Abstract
AbstractSpatio‐temporal changes of upper mantle structure play a significant role in generating and maintaining surface topography. Although geophysical models of upper mantle structure have become increasingly refined, there is a paucity of geologic constraints with respect to its present‐day state and temporal evolution. Cenozoic intraplate volcanic rocks that crop out across eastern Australia provide a significant opportunity to quantify mantle conditions at the time of emplacement and to independently validate geophysical estimates. This volcanic activity is divided into two categories: age‐progressive provinces that are generated by the sub‐plate passage of mantle plumes and age‐independent provinces that could be generated by convective upwelling at lithospheric steps. In this study, we acquired and analyzed 78 samples from both types of provinces across Queensland. These samples were incorporated into a comprehensive database of Australian Cenozoic volcanism assembled from legacy analyses. We use geochemical modeling techniques to estimate mantle temperature and lithospheric thickness beneath each province. Our results suggest that melting occurred at depths ≤80 km across eastern Australia. Prior to, or coincident with, onset of volcanism, lithospheric thinning as well as dynamic support from shallow convective processes could have triggered uplift of the Eastern Highlands. Mantle temperatures are inferred to be ∼50–100°C hotter beneath age‐progressive provinces that demarcate passage of the Cosgrove mantle plume than beneath age‐independent provinces. Even though this plume initiated as one of the hottest recorded during Cenozoic times, it appears to have thermally waned with time. These results are consistent with xenolith thermobarometric and geophysical studies.
Highlights
Spatial and temporal changes to the thermal structure of the upper mantle beneath Australia exert a primary control on the distribution of mineral deposits, geothermal heatflow, dynamic topography, relative sea-level fluctuations, and clastic sedimentary flux onto adjacent continental margins (e.g., Czarnota et al, 2013, 2014; Hoggard et al, 2020; Müller et al, 2016; Salles et al, 2017; Sandiford, 2007)
We find that volcanic activity was initiated by wholesale emplacement of hot mantle beneath Eastern Australia, and that this event was coincident with uplift of the Eastern Highlands
Since eruptions have not been continuous throughout Cenozoic times, it is possible that minor variations of mantle temperature, lithospheric structure, mantle flow and/or asthenospheric composition act to modulate the melting process (Demidjuk et al, 2007; Mather et al, 2020; Rawlinson et al, 2017)
Summary
Spatial and temporal changes to the thermal structure of the upper mantle beneath Australia exert a primary control on the distribution of mineral deposits, geothermal heatflow, dynamic topography, relative sea-level fluctuations, and clastic sedimentary flux onto adjacent continental margins (e.g., Czarnota et al, 2013, 2014; Hoggard et al, 2020; Müller et al, 2016; Salles et al, 2017; Sandiford, 2007) In this region, existing models of this thermal structure rely upon either xenolith thermobarometry, seismic tomographic imaging, or some combination of both (e.g., Davies & Rawlinson, 2014; Fishwick & Rawlinson, 2012; Hoggard et al, 2020; Kennett et al, 2013; O'Reilly & Griffin, 1985). Lava fields are defined as age-independent volcanic provinces, which consist exclusively of mafic material (Johnson, 1989; Wellman & McDougall, 1974) This age-independent activity does not obviously coincide with the passage of mantle plumes beneath the plate. We discuss how observed mantle temperature and lithospheric thickness variations contributed to the formation of the Eastern Highlands during Late Cretaceous and Cenozoic times
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