Quantifying Neogene plate-boundary controlled uplift and deformation of the southern Australian margin

Abstract

Parts of the Australian continent, including the Otway Basin of the southern Australian margin, exhibit unusually high levels of neotectonic deformation for a so-called stable continental region. The onset of deformation in the Otway Basin is marked by a regional Miocene-Pliocene unconformity and inversion and exhumation of the Cretaceous-Cenozoic basin fill by up to c. 1 km. While it is generally agreed that this deformation is controlled by a mildly compressional intraplate stress field generated by the interaction of distant plate-boundary forces, it is less clear whether the present-day record of deformation manifested by seismicity is representative of the longer-term geological record of deformation. We present estimates of strain rates in the eastern Otway Basin since 10 Ma based on seismic moment release, geological observations, exhumation measurements and structural restorations. Our results demonstrate significant temporal variation in bulk crustal strain rates, from a peak of c. 2 × 10 216 s 21 in the Miocene-Pliocene to c. 1.09 × 10 217 s 21 at the present day, and indicate that the observed exhumation can be accounted for solely by crustal shortening. The Miocene-Pliocene peak in tectonic activity, along with the orthogonal alignment of inverted post-Miocene structures to measured and predicted maximum horizontal stress orientations, validates the notion that plate-boundary forces are capable of generating mild but appreciable deformation and uplift within continental interiors.

Constraining South Atlantic growth with seafloor spreading data

“…Despite the variety of geological and geophysical data interpretations of the Cretaceous interior tectonics of South America and Africa (Figures and ), plate tectonic forward modeling that utilizes these interpretations consistently assumes that all of the continental plate‐linked deformation was focused on a small number of narrow fault‐bounded belts [e.g., Nürnberg and Müller , ; Moulin et al ., ; Heine et al ., ]. With estimates of the proportion of aseismic strain in broad deforming regions around ~30% [e.g., Tassone et al ., ], this assumption is clearly unsound. When working forward to plate reconstructions with this assumption, the general failure of the studies to agree on the locations and identities of accommodation zones, and therefore precise margin fits, should come as no surprise.…”

Cenozoic deformation in the Otway Basin, southern Australian margin: implications for the origin and nature of post‐breakup compression at rifted margins

“…In comparison with the Gippsland Basin, the timing and distribution of Cenozoic compressional deformation in the Otway Basin is far less well‐understood. The most significant compressional structures occur onshore in the eastern Otway Basin, in and around the Otway Ranges, and in the adjacent Torquay sub‐basin (Hill et al ., ; Dickinson et al ., ; Sandiford et al ., ; Clark et al ., ; Tassone et al ., , ). Similar to the Gippsland Basin, these structures comprise a combination of ~NE–SW trending high and low‐amplitude anticlines resulting from reactivation of syn‐rift normal faults.…”

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

“…This has lead Holford et al, (2011a) to suggest small incremental crustal shortening such that the apparent fault displacement remains normal, although they acknowledge that mantle-driven dynamic uplift (e.g., Sandiford and Quigley, 2009) cannot be discounted. Tassone et al (2012) show that a 5% shortening (Cooper and Hill, 1997) of a crustal column of approximately Figure 17. Crossplot of net exhumation magnitude ranges derived from both sonic transit time and thermal history data discussed in text.…”