⁴⁰Ar/³⁹Ar geochronology reveals rapid change from plume‐assisted to stress‐dependent volcanism in the Newer Volcanic Province, SE Australia

Abstract

Here we present 40Ar/39Ar ages of volcanic features in the Cenozoic intraplate Newer Volcanic Province in southeast Australia. The <5 Ma volcanic products in the Newer Volcanic Province can be subdivided into tholeiitic, valley‐filling Newer Plains basalts, and alkaline scoria cones, lava shields, and maars of the Newer Cones series. Plateau ages range from 3.76 ± 0.01 to 4.32 ± 0.03 Ma (2σ; all sources of uncertainties included) for the Newer Plains series, with production rates of volcanism decreasing post 4 Ma. We suggest that magmatism is related to the complex interplay of magma upwelling due to edge‐driven convection and the Cosgrove track mantle plume located in the northeast of the province at 6.5–5 Ma. Plateau ages range from 1290 ± 20 to 41.1 ± 2.2 ka (2σ) for the Newer Cones series, with a diffuse age progression in the onset of volcanism for these features from east to west. Analyses of the distribution and geomorphology of these volcanic features indicates a strong control of basement faults on volcanism, reflected in alignment of volcanic features along Paleozoic north‐south oriented basement faults in the east and Cretaceous northwest‐southeast oriented extensional features in the west. This age progression can be explained by a westerly migration of stress derived from the left‐lateral strike‐slip Tasman Fracture Zone. This suggests that the general mechanism of volcanism changed from upwelling due to plume‐assisted edge‐driven convection prior to ∼4 Ma to stress‐dependent upwelling at around 1.3 Ma.

The mechanisms underpinning Cenozoic intraplate volcanism in eastern Australia: Insights from seismic tomography and geodynamic modeling

“…Furthermore, a similar mechanism has been postulated to explain the Canary volcanic province off the coast of NW Africa [ Geldmacher et al , ]: here edge drive convection caused by a change in thickness, from the NW African Craton to oceanic lithosphere, is believed to interact with the Canary mantle plume to produce surface volcanism. Our EDC‐SDU‐plume hypothesis is also consistent with several other recent observations of the NVP [ Oostingh et al , ], including (i) the largest concentration of volcanic centers occurring close to the eastern margin (nearest to the Cosgrove track), (ii) a decrease in volcanic production rates after 4 Ma (waning influence of passing plume), and (iii) an overall east‐west (older‐younger) age progression in the volcanism. The latter observation could potentially be explained by dominantly westward mantle flow beneath the NVP, with our model predicting a westward velocity of the order of 2 cm/yr (see Figure c).…”

40Ar/39Ar ages and geological significance of Neoproterozoic–Cambrian mafic rocks in the Aksu–Wushi area, NW Tarim Craton

“…The trapped ratio calculated using the inverse isochron is 295.8 ± 1.3, slightly below atmospheric value. We used the 40 Ar/ 36 Ar intercept ratio measured by the isochron to calculate a mini‐plateau age of 521.0 ± 2.1 Ma (MSWD = 0.8; p = 0.67) following the approach described in Oostingh et al (). The K/Ca spectrum shows a classical pattern as expected for pyroxene, where the low temperature steps correspond to the release of a low‐Ca pyroxene (pigeonite) whereas the high temperature steps are associated with an abrupt depletion of low‐Ca pyroxene and the degassing Ca‐rich clinopyroxene (augite; Ware & Jourdan, ).…”

“…The 40 Ar/ 39 Ar isotope analyses were conducted using the step‐heating technique at the Western Australian Argon Isotope Facility at Curtin University. The analytical procedures followed the methodology of Jourdan et al () and Oostingh, Jourdan, Matchan, and Phillips (). Among all six samples, five of them (08A21‐1, 08A21‐2, 13A13‐1, 13A‐23, and 13A‐26) were analysed in static mode using MAP 215‐50 mass spectrometer, and the remaining one (pyroxene, 13A13‐2) was analysed on a more sensitive multi‐collector mass spectrometer ARGUS VI, of which mass discrimination (mean = 0.99386 ± 0.00050 per Dalton, atomic mass unit) was monitored by measuring air aliquots from an automated air pipette.…”

Timing of Seafloor Spreading Cessation at the Macquarie Ridge Complex (SW Pacific) and Implications for Upper Mantle Heterogeneity

“…Two statistically robust hornblende (MQ17‐08) and glass (MQ17‐09) 40 Ar/ 39 Ar plateau ages of 10.34 ± 0.30 Ma and 10.00 ± 0.17 Ma, supported by two groundmass (MQ17‐07, −12) 40 Ar/ 39 Ar plateau ages of 10.1 ± 2.2 Ma and 10.2 ± 3.5 Ma are all indistinguishable within error ( n = 4; p = 0.27) and indicate that basalts on Macquarie Island formed at ∼10 Ma (Figures 1 and 3). Two 40 Ar/ 39 Ar plateau ages of 11–9 Ma from two samples showing obvious evidence of alteration were published previously (Duncan & Varne, 1988), but their accuracy within the reported uncertainties cannot be verified because of the lack of (i) reported/re‐calculable statistical parameters, such as MSWD and/or p (probability of fit) to test for data internal concordance as well as closed system behavior (e.g., absence of alteration; Baksi, 2007; Jourdan et al., 2012); (ii) isochron data, to test whether the trapped 40 Ar/ 36 Ar ratio is atmospheric (i.e., 298.56; Lee et al., 2006) and if not, to calculate the age using the correct value (e.g., Oostingh et al., 2017); and (iii) neutron flux monitor standard information to which the ages were calculated relative to. However, these ages are consistent with crystallization at ∼10 Ma and with the ages presented in this study.…”

“…If the 40 Ar/ 36 Ar composition of the trapped argon measured for a statistically reliable 39 Ar/ 40 Ar– 36 Ar/ 40 Ar isochron ( p > 0.05) differs from an atmospheric value, then the measured ratio and its uncertainties are used in the age spectrum model age calculation, following the approach of Oostingh et al. (2017). Where robust mineral plateau ages are not available to constrain the age of the MRC seamount/island, relatively reliable ages that meet the following criteria are considered: (1) Mini‐plateau (with 50%–70% 39 Ar released) ages obtained from mineral separates; (2) Plateau (with > 70% 39 Ar released) ages obtained from groundmass separates.…”