Construction of an intraplate island volcano: The volcanic history of Heard Island

Abstract

Heard Island is a subantarctic volcanic island in the southern Indian Ocean and includes Australia’s only active volcano, Big Ben (2813 m high, 18 km diameter). The most recent eruption of lava at Big Ben occurred in November 2020. Heard Island is the southernmost subaerial exposure of the Kerguelen Plateau, a mainly submerged large igneous province formed as a result of the activity of the Kerguelen plume over the last 130 Myrs. Using published and unpublished data and reports, modern satellite images, and private and public rock collections, we produced a new geological map of Heard Island supplemented by new 40Ar/39Ar isotopic ages. The volcanoes on Heard Island have been constructed on a ~ 300-m-thick platform of 10–5-Myr-old submarine volcaniclastic rocks known as the Drygalski Formation, now exposed above sea level. The Drygalski Formation is underlain by the Oligocene Laurens Peninsula Limestones. Exposed Big Ben lavas are dominated by basanite, basalt, and trachybasalt compositions. Two Big Ben lavas were dated at 11.1 ± 1.1 ka and 23.9 ± 2.1 ka, expanding the range of ages previously reported for nonhistorical lavas from Big Ben (356 ± 51–33 ± 52 ka). Sector collapse occurred on Big Ben prior to the formation of the current eruptive centre, Mawson Peak (likely after 23 ± 16 ka). Laurens Peninsula lies to the west of Big Ben and consists of trachyte and basanite lavas and domes. Laurens Peninsula lavas have ages in the range 5.1 ± 3.5 to 76.6 ± 5.5 ka. Young basaltic cones are located around the coast of Heard Island and range in age from 1.9 ± 3.8 to 13.3 ± 4.1 ka. Heard Island is a relatively small volcanic edifice with a low average magma discharge rate (~0.0002 km3/yr) when compared with other intraplate basaltic volcanic islands.