Contributions to Mineralogy and Petrology

, Volume 88, Issue 4, pp 354–371

Origin and evolution of a peraluminous silicic ignimbrite suite: The Violet Town Volcanics

  • John D. Clemens
  • Victor J. Wall
Article

DOI: 10.1007/BF00376761

Cite this article as:
Clemens, J.D. & Wall, V.J. Contr. Mineral. and Petrol. (1984) 88: 354. doi:10.1007/BF00376761

Abstract

The Violet Town Volcanics are a 373 Ma old, comagmatic, S-type volcanic sequence mainly comprising crystal-rich intracaldera ignimbrites. Rock types vary from rhyolites to rhyodacites, all containing magmatic cordierite and garnet phenocrysts. Variation in the suite is primarily due to fractionation of early-crystallized quartz, plagioclase and biotite (plus minor accessory phases) in a high-level magma chamber prior to eruption. Early magmatic crystallization occurred at around 4 kb and 850° C with melt water contents between 2.8 and 4 wt.%. This high-temperature, markedly water-undersaturated, restite-poor, granitic magma was generated by partial melting reactions involving biotite breakdown in a dominantly quartzofeldspathic source terrain, leaving a granulite facies residue.

Table of Less Common Abbreviations Used

Pkb

pressure in kilobars

T° C

temperature in degrees Celsius

\(X_{H_2 O}^{Fl} \)

mole fraction of water in the fluid

aH2O

activity of water

Bi

biotite

Cd

cordierite

Gt

garnet

Py

pyrope

Gr

grossular

Alm

almandine

Sp

spessartine

He

hercynite

Ilm

ilmenite

Kfs

potassium feldspar

Opx

orthopyroxene

Pl

plagioclase

An

anorthite

Q

quartz

Sill

sillimanite

Ap

apatite

Copyright information

© Springer-Verlag 1984

Authors and Affiliations

  • John D. Clemens
    • 1
  • Victor J. Wall
    • 1
  1. 1.Earth Sciences DepartmentMonash UniversityClaytonAustralia
  2. 2.Chemistry DepartmentArizona State UniversityTempeUSA

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