A guest post from Dr Lloyd White, Lecturer in the School of Earth and Environmental Sciences at the University of Wollongong, Australia*
This year has seen celebrations for the fiftieth anniversary of plate tectonics, with many reflecting on the how tectonics continues to drive our understanding of Earth. While it is important to recognize historical achievements, for me it is more exciting to think how the concept of plate tectonics and our understanding of the Earth will evolve into the future. This is because there is still so much to learn, particularly from the seafloor and its subsurface where we still know relatively little – we could arguably say that it was the data from the seafloor that ultimately led Morgan, McKenzie and others to develop the fundamental concepts that we all still rely on.
The future promises to yield some exciting discoveries. Recent exploration of the subsurface of the (mostly) drowned continent of Zealandia is one example – another is the proposed coring of an active, deep-sea arc volcano that is due to take place in 2018. In terms of advancing our fundamental knowledge of plate tectonics, I am particularly excited by the recent work that has imaged and cored exhumed mantle domes at modern day spreading systems. Such work demonstrates that plate divergence and magnetic seafloor anomalies are not as simple as we once thought. This work potentially has quite significant implications for how we reconstruct the past position of tectonic plates.
Each of the examples mentioned above has been (or will be) facilitated by the International Ocean Discovery Program (IODP), a long-lived, international program that demonstrates the power of scientists from all across the globe, coming together to collaborate on targeted research programs. I am fortunate to be writing this, bobbing up and down in the southern Indian Ocean as part of IODP Expedition 369. I am part of an international team of 31 scientists (and another 22 highly skilled technical support staff) collecting hundreds of meters of core from beneath the seafloor, in water depths that typically exceed 3000 m.
At the time of writing, we had just begun coring in the Naturaliste Plateau offshore SW Australia – this followed on from successfully extracting a 700 m core from the Great Australian Bight. The point of all of this work is to develop a better understanding of Earth’s climate during the Cretaceous tied together with unravelling the history of break-up of eastern Gondwana (i.e., Australia, India and Antarctica). My interest mainly lies in understanding the later, and trying to produce maps that show how the environment changes as Gondwana broke-apart – the video below explains more.
Some may say that we already know how this happened. This is only partly true – we can use information, such as oceanic fracture zones and magnetic anomalies to develop a fairly good picture of where the plates existed after they broke apart. However, the major challenge lies in understanding the position of the plates before any seafloor existed between them, and when they started to split. For this we need more information from ancient plate margins. The problem is, that many of these ancient (and modern) plate margins are hidden from view, typically beneath a thick mass of rock and deep ocean. Custom-designed vessels like the IODP JOIDES Resolution are capable of collecting core from the deep sea. So, we are using this to try to collect the information we need.
Approximately 130 million years ago, India separated from Australia and Antarctica – this process led to basaltic volcanism and rifting of the submerged Naturaliste Plateau, offshore SW Australia. Stretching commenced again at approximately 95 million years ago, but this time in a different direction, which meant that a depression began to develop between Australia and Antarctica. This early stage of break-up probably produced something similar to the modern-day East African Rift Zone. However, in the Cretaceous, sea levels were about 200 m higher than they are today – so the region between Australia and Antarctica would have been a narrow seaway that progressively got deeper and wider as the plates moved further apart.
It wasn’t until about 90-85 million years ago that the first true oceanic crust formed between Australia and Antarctica, approximately the same time that Zealandia began to break-apart from eastern Australia. However, Australia’s separation from Antarctica wasn’t simple – it took tens of millions of years for the plates to free themselves of one another. The process is ultimately something similar to a giant zipper that progressively opened from west to east between 90 and 45 million years ago. Once this happened, deep waters could circulate between the Indian and Pacific Oceans. The later opening of the Drake Passage between Antarctica and South America (approximately 30 million years ago) meant that deep ocean waters could flow around Antarctica (the Antarctic Circum Polar Current) – leading to much colder temperatures and Antarctica beginning to freeze over.
We expect that the core obtained during Expedition 369 will shed light on how Gondwana’s environment changed during and after its break-up. Other primary goals include obtaining paleotemperature and biotic records that cover the rise and fall of the Cretaceous hothouse and oceanic anoxic events.
Clearly, the study of plate tectonics has developed considerably since its conception. Not only is it a cornerstone of geological research, it also offers insights into broader studies of the Earth system, with direct relevance to better understanding palaeoclimate, the opening of ocean gateways and biogeographic patterns. The past 50 years has seen many advances in our understanding of the Earth – there is no doubt that next 50 years will see us understanding so much more.
* Dr Lloyd White is a Lecturer in the School of Earth and Environmental Sciences at the University of Wollongong, Australia and an Honorary Research Fellow in the Department of Earth Sciences, Royal Holloway, University of London. Lloyd’s research focuses on understanding how plates break apart and how mountains form in plate collision zones.
- The JOIDES Resolution voyage
- Dr Vivien Cumming is the ship’s onboard Education and Outreach Officer – find out more at www.viviencumming.com or get in touch on Twitter: @drvivcumming
- The Geological Society’s Dan McKenzie archive website, featuring the story of early research into plate tectonics, can be viewed at www.mckenziearchive.org/