This article describes laboratory experiments that investigate processes occurring in magma as it rises from depth and is erupted. During magma ascent, the degassing of dissolved water disturbs the chemical equilibrium of the melt, and can trigger crystal growth without any drop in temperature. Isothermal crystal growth can dramatically increase magma viscosity, and therefore influence whether an eruption is explosive or effusive. These experiments by Jane Applegarth and colleagues use a microscope and heated stage to make the first direct observations of degassing-driven crystal growth in natural basaltic samples at magmatic temperatures. Their results therefore indicate that when melts are sufficiently water-rich, degassing can trigger rapid crystal growth. Direct observation also allows maximum crystal growth rates to be measured, which may be more important than average growth rates in determining the impact of degassing.
Jurassic accretionary complex and ophiolite from northeast Turkey: No evidence for the Cimmerian continental ribbon
Gltekin Topuz et al., Istanbul Teknik niversitesi, Avrasya Yer Bilimleri Enstits, 34469 Maslak, Istanbul, Turkey. Posted online 13 Dec. 2012; http://dx.doi.org/10.1130/G33577.1.
Permian-Triassic and Late Cretaceous accretionary complexes, ascribed to the consumption of two distinct oceans, the Paleo- and Neo-Tethys, are exposed over extensive areas in the Eastern Mediterranean region. However, a separating continental ribbon, the so-called Cimmeride continent, between the Paleo- and Neo-Tethys during early Mesozoic time cannot be defined. Topuz and colleagues report a previously unknown Early Jurassic metamorphic oceanic accretionary complex and ophiolite from northeast Turkey, bounded by oceanic accretionary comp
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Geological Society of America