Regional correlation of mesoproterozoic structures and deformational events in the Albany-Fraser orogen, Western Australia

Geologic mapping and meso- and microstructural analysis of a previously unstudied area in the western part of the Mesoproterozoic Albany-Fraser orogen, Western Australia, leads to a correlation of deformational events along the exposed length of the orogen. The earliest deformational event (D₁) accompanied granulite-facies metamorphism and is characterized by a locally preserved subhorizontal foliation and associated recumbent folds. This event is interpreted to record northwest-southeast contraction. The second event (D₂) produced a subvertical, east-northeaststriking foliation and variably plunging, upright folds. Northwest-vergent folds (toward 333°) and sparse kinematic indicators suggest southeast-up tectonic transport with a dextral component of movement. A third deformational event (D₃) is manifested by a conjugate set of mylonitic to cataclastic shear zones with a dominant, dextral set oriented at 105° and a subordinate, sinistral set oriented at 010°. The bisector of the average orientations for the shear zones is 325°, consistent with northwest-southeast shortening. Like the D₂ structures, the D₃ structures may represent deformation in a dextral transpressive setting. D₄ structures include two subvertical joint sets, one oriented at 355° and the other at 105°. All structures are similar in geometry and kinematics to structures near Albany, which have been constrained to 1190-1170 Ma (Precambrian Res., 59 (1992) 95), as well as structures east of Esperance that are associated with a major tectonothermal event at 1345-1260 Ma (Precambrian Res., 102 (2000) 155). Additional geochronological data, particularly from the Western Albany-Fraser orogen, are needed to resolve this apparent discrepancy. There is a near one-to-one correlation in lithology, structural style, metamorphic grade, kinematics, and possibly timing of deformational events between the Albany-Fraser orogen and the Bunger Hills of East Antarctica, supporting the previously suggested ties between these two areas. Marked dissimilarities, however, in model T_DM ages, U-Pb zircon dates, kinematics and timing of deformation, and timing of metamorphism between the Albany-Fraser orogen and the Oaxacan Complex of southern Mexico raise serious doubts regarding the viability of Rodinia reconstructions that juxtapose those two Mesoproterozoic terranes.