Abstract
AbstractContinental rifting is accommodated by the development of normal fault networks. Fault growth patterns control their related seismic hazards, and the tectonostratigraphic evolution and resource and CO2 storage potential of rifts. Our understanding of fault evolution is largely derived by observing the final geometry and displacement (D)‐length (L) characteristics of active and inactive fault arrays, and by subsequently inferring their kinematics. We can rarely determine how these geometric properties change through time, and how the growth of individual fault arrays relate to the temporal evolution of their host networks. Here we use 3D seismic reflection and borehole data from the Exmouth Plateau, NW Shelf, Australia to determine the growth of rift‐related, crustal‐scale fault arrays and networks over geological timescales (>106 Ma). The excellent‐quality seismic data allows us to reconstruct the entire Jurassic‐to‐Early Cretaceous fault network over a relatively large area (ca. 1,200 km2). We find that fault trace lengths were established early, within the first ca. 7.2 Myr of rifting, and that along‐strike migration of throw maxima towards the centre of individual fault arrays occurred after ca. 28.5 Myr of rifting. Faults located in stress shadows become inactive and appear under‐displaced relative to adjacent larger faults, onto which strain localises as rifting proceeds. This implies that the scatter frequently observed in D‐L plots can simply reflect fault growth and network maturity. We show that by studying complete rift‐related normal networks, rather than just individual fault arrays, we can better understand how faults grow and more generally how continental lithosphere deforms as it stretches.
Highlights
The formation of extensional basins is controlled by the development of normal faults
We find that fault trace lengths were established early, within the first ~7.2 Myr (8%) of rifting, and that along-strike migration of throw maxima towards the centre of individual fault systems occurred after ~28.5
We use depocentre mapping and fault displacement backstripping to reconstruct the geometry of the entire fault array at an earlier stage of rifting
Summary
The formation of extensional basins is controlled by the development of normal faults. There are even fewer attempts to determine the evolution of entire fault arrays at the rift scale (e.g. Claringbould et al, 2017) We suspect this may reflect the time-consuming effort required to manually interpret many seismically imaged normal faults, and to subsequently extract their related geometric properties (i.e. displacement, length). We use depocentre mapping (via the use of time-thickness maps known as isochrons) and fault displacement backstripping to reconstruct the geometry of the entire fault array at an earlier stage of rifting This allows us to determine the growth trajectory of individual fault segments and systems, which we compare to global D-L datasets (Figure 2). Our model provides an explanation for the long-recognised scatter observed in global D-L datasets and sheds light on how continental lithosphere stretches during early rifting (e.g. Cowie and Schultz, 1992; Cartwright et al, 1995; Kim and Sanderson, 2005; Rotevatn et al, 2019)
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