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Abstract 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 2 ) 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 2 . 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.
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This content will become publicly available on September 1, 2026
Not so mush: discrete pulses of high-silica rhyolite generation in the Mineral Mountains, Utah
Crystal mush systems, often referenced in the context of large silicic magma bodies, involve the reactivation of a near- solidus crystal mush by heat input from mafic injections. This model suggests that interstitial melt is extracted from the mush, leading to the generation of high-silica rhyolites and granites. Such processes have been well-documented in various tectonic settings and contribute to both large-scale eruptions and the formation of granitic plutons. However, in the Mineral Mountains, Utah, the zircon and whole rock geochemical record indicate a different scenario. The presence of sector-zoned zircons and the absence of highly evolved central domains indicative of extraction from a mush suggest rapid magma generation from partial melting of solid granitoids rather than from a long-lived crystal mush. Fractional crystallization and equilibrium partial melting models support derivation from the granitoid bodies, rather than from a common shared parental rhyolitic magma or from coeval basalts. The proposed model, presented here, for rhyolite formation in the Mineral Mountains involves episodic injections of mafic magma into the crust, leading to localized partial melting of different granitoid lithologies. Partial melting up to 30% can produce isolated, ephemeral pools of high-silica melt, which crystallize zircons rapidly and ascend to form rhyolitic domes. This process is distinct from the long-lived crystal mush model, explains the lack of intermediate compositions, and the confinement of mafic eruptions to lower elevations. By integrating geochemical data, zircon morphology, and fractionation modeling, this study provides a comprehensive framework for understanding the magmatic processes at play in the Mineral Mountains.
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- Award ID(s):
- 1940305
- PAR ID:
- 10657319
- Publisher / Repository:
- Springer Nature
- Date Published:
- Journal Name:
- Contributions to Mineralogy and Petrology
- Volume:
- 180
- Issue:
- 9
- ISSN:
- 0010-7999
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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