Thermal weakening localizes intraplate deformation along the southern Australian continental margin

Localization of intraplate deformation through fluid-assisted faulting in the lower-crust: The Flinders Ranges, South Australia

“…Thermal weakening has been cited as the cause for stress concentration in many previous studies of the FRSZ (Célérier et al, 2005;Dyksterhuis and Müller, 2008;Holford et al, 2011), as well as for SCR paleorifts elsewhere (e.g. Liu and Zoback, 1997 for the Reelfoot Rift, though this was questioned by McKenna et al, 2007).…”

“…Reynolds et al (2003) estimate differential horizontal stress in the Flinders Ranges of 12.5 MPa, for which our stress ratio estimate of R = 0.5 would imply σ 1 − σ 3 = 50 MPa, and (Fig. 6B of Holford et al, 2011) suggests even smaller values. If the lower crust in the FRSZ is characterized by such small differential stresses, then the occurrence of earthquakes at mid-to-lower crustal depths would require pore fluid pressures much closer to lithostatic than indicated in Fig.…”

“…This mechanism has been proposed for the Flinders/Mt. Lofty Ranges region itself (Holford et al, 2011), and for the Reelfoot Rift (Liu andZoback, 1997) (see, however McKenna et al, 2007), and implies a shallow seismogenic zone and ductile lower crust.…”

“…For these reasons the Flinders Ranges have been the subject of many studies trying to understand why deformation of the Australian continent appears to be localized there, with explanations ranging from erosion-driven isostatic rebound (Lambeck et al, 1984), lithospheric flexure (Célérier et al, 2005), stress concentration due to change in lithospheric strength (Dyksterhuis and Müller, 2008), and thermal weakening (Holford et al, 2011). While all of these studies have remarked on the high seismicity, none of them have considered the information provided by earthquake data -spatial and depth distribution of hypocenters, arrival time anomalies, and focal mechanisms -in any detail.…”

Quantifying Cretaceous–Cenozoic exhumation in the Otway Basin, southeastern Australia, using sonic transit time data: Implications for conventional and unconventional hydrocarbon prospectivity

“…Furthermore, given the relationship between the orientations of Neogene structural features (approximately northeastsouthwest) with the measured Nelson et al, 2006) and plate scale-modeled (Reynolds et al, 2003) contemporary in-situ stress field (Figure 18), this suggests that plate boundary forces are capable of generating mild but appreciable deformation and uplift along passive margins (Hillis et al, 2008;Holford et al, 2011a). Because both mid-Cretaceous and Neogene exhumation is focused around the Otway Ranges-an Early Cretaceous depocenter-this implies that the Otway Ranges area is a long-term zone of weakness within the basin and/or crust, in which Holford et al (2011b) proposes the thermoradiogenic properties of the Lower Cretaceous rocks exerting a major control in the distribution of intraplate deformation.…”