Introducción

The data for the Seidorechka Formation of northeast Russia used by this study comes from 41 major element analyses (Chashchin et al. 2008) and 13 major and trace element analyses (Mints et al. 1996) published in the literature. These samples were collected from komatiitic-rhyolitic Seidorechka Formation flows preserved in the extreme west of the Imandra-Varzuga rift zone of the Kola Peninsula (Fig. 3.18).

Unfortunately, precise sample location information is not provided by Chashchin et al. (2008) or Mints et al. (1996) and instead the two studies define a sample area between 67.48N, 33.50E and 67.90N, 32.90E which is centred on Imandra Lake, approximately 20 km northwest of the town of Apatity.

Little information regarding the petrography of the Seidorechka Formation is given in the literature: Chashchin et al. (2008) notes that metamorphism in the Imandra-Varzuga rift zone-hosted Seidorechka Formation rocks did not exceed lower greenschist facies while Puchtel et al. (1997), who studied equivalent rocks preserved

91 in the Vetreny Poyas belt (approximately 500 km southeast of the Imandra-Varzuga rift zone), states that alteration of the Seidorechka Formation is minimal and metamorphism likely did not exceed prehnite-pumpellyite facies.

Fig. 3.17. Photomicrographs of Viianki dykes modified from Vuolla and Huhma (2005). A) XPL view of cumulus texture in unaltered boninitic-noritic Viianki dyke; B) XPL view of typical cumulus texture and mineralogy of pristine gabbronoritic Viianki dyke; C) PPL view of unaltered tholeiitic Viianki dyke; D) XPL view of fine grained, inequigranular tholeiitic Viianki dyke with elongate plagioclase laths.

3.8. Summary

This chapter has presented how and from where the samples used in this study were collected (Table 3.1). In total, 424 individual samples will be discussed in the following chapters. Of these, 139 were collected by previous workers and were analysed prior to 1998 (Mints et al. 1996; Tomlinson 1996; Vogel et al. 1998;

Chashchin et al. 2008). The veracity of this older data is discussed in Chapter 4.

Petrographic study of the samples collected has shown that metamorphism of the Matachewan LIP suites rarely exceeds greenschist facies and preserves much of the primary mineralogy. In the East Bull Lake Suite (the one Matachewan LIP suite where metamorphism reaches amphibolite facies), metamorphism has only affected

A A A B B B

C C C D D D

92 the River Valley intrusion, while the other three East Bull Lake Suite intrusions studied have only been metamorphosed to greenschist facies. The relatively low metamorphic grade of the Matachewan LIP suites may mean that the geochemistry recorded by the rocks is, in many cases, close to primary (see Chapter 4).

Fig. 3.18. Geologic map of the Kola Peninsula, Russia showing the sample area (dashed rectangle) of Chashchin et al. (2008) and Mints et al. (1996). Map modified after Timmerman and Daly (1995).

Suite Samples Metamorph.

grade

Suite 35 Amphibolite  Amp+Qtz+Ser+Tlc

+Epi+Chl 50% -

Thessalon

Formation 79 Greenschist  Amp+Qtz+Bio+Cly

+Epi+Chl - 1

Blue Draw

Metagabbro 96 Greenschist  Srp+Tlc+Amp+Cal

+Bio+Qtz+Ser 0 – 40% -

Leopard dyke

swarm 20 Greenschist  Srp+Amp+Cly+Qtz

+Ser 40% - alteration assemblages and amounts of primary mineralogy preserved, on average, in each suite. Refs: 1 - Tomlinson (1996), 2 - Mints et al. (1996), 3 - Chashchin et al. (2008), 4 - Vogel et al. (1998). Mineral abbreviations: Qtz – Quartz, Amp – Amphibole, Ser – Sericite, Epi – Epidote, Srp – Serpentine, Cly – Clays, Bio – Biotite, Tlc – Talc, Chl – Chlorite.

93 4. RESULTS

4.1. Introduction

In the following sections, the whole-rock elemental and isotopic data for each of the magmatic suites studied in this project is presented with a summary given at the end (Table 4.2). Laboratory methods are detailed in Appendix B. All data can be found in Appendices C and D. In this study, total iron is referred to as Fe2O3(T)

. FeO^(EST) and Fe2O3(EST)

are calculated using Equation 4.1 and Mg-number (Mg#) is calculated using Equation 4.1 (Gill 2011). All the major element concentrations presented in this thesis have been recalculated on an anhydrous basis.

^{( ) ( ) ( ) ( )}

^{( )} ( ^{( ) ( )})

Equation 4.1

(

^{( )})

Equation 4.2

The major and trace element geochemistry of each suite of rocks will be described and the effects of secondary alteration and element mobility will be assessed by plotting each element against Zr. Elements which show good correlation with Zr are assumed to relatively immobile. Elements which show non-systematic scatter that cannot be explained by a petrogenetic mechanism are interpreted as having been remobilised and will not be used to assess the petrogenesis of the given suite.

Major and trace element concentrations are plotted against different fractionation indexes in order to assess the crystallisation history of the magmatic rocks. Major and trace element concentrations will also be used to classify the rocks in terms of rock type and volcanic series. Plots of trace element ratios, as well as chondrite- and Primitive Mantle- normalised diagrams are used to interpret the source composition and tectonic setting for each of the magmatic suites. REE data will also be used to estimate the extent of processes such as fractional crystallisation and crustal

94 contamination. Trace element anomalies on chondrite- or Primitive Mantle-normalised diagrams are manifested as significant enrichments or depletions in the normalised concentration of an element relative to the adjacent elements on the diagram. The size and nature of these anomalies can be important indicators of petrological processes (Briqueu et al. 1984) and in this study, are quantified using Equation 4.3 which uses Nb as an example. Isotopic data from some of the layered intrusions are also used to fingerprint the mantle source-regions important for the Ni-Cu-PGE mineralisation preserved within the Matachewan LIP.

( )

Equation 4.3

Note: chemical symbols refer to chondrite- or Primitive Mantle normalised abundances. Ti/Ti* and Eu/Eu* are calculated using the elements Gd and Sm