Geochemical characteristics of basalts related to incipient oceanization: The example from the Alpine‐Tethys OCTs

Méderic Amann (1) , Marc Ulrich (1) , Gianreto Manatschal (2) , Eric Pelt (3) , Marie‐eva Epin , Julia Autin (1) , Daniel Sauter (4)

1 IPGS - Institut de physique du globe de Strasbourg
2 IPGS-Dylbas - Dynamique de la lithosphère et des bassins sédimentaires (IPGS)
3 LHyGeS - Laboratoire d'Hydrologie et de Géochimie de Strasbourg
4 IPGS - Institut de physique du globe de Strasbourg

Basalts exposed in the Platta and Tasna nappes (SE Switzerland) derive from the Alpine-Tethys Ocean-Continent Transitions (OCT) and overlie SubContinental Lithospheric Mantle (SCLM). We show that the trace element signatures of these basalts differ from Mid-Ocean Ridge Basalts (MORB). Two types of basalts occur in the OCT: a type-1 showing a "garnet signature" that can be modeled by the partial melting of the SCLM in the spinel stability field and a type-2 characterized by an enrichment in incompatible elements that can be explained by the mixing between garnet-pyroxenite-derived melts and the melting of either a depleted MORB mantle or a refertilized SCLM. Based on geological and geochemical observations we propose that the basalts from the Alpine-Tethys OCTs result from a poly-phase magmatic system that carry an inherited SCLM signature. These basalts should therefore be referred to as OCT-basalts rather than as MOR-basalts.

Keywords: Ocean-Continent Transition; Alpine-Tethys; basalt; inheritance; subcontinental mantle; OCTbasalt

Domains: Petrography; Mineralogy; Geochemistry; Volcanology

Méderic Amann, Marc Ulrich, Gianreto Manatschal, Eric Pelt, Marie‐eva Epin, et al.. Geochemical characteristics of basalts related to incipient oceanization: The example from the Alpine‐Tethys OCTs. Terra Nova, 2019, 32 (1), pp.75-88. ⟨10.1111/ter.12438⟩. ⟨insu-02456734⟩