There is plenty of amphibole in the Siberian Traps

Alexei V. Ivanov

Institute of the Earth’s Crust, Siberian Branch, Russian Academy of Sciences, Irkutsk, Russia

aivanov@crust.irk.ru

Like most scientists, we have time to read only the titles of papers we cite (Vogt & Holden, 2007, p. 961).

Introduction

The Siberian Traps, like many other flood basalt provinces, is characterized by large volumes of low-Ti basalts and intrusions. All low-Ti rock types and some high-Ti rock types are depleted in high field strength elements, making them similar to subduction-related arc basalts (e.g., Puffer, 2001). The conventional explanation for this is crustal contamination of a primary “dry” sublithospheric melt (i.e., a plume, e.g., Lightfoot et al., 1993; Wooden et al., 1993; Reichow et al., 2005). As an alternative Puffer (2001) and Ivanov & Balyshev (2005) argued for a “wet” mantle source resembling the source of arc basalts. Puffer (2001) assumed a subcontinental lithospheric mantle source, modified by subduction processes that occurred long before Siberian Trap magmatism. Ivanov & Balyshev (2005) suggested a link between Permian subduction and this “wet” mantle source (for the latest references for this idea see Ivanov, 2007 and Ivanov et al., in press). The idea received various formal and informal critiques, including one particularly important criticism, which was mentioned by several people. That criticism amounts to:

“Wet magmas in arcs evolve through fractional crystallisation of amphibole-bearing assemblages. Why didn't amphibole crystallise from the Siberian magmas?”

The fact is, amphibole did crystallise from the Siberian Trap magmas. This information is widely available but has been overlooked (including in my own earlier publications). This webpage summarises the information on primary magmatic water-bearing minerals in the Siberian Traps.

Amphibole in arcs

Caveat: The Siberian Traps province contains mainly basaltic lavas and mafic intrusions (basalts sensu lato). More silica-rich rocks are present in minor amounts. In arc systems, basaltic magmas are important, but their volume is comparable to that of andesitic magmas. In this webpage I compare amphibole occurrences in the Siberian Traps and arcs, but my comparison is restricted to basaltic rocks. I thank several readers of an earlier version of this webpage for pointing out that amphibole occurs quite commonly in arc andesites.

Amphibole is quite a rare mineral in arcs worldwide (Bob Stern, personal communication). For example, in Kamchatka where continental arc formed above the subducting Pacific slab, amphibole-bearing rocks have often been found together with mica-bearing rocks in intrusions and volcanic bombs (which might also be fragmented subvolcanic intrusions). This amphibole and mica occur in fault systems perpendicular to the frontal arc – the Aleut-Kamchatka and Malko-Petropavlovsk fault systems. Amphibole and mica-bearing rocks are represented by moderate- and high-alkaline basic rocks (Perepelov et al., 1986; Melekestsev et al., 1991; Volynets et al., 1997). In the rear volcanic arc of the Kamchatka system, amphibole has only been found in high-K shoshonitic basalts (Melekestsev et al., 1991). Low-K intrusive and effusive rocks don’t contain amphibole in the Kamchatka arc system to my knowledge. It is worth mentioning that the Siberian Trap rocks are mainly low-K.

Amphibole and mica in the Siberian Traps

The most recent and comprehensive information on the petrography of rocks and geology in the Siberian Traps near Noril’sk was published by Ryabov et al. (2001a, 2001b). This work is particularly useful because it comprises a complete petrographic documentation (whole-rock and mineral microprobe chemical analyses plus colour photographs of thin sections) of all effusive formations and all intrusive complexes mapped in the Noril’sk region (Ryabov et al., 2001b). Table 1 is a compilation of this information for the intrusive complexes. There is no amphibole and mica in effusive rocks, which is not surprising since arc effusive rocks do not contain amphibole or mica either.

“Wet” assemblage (Table 1) signifies that the rock contains primary magmatic water-bearing minerals, either amphibole, biotite, phlogopite or combination of these minerals. “Dry” assemblage signifies the absence of these minerals in a rock. The quantity of the “dry” samples is an upper estimate, because many contain secondary minerals such as chlorite, which could have developed from primary magmatic mica.

Table 1: Water-bearing minerals in intrusive complexes of the Noril’sk region. Figures show number of described samples (compiled after Ryabov et al., 2001b).

Rock-types: B–basic, U–ultrabasic (picrites), U-B–transitional between basic and ultrabasic (e.g. picritic basalts), L–various types of lamprophyric rocks, GD–granodiorites.

Ergalakh is Late Permian complex by geologic data. Noril’sk is the Permian-Triassic boundary complex (Renne, 1995; Kamo et al., 2003). Daldykan and Avam are Middle Triassic complexes (Dalrymple et al., 1995). Bolgokhtokh is Late Triassic (Dalrymple et al., 1995; Kamo et al., 2003). Total duration of magmatism was about 22-26 Ma (see Ivanov et al., 2005; Ivanov, 2007).

It could be seen that that all the intrusive complexes except Ergalakh contain “wet” mineral assemblages (Table 1). Moreover, the “wet” mineral assemblages are dominant when compared with the “dry” mineral assemblages. Phlogopite is the most common mineral among primary magmatic water-bearing minerals. Amphibole (either alone or in combination with mica) was found in about 12% of samples of intrusive rocks listed by Ryabov et al. (2001b). An example of amphibole-bearing gabbro from the Upper-Talnakh type of Noril’sk complex is shown in Figure 1.

Figure 1: Thin section of leucocratic gabbro (sample KZ-1684/1986,0) from the Upper-Talnakh type intrusion. Crossed nicols. Margin of a large plagioclase prism dominates the image. Matrix is composed of plagioclase (white and grey), clinopyroxene (brown), amphibole (blue) and ilmenite within palagonite (black). Reproduced from Ryabov et al. (2001b, p. 241).

Beyond the Noril’sk region, mica was reported in meimechites from Maymecha-Kotuy province (Fedorenko & Czamanske, 1997), gabbros from the West Siberian Basin (Reichow et al., 2002) and dolerites of the Angara-Taseevskaya syncline (Ivanov, 2007; see Figure 2 for locations). Amphibole is probably present in the intrusive rocks of these regions too, but since it is rarer than mica, and nobody has yet searched for it. If a search were made, it might be found.

Figure 2: Siberian Traps (modified from Masaitis, 1983). WSB – West Siberian Basin, ATB – Angara-Taseevskaya syncline, N – Noril’sk, MK – Maymecha-Kotuy.

Summary

Primary magmatic minerals (amphibole and mica) are common in the intrusive rocks of the Noril’sk region. Primary magmatic mica has also been reported from other regions of the Siberian Traps. This supports “wet” source models for the Siberian Traps.

References

• Dalrymple, G.B., Czamanske, G.K., Fedorenko, V.A., Simonov, O.N., Lanphere, M.A., and Likhachev, A.P., 1995. A reconnaissance ⁴⁰Ar/³⁹Ar study of ore-bearing and related rocks, Siberian Russia. Geochim. Cosmochim. Acta. 59, 2071-2083.
• Fedorenko, V.I., Czamanske, G.K., 1997. Results of new filed and geochemical studies of the volcanic and intrusive rocks of the Maymecha-Kotuy area, Siberian flood-basalt province, Russia. Int. Geol. Rev. 39, 479-531.
• Ivanov, A.V., 2007. Evaluation of different models for the origin of the Siberian Traps. In: The origin of melting anomalies: Plates, plumes and planetary processes; (eds) Foulger G R and Jurdy D M (Princeton: Geological Society of America Special Paper), 669-692.
• Ivanov, A.V., Demonterova, E.I., Rasskazov, S.V., Yasnygina, T.A., in press. Low-Ti melts from the Southeastern Siberian Traps Large Igneous Province: Evidence for a water-rich mantle source? J. Earth System Sci.
• Ivanov, A.V., Balyshev, S.V., 2005. Mass flux across the lower-upper mantle boundary: vigorous, absent, or limited?; In: Plates, plumes and paradigms; (eds) Foulger G R et al (Princeton: Geological Society of America Special Paper 388) 327-346.
• Ivanov, A.V., Rasskazov, S.V., Feoktistov, G.D., He, H., Boven, A., 2005. ⁴⁰Ar/³⁹Ar dating of Usol’skii sill in the southeastern Siberian Traps Large Igneous Province: evidence for long-lived magmatism. Terra Nova 17, 203-208
• Kamo, S.L., Czamanske, G.K., Amelin, Yu., Fedorenko, V.A., Davis, D.W., Trofimov, V.R., 2003. Rapid eruption of Siberian flood-volcanic rocks and evidence for coincidence with the Permian-Triassic boundary and mass extinction at 251 Ma. Earth Planet. Sci. Lett. 214, 75-91.
• Lightfoot, P.C., Hawkesworth, C.J., Hergt, J., Naldrett, A.J., Gorbachev, N.S., Fedorenko, V.A., Doherty, W., 1993. Remobilisation of the continental lithosphere by a mantle plume: major-, trace-element, and Sr-, Nf-, and Pb-isotope evidence from picritic and tholeitic lavas of the Noril’sk District, Siberian Trap, Russia. Contrib. Mineral. Petrol. 114, 171-188.
• Masaitis, V.L., 1983. Permian and Triassic volcanism of Siberia. Zapiski Vserossiiskogo Mineralogicheskogo Obshestva 4, 412-425. (In Russian)
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• Perepelov, A.B., Bazanova, L.I., Florensky, I.V., Baluev, E.Yu., 1986. Geochemical evolution of the Late Cenozoic  magmatism of the southeastern flank of the Malko-Petropavlovsk zone of the cross-cut fault dislocations (Kamchatka). In: Geochemistry of magmatic rocks from different geodynamic settings (Novosibirsk: Nauka) 165-179. (In Russian)
• Puffer, J.H., 2001. Contrasting high-filed strength element content of continental flood basalts from plume versus reactivated-arc sources. Geology, 29, 675-678.
• Reichow, M.K., Saunders, A.D., White, R.V., Pringle, M.S., Al'mukhamedov, A.I., Medvedev, A.I., Kirda, N.P., 2002. ⁴⁰Ar/³⁹Ar dates from the West Siberian Basin: Siberian flood basalt province doubled. Science 296, 1846-1849.
• Reichow, M.K., Saunders, A.D., White, R.V., Al’mukhamedov, A.I., Medvedev, A.Ya., 2005. Geochemistry and petrogenesis ob basalts from the West Siberian Basin: an extension of the Permo-Triassic Traps, Russia. Lithos 79, 425-452.
• Renne, P.R., 1995. Excess ⁴⁰Ar in biotite and hornblende from the Norilsk 1 intrusion, Siberia: implication for the age of Siberian Traps. Earth Planet. Sci. Lett. 131, 165-176.
• Ryabov, V.V., Shevko, A.Ya., Gora, M.P., 2001a. Magmatic formations in Noril’sk region. Volume 1. Trapp petrology. (Novosibirsk: Nonparel Publishers) (In Russian).
• Ryabov, V.V., Shevko, A.Ya., Gora, M.P., 2001b. Magmatic formations in Noril’sk region. Volume 2. Atlas for magmatic rocks. (Novosibirsk: Nonparel Publishers) (In Russian).
• Vogt, P.R. & Holden, J.C. Plumacy reprise. In: Plates, plumes and planetary processes, Eds. Foulger G.R. and Jurdy D.M., Geological Society of America Special Paper 430, 955-974.
• Volynets, O.N., Ponomareva, V.V., Babansky, A.D., 1997. Magnesian basalts of Shiveluch andesite volcano, Kamchatka. Petrology 5, 183-196.
• Wooden, J.L., Czamanske, G.K., Fedorenko, V.A., Arndt, N.T., Chauvel, C., Bouse, R., M., King, B.-S.W., Knight, R.J., Siems, D.F., 1993. Isotopic and trace-element constraints on mantle and crustal contributions to characterization of Siberian continental flood basalts, Noril’sk area, Siberia. Geochim. Cosmochim. Acta 57, 3677-3704.