1,721,198 research outputs found
Sub-volcanic crystallization at Stromboli (Aeolian islands, southern Italy) preceding the Sciara del Fuoco sector collapse: evidence from monzonite lithic suite.
No full textItalian volcanoes as landmarks for the spreading of trade networks during the Etruscan and Roman periods: the millstones and flagstones case study
No full textTWO-STAGES FRACTIONATION HISTORY OF ALKALI BASALT-TRACHYTE SERIES OF SETE CIDADES VOLCANO (SAO MIGUEL ISLAND, AZORES).
No full textAl-in-amphibole barometry in calcalkaline magma: application to subvolcanic active systems
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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
Caratterizzazione petrografica di campioni provenienti da sarcofagi di età tardoromana ubicati nella basilica di San Paterniano e nella loggia del Palazzo Malatestiano a Fano
No full textOvercoming the paradigm of the destruction of Nasca culture due to a Mega-El Niño event: a clue from the stratigraphic survey at Cahuachi (Peru)
No full textArchaeometric study of Greek and Roman hopper-rubber (Olynthian-type) and rotary (Morgantina-type) millstones found in the Aeolian archipelago (Southern Italy)
No full textGrowth after collapse: the volcanic and magmatic history of the Neostromboli lava cone (island of Stromboli, Italy)
No full textThis study focuses on the Holocene Neostromboli lava cone which is part of the Stromboli volcano (Aeolian Islands, Italy). It represents an important example of the structure and behaviour of lava cone re-growth shortly after a large-scale volcano sector collapse. Neostromboli’s eruptive style is dominated by extrusion of sheet-like a’a lava flows and associated autoclastic breccias. The lava cone developed during five phases of activity (phases A to E) representing discrete episodes of lava effusion characterised by rapid changes in magma composition, spatial development of the feeder system and physical properties of erupted lavas through time. Although they all belong to the potassic series (KS) with SiO2 49–55 wt% and MgO 2.50–6.25 wt%, the Neostromboli lavas have distinct petrogenetic characteristics ranging from leucite-free and low-Sr shoshonitic basalts (phases A and B) to leucite-bearing shoshonitic basalts with high (phase C) and intermediate (phase D) Sr contents, and to leucite-free, biotite bearing shoshonites (phase E). Three different batches of mantle-derived, relatively primitive basic magmas fed the activity of phases A, C and D. The evolution phases A to B is inferred to have occurred in a continuously replenished, tapped and crystallizing (RTF) magma chamber whereas phase E products were dominantly generated by fractional crystallization from phase D magmas. The Neostromboli cone shows summit, flank and satellite vents and sheet intrusions with different geometry and location through time, reflecting the interplay of regional tectonics, precursory instability processes and volcano load
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