Are the Taitao granites formed due to subduction of the Chile ridge? Ryo Anma a, ⁎, Richard Armstrong b , Yuji Orihashi d , Shin-ichi Ike c , Ki-Cheol Shin a , Yoshiaki Kon e , Tsuyoshi Komiya e , Tsutomu Ota f , Shin-ichi Kagashima g , Takazo Shibuya e , Shinji Yamamoto e , Eugenio E. Veloso h , Mark Fanning b , Francisco Hervé i a Graduate School of Life and Environmental Sciences, University of Tsukuba, Ten-no dai 1-1-1, Tsukuba, 305-8572 Japan b Research School of earth Sciences, Mills Road, The Australian National University, Canberra 0200, ACT, Australia c Institute of Geoscience, University of Tsukuba, Ten-no dai 1-1-1, Tsukuba, 305-8572 Japan d Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo,113-0032 Japan e Department of Earth and Planetary Sciences, Tokyo Institute of Technology, O-okayama 2-12-1, Meguro, Tokyo,152-8551 Japan f Institute for Study of the Earth's Interior, Okayama University at Misasa, Tottori, 682-0193 Japan g Department of Earth and Environmental Sciences, Yamagata University, Kojirakawa 1-4-12, Yamagata, 990-8560 Japan h Departamento de Ciencias Geológicas, Facultad de Ingeniería y Ciencias Geológicas, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile i Departamento de Geologia, Universidad de Chile, Casilla 13518, Correo 21, Santiago, Chile abstract article info Article history: Received 25 August 2008 Accepted 27 May 2009 Available online 18 June 2009 Keywords: Granite Ridge subduction Ophiolite U–Pb Taitao Chile triple junction The Taitao granites are distributed around the Late Miocene Taitao ophiolite (5.66±0.33 Ma to 5.19± 0.15 Ma) exposed at the western tip of the Taitao peninsula, southern Chile, ~50 km southeast from the present day Chile triple junction. In this paper, we report sensitive high mass-resolution ion microprobe (SHRIMP) U–Pb ages for the Taitao granites to elucidate the temporal relationship between the ophiolite and granites, and discuss the origin of the granitic melts. Five intrusive bodies of the Taitao granites have U–Pb ages ranging from 5.70 ± 0.25 Ma (Tres Montes pluton in southeast) to 3.92 ± 0.07 Ma (Cabo Raper pluton in southwest). The Estero Cono, Seno Hoppner and Bahia Barrientos intrusions that fringe eastern margin of the ophiolite have U–Pb ages ranging from 5.17±0.09 Ma to 4.88 ±0.3 Ma. Recycled zircon cores are common only in the Tres Montes pluton. Our data indicate that the generation of the granitic melts started in the Tres Montes area when a short segment of the Chile ridge system started to subduct ca. 6 Ma ago. This magmatism involved contamination with sediments/basement rocks. A part of the subducting ridge center was emplaced to form the present Taitao ophiolite at ~5.6 Ma. Generation of granitic melts continued as the spreading center of the same ridge segment subducted, due perhaps to partial melting of the ophiolite and/or oceanic crust enhanced by heat from upwelling mantle beneath the ridge. Granitic magmas with various compositions developed during subduction of the ridge. Emplacement of the ophiolite and formation of continental crust took place almost simultaneously. © 2009 Elsevier B.V. All rights reserved. 1. Introduction “There may be granites and granites.” Earth scientists after Read (1957) repeatedly confirmed the complexity involved in the genesis of granites. In this paper, we provide evidence for the generation of granitic magmas during ridge subduction. The presence of young granite stocks at the tip of the Taitao peninsula (Fig. 1), the westernmost promontory of the Chilean coast, was first reported by Mpodozis et al. (1985). Five intrusive bodies of tonalite, granodiorite and granite, collectively referred to in this paper as the Taitao granites, are distributed around the Taitao ophiolite (Forsythe et al., 1986) exposed ~50 km southwest from the present day Chile triple junction. The five bodies of the Taitao granites are: the Estero Cono pluton (EC in Fig. 2), the Seno Hoppner pluton (SH), the Bahia Barrientos pluton (BB), the Cabo Raper pluton (CR) and the Tres Montes pluton (TM) from north to south (Fig. 2). Fig. 1 shows that two oceanic plates, the Nazca plate in the north, and Antarctic plate in the south, separated by spreading ridges of the Chile ridge system, subduct beneath the South American plate with convergent rates of 9 cm/year and 2 cm/year, respectively (Cande et al., 1982; Cande and Leslie, 1986). Because the NNW-trending central axis of the Chile ridge is oblique to the NS-trending continental margin, three short spreading centers subducted repeatedly almost at the same latitude offshore the Taitao peninsula at around 6 Ma, 3 Ma and present (Cande and Leslie, 1986; Forsythe et al.,1986; Guivel et al., 1999). The Taitao ophiolite and granites are exposed where these ridge subduc- tion events had taken place (Fig. 1). They emplaced into Pre-Jurassic meta-sedimentary rocks of the Los Chonos complex (Fig. 2). The Taitao ophiolite consists of a complete sequence expected for oceanic lithosphere (Forsythe et al., 1986; Nelson et al., 1993; Bourgois Lithos 113 (2009) 246–258 ⁎ Corresponding author. Tel./fax: +81 29 853 4012. E-mail address: ranma@sakura.cc.tsukuba.ac.jp (R. Anma). 0024-4937/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.lithos.2009.05.018 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos