Regional correlation of Mesoproterozoic structures and deformational events in the Albany–Fraser orogen, Western Australia

Abstract

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 (D 1) 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 (D 2) produced a subvertical, east-northeast-striking 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 (D 3) 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 D 2 structures, the D 3 structures may represent deformation in a dextral transpressive setting. D 4 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.