2-D finite displacements and strain from particle imaging velocimetry (PIV) analysis of tectonic analogue models with TecPIV

2-D finite displacements and strain from particle imaging velocimetry (PIV) analysis of tectonic analogue models with TecPIV

Boutelier, Schrank and Regenauer-Lieb

Solid Earth, 10, 1123–1139, 2019

We published a paper detailing the progress made on TecPIV:  2-D finite displacements and strain from particle imaging velocimetry (PIV) analysis of tectonic analogue models with TecPIV. The open-access paper can be downloaded from the link above.

More information on the software here, and the source here.

TecPIV outputs with strain rate components instead of velocity gradients



Finite deformation ellipses from cumulative Lagrangian sums.

MinEx CRC : GSNSW- embedded researcher position opened

We are looking for a post-doc to work on cover sequences in the MinEx CRC NDI areas in NSW. The role focuses on the characterisation of the cover, its key interfaces and identification of the signatures of basement geology and mineral system footprints.

The position is a GSNSW-embedded researcher, providing unparalleled access to GSNSW research environment and capacity on top of the University of Newcastle Earth Sciences group.

Being  MinEx funded the position also provides a fantastic opportunity for collaborating with other participating state surveys, GA, CSIRO, and a number of other MinEx CRC partners.


MinEx CRC at UON

Job advert: https://www.seek.com.au/job/40063569?searchrequesttoken=8feecb40-dba0-4bdd-a378-ba624defaa51&type=standout


New paper on subduction initiation

Can subduction be initiated at a transform fault? The short answer is probably not. The not so short answers are below and in the linked paper.


Initiation of Subduction Along Oceanic Transform Faults: Insights From Three-Dimensional Analog Modeling Experiments

David Boutelier and David Beckett
School of Environmental and Life sciences, University of Newcastle, Newcastle, NSW, Australia

Subduction initiation is a fundamental component of the plate tectonic theory, yet how subduction starts remains controversial. Oceanic transform faults and fracture zones have been proposed as sites of subduction nucleation because they are thought to be mechanically weak and the large buoyancy gradient across these faults because of the difference in the age of the lithosphere, was thought to facilitate foundering. Self-sustaining subduction, defined as subduction driven by the negative buoyancy of the sinking lithosphere might be achieved if at least ~100 to 150 km of convergence can be imposed on an oceanic fracture zone with sufficient buoyancy gradient across the fault.

Previous modelling however did not take into account the fact that the age of the lithosphere and therefore its strength and buoyancy not only varies across the oceanic fault zone, but also along the strike of the fault since many oceanic transform fault link segments of spreading ridges. Here we investigate using three-dimensional analog models how the spatial distribution of strength and buoyancy along and across an oceanic transform fault zone affects the polarity of subduction and whether self-sustaining subduction can be obtained. We designed three-dimensional analog experiments in which two oceanic lithospheric plates are separated by a weak transform fault and convergence is imposed in the horizontal direction perpendicular to the strike of the fault. The spatial distribution of plate thickness and buoyancy are varied along and across the strike of the transform fault, and whether self-sustaining subduction is obtained is assessed using a force sensor.

Cylindrical experiments reveal that subduction polarity is controlled by the buoyancy gradient and the strengths of the plates. With no inclined weak zones, imposed orthogonal compression results in the nucleation of a new fault in the weakest plate leading to the young and positively buoyant plate subducting. However, with an inclined weak zone, the buoyancy contrast controls subduction polarity with the most negatively buoyant plate subducting and a self-sustaining subduction regime obtained after ~300 km of imposed shortening.

Interestingly, this situation is also obtained when including an inverted triangular weak zone on top of the transform fault associated with the serpentinization of the crust and mantle.

In non-cylindrical experiments, taking into account the change along strike of plate strength and buoyancy, the capacity of the transform fault to generate a self-sustaining subduction regime is greatly reduced. Subduction initiates simultaneously with opposite polarity at the two extremities of the transform segment and, at depth, a lithospheric tear is produced that separates the two subducting slabs. In the center of the transform fault, the lack of buoyancy or strength contrast between the two plates leads to multiple thrusts with variable polarities, overlapping each other, and each accommodating too little shortening to become the new plate boundary. This indicates that additional mechanical work is required in the center of the transform fault which prevents the establishment of a self-sustaining subduction regime.

The paper is open access and can be obtained here.


Figure 1. Maps of seafloor age (Müller et al., 1997, 2008), plate thickness and buoyancy relative to underlying mantle for fast spreading ridge separating the Pacific and Antarctic plates (A–C), or slow spreading ridge separating the Africa and Antarctic plates (C,E,F). Half spreading rates from GSRM (Kreemer et al., 2003, 2014). Points labeled 1–6 refer to profiles in Figure 2. Plate thickness and relative buoyancy are calculated using the half-space cooling model and the simple plate structure discussed in the text.


Figure 8. Successive stages of Exp. 21. Panels (A–E) show the surface view of the deformed model with PIV vectors, and convergence-parallel horizontal shortening rate. Panel (F) shows the evolution of the force measured at the trailing edge of the plate on the left-hand side. The variation of plate thickness and buoyancy along the strike of the transform fault resulted in generation of multiple faults.

Structural Geology – South Coast excursion 2018

Our yearly excursion to the South Coast for GEOS2190 Structural Geology was a great success. Thanks to Murray Kendall for assisting in the field and food making. Thanks to the Beachcomber caravan park for the friendly venue, and thanks to our students for the fun.

Below are some of my photos. Many more by our students can be found here. If you have more photos of excursion with us don’t hesitate to post and tag with #uongeos


Drawing 3D geological structures with sketchup

I discovered this week-end that it is possible to script sketchup, an application to draw objects in 3D. Here is a first test with two semi-transparent inclined planes, and their intersection lineation. The possibility to use scripts instead of the mouse to draw opens up the possibility of multiple 3D drawings of geological structures.



Another way to look at strain

Here is another way to look at strain from PIV analysis of analogue models. After computing all the spatial derivatives of the velocity or incremental displacements field, the 2D small strain tensor can be assembled.

Below I calculated the principal strain direction from the small strain tensor. This is the direction of one of the principal strain, measured from the x-axis.


And then I calculated the values of the maximum principal strain and minimum principal strain. Two horizontal bands appear in the plot. The white cells in the top right and bottom left corners show that this experiment is a sinistral horizontal shear.

The data presented here is not interpolated. Each cell is a data point obtained from image cross-correlation. The maps could be interpolated and be made smoother.



and then we can claculate the maximum shear. We can see where the shear is occuring, where the difference between the maximum and minimum principal strains is largest.


Finally, since we have the directions and values of the principal small strains, we can plot them as crosses. The length of the line is linearly proportional to the magnitude of the principal strain, the orientation of the line is the orientation of the principal strain, and red indicates contraction while blue indicates extension.


A zoom-in shows the directions of S1 and S2 around the developping plastic shear zone fitting what we expect for a sinistral horizontal shear.


I will integrate this into TecPIV rapidly.

Exhumation of (U)HP/LT rocks

Crustal rocks metamorphosed at ultra-high pressure (UHP) record burial to 100–150 km depths and subsequent return to the surface. Although it is well accepted that UHP rocks are formed by deep subduction of continental passive margin rocks, the mechanisms by which these rocks are exhumed remain debated.

Here, three-dimensional thermo-mechanical analogue models investigate how diachronous slab breakoff may lead to the exhumation of subducted continental crust. Slab breakoff initiates spontaneously in one location and migrates laterally along the plate boundary, causing a transient excess downward pull force on the plate boundary in front of the propagating slab tear. This pull force locally reduces the pressure between the plates, which promotes buoyancy-driven exhumation of subducted crust.

However, both the surface area undergoing the pressure reduction and its duration are limited. Our experiments show that the rate of slab breakoff propagation controls both the duration of the pull force and the magnitude of pressure reduction. Our results further demonstrate that exhumation occurs where the slab breakoff propagation rate is lowest, rather than where the pull force is strongest, corresponding to where the slab tear initiates or terminates.

Here is the link to the JSG paper.

Analogue modelling of diachronous slab break-off causing exhumation of subucted crust


Illustration of proposed dual-mechanism exhumation of (U)HP rocks associated with propagating breakoff. 1: Horizontal propagation of detachment in the subducted lithosphere; 2: Excess slab pull generated ahead of the propagating tear; 3: Normal pull is produced on interplate zone causing reduction of pressure; 4: Pressure reduction allows buoyancy-driven exhumation of subducted crust; 5: After passage of tear, the lower plate bounces upward causing normal push on plate boundary and increase in interplate pressure; 6: Increased pressure terminates and crustal units are squeezed further upward.

CRC MinEx funded

The Assistant Minister for Science, Jobs and Innovation, Zed Seselja, and Minister for Resources and Northern Australia, Matt Canavan, announced $50 million of Australian Government funding for MinEx CRC.

MinEx CRC is a major endeavour comprising:

  • $50M cash from the CRC Programme
  • $41M cash from geological surveys and from industry
  • $49M non-staff in-kind
  • $78M or 311FTE staff in-kind
  • TOTAL $218M

MinEx CRC’s research will include:

  • Developing more productive, safer and environmentally-friendly drilling methods to discover and drill-out deposits, including coiled tubing drilling technology.
  • Developing new technologies for collecting data while drilling, bringing forward mine production.
  • Implementation of a National Drilling Initiative (NDI) – a world-first collaboration of Geological Surveys, researchers and industry that will undertake drilling in under-explored areas of potential mineral wealth in Australia.

Congratulations to all involved with the Bid.  We are delighted at this success and its scale. MinEx CRC will, at its commencement, be approximately twice the size that DET CRC was at its commencement. MinEx CRC’s 34 current participants are listed below.  Additional sponsors may apply to join MinEx CRC. If you are interested please refer to the attached and contact Andrew Bailey or www.minexcrc.com.au.

The MinEx CRC announcement was followed by a National Press Club speech by Minister Canavan which announced the commissioning of a ‘National Resources Statement’ to address the challenges facing the sector including the need to make new mineral and energy discoveries. The National Resources Statement is to be delivered by a very well credentialed ‘Resources 2030 Taskforce’ within six months.

The MinEx CRC’s current participants are: Anglo American, Barrick Gold, BHP, South32, Atlas Copco, Geotec Boyles, HiSeis, Imdex, LKAB Wassara, McKay, Olympus, Sandvik, Geoscience Australia, Geological Surveys of NSW, SA and WA, Curtin University, Universities of Adelaide, Newcastle, South Australia and Western Australia, MRIWA and CSIRO.

Current MinEx CRC Affiliates are Investigator, Minotaur, DataCode, Minalyze, Mudlogic, Southern Geoscience, Geological Surveys of NT, Queensland and Victoria, Mineral Resources Tasmania and the SA Department of State Development.

this is a re-post from : https://www.aseg.org.au/news/minex-crc-funded

Combined excursions GEOS3170-GEOS3330

This year GEOS3170 – Resource and Exploration Geology provided an excursion to Cobar NSW to explore how the mineralizations are structurally controlled in the Cobar basin. The excursion included mapping of the folded and faulted host rock as well as visits of the CSA and Peak Gold mines to demonstrate how the geology is explored from exploration and production cores. We are very gratefull to both companies to have provided such window into the real work of a mine geologist.

We combined the excursion to Cobar with our usual field trip to Broken Hill for GEOS3330 where the effects of multiple phases of metamorphism and deformation are unravelled. We had the opportunity to get a lecture by Prof. Ian Plimer on the Broken Hill ore body formation. Thank you very much Ian.


The material or views expressed on this Blog are those of the author and do not represent those of the University.  Please report any offensive or improper use of this Blog to RPS@newcastle.edu.au.
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