Unraveling Deep Structures Along A Rifted-Transform Margin: Insights From an Integrated Geophysical Study of The Northern Perth Basin

Abstract

SUMMARYThe Houtman Sub-basin lies adjacent to the Wallaby-Zenith Transform Margin, an under-explored region of Australia's continental margin located at the transition between the non-volcanic margin of the northern Perth Basin and volcanic province of the Wallaby Plateau. New seismic data acquired in the northern Houtman Sub-basin enables better understanding of the structural architecture and rifting development along a rifted-transform margin and provides the framework for a detailed integrated margin-scale basin evaluation. Profile modelling of potential field data, combined with 2D seismic, reveals complex along-strike and dip variability in the crustal thinning of the Houtman Sub-basin, with extreme thinning (<5 km thick) beneath the main Permian depocentre. Outboard of this hyperextended zone, along the basin margin, is a zone of volcanic SDRs. Five different structural domains have been mapped across the margin, reflecting abrupt change in crustal thinning and volcanic emplacement. These domains trend roughly NW-SE to NNW-SSW, parallel to major basement terrane boundaries. Magnetic modelling suggests that the nature of the basement underlying the proximal domain and the hyperextended domain in the central Houtman Sub-basin are different and that a major Proterozoic basement terrane boundary lies beneath the necking domain. The margin was structured during polyphase Permian and Late Jurassic rifting events which led to hyperextension prior to continental magmatic break-up and formation of oceanic crust during the Early Cretaceous. Our results suggest that the distribution of Early Permian rifts localised strain during Jurassic-Early Cretaceous rifting and strongly controlled the location and style of rifted margin during Valanginian continental break-up.

Structural characteristics of northern Houtman sub-basin, Perth Basin

“…New seismic data clearly images the Moho which is mapped between 30 and 35 km depth beneath the Bernier Platform and shallows to about 12 km on the western border of the Houtman Sub-basin (Figure 2c). Moho depth from seismic interpretation was independently confirmed using potential field modelling results ( Figure 3b, Sanchez et al, 2016). Crustal thickness varies considerably across the study area from over 30 km to less than 5 km (Figure 2d).…”

“…The model currently shows basement shallowing to less than 2 km on the Bernier Platform, however integrated interpretation of the seismic and potential field data suggests that a thicker (5 -6 km) pre-rift sedimentary succession may be present. This result, however is not taken into account in this study (Figures 3a and 3b) Sanchez et al, 2016;Borissova et al, 2017). New seismic data clearly images the Moho which is mapped between 30 and 35 km depth beneath the Bernier Platform and shallows to about 12 km on the western border of the Houtman Sub-basin (Figure 2c).…”

“…The Houtman sub-basin has experienced several phases of rifting, first in the early to mid-Permian and then again in the Jurassic-Lower Cretaceous which has resulted in highly extended to hyperextended crust (Sanchez et al, 2016;. The necking domain is characterised by a narrow zone of hyper extended crust (less than 5 km thick) at the eastern boundary of the Houtman Sub-basin where crustal thinning was focused during these successive extensional events (Figure3b).…”

“…Geological and geophysical modelling (Sanchez et al, 2016) integrated gravity magnetic and velocity data, as well as the initial interpretation of the GA-349 seismic data to improve the understanding of the crustal architecture and distribution and thickness of magmatic rocks in the Houtman Sub-basin. The results from the geophysical modelling were then used to further constrain the seismic interpretation in areas of poor quality data.…”

“…In the hyperextended domain (less than 5 km of crust) serpentinisation at the top of mantle may have occurred (Sanchez et al, 2016).…”