Tristan da Cunha : constraining eruptive behavior using the 40Ar/39Ar dating technique

The historically active volcanic ocean island of Tristan da Cunha exhibits a complex and dynamic history, with numerous, often compositionally distinct, parasitic centers punctuating the large edifi ce. To date, the temporal relationship between differing styles of activity has been unclear. We have applied high-precision 40Ar/39Ar dating to 15 carefully selected samples from Tristan da Cunha to ascertain spatio-temporal relationships of recent volcanism, explore episodicity, and establish if the most recent summit activity post-dated eruptions from parasitic centers lower on the fl anks. This has yielded a new suite of reliable Holocene ages, with the youngest dated deposit at 3 ± 1 ka (1σ). A recent fl ow at the summit was constrained to 5 ± 1 ka (1σ), confi rming that summit and parasitic activity on the volcano’s fl anks overlap in time. The oldest dated deposits were 118 ± 4 ka (1σ) from a parasitic cone in the southern sector, and 81 ± 10 ka (1σ) from one of the lowest sub-aerial shield-forming lava fl ows in the northern sector. Large-scale sector collapse is bracketed between 34 ± 1 ka and 26 ± 5 ka (1σ) via dating of the youngest headwall lava fl ow and oldest sub-aerial scarp-fi lling deposits. No systematic relationship between the new temporal framework, vent location, and eruptive compositions was found. Although magmatic fl ux has been inferred to be relatively low, Tristan da Cunha is capable of relatively frequent eruptions from a wide variety of vent locations across a broad range of compositions.