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Global Plate Reconstructions During the Cretaceous Normal Superchron

Final Report Summary - GEOPLATE (Global Plate Reconstructions During the Cretaceous Normal Superchron)

The evolution of past relative motions between tectonic plates has placed important constraints on the development of the lithosphere, biosphere, hydrosphere, cryosphere, and global climate. For instance, our ability to identify new prospective regions for mineral and hydrocarbon reservoirs depends on our understanding of the full tectonic context of marginal basins that have developed as a consequence of past plate motions. Furthermore, the relative motion of tectonic plates controls the heat flow budget and hence the subsidence history of the Earth’s crust. Marine magnetic anomalies constitute the backbone of plate tectonic studies as they are used to date the oceanic crust and form the basis for the quantification of past plate motions. In this project we are using, for the first time, tiny magnetic wiggles formed due to past changes in the geomagnetic field strength to constrain the age of the crust within the Cretaceous long normal superchron (lasted between 121 to 83 million years ago). Furthermore, we have set our lab with a towed, fully oriented, tri-axial magnetic sensor that allow us to investigate the magnetic signature of the oceanic crust in details. As part of this project, we have discovered the oldest known oceanic crust on Earth, still located in its original location.
In the first study we have constructed a new kinematic models for the opening of the Indian Ocean (Williams et al., Journal of Geophysical Research, 2013) and South and Equatorial Atlantic Oceans (Granot and Dyment, Earth and Planetary Science, 2015). This new model for the opening of the Atlantic Ocean shed new light on the style of rifting between South America and Africa. Its consequences extend globally. The formation of the Atlantic Equatorial Gateway probably resulted in the formation of new north-south water motion that ended of the greenhouse world that prevailed during the Cretaceous. The new model place a much younger age on the opening of the gateway (roughly 10-15 Myr younger than previously thought), which seems to agree well with independent isotopic data from various drill holes located globally. Furthermore, the new results shed new light on how continents break apart and explain various geo-biological observations from Africa and South America.
As an indirect outcome from the study of the South Atlantic evolution, the fellow, together with his collaborator, Dr. Jerome Dyment (IPGP, France) have initiated a new study aimed at quantifying the effect of sedimentation on the thermal as well as magnetic state of the oceanic crust. The results show that indeed, under thick sedimentary basin fill, part of the crust is heated up enough to erase a major component of its magnetization and hence it affects roughly 10 percent of the oceanic crust globally. The results are now being summarized as part of preparation for a new publication.

Looking for a possibly Cretaceous-aged oceanic crust in the eastern Mediterranean, we have been collected new magnetic data during four geophysical cruises, and the results showed the first direct evidence for the existence of an oceanic crust in this part of the world. Furthermore, the results showed that the age of the crust is much older than expected, making it the oldest known oceanic crust on Earth, still found in its original setting. The results have been published in Nature Geoscience (Granot, 2016) and were covered extensively in the local media as well as in the international media (35 newspapers including CNN, Business Insider, New Scientist, Nature, Science, radio interviews, etc.). The results have implications for the formation of the most-recent supercontinent (i.e. Pangea) and on the geodynamic and seismic hazard around the eastern Mediterranean.
As part of the final study, we are developing a new method to constrain the tectonic evolution of the oceanic plate through the analysis of the morphology of the seafloor. Early results show that indeed, the shape of the abyssal hills can constrain the paleo-seafloor spreading rates of the quite zones. The results will soon be submitted as a Master thesis and as a scientific publication.
As part of the project, the fellow and his colleagues from France (IPGP) were able to secure funding for two scientific cruises aim at studying the evolution of the south Indian Ocean. The cruises will take place in 2017 and 2018 and are expected to provide the data for the continuation of the project and allow undergraduate as well as graduate students to get exposed to marine research in first hand.
This project allowed the fellow to establish a research group equipped with top-of-the-line magnetic sensors, applicable for both marine and continental studies. As a result, the fellow was able to secure funding and attract graduate students (thus far, five students have been graduated or are near final completion of their thesis). It also allowed the fellow to establish new collaboration ties with other European scientists and perform outreach activities. The results of the research entitled the fellow to advance to the degree of Senior Lecturer and secure a permanent position (i.e. receive tenure).