Last 150 kyr volcanic activity on Mauritius island (Indian ocean) revealed by new Cassignol-Gillot unspiked K–Ar ages

We present new K–Ar ages extending the volcanic history of Mauritius Island towards the Holocene. Mauritius volcanism is associated with the activity of the Réunion hotspot, the magmatism of which produced the Deccan Traps across the Cretaceous-Tertiary (KT) boundary and continues up to present on Réunion Island. After shield building from before 8.9 Ma to 4.7 Ma, Mauritius Island underwent an unusual volcanic evolution involving two rejuvenation stages (3.5–1.9 Ma and <0.7 Ma) separated by a 1.2 Myr hiatus. The lower bound of the second rejuvenation stage being poorly constrained, it is not clear whether volcanism in this island has come to a rest. Given the occurrence of uneroded, and yet undated strombolian cones in Mauritius, it is important to better constrain the latest activity of this island in order to assess its volcanic hazard. The importance of dating the end of this stage is also enhanced by the fact that most of the surface of Mauritius is covered by the lavas of the rejuvenation stages, hence indicating a recent volcanic activity that needs to be better characterized for risk assessment.

We focus here on the last 150 ka interval which lacked precise age controls with only a few whole-rock and groundmass ⁴⁰Ar/³⁹Ar plateau ages available (Moore et al., 2011), ranging from 138 ± 29 to 40 ± 48 ka (uncertainties are 1 $\sigma$). Our six new Cassignol-Gillot unspiked K–Ar ages obtained on plagioclase or groundmass range from 113 ± 7 to 14 ± 3 ka, with much lower uncertainties than previous ages available. Our major and trace element analyses of the dated samples highlight the compositional homogeneity of the lavas erupted in the last rejuvenation stage, showing no geochemical evolution.

Our results, with ages as young as 14 ± 3 ka, demonstrate that near-Holocene volcanism is present in Mauritius Island, with no evidence of fading magmatism in the last 150 ka. Our second youngest age at 44 ± 5 ka implies that the latest activity occurred after a ∼30 kyr repose interval, with the consequence that Mauritius volcanism may resume at any time.