Unraveling the geometry of the New England oroclines (eastern Australia): Constraints from magnetic fabrics

Abstract

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., pre-late 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.

Subduction accretion and orocline development in modern and ancient settings: Implications of Japanese examples for development of the New England Orogen of eastern Australia

“…The position of the Hastings Block is puzzling; it is an offset and rotated portion of the forearc basin (Yan et al, 2016), that was possibly displaced during formation of the Manning Orocline (Fielding et al, 2016;White et al, 2016). Much emphasis has been placed on the development of these features in the recent literature with tectonic interpretations (Cawood et al, 2011a, b;Shaanan et al, 2015a, b), descriptions of structural trends Li et al, 2012;White et al, 2016), considerations of timing Shaanan et al, 2015b), and documentation of palaeomagnetic data (Aubourg et al, 2004;Mochales et al, 2014;Shaanan et al, 2015a). Some authors have queried the existence of these oroclines (Buckman et al, 2015) and others have challenged the southern Manning Orocline (Offler et al, 2015).…”

“…This paper examines the relationship between subduction accretion processes and the initiation of oroclines based on the Texas and Coffs Harbour oroclines of the southern New England Orogen ( Fig. 3) Mochales et al, 2014;Shaanan et al, 2014) using analogies from the more thoroughly documented accretionary units of southwest Japan and modern subduction accretion processes in the Nankai Trough ( Fig. 4) (Isozaki et al, 1990(Isozaki et al, , 2010Underwood and Moore, 2012).…”

Orocline‐driven transtensional basins: Insights from the Lower Permian Manning Basin (eastern Australia)

“…Previous studies on the oroclinal structure were mainly focused on deformation in the older tectonostratigraphic units, such as the belt of early Paleozoic serpentinites [Korsch and Harrington, 1987] Tectonics 10.1002/2015TC004021 Roberts, 2012;Mochales et al, 2014]. Nonetheless, the question whether the Manning Orocline exists has remained controversial [Lennox et al, 2013;Li and Rosenbaum, 2015;Offler et al, 2015].…”

“…The southern New England Orogen (Figure 1) is characterized by several tight oroclines that developed during the Early Permian Shaanan et al, 2015b]. Many recent studies have focused on the geometry of the oroclines [Glen and Roberts, 2012;Rosenbaum, 2012;Mochales et al, 2014], the timing of oroclinal bending [Offler and Foster, 2008;Cawood et al, 2011;Rosenbaum et al, 2012;Shaanan et al, 2014], and the possible geodynamic processes responsible for orocline formation Shaanan et al, 2015a]. Nonetheless, the structure and tectonic origin of the southernmost part of the oroclinal structure (Manning Orocline; Figure 1b) has remained controversial [e.g., Lennox et al, 2013;Li and Rosenbaum, 2015;Offler et al, 2015].…”

The geometry, kinematics, and reactivation history of major fault systems in eastern Australia: implications for deformation phases from the Permian to Cenozoic

“…The shape of the orocline is recognised by the curvature of structural fabrics (Korsch, 1981;Fergusson, 1982;Lennox and Flood, 1997;Li et al, 2012a), the pattern of paleomagnetic fabrics (Aubourg et al, 2004;Mochales et al, 2014), the repetition of forearc units on both limbs of the orocline (Hoy et al, 2014), and the curved shape of magnetic anomalies in gridded aeromagnetic data (Cawood et al, 2011b;Glen and Roberts, 2012) (Figure 2.1b). Harbour geological maps (Gilligan et al, 1992;Henley et al, 2001)), showing the axial surface foliations (S1) and primary beddings (S0) (see Figure 2.1a for location).…”