Recent plate re-organization at the Azores Triple Junction: Evidence from combined geochemical and geochronological data on Faial, S. Jorge and Terceira volcanic islands Anthony Hildenbrand a,b, ⁎, Dominique Weis c , Pedro Madureira d,e , Fernando Ornelas Marques f a Univ Paris-Sud, Laboratoire GEOPS, UMR8148, Orsay, F-91405, France b CNRS, Orsay, F-91405, France c Pacific Center for Isotope and Geochemical Research, Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, 2020-2207 Main Mall, Vancouver, BC V6T1Z4, Canada d Estrutura de Missão para a Extensão da Plataforma Continental, R. Costa Pinto, 165, 2770-047, Paço D'Arcos, Portugal e Centro de Geofísica de Évora and Dep. de Geociências da Univ. de Évora, R. Romão Ramalho, 59, 7000-671 Évora, Portugal f Universidade de Lisboa, Lisboa, Portugal abstract article info Article history: Received 30 March 2014 Accepted 14 September 2014 Available online xxxx Keywords: Azores Triple Junction Geochemistry K/Ar dating Melt production Mantle fertility Lithospheric deformation The study of volcanism near unstable plate triple junctions (TJs) offers a unique opportunity to investigate the interactions between mantle dynamics and lithospheric deformation in relation to short-term plate reconfigura- tion. From combined geochronological and geochemical analyses on Terceira, S. Jorge and Faial volcanic islands, we evidence contrasted modes of melt generation near the Azores Triple Junction during the last 1.3 Myr. The oldest lavas (N 800 ka) erupted along N150 elongated volcanic systems in S. Jorge and Faial have homogeneous isotopic compositions which partly overlap the compositional field of MORBs from the adjacent Mid-Atlantic Ridge (MAR). In contrast, the younger lavas (b 750 ka) erupted along the N110 main structural direction on the three islands are significantly more enriched in LILE and LREE, and have more variable and generally more radiogenic Sr, Pb, Nd and Hf isotopic ratios. Altogether, our data do not support the presence of an active mantle plume under the central Azores. Instead, they suggest that magma generation results from decompression melt- ing of a heterogeneously fertilized mantle (fossil plume?). The higher geochemical heterogeneity of the lavas erupted during the last 750 kyr likely reflects low-degree partial melting promoted by recent reactivation of pre-existing MAR Fracture Zones. We propose that the sub-aerial volcanism over the last 1.3 Myr in the central Azores records a sudden change in the conditions of melt generation, due to a major reconfiguration in regional deformation associated with the recent reorganization of the Eurasia–Nubia plate boundary. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The evolution of triple junctions (TJs) is a topic of major interest for plate tectonics and geodynamic reconstructions (e.g. Georgen and Lin, 2002; Georgen and Sankar, 2010). In oceanic settings, plate reconfigura- tion is generally inferred from available magnetic anomaly patterns of the seafloor. However, the mechanisms and the time over which a plate boundary changes its location remain poorly understood, especial- ly in areas where oceanic spreading occurs at very slow rates (e.g. Vogt and Jung, 2004). The study of volcanism occurring close to such TJs of- fers a unique alternative to overtake these limitations and to constrain the interactions between mantle dynamics, regional deformation, melt production and migration in relation to plate boundary reconfiguration over short geological periods (~ 1–2 Myr). The Azores volcanic province in the North Atlantic is a target of particular interest for such purpose. The Azores archipelago comprises nine volcanic islands built during the Quaternary (except the easternmost Santa Maria Island) over an oceanic plateau encompassing the present-day TJ between America, Eurasia and Nubia lithospheric plates (Fig. 1). The origin of the volca- nism in the Azores has long been attributed to plume–ridge interactions (e.g. Cannat et al., 1999; Lourenço et al., 1998; Luís et al., 1994; Schilling, 1975; Searle, 1980; Vogt and Jung, 2004; White et al., 1976). The Azores plateau, especially, is generally interpreted as a large igneous province (LIP), formed during a plume-derived episode of enhanced melt pro- duction centered on the Mid-Atlantic Ridge (MAR) between 20 and 7 Ma ago (e.g. Cannat et al., 1999; Gente et al., 2003). The plateau rough- ly has a triangular shape, and is delimited in the south by the prominent East Azores Fracture Zone (EAFZ), a presently inactive transform zone interpreted as the fossil eastern branch of the Azores Triple Junction (ATJ). During the last few Myr, the plate boundary between Eurasia and Nubia has jumped to the Terceira Rift (TR), considered an active hyper-slow spreading oceanic rift (e.g. Vogt and Jung, 2004). The Lithos 210–211 (2014) 27–39 ⁎ Corresponding author at: Univ Paris-Sud, Laboratoire GEOPS, UMR8148, Orsay, F- 91405, France. Tel.: +33 1 69 15 67 42; fax: +33 1 69 15 48 91. E-mail address: anthony.hildenbrand@u-psud.fr (A. Hildenbrand). http://dx.doi.org/10.1016/j.lithos.2014.09.009 0024-4937/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos