Transcrustal magmatic systems: evidence from andesites of the southern Taupo Volcanic Zone
Document Type
Article
Publication Date
2022
Department
Department of Geological and Mining Engineering and Sciences
Abstract
Studies synthesizing field work, numerical simulations, petrology, geochemistry and geophysical observations indicate that the compositional diversity of arc lavas results from evolution of mantle-derived magmas by mixing, assimilation and fractional crystallization. This evolution occurs within complexes called transcrustal magmatic systems. The mafic lower parts of such zones, called hot zones, are difficult to probe. However, a satellite vent near the stratovolcano Ruapehu in the southern Taupo Volcanic Zone (New Zealand) comprises materials that may originate from a hot zone. Magnesian andesites (Mg#60–65 ) from the Ohakune scoria cone contain primitive olivine (Fo85–91 ), high-Mg# clinopyroxene (Mg#81–88) and orthopyroxene (Mg#76–83), but lack plagioclase. Disequilibrium of Ohakune crystals and groundmass suggests that the crystal cargo of Ohakune andesites was scavenged from deeper and more primitive levels of the magmatic system. Mineral constraints on temperature and pressure indicate that the hot zone initially formed at mid-to lower-crustal pressures (3.5–7.0 ± 2.8 kbar). We interpret the mafic mineralogy and presence of disequilibrium features as evidence that these andesites and their crystal cargo are products of a hot zone in the middle to lower crust. Products of the hot zone may appear before products of the systems that form the bases of mature stratovolcanoes such as Ruapehu.
Publication Title
Journal of the Geological Society
Recommended Citation
Svoboda, C.,
Rooney, T.,
Girard, G.,
&
Deering, C.
(2022).
Transcrustal magmatic systems: evidence from andesites of the southern Taupo Volcanic Zone.
Journal of the Geological Society,
179(1).
http://doi.org/10.1144/jgs2020-204
Retrieved from: https://digitalcommons.mtu.edu/michigantech-p/15880