Early recumbent fold hinge in the Bradleys Creek Metamorphic Complex, near Canberra, Australia
Titel:
Early recumbent fold hinge in the Bradleys Creek Metamorphic Complex, near Canberra, Australia
Auteur:
Carson, L. J. Rickard, M. J.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 45 (1998) nr. 4 pagina's 501-507
Jaar:
1998-08
Inhoud:
Early folding (F1) in the Ordovician turbidites of the Cullarin Horst Block has long been known from the mapped zones of upward- and downward-facing F2 folds northeast of Queanbeyan. However, no fold hinges or related cleavage were found and the sense of vergence was unknown. This paper reports the first discovery of a major F1 fold hinge in a low-pressure, moderate-temperature metamorphic complex in Bradleys Creek, southeast of Canberra. This occurrence forms the northern extent of the eastern metamorphic zone in the Lachlan Fold Belt. The earliest deformation is characterised by a flat-lying, stripy, spaced S1 cleavage across steep bedding over a distance of 1.5 km. This indicates a major fold hinge and sedimentary younging shows that the fold is an east-facing anticline. In the psammites, S1 is a spaced, stripy cleavage defined by a concentration of phyllosilicates; in the pelites, it is preserved mainly as inclusion trails within porphyroblasts. Inferred recumbent folding, without cleavage, affects low-grade Ordovician turbidites, but not Late Silurian rocks in the area. The development of S1 foliation is closely associated with the formation of the metamorphic complex. Post-D1 growth of porphyroblasts indicates that the S1 foliation developed prior to peak meta-morphism, and field relations show that the metamorphic complex formed before the intrusion of Late Silurian-Early Devonian granites and dykes. Simple overprinting relationships indicate peak meta-morphism in the mid-Silurian and constrain the timing of the D1 deformation to the Early Silurian, probably corresponding with the local Quidongan deformation that preceded extensive felsic volcanism. A second phase of metamorphism accompanied folding of Silurian rocks during the Middle Devonian.
Tijdschrift beschrijving