TS
Tectonics and Structural Geology

mylonite

Features from the Field: Sheath Folds

and October 4, 2021
Features from the Field: Sheath Folds
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: S-C fabrics

, and May 19, 2021
Features from the Field: S-C fabrics

As we have seen in previous Features from the field posts, structural fabrics are both informative and spectacular. But many structural geologists will list a shear zone fabric, such as mylonite, as their favourite! As Samuele, Hannah and I wrote in a previous post, shear zones are regions of intense deformation where rocks have accommodated an extremely high amount of strain and that strain has b ...[Read More]

TS Must-Read – Lister and Snoke (1984) S-C Mylonites

March 29, 2021
TS Must-Read – Lister and Snoke (1984) S-C Mylonites

Following the impact of the global plate kinematics revolution, researchers in the 70s and 80s made significant efforts to compare records of deformed rocks in outcrops to large-scale deformation and kinematics. By publishing “S-C Mylonites” 1984, Gordon A. Lister and Arthur W. Snoke gave a step forward for the TS community. The paper contributed to transitioning from a strain-dominated framework ...[Read More]

Features from the Field: Shear Zones and Mylonites

, and January 25, 2021
Features from the Field: Shear Zones and Mylonites
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 – Sibson (1977) Fault Rocks and Fault Mechanism

December 28, 2020
TS Must-Read – Sibson (1977) Fault Rocks and Fault Mechanism

The paper “Fault Rocks and Fault Mechanisms” by R. H. Sibson (1977), was one of the first studies that established major connections between the rocks that form in faults, and their conditions and mechanics during formation at crustal scale. Concretely, Sibson (1977) established: 1.) links among the textures and lithologies that develop along fault zones (fault rocks), 2.) the rheological and crus ...[Read More]

Minds over Methods: Making ultramylonites

September 8, 2017
Minds over Methods: Making ultramylonites
The Large Volume Torsion apparatus - Credits: Andrew Cross

“Summer break is over, which means we will continue with our Minds over Methods blogs! For this edition we invited Andrew Cross to write about his experiments with a new rock deformation device – the Large Volume Torsion (LVT) apparatus. Andrew is currently working as a Postdoctoral Research Associate in the Department of Earth and Planetary Sciences, Washington University in St. Louis, USA. ...[Read More]