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Volatiles in magmas related to the Campanian ignimbrite eruption; experiments vs. natural findings

Sara Fanara, Roman E. Botcharnikov, Danilo M. Palladino, Franziska Adams, Julia Buddensieck, Andreas Mulch and Harald Behrens
Volatiles in magmas related to the Campanian ignimbrite eruption; experiments vs. natural findings
American Mineralogist (October 2015) 100 (10): 2284-2297

Abstract

The solubility of H (sub 2) O- and CO (sub 2) -bearing fluids in trachytic and trachybasaltic melts from erupted magmas of the Campi Flegrei Volcanic District has been investigated experimentally at 1100 and 1200DGC, respectively, and at 100, 200, 300, 400, and 500 MPa. The solubility of H (sub 2) O in the investigated melts varies between 3.48+ or -0.07 wt% at 100 MPa to 10.76+ or -0.12 wt% at 500 MPa in trachytic melts and from 3.49+ or -0.07 wt% at 100 MPa to 9.10+ or -0.11 wt% at 500 MPa in trachybasaltic melts. The content of dissolved CO (sub 2) in melts coexisting with the most CO (sub 2) -rich fluid phase increases from 281+ or -24 ppm at 100 MPa to 2710+ or -99 ppm at 500 MPa in trachyte, and from 727+ or -102 ppm at 100 MPa to 3565+ or -111 ppm at 500 MPa in trachybasalt. Natural samples from the Campanian Ignimbrite eruption (trachyte) and from the Solchiaro eruption (trachybasalt) were collected around the city of Naples and on Procida Island. Deuterium/hydrogen (D/H) ratios were analyzed in natural pumices pre-heated at different temperatures to remove water adsorbed and/or imprinted by glass alteration processes. It has been determined that heating of the glass to 350 degrees C efficiently removes most of secondary water and the remaining concentrations represent primary magmatic water preserved in the erupted material. Hydrogen isotope composition (with delta D values ranging between -70 ppm and -110 ppm) and its correlation with bulk water content in selected pumice samples of the Campanian Ignimbrite eruption are consistent with isotopic fractionation between magmatic fluid and melt during degassing of erupting magma. Hence, the H (sub 2) O and CO (sub 2) contents in natural glasses from pumice samples are considered as minimum estimates on volatile concentrations in the melt just prior to the eruption or at the fragmentation event. The water contents in natural glasses vary from 0.83+ or -0.07 to 3.74+ or -0.06 wt% for trachytes from the Campanian Ignimbrite eruption and from 1.96+ or -0.06 to 3.47+ or -0.07 wt% for trachybasalts from the Solchiaro eruption. The CO (sub 2) contents vary from 78+ or -120 ppm CO (sub 2) to 1743+ or -274 ppm for trachytes from the Campanian Ignimbrite eruption and from 240+ or -293 to 1213+ or -250 ppm for trachybasalts from the Solchiaro eruption. A combination of natural and experimental data provides minimum pressure estimates for the storage and ascent conditions of magmas. The Campanian Ignimbrite magma could have been stored or ponded during its rising path at two different levels: a deeper one corresponding to depth of about 8 to 15 km and a shallower one at about 1 to 8 km. Trachybasalts from Solchiaro erupted from the deepest level of about 11 km with a storage or ponding level at around 2 to 8 km depth. Although an uncertainty of at least a kilometer has to be considered in estimating storage or ponding depths, these estimates point to significantly deeper magmatic sources for both eruptions as those considered previously.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 100
Serial Issue: 10
Title: Volatiles in magmas related to the Campanian ignimbrite eruption; experiments vs. natural findings
Affiliation: Leibniz Universitaet Hannover, Institut fuer Mineralogie, Hanover, Germany
Pages: 2284-2297
Published: 201510
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 93
Accession Number: 2016-007312
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
N40°49'60" - N40°49'60", E14°07'60" - E14°07'60"
Secondary Affiliation: Universita di Roma La Sapienza, ITA, ItalyGoethe Universitaet Frankfurt, DEU, Germany
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201604
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