Winslow Heather, Ruprecht Philipp, Gonnermann Helge M, Phelps Patrick R, Muñoz-Saez Carolina, Delgado Francisco, Pritchard Matthew, Amigo Alvaro
University of Nevada, Reno, Reno, USA.
Rice University, Houston, USA.
Sci Rep. 2022 Jun 13;12(1):9734. doi: 10.1038/s41598-022-13305-y.
Two distinct types of rare crystal-rich mafic enclaves have been identified in the rhyolite lava flow from the 2011-12 Cordón Caulle eruption (Southern Andean Volcanic Zone, SVZ). The majority of mafic enclaves are coarsely crystalline with interlocking olivine-clinopyroxene-plagioclase textures and irregular shaped vesicles filling the crystal framework. These enclaves are interpreted as pieces of crystal-rich magma mush underlying a crystal-poor rhyolitic magma body that has fed recent silicic eruptions at Cordón Caulle. A second type of porphyritic enclaves, with restricted mineral chemistry and spherical vesicles, represents small-volume injections into the rhyolite magma. Both types of enclaves are basaltic end-members (up to 9.3 wt% MgO and 50-53 wt% SiO) in comparison to enclaves erupted globally. The Cordón Caulle enclaves also have one of the largest compositional gaps on record between the basaltic enclaves and the rhyolite host at 17 wt% SiO. Interstitial melt in the coarsely-crystalline enclaves is compositionally identical to their rhyolitic host, suggesting that the crystal-poor rhyolite magma was derived directly from the underlying basaltic magma mush through efficient melt extraction. We suggest the 2011-12 rhyolitic eruption was generated from a primitive basaltic crystal-rich mush that short-circuited the typical full range of magmatic differentiation in a single step.
在2011 - 12年科多恩·考耶火山喷发（南安第斯火山带，SVZ）的流纹岩熔岩流中，已识别出两种不同类型的富含晶体的罕见镁铁质包体。大多数镁铁质包体为粗晶质，具有橄榄石 - 单斜辉石 - 斜长石的互锁结构，晶体框架中填充着不规则形状的气泡。这些包体被解释为位于贫晶流纹质岩浆体之下的富晶岩浆糊的碎块，该岩浆体为科多恩·考耶近期的硅质喷发提供了岩浆。第二种类型的斑状包体，具有受限的矿物化学组成和球形气泡，代表了向流纹岩岩浆中的小体积注入物。与全球喷发的包体相比，这两种类型的包体均为玄武质端元（MgO含量高达9.3 wt%，SiO₂含量为50 - 53 wt%）。科多恩·考耶的包体在玄武质包体和流纹岩主体之间还具有记录中最大的成分间隙之一，SiO₂含量相差17 wt%。粗晶质包体中的间隙熔体在成分上与其流纹岩主体相同，这表明贫晶流纹岩岩浆是通过有效的熔体提取直接从下方的玄武质岩浆糊中衍生而来的。我们认为，2011 - 12年的流纹岩喷发是由原始的富含玄武质晶体的岩浆糊引发的，它在一步中绕过了典型的完整岩浆分异过程。
