Secondary hornblendes in some granulite fades rocks from the Mann Ranges, Australia
Titel:
Secondary hornblendes in some granulite fades rocks from the Mann Ranges, Australia
Auteur:
Sen, S. K. Oliver, R. L.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 28 (1981) nr. 1-2 pagina's 137-140
Jaar:
1981-04
Inhoud:
Green to blue-green secondary hornblendes, reportedly common in many granulite facies terrains, occur, predominantly as partial mantles around hypersthenes, in the Mann Ranges, Australia. Electron probe analyses of six such hornblendes show that they have abundant sodium and aluminium and can be classified as ferroan pargasites. Though they have an overall 'high-grade' chemistry, the titanium contents are markedly low, and it is argued that hornblendes of similar major element composition are rich in titanium only when prograde metamorphic reactions promote it. Textural evidence shows that the hornblendes formed later than the hypersthenes and are 'retrograde'. The hornblende also formed later than 'retrograde' biotite. Possibly reduced pressure and temperature, consequent on uplift, facilitated the secondary mineral development but, alternatively, increased availability of water, accompanying abundant shear-type strain at high temperatures, was responsible.
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