Geodynamic evolution of the Eastern Goldfields Superterrane: New insights for the development of Neoarchaean crust
|Location||International Geological Congress,oslo 2008|
|Author||Czarnota, Karol; Blewett, Richard; Champion, David; Henson, Paul|
|Holding Date||11 October 2008|
Mineral deposits are the products of large-scale tectonic processes. Over the last decade there have been significant advances in our understanding of Eastern Goldfields Superterrane in the Yilgarn Craton, WA (EGST): stratigraphy; magmatism; deformation; metamorphism; and timing of mineralisation, through various AMIRA and pmd*CRC projects. The integration of these disciplines, largely aided through advances in geochronology, has enabled a holistic view of the tectonic history of the EGST, thereby providing a geodynamic context for its mineralisation.
A significant advance has been the recognition of a ~2.81 Ga rifting event off the eastern margin of the Youanmi Terrane which set up the NNW trending architecture of the EGST, as expressed in the εNd model age map of the Yilgarn. This rifting event was then inverted during the subduction-dominated deposition of the 2.715-2.67 Ga EGST volcanic stratigraphy and emplacement of voluminous TTG magmatism, which resulted in magmatic thickening of the crust. Volcanism was terminated by a ~5 Ma pulse of ENE contraction triggering lithospheric and lower crustal delamination associated with mid-orogenic extension. The lack of ultra-high pressure and the presence of high geothermal gradients precludes this event from recording a continent-continent collision.
Mid-orogenic extension resulted in the introduction of metasomatised mantle melts (Mafic-granites and Syenites), deposition of late-stage siliciclastic basins (which record anticlockwise PTt paths) and the start of significant economic gold mineralisation in the EGST. The delamination associated with this event resulted in significant heat input into the base of the crust, which eventually led to the emplacement of the Low-Ca (crustal melt) granites and cratonisation of the EGST. Major Au mineralisation postdates delamination, associated with renewed compression-transpression and the development of steep sinistral and later dextral (syn Low-Ca granites) strike-slip faults.