Publication Date:
2020-12-02
Description:
Volatile elements play an important role in many aspects of the physicochemical architecture of
sub-volcanic plumbing systems, from the liquid line of descent to the dynamics of magma storage
and eruption. However, it remains difficult to constrain the behaviour of magmatic volatiles on
short timescales before eruption using established petrological techniques (e.g. melt inclusions);
specifically, in the final days to months of magma storage. This study presents a detailed model of
pre-eruptive volatile behaviour in the Campi Flegrei system (Italy), through combined analyses of
apatite crystals and glass. The deposits of eight eruptions were examined, covering the full spectrum
of melt compositions, eruptive styles and periods of activity at Campi Flegrei in the past
15 kyr. Measured apatite compositions are compared with thermodynamic models that predict the
evolution of the crystal compositions during different fractional crystallization scenarios, including
(1) volatile-undersaturated conditions, (2) H2O-saturated conditions and (3) varying P–T conditions.
The compositions of clinopyroxene-hosted and biotite-hosted apatite inclusions are consistent
with crystallization under volatile-undersaturated conditions that persisted until late in magmatic
evolution. Apatite microphenocrysts show significantly more compositional diversity, interpreted
to reflect a mixed cargo of crystals derived from volatile-undersaturated melts at depth and melts
that have undergone cooling and degassing in discrete shallow-crustal magma bodies. Apatite
microphenocrysts from lavas show some re-equilibration during cooling at the surface.
Clinopyroxene-hosted melt inclusions within the samples typically contain 2–4 wt % H2O, indicating
that they have been reset during temporary magma storage at 1–3km depth, similar to the depth
of sill emplacement during recent seismic crises at Campi Flegrei. Comparable apatite compositional
trends are identified in each explosive eruption analysed, regardless of volume, composition
or eruption timing. However, apatites from the different epochs of activity appear to indicate subtle
changes in the H2O content of the parental melt feeding the Campi Flegrei system over time. This
study demonstrates the potential utility of integrated apatite and glass analysis for investigating
pre-eruptive volatile behaviour in apatite-bearing magmas
Description:
Published
Description:
2463-2491
Description:
2V. Struttura e sistema di alimentazione dei vulcani
Description:
JCR Journal
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
Permalink