Ba- and Ti-rich oxymica from nephelinites in the Middle Atlas Volcanic Province,northern Morocco     

Lakroud  Kawtar  Remmal  Toufik  Makhoukhi  Samira  Balcone-Boissard  Hélène 《Mineralogy and Petrology》2020,114(2):119-128

Mineralogy and Petrology - A Ba- and Ti-rich mica (up to 14.0 wt% BaO and 13.1 wt% TiO2) occurs in nephelinites from the Middle Atlas Volcanic Province, Morocco. The rocks show a...  相似文献   

Textural and geochemical constraints on eruptive style of the 79 <Emphasis Type="SmallCaps">ad</Emphasis> eruption at Vesuvius     

Hélène Balcone-Boissard  Georges Boudon  Benoît Villemant 《Bulletin of Volcanology》2011,73(3):279-294

The 79 ad Plinian eruption of Vesuvius produced first a white pumice fallout from a high steady eruptive column, and then a grey pumice fallout originating from an oscillatory eruptive column with several partial column collapse events after which there was a total column collapse. This first total collapse was followed by renewed Plinian activity and produced the last grey pumice (GP) fallout deposit of the eruption. Textural characteristics (vesicularity and microcrystallinity) of a complete sequence of the pumice fallout deposits are presented along with the major element compositions and residual volatile contents (H₂O, Cl) to constrain the degassing processes and the eruptive dynamics. Large variations in residual volatile contents exist between the different eruptive units. Textural features also strongly differ between white and grey pumices, but also within the grey pumices. The degassing processes were thus highly heterogeneous. We propose a new model of the 79 ad eruption in which pre-eruptive conditions (H₂O saturation, magma temperature and viscosity) are the critical controls on the diversity of the syn-eruptive degassing processes and hence the eruptive dynamics. Cl contents measured in melt inclusions show that only the white pumice and the upper part of the grey pumice magma were H₂O saturated prior to eruption. The white pumice eruptive units represent a typical closed-system degassing evolution, whereas the first grey pumice one, stored under similar pre-eruptive saturation conditions, follows a particular open-system degassing evolution. We suggest that the oscillatory regime that dominated the grey pumice eruptive phase is linked to pre-eruptive water undersaturation of most of the grey magma, and the associated time delays necessary for H₂O exsolution. We also suggest that the high residual H₂O content of the last grey pumice, deposited after the renewal of Plinian activity following the first total column collapse event, is due to syn-eruptive saturation of GP magma and reduced H₂O exsolution efficiency resulting from speciation of dissolved H₂O in the melt.  相似文献   

Non-volatile vs volatile behaviours of halogens during the AD 79 plinian eruption of Mt. Vesuvius, Italy     

H. Balcone-Boissard  B. Villemant  G. Boudon  A. Michel 《Earth and Planetary Science Letters》2008,269(1-2):66-79

Pre-eruptive conditions and degassing processes of the AD 79 plinian eruption of Mt. Vesuvius are constrained by systematic F and Cl measurements in melt inclusions and matrix glass of pumice clasts from a complete sequence of the pumice-fallout deposits. The entire ‘white pumice’ (WP) magma and the upper part of the ‘grey pumice’ (GP) magma were saturated relative to sub-critical fluids (a Cl-rich H₂O vapour phase and a brine), with a Cl melt content buffered at ~ 5300 ppm, and a mean H₂O content of ~ 5%. The majority of the GP magma was not fluid-saturated. From these results it can be estimated that the WP magma chamber had a low vertical extent (< 500 m) and was located at a depth of ~ 7.5 km while the GP magma reservoir was located just beneath the WP one, but its vertical extent cannot be constrained. This is approximately two times deeper than previous estimates. H₂O degassing during the WP eruption followed a typical closed-system evolution, whereas GP clasts followed a more complex degassing path. Contrary to H₂O, Cl was not efficiently degassed during the plinian phase of the eruption.

This study shows that F and Cl behave as incompatible elements in fluid-undersaturated phonolitic melts. H₂O saturation is necessary for a significant partitioning of Cl into the fluid phase. However, Cl cannot be extracted in significant quantity from phonolitic melts during rapid H₂O degassing, e.g. during plinian eruptions, due to kinetics effects. Halogen contents are better preserved in volcanic glass (melt inclusions or matrix glass) than H₂O, therefore the combined analysis of both volatile species is required for reliable determination of pre-eruptive conditions and syn-eruptive degassing processes in magmas stored at shallow depths.  相似文献   

MeMoVolc consensual document: a review of cross-disciplinary approaches to characterizing small explosive magmatic eruptions     

L. Gurioli  D. Andronico  P. Bachelery  H. Balcone-Boissard  J. Battaglia  G. Boudon  A. Burgisser  M. R. Burton  K. Cashman  S. Cichy  R. Cioni  A. Di Muro  L. Dominguez  C. D’Oriano  T. Druitt  A. J. L. Harris  M. Hort  K. Kelfoun  J. C. Komorowski  U. Kueppers  J. L. Le Pennec  T. Menand  R. Paris  L. Pioli  M. Pistolesi  M. Polacci  M. Pompilio  M. Ripepe  O. Roche  E. Rose-Koga  A. Rust  F. Schiavi  L. Scharff  R. Sulpizio  J. Taddeucci  T. Thordarson 《Bulletin of Volcanology》2015,77(6):1-33

  相似文献