Publication Date:
2017-04-03
Description:
Crystal-poor, differentiated magmas are com-
monly erupted from shallow, thermally zoned magma chambers. In order to constrain the origin of these magmas, we have experimentally investigated crystallization, differentiation and crystal-melt separation in presence of a thermal gradient. Experiments have been designed taking
advantage of the innate temperature gradient of the piston cylinder apparatus and carried out on a phonolitic system at
0.3 GPa and temperature ranging from 1,050 to 800 C. Crystallization degree and melt composition in experi-
mental products vary as a function of the temperature gradient. In particular, melt composition differentiates from tephri-phonolite (starting material) to phonolite moving from the hotter, glassy zone (T B 1,050 C)
towards the cooler, heterogeneously crystallized zone (T B 900 C) of the charge. The heterogeneously crystal-
lized zone is made up of: (1) a crystal-rich, mushy region
(crystallinity [30 vol%), (2) a rigid crystal framework
(crystallinity B80 vol%) and (3) glassy belts of phonolitic
glass at the top. Thermal gradient experiments picture crystallization, differentiation and crystal-melt separation
processes occurring in a thermally zoned environment and reveal that relatively large volumes of crystal-poor melt (glassy belts) can originate as a consequence of the instability and collapse of the rigid crystal framework.
Analogously, in thermally zoned magma chambers, the development and collapse of a solidification front may represent the controlling mechanism originating large volumes of crystal-poor, differentiated magmas.
Description:
Sapienza Universita` di Roma,Istituto Nazionale di Geofisica e Vulcanologia.
Description:
Published
Description:
49-65
Description:
2.3. TTC - Laboratori di chimica e fisica delle rocce
Description:
JCR Journal
Description:
restricted
Keywords:
Explosive eruptions
;
Crystal-poor magma
;
Thermal gradient
;
Solidification front
;
04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
