Stromatolite research in the Shark Bay World Heritage Area (original) (raw)

2014, eSpace (Curtin University)

The southern New England Orogen (NEO) in eastern Australia is characterized by tight curvatures (oroclines), but the exact geometry of the oroclines and their kinematic evolution are controversial. Here we present new data on the anisotropy of magnetic susceptibility (AMS), which provide a petrofabric proxy for the finite strain associated with the oroclines. We focus on a series of preoroclinal Devonian-Carboniferous fore-arc basin rocks, which are aligned parallel to the oroclinal structure, and by examining structural domains, we test whether or not the magnetic fabric is consistent with the strain axes. AMS data show a first-order consistency with the shape of the oroclines, characterized, in most of structural domains, by subparallelism between magnetic lineations, "structural axis" and bedding. With the exception of the Gresford and west Hastings domains, our results are relatively consistent with the existence of the Manning and Nambucca (Hastings) Oroclines. Reconstruction of magnetic lineations to a prerotation (i.e., prelate Carboniferous) stage, considering available paleomagnetic results, yields a consistent and rather rectilinear NE-SW predeformation fore-arc basin. This supports the validity of AMS as a strain proxy in complex orogens, such as the NEO. In the Hastings Block, magnetic lineations are suborthogonal to bedding, possibly indicating a different deformational history with respect to the rest of the NEO. 1. Introduction The formation of curved orogenic belts (oroclines) and associated vertical-axis block rotations is commonly attributed to overriding-plate deformation in convergent margins [Rosenbaum and Lister, 2004; Cifelli et al., 2007; Capitanio et al., 2011a; Rosenbaum, 2014]. Oroclines have traditionally been defined as originally near-linear orogenic belts, which were subsequently subjected to bending [Carey, 1955]. Numerous studies have addressed the possible mechanisms associated with oroclinal bending [