Highly siderophile element and Re-Os systematics of peridotite xenoliths and basalts from Isla Floreana, Galápagos

Hot spot volcanism may reflect both contributions from sublithospheric and lithospheric mantle sources. In addition to lithophile radiogenic isotopes, Re-Os isotopic data may aid in understanding the contributions from different sources. The Galápagos archipelago is the manifestation of a long-lived mantle plume. Its source reservoirs are well characterized in terms of lithophile radiogenic isotopes, major and trace elements. A distinctive feature of the Galápagos mantle source is the presence of a strongly incompatible element-depleted component that mixes in three directions with an EM1-like plume signature and a HIMU-like endmember expressed in lavas from Floreana. However, Re-Os-systematics of Galápagos, are limited by very few basalt samples. In this contribution, we present highly siderophile element (HSE) and Re-Os isotopic data of 19 ultramafic xenoliths and 2 basalts from Isla Floreana in the southern Galápagos Archipelago.

HSE patterns in the xenoliths reveal two distinct groups: some exhibit high Pd/Ir and Pt/Ir, similar to ultramafic cumulates from ophiolites, whereas other xenoliths display low Pd/Ir and Pt/Ir, consistent with typical mantle xenoliths. Measured ¹⁸⁷Os/¹⁸⁸Os vary between 0.1265 and 0.1372 and overlap with data on basalts from Isla Floreana (0.130 to 0.140) and Isla Fernandina (0.132) (Gibson et al. 2016, EPSL 449, 345-359), where the plume centre is currently located. Cumulate xenoliths and their 187/188 Os mostly reflect the slightly suprachondritic values of the lavas, while other xenoliths with lower 187/188 Os are of lithospheric origin.