Temporal association of arc–continent collision, progressive magma contamination in arc volcanism and formation of gold-rich massive sulphide deposits on Wetar Island (Banda arc) Richard J. Herrington a, ⁎, Philip M. Scotney b,e , Stephen Roberts b , Adrian J. Boyce c , Darrell Harrison d a Department of Mineralogy, Natural History Museum, Cromwell Road, London, SW7 5BD, UK b School of Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, SO14 3ZH, UK c Isotope Geosciences Unit, SUERC, East Kilbride, Glasgow, G75 0QF, UK d School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Williamson Building, Oxford Road, Manchester, M13 9PL, UK e Waste Recycling Group Limited, Ground Floor West, 900 Pavilion Drive, Northampton Business Park, Northampton, NN4 7RG, UK abstract article info Article history: Received 29 January 2010 Received in revised form 12 October 2010 Accepted 19 October 2010 Available online 19 November 2010 Keywords: Arc–continent collision Magma contamination Massive sulphides Banda arc Whole-rock 87 Sr/ 86 Sr and δ 18 O analyses of volcanic rocks and 3 He/ 4 He analyses of sulphides and sulphates from mineralized rocks on Wetar, Indonesia indicate a variable contribution of assimilated crustal material or sediment sourced from the subducted Australian craton to the south. These new data support the idea of progressive source contamination with precisely dated events showing that Wetar Island hosts the most extreme examples of crustal assimilation in the region. The increased continental contamination occurs during the Pliocene (Zanclian to Piacenzian) during distinct magmatic events between 5 and 4 Ma, and at 2.4 Ma when 87 Sr/ 86 Sr ratios in unaltered lavas, with whole-rock δ 18 O values between 5.7 and 9.6‰, increase from 0.707484 to extreme radiogenic values of 0.711656. The earlier of these magmatic events is important in the generation of the hydrothermal systems responsible for the mineralization recorded on Wetar. Samples from this yield radiogenic 3 He/ 4 He ratios between 0.5 and 1.4 R/R A, similar to the data from volcanic rocks on nearby Romang. The later magmatic event coincides with the arrival of the Australian Continental Margin at the subduction zone along the Banda arc. Progressive incorporation of continental-sourced components into the source region below the Wetar Island edifice coincides with the formation of gold-rich volcanogenic massive sulphide deposits hosted within the contaminated volcanic pile. Crown Copyright © 2010 Published by Elsevier B.V. on behalf of International Association for Gondwana Research. All rights reserved. 1. Geological and tectonic setting 1.1. The Banda arcs The inner and outer Banda arcs, which form a continuation of the Sunda arc (see Fig. 1), record the complex interactions between the northward moving Australian plate, the Eurasian plate and a group of smaller SW Pacific plates which include the Philippine and Caroline Sea plates. Combinations of geological mapping, mantle tomography, (Hall and Spakman, 2002), seismic interpretation (Richardson and Blundell, 1996; Hafkenscheid et al., 2001; Londoño and Lorenzo, 2004) and palaeomagnetic data (Hinschberger et al., 2001; Honza and Fujioka, 2004 and references therein) have resulted in the production of various plate reconstructions for the eastern Indonesian region (Hall, 1996; 2002; Hall and Wilson, 2000; Villeneuve et al., 2010). Despite a consensus that the Banda suture marks an arc–continent collision boundary, there is ongoing discussion which suggests that the origin of mélanges and the timing and geometry of collision within this region is complex. One view is that different models may be applicable to different sections of the evolving orogen at different stages during the process of collision (Harris, 1991; 2006; Hall and Wilson, 2000; Kadarusman et al., 2010). The outer Banda arc (Fig. 1) is dominantly non-volcanic in origin, with Timor preserving an accretionary prism and ‘central collision complex’ which accreted onto the front of the Australian continental plate (Richardson and Blundell, 1996). A substantial part of the collision complex consists of a micro-continental fragment that originated some considerable distance to the north of the Australian continental margin, and which collided with the subduction zone (Barber, 1981; Audley-Charles, 1986a,b; Richardson and Blundell, 1996). Linthout et al. (1997) suggested that several micro-continental fragments are involved in the early arc–continent collision and ultramafic fragments occur from northern Timor along an 850 km chain to the reconstructed obduction site on Seram (Harris and Long, 2000; Roosmawati and Harris, 2009). Gondwana Research 19 (2011) 583–593 ⁎ Corresponding author. Tel.: + 44 2079425528; fax: + 44 2079426012. E-mail address: r.herrington@nhm.ac.uk (R.J. Herrington). 1342-937X/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. on behalf of International Association for Gondwana Research. All rights reserved. doi:10.1016/j.gr.2010.10.011 Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr