Proterozoic events recorded in quartzite cobbles at Jack Hills, Western Australia: New constraints on sedimentation and source of >4 Ga zircons
MetadataShow full item record
Rare heavy mineral bands within quartzite cobbles were identified in two conglomerate units within the Jack Hills belt, Western Australia. Seven zircon-bearing cobbles were analysed from one location (site 152) and three from another (site 154), both approximately 1 km west of the site where zircons in excess of 4 Ga are abundant (W74 ‘discovery’ site). Individual pebbles from the 152 site reveal three distinctive features, containing either zircons >3.0 Ga in age, <1.9 Ga in age or a range of ages from ∼1.2 to ∼3.6 Ga. Those from site 154 are more uniform, containing only zircons with ages between 3.1 and 3.9 Ga. Only one grain >4 Ga was discovered from the entire suite of pebbles, in contrast to the well-studied W74 site. A single detrital zircon with an age of 1220±42 Ma from location 152 is the youngest grain so far reported from sedimentary rocks at Jack Hills.It shows magmatic oscillatory zoning and thus implies at least two sedimentary cycles within the Proterozoic; requiring erosion of an igneous precursor, incorporation into a clastic sediment, induration and subsequent erosion and transport to be hosted in the conglomerate. The nearest source for rocks of this age is the Bangemall Supergroup in the Collier Basin, ∼100 km northeast in the Capricorn Orogen. This would imply tectonic interleaving of originally more extensive Bangemall rocks, possibly related to activity along the Cargarah Shear Zone that traverses the Jack Hills belt. The lack of >4.1 Ga zircons in the pebbles is highly significant, suggesting the immediate source of ancient zircons was no longer present at the Earth's surface. This equates with a general lack of ancient crystals noted in rocks that contain Proterozoic zircons from previous studies and implies that such grains diminish in number as earlier sedimentary rocks were successively recycled.
Showing items related by title, author, creator and subject.
SIMS U–Pb study of zircon from Apollo 14 and 17 breccias: Implications for the evolution of lunar KREEPNemchin, Alexander; Pidgeon, Robert; Whitehouse, M.; Vaughan, Jeffrey Patrick; Meyer, C. (2008)We report the results of a SIMS U–Pb study of 112 zircons from breccia samples from the Apollo 14 and 17 landing sites. Zircon occurs in the breccia matrices as rounded, irregular shaped, broken and rarely euhedral grains ...
Kirkland, Chris; Smithies, R.; Taylor, Richard; Evans, Noreen; McDonald, B. (2015)A comprehensive database of zircon composition in West Australian magmatic rocks reveals negative correlations between both U and Th zircon/whole rock ratio and the zircon saturation temperature, with the observed change ...
Proterozoic to Mesozoic evolution of North-West Africa and Peri-Gondwana microplates: Detrital zircon ages from Morocco and CanadaMarzoli, A.; Davies, J.; Youbi, N.; Merle, Renaud; Dal Corso, J.; Dunkley, D.; Fioretti, A.; Bellieni, G.; Medina, F.; Wotzlaw, J.; McHone, G.; Font, E.; Bensalah, M. (2017)© 2017 Elsevier B.V. The complex history of assemblage and disruption of continental plates surrounding the Atlantic Ocean is in part recorded by the distribution of detrital zircon ages entrained in continental sedimentary ...