Crystal-Mush Storage and Rhyolite Formation for the 2011-12 Puyehue-Cordón Caulle Eruption
Abstract
Silicic magmas produce some of the largest and most explosive volcanic eruptions. Their formation and eruptive triggers remain an area of intense study due to their infrequent occurrences of only a few events per century. Studies on old, exposed systems have highlighted the importance of crystal-mush storage systems. Constraining these processes in an active volcanic systems may help to refine models of melt-crystal segregation. Puyehue-Cordon Caulle Volcanic Complex (PCC) in the Southern Andes with three historic eruptions in the last century is an ideal location to study these crystal-mush dynamics. Its most recent eruption in 2011-12 (VEI 4) is compositionally identical to the previous two eruptions (all ~2-3 km3) and was accompanied with significant episodes of uplift and subsidence. This deformation indicates shallow magma storage, which is consistent with published geothermobarometry estimates for the 2011-12 rhyolite (5-7 km, 100-140 MPa, 895°C). Potential evidence of crystal-mush may exist in the presence of mafic enclaves found in the effusive rhyolite. Whether these enclaves represent mafic recharge or entrained crystalline mush from which rhyolitic melt was extracted has yet to be determined conclusively.
The mafic enclaves are crystal-rich (~55-65%) and show cumulate textures consistent with a crystal-mush. They span a wide range in bulk composition (5.2 - 9.3 wt% MgO), while their matrix glass is almost identical to the felsic glass in the rhyolite presenting one of the largest compositional gaps on record. Via mass balance calculations, new pressure estimates for the mafic enclaves, and constraints on the thermal histories for the mafic enclaves (using Mg exchange between plg and cpx) we will test the genetic and spatial relationship between mafic enclaves and the volumetrically-dominant rhyolite. Thus, mineral chemistry will help constrain whether the proposed mafic source at PCC was stored exclusively in the upper crust or if storage extended into deeper regions. Utilizing the information from the mafic enclaves combined with deformation data and physics-based models will allow us to gain new understanding on rhyolite formation and possible insight towards their eruption triggers.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMU005...02W
- Keywords:
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- 0810 Post-secondary education;
- EDUCATION;
- 0815 Informal education;
- EDUCATION