Petrographic examination of Norwegian glacio­fluvial aggregates: interpretation of mechanismsleading to high contents of cataclastic rocksB0RGE JOHANNES WIGUM & VIGGO JENSEN

Wigum, B.J. & Jensen, V. 1995: Petrographic examination of Norwegian glaciofluvial aggregates: interpretation ofmechanisms leading to high contents of cataclastic rocks. Nor. geol. unders. Bull. 428, 33-48.

Norwegian glaciofluvial aggregates have been examined microscopically and classified according to a newly esta­blished petrographic method. The results of this study and previous data show that there are high amounts of par­ticles 01cataclastic rocks in many Norwegian glaciofluvial aggregates. These rocks are unsuitable because of theexpansive effects of such rock-types in concrete, due to alkali-aggregate reactions (AAR). Some interpretationsand reasons are put forward to account for the more extensive occurrence of cataclastlc rocks in certain areas.Regional examination of glaciofluvial aggregates shows that cataclastic rocks can resist erosion over relatively longtransport distances, and that particles within specilic size ranges show higher enrichment in these rock-types. It isrecognised that the concentration of cataclastic rocks within particular particle fractions is governed by the prove­nance, distance from the source rock, and the mechanical properties of specific types of cataclastic rocks.

Barge Johannes Wigum, Department of Geology and Mineral Resources Engineering,University of Trondheim, The NOlWegian Institute of Technology, 7034 Trondheim, Norwey.(Present address: Kontrolttedet for betongprodukter, Postboks 53 Blindern, 0313 Oslo, Norwey).

Viggo Jensen, SINTEF, Structures and Concrete, 7034 Trondheim, Norway.

Introduction

Research into the lithology and transportprocesses of glaciofluviaJly derived materi­als has a long tradition, mainly as a tool formineral exploration. Most classifications ofsand and gravel fractions have usually beendone by sieve analysis and binocularmicroscope. The most commonly usedparameters in modern classification anddescription of glacial deposits are grain sizeand shape. Pettijohn et al. (1973) pointedout the need for more thin-section studies ofsand, by which varieties of lithic fragmentscan be identified.

Norwegian glaciofJuvial sand and graveldeposits have for some years been asses­sed and classified for their volume and qua­lity, and recorded in computerised databa­ses at the Geological Survey of Norway(Neeb 1993). However, over the last fewyears there has been a growing awarenessof the importance of studying the petrograp­hic and microstructural composition of natu­ral aggregates, mainly glaciofluvial materials

used for concrete purposes. This has beco­me necessary in order to meet the morestringent control for detecting aggregatewhich could exhibit slow/late-expansivealkali-aggregate reactions, which during thelast few years has been recognised as aconcrete durability problem in Norway(Jensen 1990, 1993, Jensen & Danielsen1992, 1993, Dahl et al. 1992, Lindqard et al.1993, Meland et al. 1994).

In concrete, alkali-aggregate reaction is achemical reaction between sodium andpotassium ions in the pore solution and cer­tain types of aggregates. Such types ofalkali reactive aggregates contain siliceouscomponents, particularly in the form ofmicrocrystalline and ductile deformedquartz. The reaction forms a hygroscopicalkali-silica gel that can imbibe water andswell. The swelling forces generated maybe sufficient to disrupt the surroundingconcrete, causing expansion and associa­ted deterioration. In 1992 an optional arran­gement for declaration and approval ofaggregates for concrete was introduced in

34 Barge J. Wigum & Viggo Jensen

Norway (DGB - Deklarasjon- og God­kjenningsordning for Betongtilslag). It sug­gests that aggregates should be tested inaccordance with the procedures outlined bythe Norwegian Concrete Society, publicati­on NB 19 (Norsk Betongforenings Pub­Iikasjon Nr.19, 1991). The proceduresrecommend that the first step should involvetesting by petrographic examination of theaggregate. If a low content of reactive orpotentially reactive rock-types (<20%) isobserved, the aggregate is classified as inn­ocuous with respect to its alkali-aggregatereactivity. If, however, a high quantity ofreactive rock-types (20%) is present, theaggregate is classified as reactive. In additi­on, it is recommended that the aggregate istested by an accelerated mortar bar test toconfirm the reactivity of the aggregate befo­re it is used in concrete structures. Reactiveaggregates are not recommended to beused in concrete structures situated inhumid environments unless precautions aretaken regarding cement type, protection,etc.

At SINTEF Structures and Concrete animproved petrographic method for thin-sec­tions has been developed which has beenused successfully to recognise more accu­rately reactive aggregates (Jensen 1993).This technique has been used to examine anumber of glaciofluvial aggregates inNorway. As a result a more accurate picturehas emerged with regard to the petrograp­hic and microstructural composition ofNorwegian glaciofluvial aggregates. Animportant feature of the method is that it isable to recognise and classify microstructu­ral features of quartz-bearing rocks. Thesemicrostructural features cannot be recogni­sed by ordinary binocular microscope exa­mination. Investigations of a large numberof samples from glaciofluvial deposits inNorway have revealed the occurrence ofcataclastic rocks in a majority of the sam­ples. Petrographic examination of aggrega­te from concrete samples obtained fromstructures suffering from AAR, have alsoshown a high content of cataclastic rocks.Such rock-types are now considered as thecommonest and most widely distributed

NGU • BULL 428. 1995

source of alkali reactive aggregates inNorway (Jensen 1993).

In Norway, due to the intense thrusting andfaulting, cataclastic rocks are widely presentand therefore should be expected to occurin many glaciofluvial deposits. During thecomminution and transportation of glacioflu­vial materials, more fragile materials abrademore rapidly, leading to an enrichment (ormaintenance of a high level) of quartz-bea­ring rocks exhibiting high abrasion resistan­ce, in certain fractions in the deposits. Theeffect will be more marked for longer trans­port distances.

The aim of this work was to examine therelative occurrence and distribution of cata­clastic rocks in Norwegian gfaciofluvialmaterials and to assess various mecha­nisms and processes which could accountfor the high occurrence of cataclastic rocks.The provenance, comminution and trans­portation conditions of glaciofluvial depositswere also taken into account when interpre­ting the results. Together with the resultsfrom SINTEF Structures and Concrete, twofurther areas were selected for investigationin order to obtain a more detailed picture.

Classification and properties ofcataclastic rocks

In order to understand the mechanismwhich led to enrichment of cataclastic rocksin glaciofluvial deposits it is essential to befamiliar with the classifications and properti­es of such rock-types. All rocks formed bycataclasis are termed cataclastic rocks andare generally felsic and/or silicic in composi­tion. Cataclastic rocks include metamorphicrocks that are deformed at low temperaturewith primary cohesion due to a combinationof crystalloblastic and cataclastic proces­ses. Higgins (1971) has classified cataclas­tic rocks with primary cohesion into twomain categories, depending on whethercataclasis is dominant over neomineralisa­tion-recrystallisation in their formation, orvice versa. Further classification is based

NGU - BULL 428,1 995 Barge J, Wigum & vtIggaJensen 35

100 km

r!

CATACLASTIC ROCKSI FAULTS AND TH

DRUSTS

Gneiss. stronglProt erozoic y myl onitisedFault age •

M 'ajor thrusts

FIg. 1. An outline of mapped cataclastiIC rocks (mylonite) and . ------ - - - - - -

major fault and thrust zone .s In southem Norway (Jensen 1993).

36 Barge J. Wigum & Vigga Jensen

on the occurrence of fluxion structures.Cataclasites are formed under conditions ofbrittle deformation of the rock, showing ran­dom fabric, while various types of mylonitesare formed during ductile deformation (flow)of the rock, showing f1uxion structures.Fluxion is a synonym for flow, and the termreflects the occurrence of the comminutedmatrix of mylonites 'flowing' around the por­phyroclasts in layers separated by thin linesmarked by concentrations of fine micaceousminerals . Finally, rocks without fluxion struc­ture and cataclasis dominance are definedas microbreccia and cataclasite, while rockswith fluxion structure and cataclasis domi­nance are defined as protomylonite, myloni­te and ultramyloni te. Rocks with f1uxionstructure where neomineralisation is domi­nant over cataclasis are defined as mylonitegneiss and blastomylonite.

The physical properties of the cataclasticrock are governed by its microstructural fea­tures, in particular the state of the quartz.Brattli (1994) investigated the influence ofcataclasis on abrasion resistance of graniticrocks. He observed that some types of duc­tile deformed cataclastic rocks, such as pro­tomylonite, mylonite and ultramylonite,appeared to have extremely high abrasionresistance, while at the same time exhibitinga high brittleness. This was attributed tointense ductile deformation which occursunder relatively low temperatures. Underthese conditions , high concentrat ions ofvery tightly bounded dislocations are produ­ced in the quartz grains, causing hardeningof the minerals, equivalent to cold-workingin metals.

Distribution of cataclastic rocksin southern Norway

Cataclastic rocks generally occur in thrustand fault zones resulting from dynamicmetamorphism. Fig. 1 shows the outline ofmapped cataclastic rocks (mylonite) andmajor fault and thrust zones in southernNorway where cataclastic rocks mayor maynot occur. The map has been drawn from

NGU . BULL 428. 1995

the 1:1 mill. bedrock map of Norway(Sigmond et al. 1984). Two larger areaswith mapped cataclastic rocks (mylonite)occur in the southeastern part of Norway.These are the Precambrian Mj0sa-Vanernmylonite zone which can be followed intoSweden (to lake Vanern): and further south,the mylonite zone from 0 yern to theSwedish border (Oftedahl 1980). Accordingto Oftedahl (1980) the mylonite zones werecaused by a series of microcontinental colli­sions in the Precambrian.

Fault zones occur in many areas of southernNorway, e.g. the southern and southeasternPrecambrian regions, the Oslo Region andin the areas of the Caledonian nappes.Thrust zones are also prevalent in manyareas, and reflect the extent of theCaledonian overthrusted rocks as a result ofnappe transport. The map in Fig. 1 showsthat cataclastic rocks are widely distributedin South Norway and should therefore beexpected to occur in many glaciofluvialdeposits in these areas.

The provenance, comminution,transportation and depositionof glaciofluvial materials

To understand the end product of a glacio­fluvial process it is necessary to look at thesedimentary cycle starting with the parentrock at the basal traction zone of glaciers,through transportat ion in the aqueous envi­ronment, to the eventual sedimentary depo­sit. The origin of glaciofluvial materials is eit­her the bedrock, till or englacial debris. Theglaciofluvial materials could be defined asthe net result of; plucking and abrasion of lit­hic fragments in the glacial environment,and modification during recycling in aque­ous environments (Slatt & Eyles 1981).These two factors will ultimately influencethe final petrographic composition of theglaciofluvial materials. To understand theenvironmental influence upon the potentia lenrichment of cataclastic rocks in suchmaterials, these two processes will be dis­cussed further.

NGU - BULL 428,1995

Plucking and abrasion of lithic frag­ments in the glacial environment

In the basal traction zone of glaciers, coar­ser clasts and sand-size lithic fragments aredetached from underlying bedrock surfacesby plucking, abrasion and crushing due toshear stresses exerted by the overridingice. The physical properties of the rocks andminerals have an influence on their resis­tance to fracturing. Shear fractures propa­gate along intracrystaf, as well as intercrys­tal, planes of weakness (Slatt & Eyles1981). As a result of abrasion, materialsbeneath the glacier will rapidly be crushedinto fine-grained sediments, while pluckingmight incorporate the loosened bedrockmaterial into the sole of the glacier and thenbe transported within the glacier.Cataclastic rocks that exhibit very finequartz grain-sizes, or microstructural featu­res including zones of undulatory extinction,planes of bubble wall inclusions, sub-grainboundaries and water-weakened dislocati­ons, might favour shear fractures along the­se planes of weakness. On a macroscopicscale, plucking might also exploit pre-exis­ting joints whereby large joint-boundedblocks may be pulled away from thebedrock and incorporated into the glacier(Soulton 1979).

Modification during transportation inaqueous environments

As the material enters the glaciofluvial sys­tem it becomes involved in a process ofreworking. This reworking is influenced bymany factors during subglacial meltwatertransportation such as the viscosity of thewater which can be high when temperaturesare very low. In addition, when there is acombination of heavy load and high velocityflow, then the meltwater can exert an extre­mely high abrasive action. At lower velociti­es abrasion is the most important mecha­nism causing erosion, while cavitations areimportant at higher velocities. Anotherimportant mechanism acting during trans­port is abrasion due to impinging suspen-

Barge J. Wigum & Vigga Jensen 37

ded particles during flow (Lilliesk6ld 1990).Also during glaciofluvial transportation, lithicfragments are subjected to impact-loading,which induces tensile stresses, and which inturn causes extensional fractures to propa­gate preferentially along intercrystal boun­daries (Slatt & Eyles 1981). Harrel & Slatt(1978) found very little size reduction ofpolycrystalline quartz granules (2-4 mm)during tumbling experiments. They conclu­ded that mechanical durability was inverselyproportional to the size of the crystal orgrain in an aggregate. Therefore, in a finelypolycrystalline particle, the crack path willcross more grain boundaries and grains ofdifferent crystallographic orientation. As aresult the rate of energy dissipation increa­ses, which in turn leads to a greater hin­drance of the crack propagation. This typeof behaviour is characteristic of cataclasticrocks as they commonly exhibit very finegrain sizes.

Haldorsen (1982) observed that quartzgrains, because of their great mechanicalresistance, generally erode to form particlesof coarser size fractions than compared forinstance to feldspars which have a muchlower mechanical resistance. Glaciofluvialmaterials which originated by erosion of tillswere investigated. It was found that the gla­ciofluvial materials had a sand fraction sig­nificantly richer in quartz than the originaltills. Results from a grinding test were appli­ed to explain the enrichment of quartz in thesand fraction. It was claimed that glacialtransport involves both abrasion and crush­ing, whereas the glaciofluvial transportationis dominated by abrasion. During abrasionmainly silt is formed. The silt is enriched infeldspar and sheet silicates, and the remai­ning sand in quartz.

Transportation distance

It is generally agreed that over long trans­port distances the volume fraction of variousgrain-size classes of glacial materials isaffected by their differential resistance toglacial abrasion. The transport distance isgenerally greater in glaciofluvial material

38 Barge J. Wigum & Viggo Jensen

than in the till from which it is delivered, andthus the source area is more difficult toassess. Further complications are introdu­ced as a result of sorting by water and clastweight. The transport distance might rangefrom kilometres to tens of kilometres, accor­ding to the energy level of the glacial melt­water system, the grain size and the resis­tance of the rocks (Lillieskold 1990). Mostpebbles in glaciofluvial deposits are not par­ticularly far travelled, which explains theirrelatively poor degree of rounding. In south­west Wales, it has been found that most ofthe rock-types represented in glaciofluvialdeposits are of strictly local origin. There isseldom more than 5% of exotic pebbleswhich have travelled more than 5 km fromtheir source (Sugden & John 1985). Lee(1965) found that most pebbles in aCanadian esker had travelled less than 10km from their source, whereas sand andgravel particles had travelled much further.

Deposition

The mode of deposition will control the litho­logy, the stratigraphy and the faciesassemblages. The Iithological variation indifferent beds usually reflects the grain-sizedistribution (l.illleskold 1990). It has beenreported that subglacial glaciofluvial depo­sits in eskers have commonly followedzones of structural discontinuity in thebedrock, such as faults (Shilts 1984).

Petrographic method

Most Norwegian alkali reactive aggregatesare very fine grained (microcrystalline); the­refore identification and classification ofaggregate grains cannot be made accurate­ly without the use of thin-section microsco­py. In order to obtain more realistic classifi­cations of aggregate for use in concrete, animproved petrographic examination whichinvolves point counting has therefore beendeveloped by SINTEF Structures andConcrete. This method has been used toassess rock constituents in glaciofluvialsands in the present investigation. The pre-

NGU - BULL 428, 1995

paration of samples of sand for this test isas follows: After sieving, two representativesamples of the fractions 1-2 mm and 2-4mm are selected for further petrographicexamination. The samples are then impreg­nated with an epoxy resin, in order to prepa­re thin-sections for petrographic examinati­on. Two thin-sections (25 x 50 mm) aremade with particles from the fraction 2-4mm and one thin-section with particles fromthe fraction 1-2 mm. Approximately 1000points are counted in each fraction. Thevolume percentage of reactive rock-types isbased on the average of the results fromboth fractions. A more detailed descriptionof the method is given by Haugen & Jensen(1993) and Lindgard et al. (1993). The clas­sification and identification of the differentalkali reactive rock-types are based on;knowledge of past field performance, petro­graphic nomenclature, and mineralogicaland microstructural criteria (Jensen 1993).During microstructural examination the fol­lowing factors were taken into account;grain-size of quartz, subgrain developmentin quartz, degree of deformation and recrys­tallisation. In order to obtain reliable data itis recommended that the petrographic exa­mination is carried out by a geologist who isexperienced in identifying reactive rock­types prevailing in that particular country(l.indqard et al. 1993).

In the present work the rocks were classifi­ed into the following three main categoriesin order to simplify interpretation of resultsand for use in data processing:

Category 1. - Reactive aggregates (withknown reactive field performance): sandsto­nes (1), cataclastic rocks (2), acid volcanicrocks (3), argillaceous rocks (4), greywacke(5) and other rock-types with microcrystalli­ne quartz (6).

Category 2. - Potentially reactive aggrega­tes: Quartzite (fine grained*) (7), Other rock­types containing finely divided* quartz (8).*(crystal sizes 0.06-0.13 mm).

NGU - BULL 428, 1995

Category 3. - Innocuous aggregates: Rock­types with coarse grains and/or minoramounts of quartz, e.g. volcanic rocks/gab­bro (9), granites/gneisses (10), maficrocks/pure limestone (11) and other rocks(12)

In addition, results from petrographic analy­ses carried out by SINTEF Structures andConcrete were used to determine the distri­bution and content of cataclastic rocksobtained from different sources.

Investigated areas

In addition to the results from work by SIN­TEF Structure and Concrete, we selectedtwo further areas for this study. This ensu­red data on aggregates sourced from closeto and remote from the original parent cata­clastic rocks. The work also attempted tocompare samples on a regional and localbasis, and to compare the difference betwe­en different types of cataclastic rocks. In thefirst investigated area which is part of thesoutheastern Precambrian province, twomajor mylonite zones are included, andfrom the second area, on the FosenPeninsula, smaller fault zones containingcataclasites are included.

The southeastern Precambrianprovince

The southeastern Precambrian area liesbetween the Permo-Carboniferous OsloPaleorift and the Oslofjord to the west, andthe Swedish border to the east. There aretwo major mylonite zones located in thearea (Fig. 5). The northernmost zone is theMjosa-Vanern mylonite zone, which liessouth of the Solar gneisses and the stronglydeformed Odal granites. Further south inthis region lies the second mylonite zone,which separates the Romerike grey gneis­ses (mostly metatonalites) from the 0stfoldgrey gneisses in the south (OftedahI1980).

Borge J. Wigum& ViggoJensen 39

The deglaciation and the glacial deposits inthis Precambrian area have been reportedby Serensen (1979, 1983). The Ra morainein the outer Oslofjord area was formedduring the Early Younger Dryas, whereasthe second most prominent ice-marginaldeposit in the region, the Ski Moraine, wasformed at the end of the Younger Dryas.Both the glacial striae older than theYounger Dryas and the glacial striae formedduring the Younger Dryas indicate a glacialmovement towards the south-southwest inthe region.

A total of nine samples containing glaciofJu­vial aggregates were collected from six dif­ferent locations within the area. The locati­ons nos. 1 and 2 lie just south and down­stream of the Mjosa-Vanern mylonite zone,with location 3 lying between the mylonitezones, while location 4 was situated alongthe southern mylonite zone. Locality 5 issituated south of this myJonite zone, at thesouthern end of lake 0yern. The southern­most location was at the prominent ice­marginal deposit at Mona, which is part ofthe Ski-As moraine complex. At this locationfour samples were collected (nos. 6 to 9) inorder to investigate lithological variationsbetween different layers in the deposit. Atthe distal part of the ridge, in an approxima­tely 1 m-thick part of the deposit, sampleswere collected from three different layers;nO.6 was collected from a coarse upper lay­er, nO.7 from a 15 cm-thick layer of finematerial, while sample nO.8 was collectedfrom a medium-coarse layer. Additionally,one sample (no.9) was collected from acoarse layer deep in the middle of the ridge.

Verrabotnen - the Verran Fault

The valley of Skaudalen runs ENE-WSW onthe Fosen Peninsula (Fig. 6). The valleywas developed along the Verran Fault, for­ming a topographic lineament running fromRissa to Verrasundet. The fault system nearVerrabotnen displays a variety of fault rocksproduced by both brittle and ductile defor­mation (Gmnlie et al. 1991). The glacial

40 Barge J. Wigum & Viggo Jensen NGU - BUll 428. 1995

system has produced an ice-marginal glaci­ofluvial deposit, Younger Dryas in age, inthe valley just west of Verrabotnen (Reite1994). In most valleys and fjords in thisarea, glacial striae indicate an ice move­ment strongly dependent on topographicalconditions (Reite 1994). It is therefore belie­ved that the ice moved along Verrabotnenand down Skaudalen to the southwest. Atotal of three aggregate samples were col­lected at the ice-marginal glaciofluvial depo­sit, along the valley profile west ofVerrabotnen.

in aggregate samples from different counti­es in southern Norway is presented in Fig.4. The petrographic compositions of thetwelve samples investigated in this studyare given in Table 1. Further information,such as the locations of the samples, thegraphical presentation of some rockassemblages in the 1-2 mm fractions, aswell as the ratio of cataclastic rocks betwe­en the two fractions, are given in Figs. 5 & 6.

Discussion

Results

Fig_ 2. Cataclastic rocks in glaciofluvial materials in 88 aggre­gate samples from locations in southern Norway; based onpetrographic examination at SINTEF Structures and Concrete1991-1995.

The results from this work and those frompetrographic analyses carried out on a com­mercial basis by SINTEF Structures andConcrete are presented here. Figures 2 and3 show data analysed from 88 sampleswhich were collected from different locati­ons of glaciofluvial sands in southernNorway. The distribution of cataclastic rocks

It is necessary to point out that a moreaccurate interpretation of Norwegian glacio­fluvial sand would have been possible if theaggregate samples had been sampled ran­domly. However, the results presented herewill provide a clearer picture about the con­tent and distribution of cataclastic rocks inNorwegian glaciofluvial aggregates. It is evi­dent from Fig. 2 that about 90% of the sam­ples contain various amounts of cataclasticrocks. A high proportion, about 45%, con­tain 0-5% cataclastic rocks and only a smallpercentage, about 5%, exhibit greater than20 % of cataclastic rocks, which also is thelimit of alkali reactive aggregates accordingto the Norwegian optional arrangement fordeclaration and approval of aggregates forconcrete (DGB). Fig. 3 shows the relations­hip between cataclastic rocks and alkalireactive rock-types. In this figure, cataclas­tic rocks constituted the majority of all alkalireactive rock-types in several of the sam­ples. In a few samples cataclastic rocksconstitute the main component of the alkalireactive rock (plots located on the brokenline). The distribution of samples with cata­clastic rocks is shown by county region wit­hin southern Norway in Fig. 4. The diagramshows that cataclastic rocks are present invarying degrees in samples analysed fromall the counties. Generally, the cataclasticrocks constitute less than 20 % of the volu­me fraction of the aggregate. Aggregatesamples from Telemark, Rogaland, Aust­Agder and M'He og Romsdal contain cata­clastic rocks which fall into two or less %volume fraction categories. Only samples

''K: \ -,: "<,: Limits according: to DGB

3,4: 3,4

I :0 1 0 1,1 0, , ,-

14,8

23,9

43,2

o 5 10 15 20 25 30 35 40 45

Cataclastic rocks (volume %)

5

50

45

40<I:lCl)- 35S-~ 30<I:l

0000 254-<0

1:: 20Cl)o 15"""Cl) 10,20..

10-

NGU - BULL 428. 1995 Barge J . Wigum & Viggo Jensen 41

Alkali Reactive Aggregates (volume %)

Fig. 3. Relationship between cataclastic rocks and alkali reac­tive rock-types in 88 aggrega te samples from locations inSouth Norway; based on petrographic examinat ion at SINTEFStructures and Concrete 1991-1995.

The sample from location 4 was takendirectly above the mylonite zone. In thiscase , questions might be raised whether themylon ite particles found in this aggregateare derived locally, or if the particles are theresult of glaciofluvial transportation from thenorthern mylonite zone. The low ratio bet­ween the content of catac lastic rocks in the1-2 mm and 2-4 mm fract ions indicateshowever, that the aggregate is derivedlocally.

Results from the southeastern Precambrianprovince show the samples to be dominatedby the rock assemblage granites and gneis­ses. Even though minor fract ions of otherassociated rock-types are observed, all thenine samples exam ined exhibited a relative­ly high content of cataclastic rocks , and theyappear to be the second most dominantrock assemblage in most of the samp les.The cataclas tic rocks were all class ified asmylonitic rocks, showing f1 uxion texture witha matrix of microcrystalline and subgranularquartz, and larger porphyroblasts of feld­spar. The highest amo unts of cataclasticrocks were found in samples close to themylonite zones , in general agreement withprevious observations (Figs. 7 & 8), and the% volume fraction declined with increasingtransportation distance from these zones. Itis evident from Fig. 7 that the content ofcataclastic rocks declines (for both investi­gated particle sizes) at distances greaterthen 5 km from the mylonite zone . Themax imum content of cataclastic rocks inboth fract ions is observed to occur at appro­ximately 6 km from the zone .

mentary units within the various depositsalso needs to be taken into considerationwhen select ing the samp les.

The interpretation of the results is based onpetrographic examination of the 1-2 mmand 2-4 mm fract ions according to the tech­nique described in the experimental section.Hence, the occurrence and contents ofcataclastic rocks in the coarser fractionswith regard to the effect of transportation :will not be discussed.

--

•

100

90

80 · .

70 · .

60 ·

SO ·

40 ••

30 .. •

from the count ies of Sor-Trondelag andOppland exh ibited cataclastic rocks with avolume fraction greater than 20 %, which islikely governed by local lithology.

The main objective of collecting samples forthis study was to examine glaciofluvialmaterials located over a range of transpor­tation distances from the origin of the cata­clastic rocks . It would have been preferableto obta in more information about the parti­cular glacia l and sedimentary environmentswithin these two investigated areas but thiswas not within the scope of the presentedwork . It is recommended that such a studywould enable assessment of the regionaleffects of glaciof luvial transportation to bemade and would help to understand theinfluence of other regional factors upon theend product of the glaciofluvial material. Inoutlining our data here, acco unt needs to betaken of the limited number of samples ana­lysed ; with the exception of one locat ion ,where four samples were collected withinthe same deposit, only one sample wastaken at each location. The different sed i-

42 Barge J. Wigum & Vigga Jensen

Even though the amount of cataclasticrocks declines with increasing transportati­on distance , the relatively high contents ofsuch rocks in samples located more remo­tely and downstream from the mylonitezones, indicate a high 'survival potential' forthese rock-types. It is evident from Figs. 5, 7& 8 that samples close to the mylonitezones contain a relatively higher amount ofcataclastic rocks in the 2-4 mm fraction thanin the 1-2 mm fraction. This trend is rever­sed for samples more remote from themajor mylonite zones. It appea rs that cata­clastic rocks are dominant in the 2-4 mmfraction in comparison with the 1-2 mm frac-

NGU . BULL 428. 1995

tion for transportat ion distances up to about20 to 25 kilometres downstream from bothmylonite zones. For transportation distan­ces greater than 20 to 25 kilometres, cata­clastic rocks in the 1-2 mm fraction aremore prevalent. The high 'survival potent ial'of cataclastic rocks could be explained bythe observat ion that such rocks are moredurable to mechan ical abrasion than mostother rock-types (Brattli 1994). Therefore,cataclastic rocks will be able to survive gre­ater transport distances than other rock­types of similar origin without significanterosion of material. Those particles in the 2­4 mm fraction will contr ibute to the amount

Limit acco rding to DGB

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/ /' Rogaland/ Nord-Tronde lag

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Cataclas tic Rocks (volume %)

Fig. 4. Distribution of cataclastic rocks in 88 aggreg ate samples located in different counties in southern Norway; based on petro ­graph ic examination at SINTEF Structures and Concrete 199 1·1995.

NGU • BULL 428. 1995 Borge J. Wigum & Viggo Jensen 43

\,,.:,

I

II,-,

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~ Various ot her rocks

o

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[] Cataclast ic rocks

iiI Vulcanic rocks

Fig. 5. Sample locations investigated in the southeastern Precambrian province. Graphical presentation of some rock assemblagesin the 1·2 mm fract ion, and the ratio of cataclastic rocks (1-2 mm/2-4 mm). The main glacial movement in the region has beentowards the SSW. (Geological map modified from Sigmond et al. 1984).

44 Barge J. Wigum & Viggo Jensen

of cataclastic rocks in the 1-2 mm fraction,as a result of their undergoing erosion andcomminution after travelling long distances .

The four samples (no. 6-9) which wereobtained from the same location at Monademonstrate the homogeneity between dif­ferent layers within the same glaciofluvialdeposit (Fig. 8). No significant differenceswere observed in the 1-2 mm fraction forsamples from the coarse-, fine- and medi­um-graded layers. However, in the 2-4 mmfraction an unusually high content of cata­clastic rocks was found in the medium layer(no.8). No reasons are given for this ano­malous result; however, such uncharacte-

D Granit es/gneisses

NGU - BULL 428. 1995

ristic behaviour could significantly influencethe statistical variation when testing andapproving materials for concrete purposes.

Some of the aggregate samples (nos.3 and6-9) which contained particles of cataclasticrocks were located up to 40 km downstreamfrom their origin in the mylonite zones, inrelation to the main ice movement.However, glaciofluvial transportat ion ofmateria ls will not necessar ily follow themain ice flow direction, rather it will begoverned by local topography. Hence, thetrue transportation distance for glaciofluvialmaterials will in most cases be longer thanthat indicated by the main ice movement.

[J Cata clastic rocks

§i§! Various other rock s

D Quartz it e (f ine-g rained)

~Amount of cataclastic rocks.Rati6 between fractions ;1-2 mm/2-4 mm

oI

5 kmI

[2] Mylonitic granodiorit ic gneiss

[ill Fault rock s (Cataclasite)

Fig. 6. Sample locations in the investigated area in Verrabotnen. Graphical presentation of some rock assemblages in the 1·2 mmfraction, and the ratio of cataclas tic rocks (1·2 mm/2·4 mm). The main glacial movement has been along Verrabotnen. downSkaudalen to the southwest. (Geological map modified from Gro nlie et al. 1991).

NGU - 'BULL 428, 1995 Barge J. Wigum & Viggo Jensen 45

Table 1. Rockcompositions for all twelvetested glaciofluvial samples, givenas volumepercentages of the 1-2and 2-4 mmfractions.

Sample Location Rock assemblages (%)*

No. No. 1 2 3 4 5 6 7 8 9 10 11 12

051094.05,.1-2 mm 1 23 10 1 51 15051094.05,2-4 mm, 32 -. 13 2 49 4

051094.02,1-2 mm 2 16 1 3 4 72 3 1051094.02,2-4 mm 20 1 9 64 6

061094.09,1-2 mm 3 19 8 2 67 4061094.09, 2-4 mm 13 17 6 61 3

061094.08, 1-2 mm 4 16 2 3 9 61 9061094.08, 2-4 mm 21 2 13 3 50 11

061094.05,1-2 mm 5 10 3 3 9 1 64 10061094.05, 2-4 mm 12 3 4 11 7 58 5

061094.01, 1-2 mm 6 1 13 2 4 1 72 7061094.01, 2-4 mm 11 13 8 5 57 6

061094.02, 1-2 mm 7 1 12 2 3 7 2 64 8 1061094.02, 2-4 mm 3 9 4 9 4 7 59 5

061094.03,1-2 mm 8 1 12 2 1 9 3 66 5061094.03, 2-4 mm 23 3 7 7 4 50 6

061094.04,1-2 mm 9 15 1 3 5 6 65 5061094.04, 2-4 mm 13 3 1 14 3 6 53 7

131094.01, 1-2 mm 10 8 2 89 1131094.01,2-4 mm 7 91 2

131094.02,1-2 mm 11 11 88 1131094.02,2-4 mm 18 78 4

131094.03,1-2 mm 12 17 92131094.03, 2-4 mm 8 92

"Description of the different rock assemblages: 1) sandstones, 2) cataclastic rocks, 3) acid volcanic rocks, 4) argillaceous rocks, 5)greywacke, 6) other rock-types with microcrystalline quartz (e.g. marl), 7) fine grained quartzite, 8) other rock-types containing finedivided quartz (crystal sizes 0.06-0.13 mm), 9) volcanic rockslgabbro, 10) graniteslgneisses, 11) mafic rocks/limestone, 12) otherrocks.

The three samples from Verrabotnen all this case classified as cataclasite. The threeshow a simple mineralogical composition, samples were collected from within a muchconsisting of only a few rock assemblages. smaller area than the nine samples from theThe petrographic examination indicates a southeastern Precambrian area.dominance of granites and gneisses (Fig.6), which are the predominant rock-types in From Fig. 9, it is evident that for transportthe area. The second most frequent rock distances greater than 7 km downstreamassemblage is that of cataclastic rocks, in from the origin of the fault rock, cataclasite

46 Barge J. Wigum & ViggoJensen NGU - BULL 428, 1995

351

0 ,30...-.

~

Q)

S 25=''0> 20'-'<f.l~U0

15I-<

.~ 2 'b......<f.lco::lU 10

co::l...... -'-1-2 mmco::lU 5

- 0- 2-4 mm

0

0 5 10 15 20 25 30 35 40 45

Distance from mylonite zone (km)

Fig.? Distribution of mylonitic rocks, in two different fractions,from locations in the southeastem Precambrian province, rela­ted to distance (km) from the Mjosa - Vanern mylonite zone.Numbers (1,2 & 3) represent the locations of the samples.

25 -r--------------,

rocks in the 1-2 mm fraction are more abun­dant than the 2-4 mm fraction. However, theamount of cataclasite in the 2-4 mm fractionreaches its maximum at the second location(no. 11), only 1 km downstream from theorigin of the fault rocks, and beyond thesedistances the volume fraction decreasesnear the third location (no. 12). In compari­son to results analysed for Figs. 7 and 8,the data for Fig. 9 were only from a profile of10 km. As a consequence of the differencein the area profiled and the difference in themechanical properties of cataclastic rock­types between the two investigated areas, itis unwise to make any realistic comparisonof the trends observed. However, regardingthe amount of cataclasite in the 2-4 mmfraction, it appears that the cataclasiteshows a lower potential to survive transpor­tation over longer distances, than myloniticrocks. This is in accordance with the obser­vations of Brattli (1994) who attributed thisbehaviour to the lower abrasion values forbrittle deformed cataclastic rocks (cataclasi­tes) and various granites in comparison tothe ductile deformed behaviour of myloni­tes.

20 ...

4

The following main conclusions can bedrawn from the present work:

Conclusions

* The results from the data analysis of glaci­ofluvial materials, even those that were notconsidered to be representative forNorwegian glaciofluvial sediments, showedthat cataclastic rocks are a common consti­tuent in the majority of glaciofluvial sedi­ments. This is in good agreement with thegeological bedrock map of southernNorway.- 0 - 2-4 mm

-'-1-2 mm

5

"

5

15

10

0+------+-+--+---+--------+--1o 5 10 15 20 25 30 35 40 45

Distance from mylonite zone (km)

Fig.8. Distribution of mylonitic rocks, in two different fractionsin the southeastern Precambrian province related to distance(km) from the second myJonile zone. The numbers (4,5,6,7&9) represent the different locations of the samples. For locati­ons 6-9, an average values has been applied (no.8). The outli­er (No.8) is not included in the graph.

* In some locations cataclastic rocks consti­tute the major component for all alkali reac­tive rock-types in the aggregate samplesanalysed in the present work. Only about

,.5 % of the investigated samples containedmore than 20 % volume fraction of cataclas­tic rocks. These types of aggregate sampleswere only observed in the counties of SrM­Trendelaq and Oppland.

Barge J. Wigum & ViggDJensen 47

25r---------------,

20

15

10

5

11qI ,

,

12

,, ,

'0

~1-2mm

* The occurrence of particles of cataclasitein glaciofluvial materials follows similartrends to those described for the mylonite.However, the cataclasite appears to be enri­ched in the 1-2 mm fraction rather than the2-4 mm fraction, and occurs much closer tothe fault zone than for mylonites. Thiswould seem to indicate that cataclasites areless durable to mechanical abrasion, whentransported over such long distances, thanmylonitic rocks.

Acknowledgements

Distance from fault zone (km)

The staff at the Department or Geology and Mineral ResourcesEngineering, University of Trondheim and at the SINTEFStructures and Concrete, are thanked for their technical assis­tance. The work is a part of the first author's Ph.D. study, whichhas been funded by the RoyalNorweqian Councll for Scientificand Industrial Research. He would like to acknowledge thecontribution of Dr. S.W. Danielsen and Dr. B. Brattli, for super­vlslon and discussion during the course of the Ph.D study. SIN­TEF Structures and Concrete is acknowledged for access totheir database, and special thanks gO·tD Prof. S. Lippard andDr. H.H.Patel for their help in the editing and revision of thismanuscript.

105

- 0 - 2-4 mm

O-l-------!-------!o

Fig.9. Distribution of cataclastic rocks in two different fractionsin the Verrabotnen area related to distance (km) from the faultzone. The numbers (10,11 & 12) represent the differentlDcati­ons of the samples.

References* Based on literature studies, both the pro­venance and the various processes associ­ated with the comminution and transportati­on of glaciofluvial materials have been iden­tified as the factors which can lead toenhanced amounts of cataclastic rocksoccurring in glaciofluvial materials. Exa­mination of glaciofluvial materials, locatedat various transportation distances from twomajor mylonite zones, showed relativelyhigh contents of cataclastic rocks, in boththe 1-2 mm and the 2-4 mm fractions; whe­reas glaciofluvial materials near mylonitezones show a higher content of cataclasticrocks in the 2·4 mm fraction than in the 1-2mm fraction. The opposite trend is observedfor samples located further away from themylonite zones, particularly in the directionof downstream ice movement. In samplestaken up to 30-40 km downstream from theparent rock, a high content, or an enrich­ment of cataclastic rocks (mylonites), wasfound in the fine fraction (1-2 mm)

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Brattli, B. 1994: The infiuence of cataclasis on abrasion resis­tance ot granitic rocks used as road surface aggregates.Eng. Geol. 37, 149-159.

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Manuscript received April 1995; revised typescript accepted September 1995