Global Eocene tectonic unrest: Possible causes and effects around the North American plate

Earth history is commonly characterized by long periods of steady-state evolution punctuated by catastrophic events that forced the global system to adapt to new configurations (e.g. Rona and Richardson, 1978). What causes major Earth's system turning points and how is our planet responding to them locally and globally through geological time are still unanswered questions.

It has long been recognized that a major collisional and mountain building event, such as the India-Eurasia collision and the resulting Himalaya orogeny, can have severe implications on Earth's crustal structure, by forcing a re-accommodation of a considerable amount of tectonic stresses over long distances (e.g. Patriat and Achache, 1984). However, the timing of this collisional event is still debated (e.g. Aitchison et al., 2007; Najman et al., 2017) and classical modelling of this event's effect on plate reorganisations in neighbouring areas (like the Pacific Ocean) minimized its importance (Richards and Lithgow-Bertelloni, 1996).

Other major events that impacted Earth's crust and subsequently the climate and life have been attributed to excessive volcanism, possibly generated by massive mantle plumes from Deep Earth, which resulted in so-called Large Igneous Provinces (LIPs) on the Earth's surface. Recent studies have attempted to quantify (Cande and Stegman, 2011) and model (Iaffaldano et al., 2018; van Hinsbergen et al., 2011) the effect of mantle plumes on Cenozoic plate motions variations in the Indian Ocean. The results confirm that mantle plumes are potential candidates to explain some plate motion changes, but disagree on the vigor of this trigger in time.

Apart from the LIP events that caused massive havoc in Earth's system, there are many other changes that have been registered by Earth's outer layers, but their causes and exact succession of events and associated consequences are not yet established.

For example, the oceanic crust in the Pacific realm and elsewhere has witnessed changes in the tectonic plate motions before, during, and after the well-known Hawaiian-Emperor volcanic chain “bend”, with the clearest changes spanning c. 10 Myrs, from 55 to 45 Ma (e.g. Sharp and Clague, 2006; Torsvik et al., 2017). Several other Paleocene-Eocene tectonic events have been registered in the Pacific realm (Whittaker et al., 2007; Seton et al., 2015; Torsvik et al., 2017) postulating that the subduction of an active mid-ocean ridges under Japan (e.g. Whittaker et al., 2007), or terrane collision with NE Asia (Domeier et al., 2017) led to a change in the Pacific plate motion, and that may have also been recorded by the tectonics of neighbouring plates.

To better understand how our planet's turning points were caused and whether sudden changes in plate tectonic configuration could have been related to continent collision, mountain building, major changes in the subduction geometry or catastrophic outbursts of volcanism often caused by mantle plume impingement at the base of the Earth's lithosphere, we revise the Eocene tectonic unrest which is imprinted in the world's oceanic lithosphere. A more detailed set of Eocene oceanic crust timelines (isochrons and age-grid) are constructed based on results from vintage and recent studies that dated the oceanic lithosphere from magnetic anomalies. We chose to analyse in more detail the unusual abrupt Eocene changes in seafloor spreading direction and spreading rates around the North American plate. Finally, we speculate on possible connections between subduction in the NE Pacific, mantle plume activity in the North Atlantic, and the evolution of North American oceanic lithosphere in the Eocene.

Data and methods

In this study, we rely on published magnetic anomaly and seafloor fabric (mainly fracture zones) identifications in the oceanic realm. A comprehensive global compilation of marine magnetic anomalies identified in the last few decades in all major oceanic basins, was published by Seton et al. (2014) (Fig. 1A). We complement this dataset with few more regional marine magnetic anomaly identifications shown in Fig. 1: 322 picks by Petronotis et al. (1994) in the Pacific Ocean (Fig. 1, B1), 2255

Eocene tectonic unrest in global oceans illustrated by seafloor spreading variations

Many facets of the oceanic basin development are keys to better understand planetary changes. Oceanic crust fabric reveals how tectonic plates moved, and records the age, direction and rate of seafloor spreading, together with any complex processes associated with this evolution. The global oceanic basins are also prized witnesses of lithosphere-mantle interactions through numerous volcanic edifices built on top of normal oceanic crust.

The detailed global model of kinematic parameters, derived

Discussions

According to published regional kinematic models (e.g. Cande et al., 2011; Croon et al., 2008; Gaina et al., 2009; Whittaker et al., 2007), and our present analysis, a global Eocene tectonic “unrest” is recognized in the oceanic lithosphere structure with an Early Eocene pervasive set of events located in the northern hemisphere, where it affected the NE Pacific, North Atlantic and the Arctic region. Here we have presented in more detail changes in seafloor spreading direction and rates of

Conclusions

We have used a global database of magnetic anomaly and fracture identifications supplemented with 3285 additional picks to construct a detailed model of oceanic lithosphere age and seafloor spreading rates for the Eocene time. In particular, we aim to map a series of tectonic events that occurred from 57 to 40 Ma in the North Atlantic and NE Pacific. We have revised evidence for changes in plate motion of the North American plate relative to its neighbouring plates from the Arctic to the North

Acknowledgements

The authors are grateful to Doug Wilson, Sebastian Tappe, an anonymous reviewer and the Tectonophysics Editor-in-Chief Philippe Agard for their useful comments that greatly improved our manuscript. C.G and J.J. acknowledge support from The Research Council of Norway through its Centers of Excellence funding scheme, project number 223272.