Plutonic processes in transitional oceanic plateau crust:structure, age and emplacement of the South Rallier du Baty laccolith, Kerguelen Islands

• Published in: Terra Nova
• Main Authors: Ponthus, Léandre, de Saint Blanquat, Michel, Guillaume, Damien, Le Romancer, Marc, Pearson, Norman, O'Reilly, Suzanne, Grégoire, Michel
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2020
• Subjects: alkaline magmatism; Kerguelen; oceanic plateau; pluton emplacement; syenite intrusion; Kerguelen Islands; Rallier du Baty
• Online Access: https://researchers.mq.edu.au/en/publications/04ae17ae-cb27-4422-becc-28704d0574fd; https://doi.org/10.1111/ter.12471; http://www.scopus.com/inward/record.url?scp=85086445569&partnerID=8YFLogxK

The syenitic rocks of South Rallier du Baty Intrusive Complex (SRBIC) represent intrusions into the oceanic plateau basalts of the south-western Kerguelen Islands. The SRBIC was previously interpreted as a typical ring complex due to magma emplacement with cauldron subsidence. Our new structural and geochronological data reveal that it is a laccolith built between 11.6 and 7.9 Ma by successive injections of magma sheets around the crust–mantle boundary, with an average injection rate between 0.8 and 1.4 × 10 −4 km 3 /year. These results establish strong similarities between the SRBIC, the only recorded example of a felsic laccolith in an oceanic intraplate setting, and many continental plutons emplaced in various geodynamic setting. The SRBIC thus has the characteristics of a continental plutonic complex emplaced in an oceanic plateau crust. We postulate the critical parameter relevant to causing such similarities and plutonic magmatism is crustal thickness.