In this episode, Jiří Žák describes the two main orogenies whose remnants figure prominently in central European geology: the Cadomian orogeny that lasted from the late Neoproterozoic to the early Cambrian (c. 700 Ma to c. 425 Ma) and the Variscan orogeny that occurred in the late Paleozoic (c. 380 Ma to 280 Ma). The Cadomian took place on the northern margins of Gondwana, only later to rift and travel north to form what was to become Europe. The Variscan was caused by the collision of Gondwana with Laurussia in the final stages of the assembly of the supercontinent Pangea. Both orogenies have been heavily eroded, and we see their imprint in the form of metamorphic rocks, volcanic rocks, granites, and deformation structures. These are scattered across Europe, from southern Britain to eastern Europe.

Žák has been studying the geology of central Europe for over 25 years using methods ranging from structural studies in the field to detrital zircon geochronology. He is a Professor in the Institute of Geology and Paleontology at Charles University in Prague.

Subduction zones can be very long-lived, persisting for tens of even hundreds of millions of years. During that time they rarely stay still, but instead retreat, advance, move laterally, or reverse direction. In the podcast, Claudio Faccenna discusses the processes that govern these movements. It turns out that they depend not only on the properties of the subducting slab, but also on the environment, including the proximity of other subduction zones.

Faccenna has been studying how convergent margins evolve for over 30 years, concentrating particularly on the Mediterranean region. He is Head of the lithospheric dynamics section at the Helmholtz Center for Geosciences at GFZ in Potsdam in Germany and also a Professor at the Department of Science at Roma Tre University.

In the podcast, Cees Van Staal tells us about the Paleozoic tectonic events that led to the formation of the Appalachians. The events are closely related to those involved in the Caledonian orogeny and the mountains it created in what is now Ireland, Scotland, east Greenland, and Norway, as discussed in the episode with Rob Strachan. However, the Appalachians that we see today are not the worn-down remnants of the Paleozoic mountains. Instead, they reflect much more a topography that was created during processes associated with rifting and magmatism that accompanied the opening of the Atlantic Ocean as well as the effects of the ice ages as recently as about 10,000 years ago.

Van Staal has been studying the Appalachians for over 35 years, focusing especially on the large-scale tectonics of their formation. He is Emeritus scientist at the Geological Survey of Canada and an Adjunct/Research Professor in the Department of Earth and Environmental Sciences at the University of Waterloo in Ontario.

In previous episodes of Geology Bites, Barbara Romanowicz gave an introduction to seismic tomography and Ana Fereira talked about using seismic anisotropy to reveal flows within the mantle. In this episode, Andreas Fichtner explains how, despite the many fiendish obstacles that stand in our way, we are making steady improvements in our ability to image the Earth on both regional and global scales. These give us confidence that we can make three-dimensional maps of certain structures, such as the plume below Iceland, cold continental interiors, mid-ocean ridges, and the large low shear-velocity provinces.

Fichtner is a Professor in the Department of Earth and Planetary Sciences at the Federal Institute of Technology in Zurich.

When the Earth formed, it was covered by a hot magma ocean. So when and how did thick, silica-rich continental lithosphere form? Were the first, ancient continents similar to the present-day continents? And did the continents form in a burst of activity at a certain point, or was it a gradual build-up over Earth history?

In the podcast, Renée Tamblyn addresses these questions, as well as how early geological processes created molecular hydrogen that may have powered the first forms of life. In her own research, she has focused on the critical role played by water released from hydrous minerals that formed within oceanic lithosphere on the sea floor.

Tamblyn is a Postdoctoral Researcher at the University of Bern.

From East Africa to southwest USA, many regions of the Earth’s continental lithosphere are rifting. We see evidence of past rifting along the passive margins of continents that were once contiguous but are now separated by wide oceans. How does something as apparently solid and durable as a continent break apart?

In the podcast, Folarin Kolawole describes the various phases of rifting, from initial widespread normal faulting to the localization of stretching along a rift axis, followed by rapid extension and eventual breakup and formation of oceanic lithosphere.

Kolawole is especially interested in the early stages of rifting, and in his research he uses field observation, seismic imaging, and mechanical study of rocks. He is Assistant Professor of Earth and Environmental Sciences, Seismology, Geology, and Tectonophysics at the Lamont-Doherty Earth Observatory of Columbia University.

Most of Earth’s salt is dissolved in the oceans. But there is also a significant amount of solid salt among continental rocks. And because of their mechanical properties, salt formations can have a dramatic effect on the structure and evolution of the rocks that surround them. This gives rise to what we call salt tectonics – at first sight, a rather surprising juxtaposition of a soft, powdery substance with a word that connotes the larger scale structure of the crust.

In the podcast, Mike Hudec explains the origin of salt in the Earth’s crust and describes the structures it forms when subjected to stresses. He also discusses how salt can play in important role in the formation of oil and gas reservoirs.

Hudec is a research professor at the Bureau of Economic Geology at the University of Texas at Austin.

Megafloods are cataclysmic floods that are qualitatively different from weather-related floods. In the podcast, Vic Baker explains our ideas as to what causes megafloods and describes the striking evidence for such floods in the Channeled Scablands of Washington State and in the Mediterranean.Vic Baker has been studying megafloods for over 50 years. He is a Professor of Hydrology and Atmospheric Sciences, Geosciences, and Planetary Sciences at the University of Arizona.