Abstract
Volcanic margins are a class of large igneous provinces (LIPs) characterized by rifting-derived basaltic magmatism. This is commonly attributed to extension-related lithospheric thinning, generating decompression melting. Another mechanism influencing magmatism on volcanic margins is mantle plume–induced lithospheric thinning. Unfortunately, it is difficult to differentiate between these mechanisms because they seem to take place almost contemporaneously. Whereas rifted volcanic margins produce linear denudation and magmatic addition patterns, mantle plumes or active upwellings would generate more subcircular domal patterns. Here, I use magmatic addition and denudation patterns to discriminate between these scenarios in a data set from the volcanic margin offshore NW Australia. Seismic and well data results suggest the presence of a domal component that is used to delineate the Late Jurassic Exmouth mantle plume. This upwelling was centered on a highly extended and subsided continental fragment bounded by the present-day subsea Sonne and Sonja Ridges and includes the Cuvier margin and Cape Range fracture zone. The region is characterized by ∼2.6 km of denudation and ∼500 m of tectonic uplift, with erosion products acting as source material for the Early Cretaceous Lower Barrow delta. Denudation analysis indicates that only ∼40% of the seismically detected magmatic underplate is melt related, with the effective underplate ∼4 km thick near the locus of uplift and decreasing in the outer regions. Tectonic subsidence analysis, seismic stratigraphy, and plate reconstruction suggest that the plume-induced domal uplift preceded magmatism and breakup. Plume activity was followed by a westward-propagating hotspot track, possibly terminating in Greater India (present Tibet).
Highlights
Volcanic margins are rifted margins characterized by massive igneous activity
The findings suggest the presence of a mantle plume before margin breakup in the NW Australian region
This paper proposes that a mantle plume event took place in the Exmouth region in the Late Jurassic, predating breakup and generating lithospheric thinning, magmatism, and tectonic uplift as delineated by isostatic denudation analysis
Summary
Volcanic margins are rifted margins characterized by massive igneous activity. These features have been commonly explained as a result of extension and decompression melting over a thermal mantle anomaly of 100–150 °C (e.g., White and McKenzie, 1989; White et al, 2008; Rooney et al, 2011), which is generally explained as plume induced (e.g., Courtillot et al, 1999; Montelli et al, 2004). Part of the flank uplift is transient, as a result of the thermal anomaly or plume temporarily elevating the rift margin above sea level and allowing initial flood basalts to flow downhill, before subsiding and forming seaward-dipping reflector series (e.g., White et al, 2008). These features are often difficult to unravel in outcrop studies where large flood basalt outpourings have obscured earlier vertical motions and erosion events.
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