Tectonics and Structural Geology

Features from the Field: Dikes and Sills

Samuele Papeschi and Hannah Davies May 30, 2022

Dikes and sills intruding Dalradian quartzites, Donegal, Ireland. Photo © Prof. Alan Cooper (University of Otago).

Volcanoes are everywhere along plate margins and on hot spots on the planet’s surface. Just in the past 2 years, we have witnessed enormous explosive eruptions such as that of the Hunga Tonga volcano which released an amount of energy equivalent to hundreds of atomic bombs, and massive lava flows, as at the Cumbre Vieja at La Palma, which was estimated to have a total volume of 80 million cubic me ...[Read More]

Features from the Field: Sheath Folds

Samuele Papeschi and Hannah Davies October 4, 2021

Spectacular sheath folds in Cap de Creus (Spain), produced by deformation in a Variscan shear zone. Photo by Dr. Melanie Finch.

Shear zones are areas of intense deformation that localize the movement of one block of the crust with respect to another. In previous posts, we have seen that shear zones contain some very deformed rocks called mylonites, lineations that tell us the direction of movement, and useful kinematic indicators, such as S-C fabrics, that allow geologists to understand which way the rocks moved. However, ...[Read More]

Features from the Field: Stretching Lineations

Samuele Papeschi and Hannah Davies June 21, 2021

Measuring stretching lineations is the base to understanding the kinematics of large structures, like this protomylonitic metasandstone from a shear zone in the Glengarry Basin (Western Australia). Rocks slid past each other either up or down along this lineation. Which way? We need to look at a section oriented parallel to this lineation. Photo by Rolinator via wikimedia.org.

Deep beneath our feet, deformation of rocks at high temperature produces impressive structures such as shear zones, that localize the movement of two volumes of rock with respect to one another. Shear zones are strongly deformed bands with strongly foliated structures (i.e., with rocks that look like a pile of leaves) and kinematic indicators, such as S-C fabrics, that tell us geologists which way ...[Read More]

Features from the Field: Shear Zones and Mylonites

Samuele Papeschi, Sandra McLaren and Hannah Davies January 25, 2021

Dextral, ductile shear zones crosscut foliated schist at Cap de Creus (Catalona, Spain). Photo © Jordi Carreras

The San Andreas Fault in California, the Alpine Fault in New Zealand, or the Main Frontal Thrust in the Himalayas are some of the most famous and largest fault zones that accommodate the relative displacement between two adjacent crustal blocks. Such faults, however, represent only the shallower expression of something much bigger: a crustal shear zone. In the first 10 kilometers or so of the crus ...[Read More]

TS Must-Read – Ramsay (1980) Shear zone geometry: a review

The Must-read team January 21, 2021

Ramsay’s 1980 important contribution is a practical and theoretical handbook about shear zones, where the reader can find a detailed classification of shear zones, their description, and mathematical explanation. A definition of the concept of shear zones opens the article, followed by the shear zones classification into three types, namely brittle (e.g., Fig. 1a), brittle-ductile (e.g., Fig ...[Read More]

#OnTheRocks – Because Earth is just beautiful!

Silvia Brizzi January 15, 2021

The El Gordo Megabed from the Tabernas basin in Almeria, Spain. El Gordo which directly translates to the Fat Megabed is a fitting name for this huge sedimentary structure. The photo was taken on the morning after St.Patricks day on a field camp for Irish students. The photographer's previously thought to be incurable hangover was most certainly cured by the site. Credits: Grace Fitzgerald

From the time the first Kodak camera in 1888 went on sale we can say with confidence a geologist somewhere was trying to capture field photographs. We love to capture the beauty of the field and every geologist has a story to tell. The EGU would like to connect these stories globally in our new #OnTheRocks series. #OnTheRocks will produce a compilation of geological photographs on different scales ...[Read More]

Franciszka Szymakowska (05/02/1927 – 2007): the woman whose drawings unraveled the geological history of the Carpathians

Anouk Beniest November 27, 2020

An artists illustration of Franciszka Szymakowska (credit: Annique van der Boon)

Franciszka Szymakowska was born on the 5th of February in 1927 in Krakow. She was lovingly known as “Niusia” (Antoni 2007). About her early life, not much is known. Franciszka did her studies at the Faculty of Mathematics and Natural Sciences of the Jagiellonian University and graduated in 1952. During her studies, she started to work at the Polish Geological Institute. She remained affilia ...[Read More]

Features from the Field: Angular Unconformities

Samuele Papeschi October 21, 2020

The worldwide famous angular unconformity at Siccar Point, between vertical layers of Silurian graywacke (below) and gently dipping Devonian layers of the Old Red Sandstone Fm. (above). Photo © Dave Souza via Wikimedia.commons

An angular unconformity is an erosional surface that truncates older, tilted sedimentary layers and that is overlain by younger layers, oriented parallel to the unconformity. The discovery and interpretation of angular unconformities, like the famous Hutton’s unconformity at Siccar Point, Scotland, marked a paradigm shift in the geological theories of the 18th century. At that time, the theo ...[Read More]

TS Must-Read – Hubbert and Rubey (1959)

The Must-read team August 13, 2020

“The Role of Fluid Pressure in Mechanics of Overthrust Faulting” by Hubbert and Rubey is a “groundbreaking” article from the end of the 1950s. It’s a remarkable piece of research, written in an old-fashioned way, for modern standards. Many ECS that may not have read the original paper yet are certainly familiar with its textbook content. Let’s go quickly through it! The article, as a key po ...[Read More]

100 years of Marie Tharp – The woman who mapped the ocean floor and laid the foundations of modern geology

Derya Gürer July 30, 2020

An artists illustration of Marie Tharp (credit: Annique van der Boon)

Marie Tharp (July 30, 1920 – August 23, 2006) would have turned 100 on this very day and she continues to live through her legacy of having mapped the world’s oceans. Similar to famous painters, some of whom only gain appreciation after their death, Marie Tharp is one of the most underappreciated scientists in the history of the earth sciences. Marie was born in Ypsilanti, Michigan. Due to h ...[Read More]