Tectonostratigraphic architecture and uplift history of the Eastern Yilgarn Craton:  Module 3 - Terrane Structure, pmd*CRC Project  Y1-P763

This is a public domain release of the Module 3 structural study from the Predictive Mineral Discovery Co-Operative Research Centre (pmd*CRC) and AMIRA (Australian Mineral Industry Research Association) Y1-P763 project which concluded in November 2005. An 18 month confidentiality period applied to this work but the resulting report is now able to be released.
Research into the structural evolution of the Eastern Goldfields Superterrane (EGST) continued in allied projects (Y2 and Y4) as part of the pmdCRC program. The Y2 project Final Report was released to the public as Geoscience Australia Record 2006/05. As of July 2007, the active Y4 pmdCRC project has been continuing the work from the Y1-P763 and Y2 projects. Therefore, some interpretations of the structure of the EGST presented in Geoscience Australia Record 2007/15 have changed. One of the enduring assets of the original Y1-P763 Final Report is the very extensive data preserved in the appendices, which, due to their size, are available only on DVD. The philosophy behind the Y1-P763 report was to clearly separate data from interpretation, a move which has aided continuous improvement in the understanding of the structural evolution of the EGST.
No structural difference between terranes.
The only possible terrane accretion structures are the Ida and the Hootanui since the Ockerburry is extensional.
No D1 N-S compression, early isoclinal shallowly dipping structures are interpreted to be extensional in origin.
Long-lived ENE-directed extension marked during D1 which formed the major basin architecture for the greenstone sequences.
There is a strong extensional event (D3) which postdates D2 compression and forms and deforms the late basins.
The crustal architecture (observed in seismic) is controlled by D1 and D3 extension. It is not a thin-skinned fold and thrust belt.
The NNW-trending tectonic grain in the Eastern Yilgarn was set up as a result of ENE-directed D1 and D3 extension with local extension vectors controlled by the exhumation of granite domes in the footwall to NNW striking extensional shear zones. The folding which the late basins unconformably overlay may have formed during extension. Further work is required to examine is this hypothesis holds true for every case not just around the Lawlers Anticline.
The N-S tectonic grain in the Eastern Yilgarn is a function of D2 and D5 dextral transpression which has dissected the NNW-trending extensional architecture.
D2 and D3 are spatially inversely related, i.e. where D2 is present D3 is absent and where D3 is present D2 is absent. This poses the question as to the significance or pervasiveness of the D2 contractional deformation.
P-T dihedra work has resolved D2 and D5, B1B palaeostress to be predominantly ENE- to NE-striking.
Contractional deformation is predominantly associated with strike-slip movement on N- to NNW-striking faults as opposed to thrusts.
This study has recognised a N-S to NW-SE oriented low-strain contractional D4 deformation event. This deformation is typically expresses as either sinistral N- to NNW striking faults or E-W striking N- and S-directed thrusts.
Few events have the structural style and intensity necessary for significant crustal thickening.
This study recognised that gold is present in extensional structures although the majority of Au deposits lay in contractional structures.
Gold deposits located in ductile shear zones are typically localised in the highest strain regions of the shear zone typically located at its centre. These high strain areas are typically marked by the presence of shear related foliation boudinage.

Tags: AU-WA, Earth Sciences, GA Publication, Published_External, Record, mineral deposits, pmd*CRC, structural geology
Organization: Geoscience Australia Data