Tracking plumbing system architecture in age-progressive intraplate volcanoes in Eastern Australia.

Tapu, Al-Tamini1, Ubide, Teresa1, Vasconcelos, Paulo1

1School of Earth and Environmental Sciences, The University of Queensland, Brisbane, Australia

Cenozoic age-progressive volcanism in eastern Australia crops out as the longest age-progressive continental track of shield volcanoes that extends for ~2000 km. The so-called ‘central volcanoes’ show a southward-younging trend that has been related to the motion of the Australian plate over one or several stationary mantle plumes. Central volcanoes developed in regions of contrasting lithospheric thickness and have distinct eruptive volumes, however, the relationships between regional context and extent of volcanic activity remain poorly constrained.

Here we apply a high-resolution geochemical-geochronological approach to investigate differences in the time spans of volcanism and the architectures of the magma feeder systems at depth. We investigate central volcanoes Ebor, Nandewar, and Canobolas, located in regions of different lithospheric thickness and with varied volumes of magma from 50 to 300 km3.

The rocks are porphyritic to aphyric basalts to trachytes and rhyolites, including 5-40 vol.% phenocrysts of plagioclase, clinopyroxene, and minor olivine. Clinopyroxene-melt thermobarometry indicates crystallization at 10-3 kbar (25-10km depth) and 800-1150°C. Rhythmic-oscillatory zonations in plagioclase (An55) and clinopyroxene (Mg#70) suggest steady-state growth in deep reservoirs undergoing continued magma supply and differentiation of compositionally similar magmas. K-feldspar and green-clinopyroxene (Mg#25-45) are interpreted as antecrysts recycled from pockets of fractionated melts. Successive mafic magma influx before eruption generated growth of mafic mineral zones (plagioclase An65; clinopyroxene Mg#75) over partially resorbed, sieved, and/or patchy cores (An35-50 and Mg#55-65, respectively). 40Ar/39Ar geochronology indicates that the volcanoes were episodically replenished over timescales of ~0.1Ma, and the eruptive activity lasted for ~3 – 1.5 Ma.

The combined geochemical and geochronological studies suggest three spatially separated but genetically linked volcanoes were fed through comparable plumbing system architectures. Rhythmic mafic recharge and fractionation controlled the lifespans and tempos of eruptive activity.


Biography

The primary research area of Mr. Al-Tamini focuses on igneous petrology, volcanology, geochemistry. His current research work aims to understand the long term tempos of eruptive activity and evolution of magma plumbing system architecture in plume related intraplate volcanoes in Eastern Australia by applying high-resolution petrology, geochemistry, and geochronology techniques.

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