Noble gases in the Finero phlogopite-peridotites, western Italian Alps Takuya Matsumoto a, * , Tomoaki Morishita b , Jun-ichi Matsuda a , Toshiyuki Fujioka a,1 , Masamichi Takebe c,2 , Koshi Yamamoto c , Shoji Arai b a Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan b Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192, Japan c Department of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Chikusa, Nagoya, 464-8602, Japan Received 21 January 2005; received in revised form 16 June 2005; accepted 3 July 2005 Available online 10 August 2005 Editor: K. Farley Abstract Here we report results from an investigation of noble gases in a specimen with layers of very fine-grained apatite and orthopyroxene from the Finero ultramafic complex, western Italian alps. We have also examined fresh olivine grains separated from phlogopite-harzburgites without an apatite layer. Fluid inclusions of these olivine separates appeared rich in radiogenic components such as 4 He, 21 Ne and 40 Ar, suggesting the derivation of fluids from a crust-like reservoir. Such a crust-like component also appeared to be contained in the samples with the apatite-opx layer, however, an additional isotopically distinct component is necessary to explain progressive increases in 3 He concentration and decreases in 40 Ar/ 36 Ar ratios observed approaching the apatite-rich layer. High 3 He contents and low 40 Ar/ 36 Ar ratios are consistent with the signature expected for slab-derived metasomatic fluids. There is a clear mixing trend defined in a 3 He/ 36 Ar vs. 40 Ar/ 36 Ar diagram with crustal and slab-derived fluids as end-member compositions, suggesting that the complex was metasomatised by fluids derived from geochemically distinct regions and distinct geotectonic settings. The parent melt or fluids responsible for the formation of the apatite-rich layer should be derived from the slab-derived component, which is consistent with the notion that the Finero mantle was once in the mantle wedge. An in situ component produced in the previously 0012-821X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2005.07.005 * Corresponding author. Tel./fax: +81 6 6850 5541. E-mail addresses: matsumoto@ess.sci.osaka-u.ac.jp (T. Matsumoto), moripta@kenroku.kanazawa-u.ac.jp (T. Morishita), matsuda@ess.sci.osaka-u.ac.jp (J. Matsuda), toshiyuki.fujioka@anu.edu.au (T. Fujioka), takebe@matsue-ct.jp (M. Takebe), hamchans@nagoya-u.jp (K. Yamamoto), ultrasa@kenroku.kanazawa-u.ac.jp (S. Arai). 1 Current address: Research School of Earth Science, The Australian National University, Canberra, ACT0200, Australia. 2 Current address: Department of Sciences, Matsue National College of Technology, 14-4, Nishi-ikuma-cho, Matsue, Shimane, 690-8518, Japan. Earth and Planetary Science Letters 238 (2005) 130 – 145 www.elsevier.com/locate/epsl