Potassium isotope systematics in ocean island basalts from Madeira (East Atlantic) imply recycling of distinct portions of subducted oceanic crust

Subduction of oceanic lithosphere is widely considered as the primary cause of mantle heterogeneity as reflected by the chemical variation of ocean island basalts. However, the fate of deeply subducted oceanic lithosphere (i.e., remaining intact, getting segmented or completely destroyed and intermixed with ambient mantle) is still largely unknown. Based on trace element and radiogenic isotope systematics, it has been suggested that the geochemical difference of shield and post-erosional stage lavas of the volcanic Madeira archipelago reflects recycling of different portions of subducted lithosphere (e.g., Geldmacher and Hoernle, 2000, EPSL 183; Gurenko et al. 2013, Lithos 170-171). Accordingly, the geochemical composition of the shield stage magmas reflects altered upper oceanic crust, while the isotopically less enriched post-erosional magmas preferentially stem from less-modified, lower crustal/lithospheric mantle portions of the recycled slab. New, high precision potassium (δ41K of -0.75‰ to -0.50‰) and oxygen (δ18O of 4.90‰ to 5.21‰ in olivine phenocrysts) isotope data from Madeira lavas support this model. Subduction dehydration can cause large K isotope fractionation in the upper, seawater-altered parts of oceanic crust resulting in lighter K isotopes (lower δ41K) in ocean island basalts containing such material. The measured δ41K represents the lowest range among oceanic basalts published so far and overlaps with obducted eclogite, indicating the involvement of dehydrated oceanic crust. The correlation of light K with light O and enriched radiogenic isotope ratios supports the model that Madeira’s magma source contains different portions of subducted oceanic crust, which were preserved over millions of years without significant intermixing.

Details

Author

Haiyang Liu1, Ying-Yu Xue1, Jörg Geldmacher2, Uwe Wiechert3, Tinggen Yang4, Fanfan Tian4, Hai-Ou Gu5, He Sun5, Kun Wang6, Wei-Dong Sun4

Institutionen

1Center of Deep Sea Research, Institute of Oceanology, Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, P. R. China;Deep-Sea Multidisciplinary Research Center, Qingdao Pilot National Laboratory of Marine Science and Technology, Qingdao, P. R. China; 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany; 3Institute of Geological Sciences, Freie Universität Berlin, Berlin, Germany; 4Center of Deep Sea Research, Institute of Oceanology, Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, P. R. China;Deep-Sea Multidisciplinary Research Center, Qingdao Pilot National Laboratory of Marine Science and Technology, Qingdao, P. R. China;University of Chinese Academy of Sciences, Beijing, P.R. China; 5Ore Deposit and Exploration Center, Hefei University of Technology, Hefei, P. R. China; 6Department of Earth and Planetary Sciences, Washington University in St. Louis, St Louis, USA

Veranstaltung

GeoMinKöln 2022

Datum

2022

DOI

10.48380/bs6j-ez50

Geolocation

East Atlantic

zurück zur Übersicht