Fire, and then the ice: the core of supercontinent Rodinia in the Neoproterozoic

It is now emerging that our wandering continents came together and diverged throughout Earth’s history, a process known as the Supercontinent Cycle. The last known supercontinent was Pangea, which began to break apart in the time of the dinosaurs. However, this has been shown as just one of many supercontinents back in time, with the supercontinent before Pangea known as Rodinia existing up to one billion years ago, and which was the focus of this project.

Ashley Paul Gumsley

This supercontinent occurred at a critical juncture in Earth’s history, when the hostile environments of the ancient Earth changed into the habitable world we know today. It is an exciting avenue of research to understand how the world we know today came to be. Supercontinents, driven by forces deep within the Earth, have a dramatic effect on the Earth’s environmental system. As the supercontinent Rodinia came together and began to break up approximately 700 million years ago, large and extensive volcanism erupted and covered
the surface of the Earth’s continents in lava, sometimes up to kilometres thick. Such volcanic events are unlike anything humans have ever witnessed; but they are now known to have occurred sporadically throughout Earth’s history, with many large ones even causing mass extinctions. Therefore, these large igneous provinces as they are known, are an important temporal marker.

Such catastrophic volcanism on Rodinia led to massive amounts of volcanic gases escaping into the Earth’s atmosphere and the weathering and erosion of the lavas into the oceans, which likely triggered a global glaciation, a ‘Snowball Earth’ encasing the world in ice. This volcanism formed the focus of this study. Largely undocumented fragments of this large igneous province were identified and studied
in this project. We found these fragments in Zimbabwe in southern Africa, as well as in Dronning Maud Land in Eastern Antarctica. These fragments were preserved as mafic dykes, a black rock which is the magmatic feeder to the lavas above, which have mostly long since been removed through weathering and erosion. These fragments were shown to be 700 million years old through age dating on the mineral
baddeleyite, and the mineral assemblages showed that they were unaltered by subsequent events, which can change the mineral assemblages of these rocks, destroying the primary information that is preserved. Age dating using apatite also showed they cooled quickly. Chemically, they can be seen to have formed in an intra-continental tectonic setting.

With this information, we completed a controversial, but fundamental puzzle piece in our understanding of the paleogeography of the supercontinent Rodinia.

This enabled us to show that we can place southern Africa and Dronning Maud Land of Eastern Antarctica against North America and Siberia in a new Rodinia paleogeography through high-precision geochronology and geochemistry on a large igneous province, which shows that the dykes occurred at the same time and with similar chemistry. In addition, paleomagnetic and rock magnetic evidence shows that the dykes may be connected, although at this time, these results remain preliminary. Although provenance studies on the host rocks could also have allowed us to match up the surrounding continental basement, this study instead showed us that this basement is much younger than previously thought, opening up exciting new possibilities for the future, although this is now beyond the scope of this project.

With all these results, we will now model our understanding better about how volcanism led to global glaciation. This is important, as when the world emerged from global glaciation, the nutrients trapped in the oceans led to a boom in biological production and ultimately drove photosynthesis, producing increasing oxygen concentrations in the Earth’s atmosphere. This positive-feedback loop led to the evolution of multi-cellular life, and the planet we know today began to emerge.

How did you benefit from the POLONEZ fellowship?

During my fellowship, I was lucky to be awarded two further grants funded by the National Science Centre to the University of Silesia in Katowice, which is where I work now. Additionally, my Polish partner recently had our first baby. So, I am really happy! I aim to settle here in Poland, as it has many opportunities. My fellowship enabled me to learn more about rock magnetic investigations, Understanding the Universe which directly complement my own age dating experience towards studying paleogeography. The fellowship taught me a lot about
Poland. I look forward to collaborating with researchers here on projects in Svalbard, Poland, Ukraine and Bulgaria, as well as continue my older investigations in southern Africa, Antarctica and Australia. Hopefully I will have my own world-class geochronological facility in Poland one day!

Dr Ashley Paul Gumsley, geologist and a U-Pb geochronologist. He is interested in Earth’s history in deep time, i.e. many millions of years ago. He uses his skills in geochronology to get precise ages using magmatic events to provide constraints on critical events in deep time, such as the rise of oxygen on the planet, or global glaciations. His interests also include paleogeography. He grew up in South Africa and was educated there. He did doctoral studies at Lund University in Sweden.