Publication Date:
2017-04-04
Description:
The Alban Hills volcanic region (20 km south of Rome, in the Roman Province) emitted a large volume of potassic magmas
(N280 km3) during the Quaternary. Chemical interactions between ascending magmas and the ∼7000–8000-m-thick sedimentary
carbonate basement are documented by abundant high temperature skarn xenoliths in the eruptive products and have been
frequently corroborated by geochemical surveys. In this paper we characterize the effect of carbonate assimilation on phase
relationships at 200 MPa and 1150–1050 °C by experimental petrology. Calcite and dolomite addition promotes the crystallization
of Ca-rich pyroxene and Mg-rich olivine respectively, and addition of both carbonates results in the desilication of the melt.
Furthermore, carbonate assimilation liberates a large quantity of CO2-rich fluid. A comparison of experimental versus natural
mineral, glass and bulk rock compositions suggests large variations in the degree of carbonate assimilation for the different Alban
Hills eruptions. A maximum of 15 wt.% assimilation is suggested by some melt inclusion and clinopyroxene compositions;
however, most of the natural data indicate assimilation of between 3 and 12 wt.% carbonate. Current high CO2 emissions in this
area most likely indicate that such an assimilation process still occurs at depth. We calculate that a magma intruding into the
carbonate basement with a rate of ∼1–2·106 m3/year, estimated by geophysical studies, and assimilating 3–12 wt.% of host rocks
would release an amount of CO2 matching the current yearly emissions at the Alban Hills. Our results strongly suggest that current
CO2 emissions in this region are the shallow manifestation of hot mafic magma intrusion in the carbonate-hosted reservoir at 5–6 km
depth, with important consequences for the present-day volcanic hazard evaluation in this densely populated and historical area.
Description:
Published
Description:
91-105
Description:
3.5. Geologia e storia dei sistemi vulcanici
Description:
JCR Journal
Description:
reserved
Keywords:
limestone assimilation
;
magma
;
CO2 degassing
;
experimental petrology
;
Roman Province
;
04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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