Abstract
Abstract The inclusion mineralogy of 1450 zircons over 4 billion years in age from the Jack Hills, Western Australia, was characterized for composition and phase assemblage. Results confirm that the inclusion population of these largely igneous zircons is dominated by muscovite and quartz (~ 75%). If the inclusions are original to the igneous zircons, this observation alone restricts the host melts to formation at pressure–temperature (P–T) conditions of ~ 650–800 °C and > 4 kbar. Several lines of evidence support the view that most of the analyzed mineral inclusions are primary, including their lack of association with cracks, magmatic crystal forms, and lack of exchange with fuchsitic (Cr-rich) micas in the host conglomerate. The application of Ti-in-zircon thermometry, and phengite, Ti-in-quartz, and Al-in-hornblende barometry to these inclusion assemblages yields estimates of magmatic P–T conditions from 5 to > 12 kbar and 700 ± 40 °C. These data indicate zircon formation along geotherms of ≤ 60 °C/km and imply conductive near-surface heat flow of
Published Version
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