The granulite to eclogite transition beneath the eastern margin of the Australian craton

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Abstract

Xenolith suites in kimberlitic and basaltic dykes on the eastern margin of the Australian craton (EMAC) are dominated by mafic rock types, with subordinate spinel and garnet lherzolite and felsic granulite. A range of microstructures demonstrates the transformation of primary igneous assemblages to granulites and eclogites, through exsolution, corona growth, breakdown of plagioclase and deformation. Eclogites and granulites contain similar compositional ranges of garnet and clinopyroxene; P-T estimates indicate that these two rock types coexisted over the depth range from 35 to 75 km. The P-T array defined by the EMAC xenoliths extends from ca. 10 kbar/800°C to 22 kbar/1020°C, and shows the strong curvature typical of advective heat transport. The mafic rocks show a wide range in composition, and demonstrate the control of bulk composition on the stability of eclogite vs. granulite mineral assemblages. The compositional diversity shown by the EMAC mafic xenoliths suggests that the igneous protoliths are the products of several episodes of magmatic underplating and tectonic activity, but have equilibrated toward a common geotherm, sampled at the time of entrainment. -from Authors

Original languageEnglish
Pages (from-to)293-322
Number of pages30
JournalEuropean Journal of Mineralogy
Volume3
Issue number2
Publication statusPublished - 1991

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