102,672 research outputs found
Results of atrial fibrillation ablation during mitral surgery in patients with poor electro-anatomical substrate
No full textBACKGROUND AND AIM OF THE STUDY: Enlarged (> 50 mm) atria, longstanding (> 5 years) persistent atrial fibrillation (AF) and age > 70 years are considered predictive of recurrent AF following surgical ablation. The electrophysiological and clinical outcome after AF-ablation was evaluated in high-risk patients undergoing concomitant procedures. METHODS: Between January 2005 and January 2009, a total of 45 patients who complied with the three major predictors of failure, but who had undergone AF ablation ('left + right bipolar radiofrequency Maze') during concomitant mitral surgery were followed up. Freedom from AF, atrial flutter (AFL) and atrial tachycardia (AT), without anti-arrhythmic therapy (discontinued at the sixth month) was the primary endpoint. Survival, freedom from AF/AFL/AT with anti-arrhythmic therapy, early events during post-ablation blanking period, freedom from congestive heart failure (CHF) and from re-hospitalization, and changes in NYHA functional class were registered. RESULTS: Postoperatively, 18 patients (40%) showed sinus rhythm (SR) at admission to the intensive care unit, while 16 (26%) showed junctional rhythm and five (11%) required definitive pacemaker. Eleven of the 40 patients (28%) were discharged without a pacemaker, and experienced early events during the post-ablation blanking period. After a mean of 21 +/- 14 months' follow up, the actuarial survival was 88 +/- 7%. The prevalence of SR at six, 12, and 18 months was 74%, 64%, and 64% respectively. Freedom from AF/AFL/AT was 54 +/- 10% without anti-arrhythmic medications, and 51 +/- 9% with such drugs. Freedom from CHF was 85 +/- 6%, and significantly better in SR patients (94 +/- 6%) than in AF patients (69 +/- 13%; p = 0.018). Freedom from rehospitalization was 75 +/- 8%, and better in SR patients (94 +/- 6%) than in AF patients (37 +/- 14%; p = 0.0001). Accordingly, when compared to AF patients, the NYHA class was significantly ameliorated in SR patients at both six months (1.4 +/- 0.6 versus 2.7 +/- 0.9) and at the final follow up control (1.2 +/- 0.5 versus 1.9 +/- 0.7; p < 0.0001). The E/A wave recovered in 22 (85%) of the SR patients. CONCLUSION: AF ablation during mitral valve surgery achieves good electrophysiological results, even in patients traditionally considered as poor candidates. SR recovery allows a higher freedom from CHF and rehospitalization, with a better functional recovery when compared to AF
Al-in-amphibole barometry of calcalkaline magma: assessment of active subvolcanic systems.
No full textCa-amphiboles (hornblende-hastingsite-pargasite solution) have been historically tested by many authors in order to discern their physic-chemical stability and the evolution of calcalkaline magmas at subduction-related systems. In general these amphiboles show direct proportional stability curves in P-T diagrams and, at high-T, their crystallization involves high fO2 and H2O contents of the melt.
Several mechanisms such as Edenite-reaction, Tschermak-reaction and Fe3+ = [6]Al exchange are inferred to drive the Al content of amphibole by the variation of T, P and fO2, respectively. Althought the degree of these exchanges have not been experimentally verified, the influence of T and fO2 on the Al-in-amphibole is considered to be negligible compared with pressure. In this framework, several Al-barometers were calibrated for subalkaline low-T granitoids (T < 800°C) and seem to fit well (±1 kbar) in the range of 2-12 kbar (i.e. Johnson & Rutherford, 1989; Thomas & Ernst, 1990). By contrast, these barometers tested with amphiboles synthesized at higher T, from calcalkaline basaltic andesite-rhyolite rocks (Johnson & Rutherford, 1989; Martel et al., 1999; Scaillet & Evans, 1999; Pichavant et al., 2002; Klimm et al., 2003; Rutherford & Devine, 2003) demonstrate to be inaccurate with errors up to ±2.1 kbar (±7.5 km of granitic-equivalent crust).
Using the above published data on Ca-amphiboles mainly synthesized by “crystallization methods” from calcalkaline rocks, we calibrated two new barometers suitable for basaltic andesite-andesite (BAAB) and dacite-rhyolite (DRB) series. BAAB is a 2nd order polynomial equation, i.e. P = 1.3701Al2 - 1.8457Al + 1.6116 (R2 = 0.95), valuable at high-T (825-1000°C) and fO2 (ΔNNO between +0.4 and +2.2) accounting for a maximum error of ±0.61 kbar (~2.2 km). The DRB calibrated at lower T (700-834°C) and between -0.2 and +2.0 ΔNNO, works even better (±0.49 kbar, ~1.8 km) and is characterized by a relation which accounts for the tetrahedral aluminium only (P = 3.3629[4]Al3 - 7.0947[4]Al2 + 3.8369[4]Al + 1.9063; R2 = 0.98). This is probably due to the removal of the fO2 dependence (i.e. Fe3+ = [6]Al) which should play an important role in the high-viscosity (dacite-rhyolite) magmas.
The BAAB applied to the amphiboles within the November 2002 calcalkaline products (early andesite pumice falls and late basaltic andesite-andesite lavas) of El Reventador volcano (Ecuador) allowed to constrain the magma chamber location between 8 km (pumice phenocrysts) and 11 km (lava poikilitic crystals). The poikilitic crystal depth fit well with the 10-11 km deep hypocenter earthquake swarm occurred ~1 month before the eruption, which should represent the mafic intrusion event at the bottom of the magma chamber (Ridolfi et al., submitted).
The same calculation on amphibole phenocrysts (i.e. Mg-hastingsite; Menna, 2000) within high-K calcalkaline andesites of the Petrazza pyroclastics (85-60 ka; Paleostromboli I, Italy) emphasizes crystallization depths of 12-14 km. This calculation fairly agree with the data on the early fluid inclusions within quartzite xenoliths of the Strombolicchio (200 ka) and Paleostromboli II (60 ka) extrusives, which suggest significant magma rest at depths of ~11 km (Vaggelli et al., 2003).
The Al-in-amphibole is strongly dependent on both P and composition of the magma and it is worth to note the use of inappropriate amphibole barometers could lead to blunders in locating magma chambers up to 9.5 kbar as shown by the pressure difference between BAAB and DRB calculations on the Stromboli amphiboles
REFERENCES
Johnson, M.C., Rutherford, M.J., 1989: Geology 17, 837-841.
Klimm, K., Holtz, F., Johannes, W., King, P. L., 2003: Precam. Res. 124, 327-341.
Martel, C., Pichavant, M., Holtz F., Scaillet, B., Bourdier, J.L., Traineau, H., 1999: J. Geoph. Res. 104, 29453-29470.
Menna, M., 2000: Unpublished Degree Thesis, Univ. Urbino, IT, pp. 109.
Pichavant, M., Martel, C., Bourdier, J. L., Scaillet, B., 2002: J. Geoph. Res. 107, B5, 2093, 10.1029/2001JB000315.
Ridolfi, F., Puerini, M., Renzulli, A., Menna, M., Toulkeridis, T.: J. Volc. Geoth. Res., submitted.
Rutherford, M.J., Devine, J.D., 2003: J. Petrol. 44, 1433-1454.
Scaillet, B., Evans, B.W., 1999. J. Petrol. 40, 381-411.
Thomas, W.M., Ernst W.G. 1990: Geochem. Soc., Spec. Publ. 2, 59-63.
Vaggelli, G., Francalanci, L., Ruggeri, G., Testi, S. 2003: Bull. Volcanol. 65, 385-404
Environmental life cycle assessment of fresh and processed sweet cherries in southern Italy
No full textStratigraphy, eruptive mechanisms and depositional processes of the Pitigliano Formation (Latera Volcanic Complex, Vulsini District, Italy)
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An evolutionary model for the Paleobolsena and Bolsena volcanic complexes: a structural and petrographic study
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Crustal- vs. mantle-derived magmas in the San Vincenzo rhyolites (Tuscan Magmatic Province, Italy) as constrained by texture and thermobarometry
No full textThis work focuses on the physical-chemical conditions of genesis and evolution of the San Vincenzo rhyolites, one of the most significant examples of mixing between anatectic and mantle-derived magmas [1 and reference therein]. Rhyolite lavas often show quenched andesite/latite enclaves with clinopyroxene and plagioclase phenocrysts and a large variety of petrographic domains (e.g. quartz syenite autholiths, sillimanite-cordierite-quartz-spinel-ilmenite xenoliths, clinopyroxene-rich cumulates), and restitic and melt inclusion-bearing magmatic phases (plagioclase, sanidine, quartz, biotite, cordierite). Melt inclusion-free, mafic phenocryts (amphibole, garnet, clino- and orthopyroxenes), often showing reaction/overgrowth rims of biotite, are relatively widespread. In particular, the evidence of amphibole nucleation, growth and quenching is found in mixed domains next to the basic enclaves, whereas clinopyroxene-rich cumulates show inclusion and interstitial amphiboles with homogeneous compositions.
Various thermobarometric methods [2, 3, 4] were applied to the EMP data from the different domains showing equilibrium textures and compositions. In addition, we calibrated new cordierite-saturation thermobarometric formulations for peraluminous H2O-undersaturated melts. These latest formulations are particularly suitable for constraining the P-T conditions of San Vincenzo peraluminous melts (ASI 1.05-1.32, H2O 0.2-3.5 wt%) as only a few plagioclase inclusions are inferred to approach water-saturation (H2O 3.8-4.1 wt%). In contrast, single-crystal amphibole thermobarometry indicates higher H2O contents (3.7-6.8 wt%) and shows a continuous P-T crystallization pattern from 991°C and 1085 MPa (amphibole crystals from clinopyroxene-rich cumulates) to 869°C and 207 MPa (micro-phenocryst cores) crossing the MOHO [22-23 km, ca 600 MPa, 5] at 900-950°C. These results are consistent with a population of plagioclase-melt inclusion pairs indicating temperatures of 885-950°C. Clinopyroxene-liquid thermobarometry constrains the crystallization of basic enclave phenocrysts to higher-T (1060-1120°C) and mantle depths (800-1250 MPa). Sanidine-melt, sanidine-plagioclase and most of the plagioclase-melt pairs indicate temperatures of 837-720°C, closely matching the entrapment conditions of H2O-undersaturated melt inclusions of cordierite phenocrysts (790-850°C; 275-370 MPa). Temperatures of micro-quartz syenite autoliths (662-713°C) and those of “flame”-like restitic biotites (640-735°C) are similar. Finally, the application of THERMOCALC program (average P–T calculation mode) to a sillimanite-cordierite-quartz-spinel-ilmenite xenolith suggests equilibrium conditions of 700-750°C and 320-350 MPa.
This textural and thermobarometric picture is consistent with the formation and evolution of the anatectic magma of San Vincenzo by “gas sparging” [i.e. rising of temperature and melting via fluid percolation, 6], magma mixing, assimilation and fractional crystallization processes at upper-mantle/crustal depths.
References. [1] Poli, G. & Perugini, D. (2003): Periodico di Mineralogia, 72, 141-155; [2] Ridolfi, F., Renzulli, A., Puerini, M. (2010): Contributions to Mineralogy and Petrology, 160, 45-66; [3] Putirka, K.D. (2008): Reviews in Mineralogy and Geochemistry, 69, 61-120; [4] Henry, D.J., Guidotti, C.V., Thomson, J.A. (2005) American Mineralogist,, 90, 316–328; [5] Accaino, F., Tinivella, U., Rossi, G., Nicolich, R. (2005): Journal of Volcanology and Geothermal Research, 148, 46-59; [6] Bachmann, O., Bergantz, G.W. (2006): Journal of Volcanology and Geothermal Research, 149, 85-102
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