism in terms of thermally driven, ionic diffusion alone, because the role of fluids may be significant, if not overwhelming, in the domains closest to the magmatic source.21 page(s

Kinetic aspects of major and minor elements in olivine from variably cooled basaltic melts

Olivine is an important mineral phase in naturally cooled basaltic rocks. The texture and composition of olivine are strictly related to the interplay between the degree of magma undercooling and crystal growth rate. Crystals formed at low undercoolings and growth rates generally show polyhedral-hopper textures and quite homogeneous compositions, while skeletal-dendritic textures and strong crystal zonation occur at high undercoolings and growth rates. In this context, we have performed disequilibrium crystallization experiments to better understand the effects of crystallization kinetics on the incorporation of major and minor cations in the olivine lattice. Experiments were carried out in a 1 atm vertical tube CO-CO2 gas-mixing furnace using basaltic glass (i.e., OIB) as starting material, imposing different undercooling and cooling rates. We used room pressure and QFM-2 oxygen fugacity. Each experiment started at superliquidus temperature, which was kept constant for 2 h before cooling. After this stage, we linearly decreased the temperature to the final target of 1125 and 1175 °C, for a total undercooling (-ΔT) of 85 °C and 35 °C, respectively. Each experiment was tested at different cooling rates: 2 °C/h, 20 °C/h, and 60 °C/h. Finally, samples were quenched for recovery. Results show that the olivine texture shifts from euhedral (i.e. polyhedral texture) to anhedral (i.e. dendritic texture) as function of the undercooling during rapid crystal growth. In -ΔT = 35 °C experiments, olivine crystals show a faint zonation. Conversely, a strong zonation develops in crystals grown during - ΔT = 85 °C. The compositional gradient in the melt increases with increasing cooling rate and undercooling, forming a diffusive boundary layer that expands towards the far field melt (15 μm wide for low undercooling and minimum 2 time wider for high undercooling). Because of the effects of crystallization kinetics, skeletal-dendritic olivine incorporates higher proportions of minor elements, which are generally incompatible within the crystal lattice at equilibrium conditions. Al, P, Ti and Cr distribution seem to follow the primary and secondary olivine branches