Publication Date:
2020-01-08
Description:
We present new electron microprobe and Sr-isotope analytical results from mixing experiments using
natural volcanic samples. In order to constrain the dynamics of such mixing events, we applied a Taylor–
Couette flow, simulating forced convection under very low Reynolds numbers, in a time series ranging
from 1 h up to 1 week. The end-member melts derive from samples of the Campanian Ignimbrite (CI), in
Italy. The CI is thought to represent a layered reservoir formed in 3 stages: 1) a resident phono-trachytic
magma reservoir (end-member A); replenished by 2) a less evolved trachybasaltic–trachytic magma (endmember
B of trachytic composition); 3) short-term pre-eruptive mixing in the shallow chamber between
a new trachytic and the phono-trachytic resident magmas. Our experiments are motivated by this
hypothesis.
The two end-members are stirred together, under constant low flow velocity (0.5 rotations per minute).
This initially generates single convection cells, which cause progressive homogenization of some major
components. This is the case after 1, 4 and 9 h. After 16 h the 87Sr/86Sr-isotopic system is homogenized and
the starting compositions are fully mixed. Then separate convection cells and compositional layering for
major and minor elements emerged.
Based on microprobe measurements of quenched melts (glass) from the 16-hour, 25-hour and 1-week
long experiments, we confirm the separation of layers having different densities. This phenomenon is
locally complicated by the production of micro-volumes of unmixed melts.
Our results support the effectiveness of the interplay between convection and diffusion, enhanced by a
double-diffusive–convection-driven differentiation for moderately high-silica magmas under high (nearliquidus)
temperatures, attesting that differentiation initiates in the liquidus before the onset of fractional
crystallization.
Description:
Published
Description:
131-145
Description:
2.3. TTC - Laboratori di chimica e fisica delle rocce
Description:
3.5. Geologia e storia dei sistemi vulcanici
Description:
JCR Journal
Description:
reserved
Keywords:
Magma mixing
;
Experiments
;
Major and minor elements
;
Advection/diffusion
;
04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
Permalink
