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Petrogenesis of antecryst-bearing arc basalts from the Trans-Mexican Volcanic Belt: Insights into along-arc variations in magma-mush ponding depths, H2O contents, and surface heat flux
- Source :
- American Mineralogist. 101:2405-2422
- Publication Year :
- 2016
- Publisher :
- Mineralogical Society of America, 2016.
-
Abstract
- The Trans-Mexican Volcanic Belt (TMVB) is known for the chemical diversity in its erupted products. We have analyzed the olivine, pyroxene, and plagioclase mineral chemistry of 30 geochemically well-characterized mafic eruptives from Isla Maria at the western end of the arc to Palma Sola in the east. The mineral major oxide data indicate the dominance of open system processes such as antecryst uptake, and the scarcity of mineral-mineral and mineral-melt equilibria suggests that apart from forming microlites, erupted melts do not significantly crystallize during ascent. A combination of plagioclase antecryst chemistry and MELTS thermodynamic modeling of H2O-saturated isobaric fractional crystallization was employed to develop a pressure sensor aimed at determining the ponding depths of the co-genetic magmas from which the erupted plagioclase crystal assemblage originates. We show that the depth of magma-mush reservoirs increase eastward along the TMVB. We suggest that magma ponding is triggered by degassing-induced crystallization during magma ascent, and that the pressure sensor can also be regarded as a degassing sensor, with more hydrous melts beginning to degas at greater depths. Modeled initial magma H2O contents at the Moho range from ~4 to ~9 wt%. Magma-mush ponding depth variations fully explain the observed westward increase of average surface heat flux along the TMVB, supporting a new model of mafic arc magma ascent, where rapidly rising, initially aphyric melts pick up their antecrystic crystal cargo from a restricted crustal depth range, in which small unerupted batches of previously risen co-genetic magmas typically stall and solidify. This implies that, globally, mafic arc magmas may be used to constrain the depths of degassing and mush zone formation, as well as the amount of H2O in the primary melts.
- Subjects :
- Basalt
Mush zone
Fractional crystallization (geology)
Olivine
010504 meteorology & atmospheric sciences
Volcanic belt
Geochemistry
engineering.material
010502 geochemistry & geophysics
01 natural sciences
Geophysics
Geochemistry and Petrology
engineering
Plagioclase
Mafic
Geology
0105 earth and related environmental sciences
Petrogenesis
Subjects
Details
- ISSN :
- 0003004X
- Volume :
- 101
- Database :
- OpenAIRE
- Journal :
- American Mineralogist
- Accession number :
- edsair.doi...........29f8a794dfd0f8bda3d6a3d7e3aa9295