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http://hdl.handle.net/2122/7910
Authors: | Masotta, M.* Freda, C.* Gaeta, M.* |
Title: | Origin of crystal-poor, differentiated magmas: insights from thermal gradient experiments | Journal: | Contributions to Mineralogy and Petrology | Series/Report no.: | /163 (2012) | Publisher: | Springer Verlag Germany | Issue Date: | 2012 | DOI: | 10.1007/s00410-011-0658-8 | Keywords: | Explosive eruptions Crystal-poor magma Thermal gradient Solidification front |
Subject Classification: | 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology | Abstract: | 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. |
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