Tectonics and Structural Geology

TS Must-Read – Mancktelow (2008): Tectonic pressure: Theoretical concepts and modelled examples

The Must-read team February 15, 2024

Neil Mancktelow published this Must-Read paper on the concept of “tectonic pressure” in 2008. The paper reviews previous work and theoretical concepts published on this fundamental topic. Additionally, numerical models that estimate the magnitude of tectonic pressure variations are presented for several realistic natural structures, such as folds, boudins, and inclusions. The premise of tectonic p ...[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: Pencil Cleavage

Sandra McLaren August 7, 2020

A selection of the author’s pencil shale collection, appropriately with a pencil for scale! Neoproterozoic Tapley Hill Formation from South Australia, Ordovician Liptrap Formation, Victoria, Balcanoona Formation shales from Mount Fitton, South Australia and a sample from an unknown location rescued from a departmental clean out (source: Sandra McLaren)

This edition of ‘Features from the field’ is brought to you by Sandra McLaren, a senior lecturer at the University of Melbourne. She will be talking about type of rock formation called “Pencil Cleavage” so called because it looks like pencils. Sandra even has a small collection of pencil/crayon shale which is the cover image of this post. I have seen quite a range of differ ...[Read More]

Features from the field: Foliation

Samuele Papeschi August 30, 2019

Jurassic slate in La Grave (Hautes-Alpes, France). These rocks easily split along foliation surfaces that dip towards the left of the image. Don’t believe me? Try to hammer them! Photo © Samuele Papeschi

Have you ever walked on a mountain trail, passing past outcrops of rocks and noticed that many rocks appear to be split along a well-defined orientation? If you have, you might have seen one of the most important structures in metamorphic rocks – called foliation. The term ‘foliation’ derives from the Latin folium, meaning ‘leaf’. A rock with a foliation looks like a pile of R ...[Read More]