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Distribution of Porphyry Copper Deposits Along the Western Tethyan

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Distribution of Porphyry Copper Deposits Along the Western Tethyan Distribution of porphyry copper deposits along the western Tethyan and Andean subduction zones: Insights from a paleotectonic approach Guillaume Bertrand, Laurent Guillou-Frottier, Christelle Loiselet To cite this version: Guillaume Bertrand, Laurent Guillou-Frottier, Christelle Loiselet. Distribution of porphyry copper deposits along the western Tethyan and Andean subduction zones: Insights from a paleotectonic approach. Ore Geology Reviews, Elsevier, 2014, 60, pp.174-190. 10.1016/j.oregeorev.2013.12.015. insu-00931971 HAL Id: insu-00931971 https://hal-insu.archives-ouvertes.fr/insu-00931971 Submitted on 13 Feb 2014 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. 1 Distribution of porphyry copper deposits along the western Tethyan and 2 Andean subduction zones: Insights from a paleotectonic approach 3 4 Guillaume BERTRANDa,b,c (*) , Laurent GUILLOU-FROTTIERa,b,c and Christelle LOISELET a,b,c 5 6 7 8 9 a BRGM, ISTO, UMR 7327, 45060 Orléans, France 10 b CNRS/INSU, ISTO, UMR 7327, 45071 Orléans 11 c Université d’Orléans, ISTO, UMR 7327, 45071 Orléans 12 13 14 15 16 17 18 19 20 21 22 Revised manuscript submitted to Ore Geology Reviews – December 20th, 2013 23 24 25 26 27 28 29 30 31 32 33 34 (*) Corresponding author: Guillaume BERTRAND, BRGM, ISTO, UMR 7327, Georesources Division, 3 av. C. Guillemin, 35 45060 Orléans Cedex 2, France; [email protected]; tel: +33 2 38 64 36 69 ; fax : +33 2 38 64 34 02 36 37 1 38 39 Abstract 40 41 Along the western Tethyan and Andean subduction zones the distribution of 42 Cretaceous and Cenozoic porphyry Cu deposits is not random and shows that they 43 were emplaced in distinct regional clusters. To understand the appearance of these 44 clusters within their geodynamical contexts and identify kinematic features which would 45 favor the genesis of porphyry-type ore bodies, we use a paleotectonic approach. Two 46 clusters in the Aegean-Balkan-Carpathian area, which were emplaced in upper 47 Cretaceous and Oligo-Miocene, and two others in the Andes, which were emplaced in 48 late Eocene and Miocene, are sufficiently well constrained to be studied in detail. It 49 appears that they are associated with a specific polyphased kinematic context related 50 to the convergence of tectonic plates. This context is characterized by: 1) a relatively 51 fast convergence rate shortly followed by 2) a drastic decrease of this rate. From these 52 observations, and assuming that the major part of plate convergence is accommodated 53 along subduction zones, we propose a two-phase geodynamic model favoring 54 emplacement of porphyry Cu deposits: 1) a high melt production in the mantle wedge, 55 followed by 2) an extensional regime (or at least relaxation of the compressional stress) 56 in the upper plate, promoting ascension of fertile magmas to the upper crust. Melt 57 production at depth and the following extensional regime, which would be related to 58 variations in convergence rate, are thus associated with variations in plate and trench 59 velocities, themselves being controlled by both plate kinematics at the surface and slab 60 dynamics in the upper mantle. In particular, along-strike folding behavior of the 61 subducting slab may strongly influence trench velocity changes and the location of 62 porphyry Cu deposits. Metallogenic data suggest that periods of slab retreat, which 63 would favor mineralization processes during ~40 Myrs, would be separated by barren 64 periods lasting ~10 to 20 Myrs, corresponding to shorter episodes of trench advance, 65 as observed in laboratory experiments. These results confirm the control of the 66 geodynamic context, and especially subduction dynamics, on the genesis of porphyry 67 Cu deposits. This study also shows that the paleotectonic approach is a promising tool 68 that could help identify geodynamic and tectonic criteria favoring the genesis of various 69 ore deposits. 70 71 Keywords: porphyry Cu deposits, paleotectonics, subduction, slab dynamics, Tethys, Andes 72 2 73 1 - Introduction 74 Assessing the most favorable areas for mineral prospecting has always been a major concern 75 for exploration geologists. The spatial approach of mineral resources predictivity focuses on the 76 geological context of ore deposits and on distinct parameters that control their distribution, from 77 district to continental scales, defined from geology, tectonic structures, geophysics and 78 geochemistry (e.g. Cassard et al., 2008; Carranza, 2011) but also geodynamics and 79 paleogeography (Scotese et al., 2001). It is an upstream phase of prospection campaigns, the goal 80 of which is to guide exploration strategy by predicting a priori the most favorable areas. 81 Porphyry Cu deposits were studied and described by many authors (see the reviews by e.g. 82 Seedorff et al., 2005, and Sillitoe, 2010). They are closely linked to their geodynamic surroundings 83 and are most often associated with calc-alkaline and adakitic magmatism in subduction zones (e.g. 84 Burnham, 1979; Cline and Bodnar, 1991; Thieblemont et al., 1997). These deposits result from a 85 dual melting process with: 1) an initial melting in the metasomatized mantle wedge, above the 86 subducting oceanic slab, which generates relatively oxidized and sulfur-rich mafic magmas with 87 incompatible chalcophile or siderophile elements (such as Cu or Au), and 2) a secondary melting 88 by injection of dykes and sills in the MASH (Melting, Assimilation, Storage, Homogeneization) zone 89 of the lower crust, yielding a crustal- and mantle-derived hybrid magma, with a high content of 90 volatile and metalliferous elements, and a density that is low enough to allow its upward migration 91 through the crust (Richards, 2003, 2011). They are generally associated with plutonic apexes of 92 granitic bodies (e.g. Burnham, 1979; Shinoara and Hedenquist, 1997; Cloos, 2001; Guillou-Frottier 93 and Burov, 2003) emplaced in the upper crust of the overriding plate (usually 1-4 km depth). Ore 94 grades are often low, but volumes can be huge, which can possibly make them very large deposits 95 (e.g. El Teniente, Chuquicamata or Rio Blanco-Los Bronces, all in Chile, with 78.6, 65.2 and 52.4 96 Mt of copper respectively; Jébrak and Marcoux, 2008). In addition, porphyry Cu deposits can yield 97 valuable new-technology metals, such as rhenium which is used in strong high-temperature 98 resistant alloys and often produced as by-product of molybdenum (e.g. Melfos et al., 2001; Berzina 99 et al., 2005). 100 For more than 40 years, authors have demonstrated relationships between tectonics and 101 mineralizing processes (e.g. Sillitoe, 1972, and compilation by Wright, 1977). The new paradigm of 102 plate tectonics, along with numerous metallogenic studies, allowed proposals of new genetic 103 models linking the lithosphere and mantle dynamics to the occurrence of deposits (e.g. Mitchell 104 and Garson, 1981; Sawkins, 1984; Barley et al., 1998; Tosdal and Richards, 2001; Kerrich et al., 105 2005; Bierlein et al., 2006). Although the close relationship between porphyry Cu deposits and 106 subduction zones is well established, there is, however, no consensus on which subduction 107 parameters primarily control the genesis of porphyry deposits. This is not surprising since, 108 following decades of seismic tomography and modeling studies, distinct modes of lithosphere 3 109 deformation have been suggested and the number of physical parameters controlling the 110 subduction process has continuously increased (slab density, mantle viscosity, slab to mantle 111 viscosity ratio, etc). The way the subducted lithosphere behaves beneath the overriding plate 112 appears to depend not only on these physical properties but also on plate features at the surface 113 (plate velocity, slab dip angle, amount of retrograde motion, varying ages along trench, etc). Deep 114 subducting lithosphere behavior is also controlled by plate motion and plate layout at the surface 115 (Yamato et al., 2009). One objective of this study, rather than promoting a single parameter as key 116 to ore formation, is to investigate what control a single selected process, subduction dynamics, has 117 on formation of porphyry Cu deposits. 118 In the Tethys belt it is widely accepted that the genesis of many types of mineralization is 119 closely linked to the geodynamic context (e.g. de Boorder et al., 1998; Lescuyer and Lips, 2004; 120 Lips, 2007). Neubauer et al. (2005) and Loiselet et al. (2010a) have shown the strong impact of the 121 geometry and dynamics of the eastern Mediterranean subduction on the distribution of porphyry 122 and epithermal deposits in the Carpathian and Aegean regions. Similarly, in the Andes numerous 123 studies have suggested specific relationships between subduction parameters and the occurrence 124 of porphyry Cu deposits: conditions of flat-slab subduction (Kay and Mpodozis, 2001; Billa et al., 125 2004), stress relaxation and transtensional structures (Richards et al., 2001). In particular, the 126 convergence configuration between the subducting and the overriding plates (velocities and 127 obliquity) would dictate how mineralized bodies emplace in the shallow crust (Tosdal and Richards, 128 2001). Rosenbaum et al. (2005) have suggested that subduction of topographic anomalies (ridges 129 and plateaus) triggered the formation of ore deposits. According to Cooke et al. (2005), 130 topographic and thermal anomalies on the subducting slab could trigger the formation of giant 131 porphyry deposits. All these studies clearly show that past subduction history and, in particular, the 132 convergence parameters have to be accounted for when genesis of porphyry Cu deposits is 133 studied.
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