Tectonostratigraphic architecture and uplift history of the Eastern ...

Barrett WellBarrett Well is a series of gneissic outcrops located 10 km east-northeast of Edjudina station. Abiotite monzogranite dyke, dated at 2675±2 Ma (Swager and Nelson, 1997), overprints a gneissosityand leucosome sheets (sills). This is an important observation as it provides a minimum ageconstraint on gneissic fabrics across the region. Many of the gneisses have been dated at around2675 Ma (Cassidy et al., 2003), suggesting the Eastern Yilgarn underwent significantmetamorphism and melting at this time. The gneissosity is isoclinally folded about recumbent folds,and like other gneissic sites in this terrane, is possibly related to extension(?). These folds arerefolded and crenulated by upright north–trending folds, and overprinted by intense NNW– tonorth–trending dextral shear zones NNE–SSW contraction. A palaeostress switch to NW–SEcontraction resulted in sinistral reworking, transposition and boudinge. Minor dextral shearingduring E–W contraction records the last brittle–ductile movements (Blewett et al., 2004a).Hanns CampThe Hanns Camp Syenite is located around 5 km east of Laverton. It was emplaced at 2664±2(Cassidy et al., 2003), probably during regional extension. The syenite has a pronounced flat–lyingmylonitic foliation (see photograph to right) with a NNWto SSE movement direction. It is not clear whether thisfoliation developed during a contractional event (asinterpreted by Blewett et al., 2004a), or an extensional one(as favoured here). The mylonitic fabric is overprinted byspaced N– and NNW–trending sinistral shear zones andopen to tight upright folds that developed during NW–SEcontraction. Later minor dextral shears reflect a switch toNE–SW contraction, with the final event NE–trending kinkbands of the main penetrative foliation (Blewett et al.,2004a).Two Lids SoakThe main gneissic phase at Two Lids Soak, located 30 km NE of Yarrie, has been dated at 2672±2Ma (Swager and Nelson, 1997). The granite host was metamorphosed and a sheet–like gneissicfabric developed, probably during regional extension. Sheath–like isoclinal folds of the ‘S1’gneissic fabric are upright and plunge gently to the north and NNW. The folds are partly transposedby S–C mylonites and associated boundinage during sinistral shear under NW–SE contraction. Apalaeostress switch to NE–SW contraction resulted in the dextral reworking of the earlier fabricsand offset of dyke markers. Minor open folding and NW–trending sinistral faults likely reflect late–stage E–W contraction.19