I am re-addressing your question to our PhD student Matt Ferguson, who is currently working on this topic.

Thanks Vadim Kamenetsky,

I'll see the info from Matt Ferguson as he posts it.

Jeffrey Spence

Hi Jeffrey, I think that the Hiltaba granites are dated at about 1590–1575 Ma. You may find more info in the paper by McLean and Betts (2003) in the Australian Journal of Earth Sciences 50: 525–541.

Best regards

Daniel

Daniel Muller,

Thanks for a fine mid-Proterozoic age, and a direction to learn more.

Jeff Spence

Hi Jeffrey

The Gawler Range Volcanics and the Hiltaba Suite together comprise the Gawler silicic large igneous province. The high temperature-low pressure Hiltaba event is broadly coeval with a much more extensive series of tectonothermal events occurring throughout Laurentia and Baltica in the Mesoproterozoic.

Hiltaba Suite magmatism spanned from at least 1598 ± 7 Ma for the Tickera Granite (Fanning, 1997), to 1574.7 ± 4.3 Ma for the Kychering Granite (Budd, 2006). Alex Cherry and others will soon be publishing high precision ages for the intrusive complex around Olympic Dam, as part of a study of the sedimentary units within OD, but these won’t change this broad picture. The preserved GRV volcanic package is at least 4km thick, and it is thought that at least 1km of this rock column has been eroded (Allen et al., 2008). Just prior to the Hiltaba event at ~1.62 Ga, arc-affinity rocks of the St. Peter Suite were emplaced in the southwest of the Gawler Craton. The Hiltaba event was also followed up by rocks of the Spilsby Suite from ~1.55 to 1.5 Ga… so magmatism in the Gawler was protracted and complex in the Paleo-Mesoproterozoic.

The magmas that fed the volcanic units were dry, high temperature, Fe-, K-, F-, and HFSE-rich. Similar statements can be made for the intrusive units, but constraining the precise nature of the primary melts to the extrusive and intrusive units is complicated by the fact that these systems are such large volume and were active over very long period of time, and the majority of the final products are differentiated. Significantly, not all the Hiltaba rocks are granites… a decent proportion are < 70 wt. % SiO2, including some of the bodies around Olympic Dam.

One of the aims of this project is to further our understanding of what went into making the Hiltaba event rocks. We see many similarities between the Gawler rocks and young and active, large volume silicic systems around the world (see posters and recent abstract on RG), and have many new findings to publish in the near future. But… as far as the massive lavas in the Gawler Range Volcanics go (some of the largest felsic lavas in the world), it looks like they reached higher crystallinity in the magma reservoir, and then a lot of quartz and feldspar resorption was required to form the lavas as we see them at surface today. At least some of the Hiltaba Suite granites had a similarly dynamic crystallisation history. Rubidium-Sr, Sm-Nd, U-Th-Pb, and Lu-Hf systematics all require significant juvenile involvement at ~1.59 Ga, and we have direct geological evidence of mafic-felsic interaction. It’s likely that this interaction is related to the decreasing crystallinity of the GRV magmas prior to lava emplacement, and there is some really exciting potential for mafic-felsic interaction to improve the economic potential of these systems.

Kind regards,

Matthew Ferguson

Matthew Ferguson

Thanks for an informative and encompassing answer to my curiosity and request. You have covered the age in relation to other regional plutons in South Australia and placed them in the tectonic setting of Mid-Proterozoic.

Chemistry, petrologic variation and age between granites, with the less-siliceous intrusive complex near Olympic Dam, for which you await a refined age; and so on.

Sounds like a great project.

Jeffrey Spence