Investigation of the Särna Alkaline Complex in Dalarna, Sweden

UNIVERSITY OF GOTHENBURG Department of Earth Sciences Geovetarcentrum/Earth Science Centre

Investigation of the

Särna alkaline complex

in Dalarna, Sweden

John Eliasson

ISSN 1400-3821 B1019 Master of Science (120 credits) thesis Göteborg 2018

Mailing address Address Telephone Geovetarcentrum Geovetarcentrum Geovetarcentrum 031-786 19 56 Göteborg University S 405 30 Göteborg Guldhedsgatan 5A S-405 30 Göteborg SWEDEN Table of Contents 1.0 Introduction ...... 3 1.1 Alkaline systems ...... 3 1.2 Regional geology ...... 5 1.3 Särna alkaline complex (SAC) ...... 6 1.4 Cancrinite ...... 7 2.0 Methodology ...... 8 2.1 Fieldwork ...... 8 2.2 Scanning electron microscope (SEM) ...... 9 2.3 LA-ICP-MS ...... 9 2.4 Raman spectroscopy ...... 10 3.0 Results ...... 11 3.1 Mineral and sample description ...... 11 3.1.1 Cancrinite (nepheline) syenites: fine grained samples ...... 11 3.1.2 Cancrinite (nepheline) syenites: coarser samples ...... 16 3.1.3 Other samples: the southeastern outcrop ...... 18 3.1.4 AS13-02: Tinguaite ...... 24 3.2 Major and minor chemistry ...... 25 3.2.1 Whole-rock analysis...... 25 3.2.2 Clinopyroxenes ...... 29 3.2.3 Titanite and Cancrinite ...... 32 3.3 87Rb–87Sr dating ...... 37 3.3.1 Cancrinite (nepheline) syenite: K-feldspar, titanite and cancrinite grains ...... 37 3.3.2 Tinguaite: Biotite grains with a forced initial ...... 38 3.3.3 Weighted mean age: Särnaite and Tinguaite ...... 39 4.0 Discussion ...... 40 Emplacement time of the SAC ...... 40 Cancrinite ...... 41 On the controls of oxygen fugacity ...... 41 Extreme MREE depletion ...... 43 Evolution of the system ...... 44 (1) Fractional crystallization of CPX (large Ca-Ti Tschermaks component) from a parent melt ... 44 (2) Potential silicate-carbonate immiscibility ...... 47 5.0 Conclusions ...... 50 6.0 Acknowledgements ...... 50 7.0 References ...... 51

1.0 Introduction Rocks with alkaline affinity tend to display an exotic minerology, which often contain high concentrations of rare earth elements (REE), thereby making them of economic importance. Additionally, alkaline complexes are rare. Only a handful of complexes have been found in Sweden and even fewer has been thoroughly investigated, thereby elevating the academic importance of Särna alkaline complex. These factors combined is why more studies are needed to get an understanding of how they form and develop.

Alkaline to peralkaline igneous rocks are typically found within intracontinental extensional settings, for instance this is well illustrated in the alkaline Illímaussaq intrusion in the Gardar province in South Greenland. However, they have also been observed within Oceanic Islands (Sørensen, 1992). Given the stable nature of the Baltic shield the scarcity of alkaline complexes in Sweden is understandable, but this is also a reason to study them. Why would they be found in a tectonically stable environment?

Sørensen (1992) further describes, to some extent, the pre-requisites needed to form rocks with alkaline affinities. Among others, the need of low degree of partial melting and crystallization in a fluid- or gas-rich magmatic system is crucial. The low degree of partial melting results in a silica deficiency and can be the start of potential alkalinity.

This study aims to further constrain the time of emplacement of the Särna alkaline complex (SAC) and further correlate the time of emplacement to coeval tectonic events on a regional scale in the Fennoscandian Shield. Furthermore, it sets out to contribute with additional insights into the magmatic evolution of the system, such as:

• What parent melt composition was needed to form the SAC? • What fluid phases appear to have been present during the formation of the SAC? • How is the oxygen fugacity in the melt affecting the mineralogy?

By attempting to answer questions such as these, this thesis aims to clarify some aspects of how and when the SAC formed. Additionally, by placing the SAC in a larger context it might provide new insights into how alkaline complexes can form and evolve.

1.1 Alkaline systems Rocks with a large ratio of alkalis (sodium and potassium) compared to silica or alumina are typically considered to be alkaline. This can for instance be syenites, which are found in the left corner of a QAPF diagram (Quartz, Alkali feldspar, Plagioclase, Feldspathoid (Foid) diagram). Syenites are compositionally very similar to granites but inherently have a quartz deficiency. This does not, however, make it alkaline. It does simplify the process of becoming alkaline because it inherently has one of the components necessary. Due to this specific composition, large alkali to silica and alumina ratio, alkaline rocks tend to adhere to an unusual mineralogy. Nepheline, for instance, is a commonly found mineral in alkaline rocks and can to some extent be seen an indicator mineral. Nepheline has a chemical formula of Na3K(Al4,Si4O16), or simplified (Na,K)AlSiO4 (Hålenius et al., 2018). It is quite evident that this stoichiometric structure is more suited for a system with lower silica concentrations than for instance albite (NaAlSi3O8). The sodium±potassium to alumina to silica ratios are 1:1:1 and 1:1:3 respectively, further illustrating this. Furthermore, pyroxenes such as aegirine are quite common in alkaline rocks, often crystallizing as elongated needles. It has a chemical formula of 3+ NaFe Si2O6 and is typically only formed in systems that have an abundance of sodium and where feldspars have used most of the alumina. The reason why high concentrations of sodium are needed for aegirine to form is that it can readily incorporate quite substantial amounts of Na while still being

3 silica and alumina conservative. Similar pyroxenes, like jadeite (NaAlSi2O6), requires higher concentrations of Al2O3 to be left in the melt to form. Therefore, the ratio of alkalis to silica and alumina is essential to create an alkaline rock.

These uncommon minerals, such as nepheline and aegirine or augite are often rock forming together with K-feldspar and albite. They produce rocks such as syenites, nepheline syenite (syenite with a large nepheline component) and nephelinites, which are almost entirely made up of nepheline and augite. Other than these igneous bodies, there are associated intrusive rocks. Tinguaite is an example of this. It is a dike variety of the aphanitic (to porphyritic) volcanic phonolite consisting of mainly alkali feldspar, nepheline and aegirine(-augite) ± biotite ± other foids and typically display what is known as ‘tinguaitic texture’ (Bergstøl, 1979). Where larger needles of aegirine grow interstitially in a mosaic of feldspars and foids as well as smaller aegirine crystals.

Because of this unusual chemistry, the mineralogical composition of alkaline rocks can be quite exotic. This often results in suites or complexes with a potential economic interest, due to the concentration of rare earth element (REE) and other various trace elements, such as high field strength elements (HFSE) (Marks et al., 2008a; Marks et al., 2008b; Sørensen, 1992)

Nomenclature and terminology The nomenclature, and classification, of alkaline rocks is somewhat complex. However, Frost and Frost (2008) have summarized and expanded on previous research and created a series of indexes that can geochemically account for different alkaline rocks. For example, alkalinity index (AI) is defined, on a molecular basis, as 퐴퐼 = 퐴푙 − (퐾 + 푁푎) (Shand, 1947). An AI below 0 indicates a peralkaline rock while an index above 0 is representing a metaluminous or peraluminous rock (depending on the ASI value). The AI was first used to define agpaitic rocks (Ussing, 1912), however, in modern nomenclature the term agpaitic is used on peralkaline nepheline syenites containing complex Zr- and Ti-minerals (Frost and Frost, 2008; Le Maitre et al., 2002; Sørensen, 1992). Furthermore, a peralkaline igneous rock should have a molecular (푁푎 + 퐾)/퐴푙 ratio > 1 (Harris et al., 2018).

Geochemistry of alkaline systems Mafic silicate phases, often pyroxenes and amphiboles, are large components in many alkaline systems. These mineral phases are present in all stages of formation, with large compositional variance. Because of this, they provide spectacular insight into the evolution of a magmatic system as well as the mineral fractionation and the effects of contamination (Marks et al., 2004; Reguir et al., 2012).

Studying the evolution of clinopyroxenes (CPX) from alkaline systems a distinct geochemical trend is notable in terms of major elements (Figure 1). They usually progress from diopsidic with low sodium content towards a sodium rich, aegirinitic composition with an intermediate hedenbergitic CPX.

This evolution is, according to Marks et al. (2004), ascribed to fractionation dependent on, among other things, oxygen fugacity (fO2). However, the opposite correlation has been argued, that the compositional changes are controlling the fO2 of the system (Markl et al., 2010). A weighted combination of the two might be even more likely.

Geochemically alkaline rocks contain a high abundance of alkalis and relatively high concentrations of incompatible Figure 1. Clinopyroxene evolution in the elements, most notably high field strength elements (HFSE) Illímaussaq alkaline intrusion, based on data such as Ti and Zr (Marks et al., 2008a; Marks et al., 2008b). from Marks et al. (2004). There are several intricate relationships between incompatible

4 elements and major element composition in alkaline rocks. For instance, a study by Piilonen et al. (2013) showed that titanium displays an inverse correlation with sodium. In case of Piilonen et al. (2013), Ti decreases as Na increases. Furthermore, Marks et al. (2004) show light rare earth element (LREE) to heavy rare earth element (HREE) preference in clinopyroxenes dependent on major element composition. They argue that CPX exhibits a continuous evolution from LREE-enriched pattern in Ca- rich minerals to a more prominent HREE trending pattern towards the clinopyroxene Aeg-endmember. This transition appears as a wave-shaped REE pattern. Additionally Marks et al. (2004) discuss the increase in Zr, Hf, Sn and HREE concentrations with increasing Na/Ca ratio of the CPX.

1.2 Regional geology The Särna alkaline complex intrudes a postsvecokarelian porphyry rhyolite (ca. 1.74-1.66 Ga) inlier in the Dala Sandstone (Lundqvist and Persson, 1999). The porphyry belongs to the Transscandinavian Igneous Belt (TIB) and is dated to 1711 ± 7 Ma using U-Pb on zircons (Lundqvist and Persson, 1999).

The Dala Sandstone is Mesoproterozoic sandstone in the Dalarna region, western Sweden, underlying thick covers of glacial till. It is characteristic of the area and is a continental red sandstone (Lundmark and Lamminen, 2016). It is a part of the so called Jotnian sandstones, which are low-grade siliciclastic rocks of the same age (Lundmark and Lamminen, 2016; Sederholm, 1897). The Dala Sandstone has a maximum depositional age of roughly 1.58 Ga and according to Lundmark and Lamminen (2016) the sources of sediment are found in the surrounding area (Svecofennian, TIB and Gothian domains).

The Transscandinavian Igneous Belt is spanning the age range of approximately 1.85 Ga to 1.65 Ga. It is extending roughly 1500km from the southeast corner of Sweden, beneath the Caledonides, to the northwestern part of Norway and is divided into four major tectonic and lithological units. The units, from southeastern Sweden to northwestern Norway, are: Småland-Värmland belt, Dala Province, Rätan Batholith, Revsund granitoid suite (Högdahl et al., 2004; Lundqvist and Persson, 1999). TIB rocks are generally coarse grained, porphyritic monzodiorites to granite. There are, however, some calc- alkaline or alkaline rock segments within the belt (Högdahl et al., 2004). Additionally there are several generations of dike swarms and sills covering Fennoscandian Shield, ranging from around 1600 Ma to 280 Ma (Söderlund et al., 2005). The last of which (280 Ma) are dolorites and basalts found mostly in the southern Sweden and Norway. They are believed to be connected to the extension of the western margin of Fennoscandia which in turn might be connected to the Variscan orogenic event. This extensional stress yielded widespread magmatic activity in the Oslo region as well as the graben formation in the area (Söderlund et al., 2005).

1.3 Särna alkaline complex (SAC) The Särna alkaline complex is located a few km to the northwest of Särna, Dalarna (Figure 2A). The main study area is divided between two hills, Ekorråsen to the west (61.725342, 12.848931) and Siksjöberget to the east (61.727805, 12.878534) (Figure 2B).

A B

Figure 2. (A) Map illustrating with a star where in Sweden the Särna Alkaline Complex is located. (B) Zoomed in satellite image of the SAC. Marked in red is the approximate area of the study site, Ekorråsen to the west and Siksjöberget to the east.

The alkaline complex is mainly composed of two rock types, the särnaite and the crosscutting tinguaite dikes. The tinguaite was first mentioned by Hjelm (1805) but under the name serpentine porphyry, however it was later more correctly described as a phonolite (Erdmann, 1846). The tinguaite had by this time been found only as boulders but through the works of A. E. Törnebohm outcrops were found and it was microscopically studied (Törnebohm, 1875; Törnebohm, 1881; Törnebohm, 1883). Furthermore, Törnebohm (1883) compositionally describes the tinguaite. Its’ main constituents are pyroxene (mostly aegirine), feldspar and cancrinite. The tinguaite is characterized by the so called tinguaitic texture where pyroxene needles have grown interstitially between the feldspars and foids

The särnaite is compositionally similar to the tinguaite. It was described as consisting of feldspar (sodium rich orthoclase and albite), cancrinite, aegirine, ± nepheline and with accessory biotite, titanite and apatite (Törnebohm, 1883; Magnusson, 1923). Magnusson (1923) further described the general mineral succession of the SAC (Figure 3). Additionally, Törnebohm (1883) determined that the cancrinite must have formed as a primary mineral phase in this assemblage, and therefore the rock should be called cancrinite nepheline syenite. Cancrinite has previously mostly been known as an alteration product of nepheline through different reactions, later described by Finch (1990) among others.

6 NaAlSiO4 + 2 CaCO3 = Na6Al6Si6O24 Ca2(CO3)2 (reaction 1) Nepheline from the fluid cancrinite

Due to this it was in the late 1800s proposed that nepheline syenites carrying cancrinite as a primary phase should be called särnaite (Brögger, 1890).

Figure 3. General mineral succession of the Särnaite according to Magnusson (1923).

Magnusson (1960) dated the särnaite to approximately 423 Ma using K-Ar whole-rock data. However, K-Ar whole-rock dating is prone to errors due to potential loss of radiogenic Ar or by incorporation of excess Ar. A more recent study re-dated the complex using the Rb–Sr systematics of mineral separates from the särnaite (Bylund and Patchett, 1977). This yielded an age of 287 ± 14 Ma (2σ) using a λ87Rb constant of 1.39 ∗ 10−11 푦푟−1. The tinguaite has not been dated before this thesis and the relationship between the two has been assumptive to some extent.

1.4 Cancrinite As previously mentioned, cancrinite is mostly known as a secondary reaction phase. The alteration mechanism which form cancrinite was first described by Edgar (1964) and further examined by Sirbescu and Jenkins (1999). It has been discussed that cancrinite can be formed only when there is a reaction between nepheline, calcite and a mixed fluid such as H2O-CO2 (Dumańska-Słowik et al., 2016). But they also discuss the option where CaCO3 is dissolved in the interacting fluid, such as reaction 1 described by Finch (1990). This second option is explored further. Depending on the complexing agent of the fluid several minerals can form from the alteration of nepheline and albite (Fall et al., 2007). For instance, if the fluid is carrying NaCl rather than CaCO3 when reacting with nepheline, the alteration product becomes sodalite instead of cancrinite (reaction 2; Fall et al., 2007).

6 NaAlSi3O8 + 2 NaCl = Na8(AlSiO4)6Cl2 (reaction 2) Nepheline from fluid Sodalite

There is a solid solution series between the most common endmembers, cancrinite [(Na, Ca)6(CO3)1.4- 1.7][NaH2O]2[Al6Si6O24] and vishnevite [(Na, K)6(SO4)][NaH2O]2[Al6Si6O24]. Essentially, the complete solid solution series is characterized by the coupled substitution 2Ca + 2CO3 ↔ 2Na + SO4. However, other sodium and anion substitutions are possible (Martins et al., 2017).

2.0 Methodology 2.1 Fieldwork The fieldwork was conducted over a period of 2 days, 15th and 16th of August, 2017. During this time detailed mapping of field relationships as well as sampling took place. 22 samples were collected (JE17- 01 to JE17-22), most of which from boulders that were deemed to be in close proximity to its originating outcrop. However, some outcrops were found and it was therefore possible to collect samples directly from the source (Figure 4). These samples were preferred when conducting further studies.

A During the early 20’s when Nils H. Magnusson visited the study location it was somewhat more accessible in terms of vegetation. More specifically, in terms of moss. During our time in the field few outcrops were found, mainly due to the abundance of vegetation. The moss is covering the boulder-rich till which, in itself, is covering the bedrock. However, with some determination and a hammer we were able to locate a few outcrops.

Figure 4. Field photographs of John Eliasson. Photo by: A.S.L. Sjöqvist

2.2 Scanning electron microscope (SEM) Energy-dispersive X-ray spectrometry (EDS) was conducted at the Department of Earth sciences, University of Gothenburg. The SEM utilized was a Hitachi S-3400N equipped with an Oxford Instruments INCA EDS system. The SEM was run at an accelerating voltage of 20 kV with a beam current of 6 nA, counting times varied between 5 and 100 seconds depending on the objective. 100 second counting time was used when performing quantitative analyses of pyroxenes while the shorter counting times were used when identifying the typical mineral phases.

EDS spectra were used to determine mineral phases within samples, whereas backscatter electron (BSE) images were used to attain detailed textural knowledge. Additionally, thorough chemical analyses (~100 second counting time) it was possible to differentiate the geochemical signature of phases, e.g. variable TiO2 content and endmember composition in pyroxenes.

The SEM further provides the information needed to determine suitable phases to perform micro- analytical dating using the LA-ICP-MS. This means that besides the chemical and textural information attained by the SEM it can also be used a preliminary investigational tool. Through the SEM it is quite easy to predetermine favorable LA-ICP-MS spot locations. Essentially, the high contrast BSE images provided by the SEM allows for quick and easy determination of zonations. Knowledge about zonations is crucial when using the LA-ICP-MS as it allows not only for more reliable results, but also for good signal interpretation when the signal displays an unusual behaviour. Furthermore, phase determination by assessing EDS spectrums allows for higher LA-ICP-MS resolution. Accurate determination and characterization of the targeted phase results in enhanced analyses as well as greater potential for what is possible within the field of microgeochemistry.

2.3 LA-ICP-MS Laser Ablation Inductively Coupled Plasma Mass Spectrometry, or LA-ICP-MS, was performed at the University of Gothenburg using an ESI 213NWR (TwoVol2) operating at MS/MS mode. The laser ablation system is connected to an Agilent 8800 QQQ ICP-MS. Material is collected, and essentially turned into an aerosol, in the sample cell area by ablation via a constant stream of helium which is mixed with N2 downstream and later also with argon before being exposed to the torch of the ICP-MS. 87 87 To ensure mass separation, e.g. differentiating between Rb and Sr, N2O was used as a reaction gas within a reaction cell between the two ICP-MS quadrupoles and thus allowing for measurement before and after reactions per routine developed by Zack and Hogmalm (2016).

Because of the set-up available at the department of Earth sciences at the University of Gothenburg, where the instrument is equipped with double quadrupoles surrounding, or sandwiching, a reaction cell or octopole reaction system (ORS3), spectral interferences (isobaric and polyatomic interferences) can be avoided. The first quadrupole (Q1) can separate out a specific mass/charge ratio which will then enter the reaction cell. Inside the reaction cell element separation is possible by introduction of a reaction gas which can eliminate spectral interferences. Determination of which reaction gas to use varies depending on the reaction efficiency towards the targeted element. When the element of interest has reacted with the appropriate gas, forming a ‘reaction product’, the mass/charge ratio differentiate from the previous ratio. Thereby allowing the second quadrupole (Q2) to separate the unwanted interfering ion from the targeted reaction product before reaching the detector, or vice versa, were separation of the reaction product from targeted ion is of interest.

2.4 Raman spectroscopy Raman spectroscopy utilizes the inelastic scattering, or Raman scattering, of monochromatic light. By shooting a laser at a mineral phase the light will interact with vibrations on a molecular level. This will result in photons being shifted up or down depending the excitations occurring in the mineral. This photon shift yields information about the vibrational modes and thereby about what elements or molecules are present. Each mineral has a specific and unique Raman spectrum. This makes it possible to separate for example hematite and magnetite in a quick and easy way in comparison to e.g. the SEM.

Raman spectrums were recorded using a LabRAM HR Evolution (HORIBA) equipped with an electron multiplier detector (EMCCD). Two solid state lasers are connected, emitting at 532 nm and 785 nm respectively. The solid state laser emitting at 532 nm was chosen as the excitation source as there is little to no fluorescence interfering at the selected wavelength. Using a x100 objective the beam was focused to approximately 1 μm and all spectrums was acquired at roughly room temperature operating in confocal mode. A diffraction grating of 600 cm-1 was used during the collection of spectrums. Calibration of the spectrometer was performed on a polished silicon wafer for the 520.7 cm-1 calibration line, as is the norm. Additionally the software KnowItAll was connected to the LabRAM HR Evolution which can match the collected spectrums with a database of spectrums. Data from RRUFF.info was imported into a database which could later be used to compare the collected spectrums to a variety of mineral phases.

3.0 Results

3.1 Mineral and sample description 3.1.1 Cancrinite (nepheline) syenites: fine grained samples

JE17-05: Särnaite (Cancrinite nepheline syenite) JE17-05 was collected from an outcrop, or potentially a boulder in close proximity to its original source, at the northwestern part of Ekorråsen (Figure 2B). A lineation was observed in the field (Figure 5) which could potentially be a foliation with a fold axis having a strike direction of N-S.

Figure 5. Picture of an outcrop or boulder in close proximity to its original source. Note what could potentially be a foliation with a strike direction of N-S. The sample is fine grained, much like JE17-08 and JE17-08A, which all show the same kind of lineation.

JE17-05 main constituents are aegirine-augite (ranging from Ae61Di24Hd15 to Ae90Di2Hd8), K-feldspar, Na-plagioclase, cancrinite and nepheline. It has a notable amount of titanite, quite often with inclusions of nepheline, K-feldspar and/or CPX (Figure 6A). Rutile and apatite are minor accessory phases in this sample, and can even be found as interstitial secondary hydrothermal phases (Figure 6B)

A B

Figure 6. BSE images of sample JE17-05. (A) Showing a titanite grain with inclusions of nepheline and K-feldspar. (B) Rutile and apatite found as interstitial secondary hydrothermal phases.

JE17-05 is the only studied sample which contains nepheline. The nepheline in the sample is abundant and euhedral and is, together with mainly cancrinite and to some degree K-feldspar, the main groundmass component in between the pyroxene crystals.

The cancrinite belonging to JE17-05 is not only abundant, it is also displaying euhedral, hexagonal crystal structure (Figure 7). This is a strong indicator suggesting the cancrinite to be of primary origin, which has been proposed by Magnusson (1923) among others.

Figure 7. Marked in red is a euhedral cancrinite grain with a clear hexagonal crystal structure.

Throughout the sample tinguaitic texture can be observed (Figure 8), where the pyroxene orients themselves in a flow-like manner and where both acicular clinopyroxene crystals as well as smaller, interstitial CPX grains have grown in a mosaic of alkali feldspar and foids (mindat.org, 2018; Ulrych et al., 2006).

Figure 8. BSE image of sample JE17-05. The flow-like texture observed in the image is called ‘tinguaitic texture. Where the pyroxene orients themselves in a flow-like manner and where both acicular clinopyroxene crystals as well as smaller, interstitial CPX grains have grown in a mosaic of alkali feldspar and foids

JE17-08: Cancrinite syenite This sample was collected from an outcrop, or boulder in close proximity to its source outcrop, in the southeastern part of Ekorråsen (Figure 2B). A lineation, or possibly a foliation with a fold axis with a N- S orientation, was observable in the field (Figure 9)

Figure 9. Picture of the outcrop from which sample JE17-08 was retrieved. Note the potential foliation visible with a strike direction of the fold axis in N-S.

JE17-08 mainly consists of aegirine-augite (Ae69Di15Hd16 to Ae89Di6Hd5), K-feldspar, Na-plagioclase and cancrinite. It also carries moderate amounts of apatite and titanite with minor accessory minerals such as rutile, zircon, pyrophanite and zeolites (mostly analcime and natrolite). Additionally, sulphides are present in the sample, such as sphalerite, but no calcite association have been found. Generally, the rutile and zircon is found in connection to the titanite grains.

The abundance of CPX in this sample is lower than in the coarser samples, but it is distinct nonetheless. The crystal shape is euhedral and the CPX is typically elongated and tabular or stubby prismatic and in general there are few inclusions within the CPX of this sample (Figure 10A).

A B

Figure 10. BSE images from sample JE17-08. (A) Illustrating the growth preference of the CPX, either elongated and tabular or stubby prismatic. (B) Hypersolvus texture visible in the sample. Where, to some degree, K-feldspar essentially recrystallizes into albite or vice versa.

The potash feldspar and the albite are both found as individual crystals but most often together with a hypersolvus-indicative texture (Figure 10A and 9B). Cancrinite has a high modal abundance of above 25%.

In connection to a vein (Figure 11), primarily consisting of CPX, which is crosscutting the sample a distinct reaction texture has been observed (Figure 12).

Figure 11. Microscopic map of JE17-05.

Figure 12. Reaction texture close to the vein in figure 10. It appears to be producing an albite core, rimmed with K-feldspar and later analcime and natrolite. The reaction appears to end as it breaches the cancrinite.

As is evident in Figure 12 (ovan) the reaction appears to produce an albite core, rimmed by K-feldspar which in turned is rimmed by at least two different zeolites before the reaction breach into the cancrinite crystals.

JE17-08A: Cancrinite syenite Much like JE17-08 this samples consists of aegirine-augite (Ae69Di14Hd17 to Ae91Di4Hd5), K-feldspar, Na- plagioclase and cancrinite. Although little apatite has been observed, it does contain moderate amounts of titanite and rutile as well as minor accessory oxide- and sulphide-phases. This sample essentially display the same characteristics as JE17-08, texturally and in terms of mineralogy, and was made in order establish the above mentioned features of JE17-08. The main difference being that this sample has no vein in which a noticeable amount of zeolites could be found.

3.1.2 Cancrinite (nepheline) syenites: coarser samples JE17-22: Cancrinite syenite Sample JE17-22 is a coarser variety of cancrinite syenite and was collected from an outcrop or potentially a boulder in close proximity to its originating outcrop. There was no lineation or foliation observed in the field, however, microscopically there is a lineation visible adhering to the CPX orientation (Figure 13A).

It predominantly carries aegirine-augite (Ae70Di15Hd15 to Ae86Di7Hd7), K-feldspar, Na-feldspar and cancrinite with minor accessory apatite and interstitial secondary rutile, titanite and zircon in minor amounts. Furthermore JE17-22 contains trace amounts of microscopically visible sulphides such as sphalerite, and galena but also trace amounts of microscopically visible iron oxides. However, there is no calcite association in this sample.

The CPX in the sample are up to a few mm in size and prismatic tabular or stubby crystal shape, suggesting it to be an early magmatic phase in accordance with Magnusson (1923) (Figure 3). To a large extent inclusion are absent in the CPX in this sample.

A B

Figure 13. BSE images from sample JE17-22. (A) Displaying a potential microscoping lineation based on the orientation of the CPX. (B) Hypersolvus texture between K-feldspar and plagioclase. Additionally, note the cancrinites euhedral to subhedral crystal shape.

The K-feldspar and albite are intergrown and a hypersolvus texture is evident (Figure 13B). Furthermore these feldspar phases are not only common in the sample, but also subhedral to euhedral, indicating it to be an early phase in the system essentially reflecting the observations made by Magnusson (1923).

As seen in (Figure 13B) the cancrinite has a subhedral to euhedral crystal shape, further strengthening the original idea of cancrinite being a primary mineral phase. Additionally, in this sample there is little to no reaction boundaries present with the cancrinite.

The feldspars dominate the sample in terms of modal abundance, with these large distinct CPX grains being omnipresent. However, the cancrinite is estimated to have a modal abundance of about 20% in this sample.

JE17-22A: Cancrinite syenite Much like JE17-22 this sample carries aegirine-augite (Ae73Di14Hd13 to Ae82Di8Hd6), K-feldspar, Na- plagioclase and cancrinite with minor accessory apatite, rutile, titanite and zircon. JE17-22A lacks a calcite association completely. However, the abundance of CPX in this sample is slightly lower than that of JE17-22. In general, this sample shows the same characteristics as JE17-22 and was made in order to establish the above mentioned features of the coarser cancrinite syenite.

JE17-19: Cancrinite syenite This sample was collected from a boulder found on the western side of Siksjöberget, but due to the brittle nature of elongated pyroxene needles and the size of the needles in this sample the source ought to be in somewhat close proximity.

JE17-19 differentiates from JE17-22 and JE17-22A quite distinctly. It is slightly coarser than the other two samples, the coarsest sample collected, and it has similar mineralogy. It carries a more diopsidic aegirine-augite (Ae32Di42Hd26 to Ae58Di23Hd19), K-feldspar, Na-plagioclase and cancrinite. Furthermore it does contain minor amounts of interstitial secondary rutile and titanite and lacks a calcite association. However, in this sample there are large grains of apatite and titanite (Figure 14A and B), the CPX is more often zoned and inclusion-rich (often cancrinite) (Figure 14B) and also there appears to be less Na-plagioclase than in the other coarse samples.

A B

Figure 14. BSE images from sample JE17-19. (A) Large subhedral to euhedral titanite crystal). (B) Large apatite crystal, as well as CPX, cancrinite and K-feldspar. Note that the CPX from this sample has a distinct zonation and an abundance of inclusions (mainly cancrinite).

The CPX crystals in this sample are euhedral and are either elongated and tabular or stubby concordant with earlier descriptions (Magnusson, 1923). But as mentioned, they are inclusion-rich, cancrinite being the most common inclusion phase. They are often zoned which is especially visible in Figure 14B.

3.1.3 Other samples: the southeastern outcrop

This outcrop is located in the southeastern A part of Siksjöberget (Figure 15A) at around N61.723287, E12.892187. The outcrop illustrates complex field relationships (Figure 15B) and several samples were collected, some of which are presented below.

Figure 15. The southeastern outcrop. (A) Map with Ekorråsen (west) and Siksjöberget (east), the red star marks the location of the outcrop. (B) Picture showing the complex fieldrelationships observable in the area. Photo taken by A.S.L. Sjöqvist.

JE17-11: Druzy feldspar vein The druzy feldspar vein cuts through the southeastern outcrop on the right hand side (Figure 15B). According to observed crosscutting relationships in the field the vein is one of latest features (Figure 16A), only being crosscut by smaller leucocratic veins and a tinguaite dike, which is the youngest feature of the outcrop. Most notably this vein displays a druzy texture, meaning that crystals grow inwards, from the edge of the vein towards the center. This texture is typical when the growth occurs in a hollow environment (Lowe et al., 1989). This could occur when crystallizing in a shallow environment due to the lack of pressure forcing the vein to close and thereby preventing this type of crystal growth.

A B

Figure 16. (A) Picture showing the crosscutting relationship between the druzy feldspar vein and the surrounding leucocratic feldspar rock and weather cancrinite syenite (photo by: A.S.L. Sjöqvist). (B) BSE image from sample JE17-11. CPX grain in poor condition with an abundance of K-feldspar and plagioclase inclusions.

Essentially this rock has a modal abundance of approximately 95% K-feldspar and Na-plagioclase, often as perthite and anti-perthite. The dominant feldspar grains are often tabular and euhedral, up to 1cm in size. There are CPX grains within the sample, however, these tend to not be in pristine condition. Most of which are riddled with inclusions, such as K-feldspar and plagioclase (Figure 16B). It also contains accessory apatite and titanite.

JE17-13: Leucocratic feldspar-rock This leucocratic rock of the southeastern A outcrop is, interpreted according to field relationships, one of the earliest features of the outcrop. The most notable part of this is marked in red (Figure 17A).

The leucocratic rock consists of roughly 90% feldspars, the internal modal abundance of the feldspars is approximatly 50% K-feldspar and 50% albite. Furthermore it contains a modal abundance of 5-7% CPX, as well as 3-5% apatite, titanite and minor amounts of (La-)monazite. Additionally, there are trace amounts of sulphides within the sample.

The CPX grains are distributated quite evenly throughout the sample although they are found a higher concentration around a vein-like feature. Typically they are subhedral and exhibit a stubby crystal habit, however in proximity to the vein like structure the crystal habit changes towards a more stubby-prismatic appearance (Figure 17B). Grains of clinopyroxene from the leucocratic JE17-13 sample is often free from inclusions. There are, B however, exceptions (Figure 17C). In Figure 17B there are inclusion like grains of K-feldspar and albite that appear to be intergrown with the CPX. Genereally these follow grain boundaries and microfractures.

The accessory apatite and titanite are spread out across the sample. However, the minor amounts of (La-) monazite is found together with titanite in one part of the sample that appear to be hydrothermally altered. Furthermore, inclusions of titanite has been found within CPX grains (Figure 17C) suggesting C that titanite is a quite early phase of the JE17- 13 rock. The apatite displays a similar relationship as titanite to albite, K-feldspar and CPX in this sample.

Figure 17. (A) Marked in red is the leucocratic feldspar rock within the southeastern outcrop. Photo by: A.S.L. Sjöqvist (B) BSE image from JE17-13. CPX crystals towards the vein like feature, where the crystal habit changes from subhedral stubby to stubby-prismatic. (C) BSE image from JE17-13. Titanite inclusions found within the CPX, note also that there is a small pyrite inclusions although these are not common.

JE17-16: Aegirine-augite rich zone This sample is focused on the extremely dark, almost tourmaline colored, part of the rock which is found both below, within and above the leucocratic part. Most notably it can be seen between the red markers in Figure 18A. There are slight color variations, from this tourmaline dark to a slightly brighter greenish-black, where the darker variation appears to be more crystalline and the brighter greenish- black variation displays a more smeared and microcrystalline behavior (Figure 18B and C).

A B

Figure 18. The southeastern outcrop. (A) Between the red lines the aegirine-augite rich zone can be found. The aegirine-augite behaves in two ways seen in figure 18B and C. (B) The greener aegirine-augite with a more smeared and microcrystalline behavior. (C) The darker variation with a more notable crystal shape and habit. (Photos by: A.S.L. Sjöqvist)

Compositionally this rock is dominated by anhedral pyroxene (aegirine-augite), with a moderate amount of Na-plagioclase and K-feldspar, both of the latter minerals being subhedral to euhedral in crystal shape. The albite in Figure 19A seems to exhibit two different habits. To the left (marked in blue) a hypersolvus-like texture is observable while to the right (marked in red) more subhedral to euhedral grains of albite is present. The sample contains minor accessory titanite which is present as subhedral to euhedral crystals. Additionally, apatite appears as subhedral to anhedral crystals, much like the pyroxene, covering quite extensive areas of the sample (Figure 19B).

A B

Figure 19. BSE images from sample JE17-16. (A) Albite with different crystal habits. Blue circle showing hypersolvus texture between Kfs and albite. Red circle is highlighting the subhedral to euhedral albite. (B) Apatite grains with similar behavior. Ranging from subhedral to anhedral.

Additionally, the CPX illustrate the same druzy habit as JE17-13 in a few places (Figure 20), where needles of CPX grow inwards from a spherical feature, and is as mentioned previously a texture indicative of an initially hollow growth environment (Lowe et al., 1989).

Figure 20.Close-up of the druzy texture observed from the aegirine-augite zone where needles of CPX grow inwards in a spherical manner. Scale of the feature seen in the top right corner. (Photo by: A.S.L. Sjöqvist)

The smeared, greenish-black pyroxene part of the aegirine-augite rich zone often appears as extensions of the tourmaline black euhedral CPX (Figure 21A) and it has also been observed as the core of smaller, crosscutting veins (Figure 21B and C).

A B

Figure 21. (A) Overall image illustrating the microcrystalline aegirine-augite as extensions of the darker more euhedral CPX. (B) This smeared CPX can further be seen as the core of smaller, crosscutting veins. (C) Close-up from the red marker in (B) of one of the crosscutting veins. (Photos by: A.S.L. Sjöqvist)

JE17-12: Weathered cancrinite syenite

A B

Figure 22. (A) Overall image of the outcrop, marked in red is where weathered cancrinite syenite has been found. (B) The cancrinite syenite appearing as blocks in a matrix of leucocratic feldspar rock, ranging in size from credit card to roughly 0.5m by 0.5m. Note the white corona featuring each ‘block’. (C) Additional photo illustrating the cancrinite syenites behaviour. The area marked in red (Figure 22A) illustrates an area where weathered cancrinite syenite has been observed. It essentially forms a ‘skeleton of tables’ within the leucocratic feldspar rock. The size of each block adhering to this feature ranges from credit card in size up to approximately 0.5m by 0.5m. Studying these blocks a little closer (Figure 22B and C) a white corona can be seen rimming each block. Furthermore the texture and appearance of the cancrinite syenite located within the southeastern outcrop is due to a 0.5cm thick weathering hide.

3.1.4 AS13-02: Tinguaite The tinguaite sample was collected by A.S.L. Sjöqvist in 2013. It consists mainly of slender prismatic needles of CPX as a groundmass with larger interbedded Na-plagioclase crystals. Additionally, larger grains of biotite and apatite are found scattered across the sample. Tinguaitic texture can be observed to some degree within the sample but more notably the hand specimen exhibits large CPX crystals displaying what is thought to be magmatic flow lineation.

3.2 Major and minor chemistry

3.2.1 Whole-rock analysis

퐸푙푒푚푒푛푡푃−(%푠∗퐸푙푒푚푒푛푡푠) 퐸푙푒푚푒푛푡퐷 = (equation 1) 1−%푠

ElementD = ElementDaughter melt, e.g. särnaite ElementP = ElementParent melt, e.g. basalt ElementS = ElementSolid, e.g. Ti-augite which has been fractionated out from the parent melt %S = Amount (%) of ElementS which is being fractionated out of parent melt.

Using equation 1 above, it is possible to calculate the amount of fractional crystallization needed from a certain parent melt to reach the major and minor chemistry which has been recorded in the SAC. The parent melt was assumed to be of basaltic composition (Table 1) and the fractionating phase was assumed to be a clinopyroxene of a known composition, Ti-augite (Table 1; Claeson et al., 2007). The average basalt is based on samples *28-022-VG3098, *BA52-005-051, *BA52-005-052, *BA52-005-053 (Jenner and O'Neill, 2012; Melson and O'Hearn, 2003).

Table 1. The relevant major chemistry in wt% of WR1, WR2, the average of four basalts, and a Ti-augite.

WR1 WR2 Basalt Ti-augite SiO2 57.79 50.62 50.08 49.86 TiO2 0.31 0.44 2.9 1.93 Al2O3 20.48 19.21 18.77 3.67 FeO 2.51 4.78 5.13 10.95 MnO 0.08 0.16 0.15 0.21 MgO 0.16 0.93 4.5 12.96 CaO 1.62 3.71 7.3 20.71 Na2O 11.85 10.23 4.16 0.38

Looking at the basalt-normalized diagram below (Figure 23) an inverse relationship between WR1 and WR2 in comparison to Ti-augite is quite evident for most major elements. For example, CaO in Ti-augite is at a value of around 2.8 while WR1 and WR2 are at values of 0.2 and 0.5, approximately cancelling each other out given that they are enriched or depleted at a similar order of magnitude. Note however, that TiO2 and Al2O3 has a slightly different relationship.

Major chemistry: Basalt-normalized 10

1 Basalt WR1 WR2

0.1 Ti-augite

0.01 SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O

Figure 23. Basalt-normalized diagram with the major chemistry on the x-axis and a logarithmic y-axis. Note the inverse correlation between the whole rock analyses (WR1 and WR2) and the Ti-augite. However, certain elements adhere to a slightly different relationship (e.g. TiO2 and Al2O3).

Varying the degree of fractional crystallization yielded different results, however, by adjusting the %S variable the särnaite major chemistry composition was eventually attained (Table 2).

Table 2. Showing the degree of fractional crystallization of Ti-augite needed to produce the major chemistry measured in WR1 and WR2 from a basaltic parent melt. E.g. 97% fractionation of Ti-augite from the average basalt is need to form WR1. Note that the model was unable to calculate the degree of crystal fractionation needed for TiO2.

WR1 WR2 SiO2 97.2% 72.0% TiO2 - - Al2O3 10.0% 3.0% FeO 31.0% 6.0% MnO 52.0% 0.0% MgO 34.0% 29.5% CaO 30.0% 21.0% Na2O 67.0% 61.5%

Table 2 is displaying the degree of fractionation needed to attain the särnaites and tinguaites major chemistry composition. Approximately 30-60% of fractionation would be required, given that only Ti- augite is fractionating out from a basaltic parent melt. However, the model was unable to calculate the degree of crystal fractionation needed for TiO2, i.e. by crystal fractionaton of Ti-augite from a basaltic melt the TiO2 concentrations of the SAC was not attainable through this model.

Minor chemistry

In this section rare earth elements (REE) and other trace elements will be studied.

Chondrite normalized REE diagram: whole rock analyses 100

10 Särnaite, WR1 Tinguaite, WR2 Basalt (AVG)

Figure 24. Chondrite normalized REE diagram. WR1 and WR2 has significantly lower concentrations than the average basalt, with a factor of approximately 5 and 3 respectively.

Figure 24 is showing a chondrite-normalized REE diagram. The whole rock analysis (Särnaite, WR1), carried out by SGU, is displaying a significantly lower abundance of REE’s compared to the average of four basalts (Jenner and O'Neill, 2012). The särnaite has a La/Yb ratio of ~4, yielding a REE curve favoring LREE in comparison to HREE, whilst the basalt has a La/Yb ratio of ~1. Both whole rock analyses display extremely low concentrations of REE. The särnaite has lower REE concentrations than the basalt by factor of 5 (varying between 1.3 and 7.6). The tinguaite is depleted compared to the basalt by a factor of 3 (varying between 0.8 and 5.2).

Additionally, it is worth noticing that there is a quite distinct negative europium anomaly (Eu/Eu*) which can be observed in the särnaite sample. There are also Tb and Ho anomalies observable within the särnaite analysis, which aren’t recognizable in any other sample or analysis. The tinguaite sample (WR2) is slightly more enriched than the särnaite, however, it is still significantly lower than the basalt (with a factor of 5). The La/Yb ratio of the whole rock tinguaite sample is approximately 5, corresponding to a steeper curve. Furthermore, the tinguaite does not display the same negative Eu anomaly which is seen in the särnaite.

By using equation 1, which was previously introduced, it was possible to calculate the degree of fractionation needed to reach the rare earth element as well as trace element concentrations (Table 3). The results span from a minimum degree of fractionation of approximately ~70% for the särnaite and a maximum degree of fractionation of ~96%. The fractionation needed for the tinguaite would be slightly less, with a minimum fractional crystallization of ~30% for Zr, and a maximum fractionation of ~98% for Ba.

Table 3. Amount of fractional crystallization of Ti-augite needed to reach the REE and TE concentrations measured in WR1 and WR2. Elements which the model was unable to calculate the degree of crystal fractionation needed has been marked with ‘-‘.

WR1 WR2 La -70.0% 25.0% Ce - -50.0% Nd 74.0% 74.0% Sm 71.5% 67.0% Eu 86.0% 81.0% Gd 75.5% 73.5% Dy 86.5% 85.3% Er - - Yb - - Lu - - Pb 92.7% 96.4% Th 83.0% 72.0% U 89.0% 80.0% Zr 90.8% 28.0% Ba 96.2% 97.6% Sr 87.0% 85.0%

The basalt-normalized diagram (Figure 25) is displaying a quite coherent relationship between the whole-rock analyses and the Ti-augite. Generally, when Ti-augite is enriched in an element the WR- analyses are depleted in said element, with roughly the same order of magnitude. However, looking at the REEs, this trend is not evident as there appears to be a more depleted overall trend within these elements.

Minor chemistry: basalt-normalized 100

Basalt

1 WR1 WR2 Ti-augite

0.1

0.01 La Ce Nd Sm Eu Gd Dy Er Yb Lu Pb Th U Zr Ba Sr

Figure 25. Basalt normalized diagram for the minor chemistry, with elements on the x-axis and a logarithmic y-axis. It is displaying a quite coherent relationship between the while-rock analyses and the Ti-augite. Generally, elements that are enriched in the Ti-augite is depleted in WR1 and WR2. The REE show a slight inconsistency towards this. 3.2.2 Clinopyroxenes The CPX range in composition from Ae32Di42Hd26 to Ae91Di4Hd5 throughout the samples (Figure 26). JE17-19 (blue triangles) is the coarsest sample has the strongest diopside component while JE17-08A, being one of the finer grained cancrinite syenites has the most pronounced aegirine component (Table 4).

Je17-22 Aegirine JE17-22A JE17-19 JE17-08 JE17-08A JE17-05

Diopside

0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 Hedenbergite

Figure 26. Triangle plot where clinopyroxene composition (aegirine-diopside-hedenbergite) is plotted from SEM analyses. Generally, all the samples have a distinct aegirine-component.

As Table 4 clearly illustrates, the strongest aegirine components are found within the fine grained samples (JE17-08, 08A and 05) and the most diopside-rich pyroxenes are found within the JE17-19 sample.

Table 4. Each samples’ (JE17-22, -22A, -19, -08, -08A & -05) end-member composition (Aeg-Di-Hd).

Sample Aeg-Di-Hd end-member composition

JE17-22 Ae70Di15Hd15 to Ae86Di7Hd7

JE17-22A Ae73Di14Hd13 to Ae82Di8Hd6

JE17-19 Ae32Di42Hd26 to Ae58Di23Hd19

JE17-08 Ae69Di14Hd17 to Ae91Di4Hd5

JE17-08A Ae69Di15Hd16 to Ae89Di6Hd5

JE17-05 Ae61Di24Hd15 to Ae90Di2Hd8

SEM analyses showed that the pyroxenes from the SAC has quite high TiO2 concentrations, varying throughout the samples from roughly 0.5 to 3.5 wt% (Figure 27). The average combined TiO2 concentration of the samples is around 0.9 wt%, with a slight preference for the coarser samples (JE17- 22, -22A, -19) in comparison to the fine grained samples (JE17-08, -08A, -05), 1.02 wt% and 0.76 wt%

30 respectively. However, note that sample JE17-05 has a span of TiO2 concentration between 0.6 and 3.5 wt%.

Figure 27. SEM analyses of samples (JE17-22, -22A, -19, -08, -08A & -05) yielded a difference in Wt% TiO2. There is potentially a slight preference in TiO2 incorporation in the coarser samples (JE17-22, -22a and -19).

The diagram below depicts all the clinopyroxene samples, as well as the WR analyses, plotted on a chondrite-normalized spider-diagram (Figure 28). The CPX has been recalculated using partition coefficients (KD) from Marks et al. (2004), therefore the CPX plotted on the spider-diagram above should reflect the parent melt in which they grew.

The europium concentration is low in all samples but there is a slight difference between the pyroxene analyses and the whole rock analyses. Furthermore, the Sr levels are quite stable at around 100 times chondrite concentrations.

Chondrite norm - High KD 10000.00

1000.00

100.00 JE17-22 JE17-19

10.00 JE17-08 Je17-05

1.00 WR1, Särnaite WR2, Tinguaite 0.10

0.01 Ba Th U K Ta Nb La Ce Sr Nd Hf Zr Sm Tb Eu

Figure 28. LA-ICP-MS measurements of CPX from the different samples as well as WR1 and WR2 plotted on a chondrite normalized spider diagram. The CPX concentrations have been recalculated using partition coefficients from Marks et al. (2004). Note the low Eu concentrations and the difference between the CPX and the whole-rock.

3.2.3 Titanite and Cancrinite Comparing the REE patterns of the titanites and the recalculated CPX (Särna, avg) it is clear that the titanites as well as the parent melt in which the CPX grew in are missing the Eu anomaly. The cancrinite appears to have a positive Eu anomaly, although it is still depleted in comparison to a chondrite as the value is below 1 (Figure 29).

Additionally, the titanites have a La/Yb ratio of ~10 thereby favoring LREE over HREE quite heavily, while the cancrinite has a ratio of 0.98.

Average (KD calculated, syenite -> aegirine) vs Ttn vs Ccn 1000

100

Wholerock, Särna 10 Särna (AVG) Ttn Ccn

0.1

Figure 29. Chondrite normalized REE diagram. Comparing REE concentrations between the CPX (Särna, AVG), WR1 (Whole- rock, Särna), titanite and cancrinite. Note that the Eu anomaly is not present in the CPX, the titanite or the cancrinite, which appears to have a positive Eu anomaly.

Raman: Cancrinite A D116 JE17-05 1800 1052 1600 1400 1200 1000

800 Intensity 600 279 100 400 511 437 977 201 200 698 1413 0 0 200 400 600 800 1000 1200 1400 RS

B D112 JE17-01

1600 1054 1400 1200 1000 274 800

Intensity 600 106 504 400 426 975 230 346 459 200 693 778 1385 190 0 0 200 400 600 800 1000 1200 1400 RS

Figure 30. Two Raman spectrums from different samples each showing similar signature. Note however the differences presented within the red circles, where the spectrum from sample JE17-01 has a stronger cancrinite-component.

Some minor differences has been observed within the cancrinite Raman spectroscopy signature (Figure 30). The main differences has been marked with red circles and can be compared to the illustration made by Martins et al. (2017) (Figure 31). Note the height difference of peaks (426, 459 and 504) in the first circle (left-most circle), the slight difference in intensity between Raman shifted bands 690-778, and the minor difference around 975. To compare the bands to molecules, see (Table 5)

Figure 31. Representative Raman spectrum for the cancrinite-vishnevite solid solution from Cinder Lake. (A) Represents Ccn6.5. (B) Ccn70.6. (C) Ccn91.3. (Martins et al., 2017)

Table 5. Vibrational modes at different Raman bands in the cancrinite-vishnevite solid solution series. The table is comparing the results from three different papers. (Martins et al., 2017)

3.3 87Rb–87Sr dating 3.3.1 Cancrinite (nepheline) syenite: K-feldspar, titanite and cancrinite grains

The 24-point isochron (Figure 32) from särnaite and cancrinite syenite samples was calculated using isoplot (v. 4.15) and is based on K-feldspar, titanite and cancrinite grains. It yielded an age of 294±22 Ma (2σ) with a mean squared weighted deviation (MSWD) of 1.01. The age was calculated using BCR- 2G as the main standard. Additionally, signals which were stable but below 10 seconds of coherent count time were deemed unreliable and therefore removed from the isochron.

data-point error crosses are 2σ

0.76

0.74

Sr 86

0.72

Sr/ 87

0.70 Age = 294±22 Ma Initial 87Sr/86Sr =0,70488±0.00087 MSWD = 1,01 0.68 0 2 4 6 8 10 12 87Rb/86Sr

Figure 32. A 24-point Rb–Sr isochron of the cancrinite syenite and särnaite based on K-feldspar, titanite and cancrinite grains. It yielded an age of 294 ± 22 Ma (2σ) with a MSWD of 1.01.

3.3.2 Tinguaite: Biotite grains with a forced initial The 18-point isochron (Figure 33) calculated in isoplot (v. 4.15) from a tinguaite sample based on biotite grains yielded an age of 301.9 ± 7.8 Ma (1σ) with a MSWD of 0.81. The initial value was forced to 0.706 based on data from Bylund and Patchett (1977). Note that this initial value concurs with the initial value attained from apatites in the särnaite (~0.705). Additionally, signals which were stable but below 10 seconds of coherent count time were deemed unreliable and therefore removed from the isochron.

data-point error crosses are 1σ 0.98

0.94

0.90

Sr 0.86 86

Sr/ 0.82 87

0.78

0.74 Age = 301,9±7.8 Ma 0.70 Initial 87Sr/86Sr =0,706* MSWD = 0,81 0.66 0 10 20 30 40 50 60 87Rb/86Sr

Figure 33. 18-point Rb–Sr isochron from a tinguaite sample based on biotite yielded an age of 301 ± 7.8 Ma (1σ) with a MSWD of 0.81.

3.3.3 Weighted mean age: Särnaite and Tinguaite

The weighted mean age of the särnaite (294 ± 22 Ma) and the tinguaite (301.9 ± 7.8) is 301 ± 14 Ma Figure 34. It was calculated using isoplot (v. 4.15).

box heights are 1σ 325

315

305

295

285

Mean = 301±14 [4.8%] 95% conf. 275 Wtd by data-pt errs only, 0 of 2 rej. MSWD = 0,115, probability = 0,74

265

Figure 34. A weighted mean age of the cancrinite syenite (and särnaite), to the left, and the tinguaite, to the right, yielded a mean age of 301 ± 14 Ma.

4.0 Discussion Several aspects of this study will be discussed below, such as the age of the complex and what implication that might have. Additionally, a large emphasis will be placed on the chemistry of the rocks. Mainly REE concentration will be addressed. Emplacement time of the SAC The särnaite age (298±24 Ma) is overlapping with the age of the tinguaite (302±8 Ma). The calculated ages for the SAC conducted in this thesis also strengthens the previous dating, 287±14 Ma, by Bylund and Patchett (1977) as they are within error of each other.

The emplacement of the SAC is during a time of little to no tectonic activity, suggesting that the SAC has to originate from somewhere else. In age the SAC corresponds well to the Oslo rift (ca. 310-245 Ma: Larsen et al., 2008), however, specifying during which event the SAC would originate from is difficult given the large error of the särnaite itself. However, the weighted mean age of the särnaite and the tinguaite is 301 ± 14 Ma (Figure 34). This suggests that the SAC would stem from one of the earlier stages of formation of the Oslo rift. Potentially somewhere between stadium 1 and 3 (310-275 Ma). However, crosscutting relationships observed in the field convincingly shows that the tinguaite ought to be younger than the särnaite. Therefor the särnaite ought to be no younger than 294 Ma making stadium 3 (292-275 Ma) less likely, constraining the emplacement time of the särnaite to stadium 1 or 2. The tinguaite could still form during stadium 3 which is during the maximum activity of the rift (Larsen et al., 2008)

Särna is located approximately 150km to the north east, which is a large but manageable distance. Additionally, the north easterly direction further enhances the connection as it is roughly the same direction as the strike of the rift (Larsen et al., 2008). Hence, it appears reasonable from a geographical perspective.

Cancrinite Essentially, D112 JE17-01 (Figure 30) is displaying a slightly more distinct cancrinite component while D104 JE17-05 (Figure 30) yields a more vishnevite heavy signature, comparable to Table 5 (Martins et al., 2017). This difference fluctuate throughout the samples, meaning that both of these signature co- exists within each studied sample. Comparing the spectrums the main differences are quite subtle but noticeable none the less. The additional peaks at 950-975 in D104 Je17-05 as well as the configuration of peaks in between 693 and 778 are the main separating factors together with the intensity difference between the bands 426, 459 and 504. According to Martins et al. (2017) the bands between 693 and 778 bands represent various constellations of CO3 and SO4 (Table 5), which essentially indicates where in the solid solution series the analyzed sample can be found.

Additionally, this could give some insight into the fluids that acted in the system. Clearly both CO3 and SO4-type fluids has been essential in the system, given that cancrinite-vishnevite is a primary mineral phase. However, this does not exclude the presence of, for example, methane. Furthermore, given the cancrinite-heavy composition, approximately Ccn60-80, carbon-based fluids seem to be dominant in comparison to sulfur-based fluids.

Additionally, the euhedral shape of the cancrinite (-vishnevite) (Figure 7) in conjunction with the non- existent presence of calcite in the samples further suggests that the cancrinite-vishnevite is of primary origin. Essentially due to the nature of the reaction which transforms nepheline to cancrinite. As this reaction takes place an intermediate zone of calcite crystallizes between the unaltered nepheline and the newly formed cancrinite (Dumańska-Słowik et al., 2016; Finch, 1990).

On the controls of oxygen fugacity Given that most of the iron in the melt is present as Fe2+ a controlling factor on the oxygen fugacity of the system might be the lowering of calcium in conjunction with the crystallization of aegirine. This 2+ 3+ would promptly force the fO2 to be lowered due to the oxidation of iron (Fe to Fe ). Additionally, this would force the pyroxene to become a Ti-sink as there are no other viable phases to crystallize. The lowered oxygen fugacity, i.e. the reduced melt, is prohibiting minerals such as rutile to form and lack of Ca is preventing phases such as titanite and apatite to form. However, given that there appear to be a fluctuating fO2 during the course of the systems evolution it cannot be the sole controlling factor. This fluctuation manifests through presence and subsequent absence of apatites and titanites throughout the samples.

Looking at figure 12 there is a reaction occurring, creating an albite core, rimmed by K-feldspar which in turned is rimmed by natrolite and analcime before it breaches into the cancrinite where the reaction appears to stop. If one was to assume that this used to be a särnaite and nepheline was present before the (potentially hydrothermal) reaction occurred, it could be theoretically described (P/T conditions unknown) as

4푁푒 + 5푄푧 + 1퐻20 = 1퐴푏 + 1퐾푓푠 + 1푁푡푟 (reaction 3)

Reaction 3 works under the assumption that 25% of the hexagonal sites in the nepheline crystal structure is occupied by K (Buerger et al., 1954; Hålenius et al., 2018; Marcial et al., 2016). However, a few difficulties arise. First of all, a substantial amount of silica is needed in order for this reaction to actually occur. It can be either of external or internal origin, i.e. the silica is either transported in the fluid during the crystallization of the vein or it is release through the breakdown of silicates in the surrounding crystals. This should be recorded in the petrology of the rock. One would observe silicates being replaced in proximal crystals or it would be recorded as microcrystalline quartz within or close to the vein itself. None of which has been found.

So another possibility is considered. Creation of the reaction texture (Figure 12) is the result of two separate reactions, essentially taking place simultaneously. The first reaction in the 2 stage series being

푁푎퐴푙푆푖3푂8 = 푁푎퐴푙푆푖푂4 + 2 푆푖푂2 (reaction 4) In feldspar nepheline

The first reaction would be reaction 4 where the sodium component in feldspar would deplete, forming nepheline and quartz, in order to buffer the silica activity at values below unity (Markl et al., 2010). This would be needed in order to buffer the fO2, which is normally done in nepheline syenite systems via the displaced FMQ equilibria (Markl et al., 2010)

3 푓푎푦푎푙푖푡푒 + 푂2 = 2 푚푎푔푛푒푡푖푡푒 + 3 푆푖푂2 (reaction 5)

However, due to the quartz deficiency in a syenite reaction 4 is needed to create the components necessary to buffer the fO2. The second reaction in this 2 stage series would then be reaction 3. This means that as the fluid passes through and crystallizes the vein, it utilizes the newly freed SiO2 from the breakdown of albite in order to reform albite, k-feldspar and the two zeolites.

It is possible to replace reaction 4 with reaction 6 (Markl et al., 2010), given that less silica is needed to buffer the system or because the availability and breakdown of the pyroxene is easier than that of the feldspar. If this is the case the 2-stage series would go from reaction 6 to reaction 3.

푁푎퐴푙푆푖2푂6 = 푁푎퐴푙푆푖푂4 + 푆푖푂2 (reaction 6)

The lack of magnetite in my samples, which could be there according to the FMQ construct, could be 2+ due to the iron activity in the melt. Pyrophanite (Mn TiO3) has been observed in several places, 2+ suggesting a lower fFeO. Instead of forming for instance ilmenite (Fe TiO3), the low iron activity could prohibit Fe2+ to enter the crystal structure. Instead manganese can be incorporated and thereby crystallizing pyrophanite.

Extreme MREE depletion

Calculated parent composition based on CPX, särnaite 1000.0

100.0

Särna (AVG)

10.0

1.0

Figure 35. Chondrite-normalized REE diagram. The CPX from all the cancrinite syenite and särnaite samples have been averaged and recalculated using KD values from Marks et al. (2004). These should reflect the parent melt composition.

Based on partition coefficients from Marks et al. (2004) for aegirine-augites there was a strong MREE depletion in the parent melt. This depletion in the SAC could be explained by crystal fractionation of a parental basanitic magma. However, through this development of composition the alkaline magma tends to become increasingly depleted in other trace elements (e.g. Nb and Ta) (Weaver, 1990). Weaver (1990) shows that Nb/Ta ratio as well as Zr/Hf ratios are highly fractionated in phonolites, 60- 65 and 64-77 respectively in Fernando de Noronha phonolites, while basanites typically shows ratios around 14 and 45. Furthermore, Weaver (1990) attributes this fractionated pattern together with the heavy MREE depletion to a minor sphene component (< 5%). However, only a few small grains has been observed throughout all the samples of the SAC. This observation in conjuction with Nb/Ta and Zr/Hf ratios of ~1.2 and ~1.1 would suggest that this explanation of is not applicable to the SAC.

The LREE abundance of the SAC is higher than that of a normal basalt, which according to Downes et al. (2005) would indicate either an extreme metasomatized mantle source or a significantly smaller degree of partial melting. The HREE being lower than that of a basalt could suggest that there would a presence of residual garnet. However, this has not been observed.

Evolution of the system The evolution of the SAC is currently enigmatic, the extreme depletion in REE’s as well as other various trace elements is difficult to explain. Two potential explanations are presented below.

(1) Fractional crystallization of CPX (large Ca-Ti Tschermaks component) from a parent melt

It could be possible to form the rocks found in the SAC through a complex series of fractional crystallization and metasomatism or the introduction of exotics, for example xenoliths. By calculating the amount of solid which needs to be removed from the parent melt to create a certain daughter rock (equation 1) it is possible to discern some of the process which might be acting in the system.

Assuming that särnaite is the daughter rock (ElementD) and using different parent composition (ElementP) one is able to calculate how much CPX (Ti-augite with a Tschermaks component) which needs to be removed from the system in order to reach the särnaite composition, both for trace elements and REE’s as well as the major chemistry of the rock. Using a basaltic parent composition yields the most coherent result, where we can account for almost all elements via fractionation of the parent composition (i.e. removal of elements) and via the introduction of exotics (i.e. addition of elements). Metasomatism would in this instance be a process which can elevate element concentration of the composition, but it could also be accounted for by hydrothermal alteration which has been observed in the area. Alkaline system, as previously mentioned, are prone to pervasive open- system behaviour.

Table 3 is illustrating the percentage of solid which needs to be removed from a parent melt with a basaltic composition in order to reach the REE and trace element (TE) composition of the särnaite (WR1) and the tinguaite (WR2). Red values of zero indicate that the concentration of the whole-rock analysis was not reachable through fractionation of Ti-augite with Ts-component studied by Claeson et al. (2007). Negative values suggest that in order to evolve the parent composition to the daughter composition, an enrichment process ought to occur. In general, however, it would require something in the range of 60-95% of CPX fractionation to arrive at the SAC REE and TE composition. Essentially, quite substantial fractionation is needed to attain the SAC REE and TE signatures

Studying the major chemistry of the SAC in the same manner (Table 2), the range fractionation needed depending on element dramatically expands. Spanning from approximately 3% to 95%, which might be unrealistic.

Given that this varying amount of fractionation is feasible, it could also explain the TE pattern as well as, to a certain degree, the substantially depleted REE patterns. It has been shown that trace element partitioning can be a function of their valence (Hill et al., 2000). Hill et al. (2000) conducted experiments at isobaric P-T condition to assess the relation between the Ts-component of a Ti-augite and trace elements as well as rare earth elements. Among other things, Hill et al. (2000) concluded that with a stronger Ts-component there should be an increase in D for HFSE as well as REE, which has also been shown by Claeson et al. (2007). This would mean that the REE and TE signatures of WR1 as well as WR2 could be ascribed to a significant Ts component in the system. The high concentration of Ba in WR1 and WR2 could potentially be explained by this Ts component as Ba tends to show a strong correlation to Ts-rich CPX (Claeson et al., 2007). Conversely, the low Mn concentration can be ascribed to the fact that there is little differential partitioning of Mn in Ts-rich CPX. Additionally, the small differences in certain elements, such as Mn, can be further explained by crystallization of other phases. For instance, crystallizing small amounts of iron oxide could provide a structure where Mn can readily be incorporated, effectively reducing the amount of Mn remaining in the melt.

To further enhance this explanation there is a good correlation between the Ti-augite and WR1 when normalized to the basalt. The major chemistry (Figure 36A) generally illustrates a balance between the Ti-augite and the särnaite. For instance, the FeO is slightly enriched in the CPX while simultaneously being slightly depleted in the särnaite. This balance is, more or less, in the same order of magnitude for the major elements, except TiO2. Potentially the TiO2 difference could be explained through a series of phases being crystallized during the evolution of the system, such as ilmenite and titanite.

A Major chemistry: Basalt-normalized 10

1 Basalt WR1 WR2 Ti-augite 0.1 e.g. Titanite

0.01 SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O

B Minor chemistry: basalt-normalized 100

Basalt WR1 1 WR2 Ti-augite e.g. Apatite 0.1

0.01 La Ce Nd Sm Eu Gd Dy Er Yb Lu Pb Th U Zr Ba Sr

Figure 36. Modified after figure 23 and 25, with hypothetical red lines as examples. Showing both the major and minor chemistry normalized to the average basalt. (A) Addition of a TiO2 peak which might be produced by the fractional crystallization of e.g. titanite. (B) Example of how apatite fractionation could strengthen the REE depletion and thereby compensate for the skewed ratio of Ti-augite and WR1+WR2.

The minor chemistry, normalized to the basalt, is yielding similar, coherent results (Figure 36B). This would mean that, for both major and minor chemistry, CPX fractionation from a parent melt of basaltic composition can account for the formation of the SAC. However, there are quite likely more phases being fractionated out of the melt than just Ti-augite. For instance, some degree of fractional crystallization of apatite could compensate for the skewed ratio between the Ti-augite and WR1 + WR2 in terms of REE.

In summation, SAC can be formed through a medium (30-60%) or heavy (60-90%) fractional crystallization of Ti-augite with a Ts-component of a basaltic parent magma. During the evolution of the system other phases, such as oxides, also fractionate which yields the peculiar composition measured in the SAC. The Ts component in the Ti-augite could explain the extremely low REE and TE concentrations observed due to the changes in partition coefficients, i.e. the Ts component is increasing the compatibility of REE’s and TE’s in the melt with a preference towards the CPX (Claeson et al., 2007).

(2) Potential silicate-carbonate immiscibility

Särna (parent avg) vs WR1 vs WR2 1000.0

100.0

Särna (AVG) WR1, Särnaite WR2, Fonolit 10.0

1.0

Figure 37. Chondrite-normalized REE diagram modified after figure 24 and 29. Note the difference in Eu2+ concentration between WR1 and WR2 + Särna (AVG).

Studying the chondrite-normalized diagram above (Figure 37) it is possible that the whole-rock analysis of the Särnaite (WR1), provided by SGU, has a negative europium anomaly. This anomaly is typically ascribed to fractional crystallization of plagioclase from a basaltic magma, where Eu2+ substitutes for Ca2+, with a large partition coefficient and thus effectively depleting the melt in Eu. Assuming that this negative anomaly is not caused by the introduction of a false variation. For example, extremely low concentrations can lead to a deviation from a ‘true’ value due to rounding errors. However, if the Eu anomaly is present it is important to explain why the terbium and holmium anomalies are not. Because typically there are no geologic reasons for these anomalies, for example it is not the result of any normal fractionation. The Tb and Ho anomalies could be explained by the tetrad effect, more specifically the w-shape tetrad effect (Irber, 1999; Masuda et al., 1987; Takahashi et al., 2002). Where variations within the electron cloud for a specific element introduces false anomalies.

Assuming that the europium anomaly is present in the särnaite it is important to consider the relation between the särnaite and the tinguaite. In the whole-rock analysis of the tinguaite (WR2) the anomaly is non-existent, which is also the case for the CPX, the titanite and the cancrinite. From this there are two possible conclusions which one needs to consider. (i) During the growth period of the CPX there was no fractional crystallization of plagioclase in the parent melt, thus no negative Eu2+ anomaly. (ii) The tinguaite is thought to originate from the same, although more evolved, magma as the särnaite and should therefore display the same or a greater anomaly. There are two alternatives which could describe the difference in europium between WR1 and WR2. There could have been an influx of europium in the time between the emplacement of the särnaite and the crosscutting tinguaite (e.g.

47 metasomatic, hydrothermal or introduction of exotics). The second alternative would be that the tinguaite originates from another melt, one which has not undergone plagioclase fractionation.

The Nb and Hf concentrations found in the SAC are approximately 60 times chondrite values (Figure 28). An average MORB has around 10 times chondrite values (Rollinson, 1993), and can be considered depleted in these elements. This could indicate that instead of plagioclase fractionation of a basaltic parent melt the formation of the SAC originates from a nephelinitic parent melt. If the parental melt is in fact of nephelinitic composition there would be no plagioclase fractionation due to the high ratio of alkali to alumina and silica, i.e. the composition does not allow for substantial plagioclase formation. If this is the case it is possible that nepheline and/or clinopyroxene is the controlling factor in creating this alkaline body. However, this cannot be the entire explanation given the difference in europium between the whole rock analyses of the särnaite and the tinguaite. If this difference is caused by the tinguaite originating from a different melt than the särnaite, it is possible that the melt, resulting from fractionation of a nephelinitic parent melt, has undergone liquid immiscibility. Thereby creating two separate parts of the melt, a silicate part and a carbonate part, which cannot mix. This explanation could not only account for the negative europium anomaly in the särnaite and the lack of a negative europium anomaly in the tinguaite, but it would also help explain the extraordinary low concentrations of REE’s in the särnaite, as rare earth elements preferentially partition into the carbonate part (Wendlandt and Harrison, 1979).

To further strengthen this silicate-carbonate immiscibility there is a difference in CaO% between the tinguaite and the särnaite, 3.71 wt% and 1.62 wt% respectively. Given the mineralogy of the different rocks this difference could be quite significant. The tinguaite consists essentially of a groundmass of augite/aegirine-augite, prismatic CPX crystals as well as some larger, euhedral K-feldspars and apatites (Bergstøl, 1979). Stoichiometrically there is only so much calcium which can be accommodated within the rock. Comparing this to the särnaite which ought to be able to facilitate more Ca due to the abundance of for instance plagioclase and to some degree apatite. If this difference is significant enough, it would further allow for the hypothesis of an immiscible silicate-carbonate melt. The reason for the elevated CaO% in the tinguaite would then be attributed to the carbonatite situated in the vicinity of the SAC.

SAC compared to Alnö and Fen 10000.0

1000.0 Parent melt, SAC, recalc. From CPX WR1, Särnaite

WR2, Fonolit 100.0

Alnö Ne syenite (AVG)

Fen, nepheline syenite, 10.0 interpolated Norra Kärr (avg)

1.0

Figure 38. Chondrite normalized REE diagram illustrating the similarities between the SAC and Alnö complex as well as Fen Alkaline Complex and Norra Kärr. The REE data from Fen Alkaline Complex was incomplete so lines between certain elements are interpolated. Note the depleted levels of REE in all complexes in comparison to Norra Kärr.

Comparing the concentrations of REE’s in the SAC to that of both Alnö Complex and Fen Alkaline Complex it is quite evident that they have similarities (Figure 38). All three are relatively depleted in REEs while concentrations found in Norra Kärr (Sjöqvist et al., 2013) are enriched at roughly 1000 times chondrite values, except for the europium which is at 200 times chondrite concentration. Both Alnö and Fen are complexes that show both alkaline silicate rocks as well as carbonatites (Mitchell, 1980; Vuorinen and Hålenius, 2005; Vuorinen et al., 2005), presumably they have undergone liquid immiscibility. Given that the nepheline syenites from the complexes show a depleted rare earth element signature it further strengthens the idea of liquid immiscibility in the SAC, which displays a very similar signature. The similarities are especially pronounced in the whole rock analyses.

This potential carbonatite part of the SAC has yet to be found, but there are tinguaite dikes further to the east of Särna which also could originate from the part of the melt, given that they display the same chemical behaviour as the dikes found in Särna.

5.0 Conclusions Given the weighted mean age of the SAC (301 ± 14 Ma) it is reasonable to connect the formation of the SAC to the earlier stages of formation of the Oslo rift (stadium 1-3: 310-275 Ma; Larsen et al., 2007). Although the särnaite can be constrained through crosscutting relationships to between stadium 1 and 2 (310-292 Ma).

The cancrinite present in both rocks in SAC, although more prominently in the cancrinite (nepheline) syenite, is of primary origin. Through Raman spectroscopy it is quite evident that carbon-based fluids dominate the fluid composition. However, sulfur-based fluids are also a crucial part of the system.

The SAC is an intricate and complicated complex with what appears to be an unusual way of formation. Two possibilities of formation have been presented in this thesis:

• The parent melt has undergone liquid immiscibility, creating a silicate and a carbonate part. The särnaite would then originate from the silicate part and the tinguaite form the carbonate part. This carbonatite is undiscovered. • By a medium degree of fractional crystallization of a parent melt with basaltic composition. Where fractionation of mainly pyroxene (Ti-augite) with a large Tschermaks components (Ts) is moving the melt towards the alkaline field.

However, most often the simplest solution is the one closest to the truth. The process of fractional crystallization is perhaps the more likely explanation concerning the formation of the SAC rather than that of liquid immiscibility and the formation of an undiscovered carbonatite. The results from this thesis shows that fractionation of pyroxene with a large Ts-component from a basaltic parent melt can move the melt into the alkalinity field, in conjunction with some degree of fractional crystallization of other phases.

6.0 Acknowledgements First, I would like to thank Axel Sjöqvist, who presented this idea for a master thesis to me. Your valuable input and thorough support throughout the entire process of writing this thesis as well as your massive help during fieldwork has been invaluable. I would also like to thank Thomas Zack, Johan Hogmalm and Matthias Konrad-Schmolke for their enthusiastic and motivating support. Lastly, to all the people in office, thank you.

7.0 References

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