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The Central European, Tarim & Siberian LIPs, Late Palaeozoic orogeny, & Coeval Metallogeny

Hugo de Boorder

Institute of Earth Sciences, Utrecht University, Utrecht, The Netherlands & Centre for Russian and Central Asian Mineral Studies,
Natural History Museum, London, U.K., H.deBoorder@uu.nl

 

This webpage is a summary of: de Boorder, Hugo, The Central European, Tarim and Siberian Large Igneous Provinces, Late Palaeozoic orogeny and coeval metallogeny, Global Tectonics and Metallogeny, Published online November 2013

 

 

Orogens and LIPs in Europe and Central Asia

About the latest Carboniferous to early Permian, the Variscan and Tianshan orogens  of present Western Europe and southern Central Asia, respectively, degenerated to intracontinental peneplanes. The setting of the demise of the two orogens was dominated by translithospheric strike-slip deformation (Arthaud & Matte, 1977; Bard, 1997; Laurent-Charvet et al., 2003; Charvet et al., 2007; Charvet et al., 2011; Yakubchuk et al., 2005; De Jong et al., 2009; Wang et al., 2009), possibly in combination with collapse and delamination of the lithosphere (Ménard & Molnar, 1988; Costa & Rey, 1995; Diez Balda et al., 1995; Doblas et al., 1998; Echtler & Malavieille, 1990; Echtler & Chauvet, 1991–1992; Escuder Viruete et al., 1998; Fernández-Suárez et al., 2000; Gutiérrez-Alonso et al., 2011; Malavieille et al., 1990; Schulmann et al., 2002; Valle Aguado et al., 2005; Pirajno et al., 2008). In both cases, dissection and thinning of the lithosphere preceded and coincided with emplacement of mantle-derived magmas in the upper lithosphere and emanation at the surface. Where magmas stalled at the Moho, melting of the lower crust produced granitoid complexes, felsic lavas and ignimbrite, preserved in associated pull-apart basins. In western Europe the resulting magmatic complexes were defined as a Scattered Igneous Province by Doblas et al. (1998). Dobretsov et al. (2010) formally defined this as the Central European LIP (Figure 1). Isotope-geochronological age estimates, together with cross-cutting relations, suggest that the majority of late Palaeozoic ore deposits in western Europe and Central Asia, including tungsten-tin, tin-copper, gold-arsenic-tungsten, gold-antimony, gold-mercury with variable bismuth and tellurium, nickel-arsenic-cobalt formed during the transition from orogen to LIP (De Boorder, 2013).

 

Figure 1: Schematic distribution of the central European, Tarim and Siberian LIPs, modified after Nikishin et al. (2002).

 

The Siberian Large Igneous Province and its Palaezoic basement

In Western Siberia the largest known continental Siberian LIP was formed in the early and middle Triassic (e.g., Dobretsov, 1997; Dobretsov et al., 2010; Ivanov et al., 2013) in the wake of the demise of the Western Altaid orogen between the Siberian Craton and the Urals (Şengör & Natal'in, 1996; Allen et al., 2006). This Palaeozoic basement is largely covered by the West Siberian Basin. The complexes of the Siberian LIP are particularly widespread on the Siberian Craton and have also been recorded on the Palaeozoic basement in boreholes and seismic sections throughout the Basin. As in the Variscides and the Southern Tianshan, deep-reaching strike-slip deformation along the length of the West Siberian Basin dissected the Palaeozoic Altaid basement and caused the formation of the constituting rift basins as pull-apart structures (Allen et al., 2006). This deformation was associated with the strike-slip belt along the northeasterly striking Yenisey-Khatanga rift, cutting the northwestern edges of the Siberian Craton in the Noril’sk region.

Ore deposits

The complexes of the Siberian LIP are particularly known for giant Ni-Cu-(PGE) deposits. Yet, in the Noril’sk district, Spiridonov (2010) also found gold and sulphides and alloys of silver, bismuth, tellurium, antimony, cobalt and mercury.  Moreover, Borisenko et al. (2006) and Dobretsov et al. (2010) presented overviews of additional ore deposit types associated with the Siberian and other LIPs including hydrothermal Ni-Co-As, (±Ag, U, Au), Au-As, Ag-Sb, Au-Hg, and Sb-Hg. In Western Europe and in Central Asia, however, comparable mineral deposit types are traditionally viewed in association with the orogens. This is reflected in classifying adjectives as ‘orogenic’, ‘late-orogenic’, ‘post-orogenic’, ‘anorogenic’, ‘post-peak-metamorphic’, and ‘post-tectonic’. These similar ore deposit types and the assorted classifications of the orogenic settings illustrate the metallogenic dilemma of the transition from orogenic domain to LIP.  In view of their mantle sources in their association with the Siberian LIP, the mantle contribution to these late Palaeozoic hydrothermal ore deposits in the orogenic belts may have been more significant than previously thought, even casting doubt on an orogenic association at the time of mineralization other than a non-fortuitous localization within the orogens. Yet, a contribution by orogenic processes may have resided in the early modification of subcontinental mantle domains by subduction of oceanic lithosphere.

Temporal coincidence

In view of their repeated occurrence, the orogen-LIP sequences were probably not accidental and the above temporal coincidences may well result from the same processes. There is no fundamental difference between the three orogen-LIP occurrences and their differences represent only variations on a theme. The exorbitant volumes of the Siberian LIP, however, remain bewildering if they were produced with the same strike-slip mechanisms as observed in Western Europe and Central Asia. Yet, at an even larger scale the three events compare within the stress fields that governed the formation of the Pangaea supercontinent.

Pangaea context

In addition to the lithosphere-scale strike-slip deformation of the region between the Siberian and the Baltic Cratons, which may have brought about the juxtaposition of the two cratons along the British Columbia Transform (Sears, 2012), the peripheral extension of Pangaea proposed by Gutiérrez-Alonso et al. (2008) in the context of the closure of the Palaeotethys Ocean may have played an important, additional role in the production of the Siberian LIP. This proposal also provides for the strike-slip processes in the Southern Tianshan and the Variscides in a compressional stress field.

Upward or downward control of lips and ores?

The interaction of mantle and crust has become increasingly important in the understanding of ore-forming processes. This means that these processes are relevant to the issue of mantle plumes vs. the dynamics of the lithosphere plates. The large temperature gradient between core and crust is bound to sustain the hypotheses concerning active mantle plumes despite the weakness of direct evidence (Class, 2008; White, 2010; Rickers et al., 2012). Lithosphere delamination, however, has been suggested as the most plausible alternative (e.g., Begg et al., 2010; White & McKenzie, 1995). At the same time, this process has been dismissed in the same papers on the grounds that it could not possibly produce the observed large volumes of mantle melts, despite proposals to the contrary (e.g., King & Anderson, 1995; Puffer, 2001; Elkins-Tanton, 2005; Ivanov, 2007). The weakness of active plume proposals is further emerging with auxiliary proposals of gravitational instability or indeed delamination to explain the very magma volumes of the Siberian LIP (Saunders et al., 2007), the largest of the known LIPs. The intracontinental mantle melts were formed by decompression melting in the deeper lithosphere and the asthenosphere. The indicated mechanisms are large-scale extension in the lithosphere, and translithospheric strike-slip deformation providing localized decompression and channels for  migration of magmas, fluids and metals and emplacement in the crust and emission at the surface. This possibly occurred in combination with gravitational collapse and delamination of the lithosphere. Active mantle plumes are not necessarily relevant.

References


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