An Archean Quartz Arenite–Andesite Association in the Eastern Baltic Shield, Russia: Implications for Assemblage Types and Shield History

Precambrian Research 101 (2000) 313–340

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An Archean quartz arenite–andesite association in the eastern Baltic Shield, Russia: implications for assemblage types and shield history

P.C. Thurston a,*, V.N. Kozhevnikov b

a Precambrian Geoscience Section, Ontario Geological Sur6ey, 933 Ramsey Lake Rd., Sudbury, Ont., Canada P3E 6B5 b Institute of Geology, Karelian Research Centre, Pushkinskaya, 11, Petroza6odsk, 185610, Russia

Abstract

Shallow water sedimentary units are generally considered scarce in Archean greenstone belts. We describe an unusual quartz arenite-subaerial andesite association within the Archean Hisovaara greenstone belt, a fragment of the Parandovo-Tikshozero belt within the Karelian craton of the Baltic Shield. The Hisovaara greenstone belt consists of several lithotectonic assemblages: (1) a komatiite-tholeiite assemblage\2803 Ma (based on ages of cross-cutting dikes); (2) an andesite-quartz arenite assemblage cut by similar dikes; (3) an assemblage of coarse volcaniclastic rocks, and (4) an upper mafic assemblage of tholeiitic basalts with minor pyroxene komatiite volcanic rocks. The andesite-quartz arenite assemblage (100 to ca. 750 m thick) has basal amygdaloidal fragmental andesites overlain by massive andesites, then amygdaloidal and plagioclase phyric andesites. Unconformably overlying the andesite is a unit of quartz-rich sandstones (6–40 m thick) dominated by quartz arenite extending several km along strike. At the north end, the quartz arenite succession consists of basal andesite overlain by quartz arenite exhibiting hummocky cross-stratification followed by aluminous coarse metasediments and sulfidic argillite and an unconformably overlying tholeiite/komatiite unit. At the south end, the succession is basal andesite, regolith, cross-bedded quartz arenite, weathered andesites, a second quartz arenite, argillite and then subaerial rhyolite. REE and HFSE geochemistry has been obtained on the rocks of the andesite-quartz arenite assemblage. The quartz arenites contain low abundances and chondrite normalized patterns vary from relatively fractionated to flat with most of the variation related to grain size, with pebbly units having higher abundance and more fractionated patterns. Combined major and trace element geochemistry indicates that a sodic felsic source with some admixture of mafic material will explain the geochemistry of the quartz arenites. The andesites display moderately fractionated spidergrams with negative anomalies at Ti, Ta and Nb typical of arc volcanism. The andesite-quartz arenite assemblage represents accumulation of shallow water quartz rich sediments in a setting typical of the later stages of arc volcanism in which the volcanic edifice is subaerial at the southern end of the assemblage. However, at the north end, our evidence is interpreted as indicating subaerial andesitic volcanism, subsidence to a shallow marine basin which then deepens and rifts. Therefore the Hisovaara andesite-quartz arenite assemblage provides a linkage in Archean greenstones between assemblages representing continental volcanism and a platform-to-rift setting. The presence of an erosional interval in\2.8 Ga greenstones suggests possible pre-2.7 Ga orogeny in the Baltic shield. The pre-2.7 Ga quartzrich sedimentation is similar in age

* Corresponding author.

0301-9268/00/$ - see front matter Crown copyright © 2000 Published by Elsevier Science B.V. All rights reserved. PII: S0301-9268(99)00093-5 314 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 to platformal assemblages in the pre-2.7 Ga North Caribou terrane of the Superior Province, Canada. Crown copyright © 2000 Published by Elsevier Science B.V. All rights reserved.

Keywords: Archean; Sediments; Volcanism; Quartz arenite; Andesite; Baltic; Superior

1. Introduction The literature on Archean greenstone belts shows that similar quartz arenites have been re- Quartz-rich metasedimentary rocks and spa- ported from platform assemblages in the many tially associated sedimentary carbonates, typical cratons (Thurston and Chivers, 1990). They are of stable platforms, are generally scarce in known in the Dharwar craton, India (Srinivasan Archean greenstone belts (Ojakangas, 1985). Re- and Ojakangas, 1986), in the Bulawayo green- cent work in the Superior Province has revealed stone belt on the Zimbabwian Shield (Bickle et Archean greenstone assemblages containing al., 1975), in the Moodies Group in the Barberton quartz-rich sedimentary units in at least three belt of the Kaapvaal craton (Eriksson, 1980), geodynamic settings: stable shallow water plat- within the Tanzanian craton in the Dodoman forms (Wood et al., 1986; De Kemp, 1987; system (Kimambo, 1984), in the West African Thurston and Chivers, 1990), submarine fans with craton (Rollinson, 1978) and in the Yilgarn (Gee, evidence for cannibalization of platformal rocks 1982) and Murchison (Watkins and Hickman, (Cortis, 1991), and quartz-rich conglomerates and 1988) blocks, Australia. arenites in pull-apart basins (Born, 1995). In the Baltic Shield, quartz arenite-bearing as- Kozhevnikov (1992) identified a spatial associa- semblages have been described in some greenstone tion of andesites and quartz arenites within belts (Fig. 1). In the Koitelainen area, Central Archean greenstones of the Parandovo-Tik- Lapland, the sequence which consists of quartz shozero greenstone belt near the Karelian Belo- arenites, mica schists, phyllites, volcanic conglom- morian collision zone boundary (Glebovitsky, erates and mafic to ultramafic volcanics has an 1973; Volodichev, 1990; Glebovitsky, 1993; age of less than 2.7 Ga and rests on ca. 3.1 Ga Lobach-Zhuchenko et al., 1995; Glebovitsky et granitoids (Kroner et al., 1981). It represents a al., 1996) which caused us to investigate two Lapponian sequence of presumably Lower quartz-rich sedimentary assemblages in this region to assess their similarity with possible Superior Proterozoic age (Gaa´l and Gorvatschev, 1987). In Province analogues. The andesite-quartz arenite North Karelia, Russia, a possible age analogue of association has not been seen in the Superior the above strata is represented by Sumian rocks Province quartz-rich sedimentary units (Thurston, that lie with a regolithic lower contact on Archean 1990). granitoids. In these successions, cross-bedded In the classification of assemblages for Archean quartz arenites form a basal horizon overlain by greenstone belts, quartz-rich sedimentary units andesite-basaltic lava (Korosov, 1991). In the (including quartz arenites) are typical of platform Kostomuksha greenstone belt (Fig. 1), cross-bed- assemblages (Thurston and Chivers, 1990; ded staurolite-sillimanite quartz arenites are asso- Thurston, 1994). The high mineralogical and tex- ciated with pillow basalt (Kozhevnikov, 1982). In tural maturity of these rocks, the presence of the Tipasjarvi belt (Fig. 1), kyanite-staurolite trough and hummocky bedding in them, associa- quartz arenites associated with BIF and black tion with stromatolitic carbonates, and, finally, shales are present in the upper part of the felsic their occurrence over thousands of km2 in the volcanic unit in the lower Koivomaki Formation Sachigo and central Wabigoon subprovinces, (Taipale, 1983). Discussing the origin of these provide a basis for regarding many as members of quartz arenites (weathering, fumarolic activity be- platform successions formed under shallow-water tween volcanic eruptions and metasomatic alter- conditions along a passive continental margin ations), Taipale (1983) concluded that the quartz (Thurston and Chivers, 1990). arenites could be produced during alteration of P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 315 felsic volcanics in the course of ore formation. In According to Thurston (1990), so far no andesites the Kuhmo belt (Fig. 1), quartz arenites with have been found in platform assemblages. When 2.8–3.0 Ga detrital zircons (Hyppo¨nen, 1983) distinguishing the types of assemblages most re- were described from the Hietapera-Kivivaara area cently proposed for Archean greenstone belts, the (Piirainnen, 1988), where they form part of a felsic andesite-quartz arenite association revealed in the volcanic-sedimentary unit in the Juurikkaniemi Hisovaara greenstone belt is considered a fairly Formation which consists of metarhyolites, rare type of assemblage with a ‘continental’ style metadacites, volcanic breccia, lapilli tuffs, tuffites of volcanism whose depositional environment is and tuffaceous turbidites. The age of this unit is ‘open to speculation’ (Thurston, 1994). However, estimated at 2798915 Ma (Hyppo¨nen, 1983). knowledge of such an assemblage type may be Northwards, in the Moisiovaara area (Fig. 1), useful in discussing models for the tectonic evolu- immature sericitic quartz arenites associated with tion of greenstone belts and in comparative analy- polymictic conglomerates lie between tholeiites sis and correlation of Archean cratons. and komatiites. An old tonalite–trondhjemite– granodiorite complex and felsic rocks from the Kuhmo belt are regarded as sources of 2996960 2. Geological setting and 28039238 Ma detrital zircons (Hyppo¨nen, 1983) as well as clasts in congomerates (Lu- 2.1. Regional setting ukkonen, 1988). In the Hisovaara greenstone belt (Fig. 2), quartz arenites are described in associa- The Hisovaara greenstone structure is a frag- tion with underlying andesites as well as overlying ment of the Archean Parandovo-Tikshozero felsic volcanics and sedimentary rocks greenstone belt which extends for 300 km along (Kozhevnikov, 1992; Kozhevnikov et al., 1992). the Belomoride-Karelide boundary, i.e. along the

Fig. 1. Map showing Archean greenstone belts in the Fenno-Karelian craton (after Rybakov and Kulikov, 1985). Revised after: (Lobach-Zhuchenko, 1988; Kozhevnikov, 1992; Glebovitsky, 1993). Numbered localities represent occurrences of Archean quartz- rich metasediments. 316 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340

Fig. 2. Geological map of the Archean Hisovaara greenstone belt. P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 317 boundary between the Karelian granite-green- 2.3.1. Lower mafic assemblage stone province and the Belomorian collision zone The lower essentially volcanic assemblage is (Glebovitsky, 1973; Volodichev, 1990; Glebovit- comprised from the base upwards of cumulate sky, 1993; Slabunov, 1993; Lobach-Zhuchenko et peridotitic komatiites, tholeiitic massive and rarer al., 1995; Glebovitsky et al., 1996) (Fig. 1). pillow basalts, basaltic to pyroxenitic komatiites and ferrobasalts. This sequence is characterized 2.2. Structural geology and metamorphism by thick (up to 10 m) massive and fairly uniform flows with scarce thin-bedded tuff horizons, the The Hisovaara greenstone structure is a syn- absence of interflow sediments, and amygdaloidal form thrown into composite folds, composed textures all indicative of a mafic plateau type of largely of supracrustal rocks and surrounded by volcanic setting (Thurston, 1994). The U-Pb zir- crosscutting granitoids (Fig. 2). It displays evi- con age of felsic dykes cutting this assemblage was dence for multiple folding events (Systra and Sko- estimated by O.A. Levchenkov to be 2803935 rnyakova, 1986; Shchiptsov et al., 1988) Ma (Kozhevnikov, 1992). subsequently generalized into three deformation stages (Kozhevnikov, 1992). The rocks have suf- 2.3.2. Second 6olcanic-sedimentary assemblage fered polymetamorphism of Archean and Sve- The second assemblage consists of volcanics, cofennian (1.8–2.0 Ga) ages, the latter taking volcano-sedimentary, and chemical sedimentary place in a high pressure regime with the following rocks of intermediate to felsic composition. Its parameters: T=580–640°C, P=6.5–7.5 kbar lowermost unit is comprised of calcalkaline andes- (Glebovitsky and Bushmin, 1983). Archean hy- ites. They are overlain by quartz arenites, and at drothermal processes associated with felsic mag- point B (Fig. 2) there is an alternation of andesite matism (Kozhevnikov, 1992, 1995) are apparent and quartz arenite. Resting on the quartz arenites together with Svecofennian metasomatic rocks is a thick sequence of felsic rocks including lavas, represented by retrograde metamorphism (T= ash-flows, tuffaceous turbidites and chemical sedi- 300–350°C) (Bushmin, 1978; Glebovitsky and ments with a clastic component that show compli- Bushmin, 1983). The complicated tectonic and cated lateral relationships. Intense metasomatic metamorphic history of the Hisovaara greenstone and deformational processes strongly distort and belt is largely due to its proximity to the 2.70– sometimes obliterate the primary textures and 2.68 Ga Belomorian collision zone (Lobach- compositions of these strata making interpreta- Zhuchenko et al., 1995) and later Proterozoic tion difficult. Where these processes are least in- events (1.95–1.75 Ga) (Bibikova, 1995). tense, there are some indications of graded ash flows and pyroclastic breccias as well as flows 2.3. Lithologic assemblages with massive and flow top breccia textures. The volcano-sedimentary rocks have some features in- Several major assemblages of supracrustal dicative of graded rhyolitic turbidites with alu- rocks are distinguished in the Hisovaara green- mina-enriched upper parts. Transitional stone belt (Kozhevnikov, 1992). The northern and clastic-chemical sedimentary rocks represented by southern flanks of the synform differ substantially carbonaceous schists (sulfidic argillites), alumino- in character, largely as a function of lateral facies silicates and cherty rocks occur as thin horizons variation, and the types of crosscutting intrusive and lenses among felsic volcanosedimentary rocks etc. (Table 1). Because the andesite-quartz rocks. The uppermost 100 m of this sequence arenite association is revealed only on the north- consists of thin, graded carbonaceous and carbon- ern flank of the structure, only units on the north ate-bearing silty sandstones. flank are described below in detail. The unit ter- minology of Kozhevnikov (1992) is retained in 2.3.3. Third rudaceous assemblage subsequent sections of this paper for ease of ac- Coarse clastic rocks dominate a third assem- cess to the Russian literature. blage forming two wide zones in the centre of the 318 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 0.15 km. 5 structure Southern flank Intensely foliated tholeiitic basalts and minor tuffs. Thickness Predominantly bedded andesite tuffs. Thickness 0–300 m.tuffs Quartz-rich with oxide- and silicate-facies BIF horizons. Carbonaceous schists belt. structure in the south.not Scarce found. rhyolite Gabbro, dykes. gabbro-pyroxenite,and Andesite-basalt–dacite granodiorite dykes. sills and komatiite sills 0–100 m. Graded + –40 m. Rhyolitic lava and not found. Individual beds and units laterally persistent in thickness, n + Northern flank Quartz-rich arenite horizons withcross-bedding. hummocky Thickness and trough graded bedded ashflows, gradedCarbon-bearing rhyolitic sulfidic turbidites. argillites, conglomerates,alumino-silicate and siliceous rockswith closely felsic associated volcanics. Thickness thin-laminated bedding carbon- parallel and in carbonate-bearingVariable plan siltstones. thickness view, of absence no individual ofas indications beds sharp complex of and lateral lateral cross-bedding units transitions transitions andassociation. as are are the Indications well characteristic. characteristic of of cross-beddingthe the are quartz common arenites. in Thick oligomictic conglomerate (?) or volcaniclastic rock the north. Rhyodacite-rhyolite dykesAndesite-basalt–andesite-dacite and sills. stocks. Gabbro, gabbro-diorite and komatiite sills and dykes. Komatiitic, tholeiitic and ferrotholeiitictuffs. lavas Thickness and 0.5–1.7 scarce km. Andesitic lavas and pyroclasticsubaerial–subaqueous flows volcanism. with Thickness indications 100–700 of m. with felsic lava breccia. Massive and pillowed tholeiitickomatiite basalts horizons with (?) thin atLocally the microclinized base. tonalites rimming the structure in volcanic–sedimentaryassemblage units with tuffmatrix (?) in the east closely associated sediments not found. Felsic volcanics not characteristic. Coarse-bedded assemblage Table 1 Some characteristics of associations at the northern and southern flanks of the Hisovaara greenstone belt that illustrate its asymmetric geological Assemblages Third Rudaceous Polymictic conglomerates with dominantly felsic volcanic pebbles of the Lower Mafic assemblage Second Upper Mafic assemblageIntrusive rocks Massive and pillowed tholeiitic basalts. Plagiomicrocline and garnet-muscovitic microcline granites rimming the P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 319

tion pattern with the sills and dikes concentrated on the northeast side of the belt (Fig. 2, Table 1). As the goal of the present paper is to character- ize and interpret a quartz arenite–andesite association, uncommon for Archean greenstone belts, these units are described in more detail below.

3. Quartz arenite-bearing assemblage

This assemblage is comprised of three members: calc-alkaline andesites (unit A), quartz arenite horizons (unit Q) and a unit dominated by felsic Fig. 3. Fragmental andesite with 15–30 cm fragments of massive andesite with fragments of uniform mineralogic com- volcanic, volcano-sedimentary, reworked volcanic position but varying in colour from grey to green. North shore and chemical sedimentary rocks (unit F). The of Lake Verkhnee; hammer 35 cm long. boundary between the andesites (unit A) and the underlying Lower Mafic assemblage is most prob- belt as well as thin lenticular units among the ably a thrust, indicated by intense carbonatization rocks of the previous assemblage. Some indica- and silicification near the contact as well as tions of discordance between these rocks and the marked (up to 1300%) stretching of the andesite underlying and overlying assemblages are appar- (amygdale elongation along the a-lineation paral- ent in the map patterns (Fig. 2). The dacite-rhyo- lel to dip) (Kozhevnikov et al., 1992). The upper lite to rhyolite clasts within these rocks are boundary of the assemblage is the unconformity compositionally uniform and are more felsic than at the base of the coarse clastic assemblage and the dacitic matrix. This unit may represent either the upper mafic assemblage. oligomictic conglomerates or matrix-supported volcaniclastic rocks. The latter interpretation is 3.1. Andesite unit (unit A) favoured by their close association with felsic flow top breccia observed at some localities. 3.1.1. Field description Massive amygdaloidal, glomeroporphyritic and 2.3.4. Upper mafic assemblage coarse pyroclastic andesites are distinguished. The The fourth essentially volcanogenic assemblage andesite unit varies markedly in thickness (100– is represented by a thick pile of pillowed tholeiitic 700 m) laterally (Fig. 2). In the thickest part of basalts with some thin pyroxenitic komatiite flows the andesite unit, the following succession of rock and sills in the lower part. This unit rests uncon- types is observed from the base upward: (1) ca. formably on the second and third assemblages 200 m-thick amygdaloidal, partly coarse, frag- and is cut by individual undated rhyodacite and mental andesites (Fig. 3); (2) massive andesites granodiorite dykes. locally showing some vague indications of internal heterogeneity (thickness about 450 m); (3) amyg- 2.3.5. Intrusi6e rocks daloidal types, seldom with indications of primi- Near the margins of the belt, supracrustal rocks tive pillow textures; thickness on the scale of a few are cut by tonalites in the north and by granites in metres to tens of metres; and (4) thick andesite the south. The interior of the belt is cut by flows with concentrations of plagioclase phe- andesite-dacite sills, rhyodacite-rhyolite (quartz nocrysts (occasionally glomerophenocrysts) to- and quartz-plagioclase porphyry) dykes and ward the top. The thin glomeroporphyritic stocks as well as mafic and ultramafic sills and andesite horizon is overlain by the quartz arenite dykes. The rocks that cut the volcano-sedimentary unit that can be mapped laterally for several km. assemblages show an asymmetric areal distribu- However, there are substantial structural differ- 320 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 ences between detailed sections A and B (Fig. 2). quartz arenite horizon (Fig. 6). In the ca. 50 The basic difference lies in the fact that on the cm-thick zone near the contact, weathering in the southern shore of Lake Verkhneye (section B) two andesite is indicated by rock disintegration and stratigraphic subunits of andesites (A1 and A2) fine regolith-filled cracks. The andesite immedi- are distinguished (Fig. 4). Here, as in section A, ately beneath the quartz arenite contact displays glomeroporphyritic andesites are overlain by a coarse garnet and quartz stringers not found else- cross-bedded quartz arenite unit. Resting on the where in the unit. These features suggest modifica- quartz arenites are two texturally similar andesite tion of original chemical composition near the horizons, each 6–7 m thick. The horizons consist contact. At two points, the reddish colour of of flow material succeeded upwards by subunits andesite, observed near the contact within a ca. which display vertical grading from pyroclastic 1.0 m-wide band, is due to groundwater circula- breccia to tuff and lapilli tuff. The third horizon, tion in the more porous contact zone. a massive flow is overlain by a ca. 7.0 m-thick quartz arenite bed (Fig. 5). Except for this local- 3.1.2. Petrography ity, no sedimentary rocks have been found in the All varieties of andesites have consistent min- andesite unit. All the contacts between andesites eral compositions. Their distinct crystallization, and quartz arenites are well-defined and occasion- schistosity, mineral or aggregate lineation and ally tectonized. nematogranoblastic structure indicate the meta- In section B, A.B. Samsonov exposed a contact morphic nature of the mineral assemblages. The between glomeroporphyritic andesites and a lower assemblage green hornblende+plagioclase (An=

Fig. 4. Outcrop map of the andesite-quartz arenite association in the section B area. P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 321

23%)+quartz+brown biotite+chlorite+epi- dote is most common. Magnetite and apatite occur as accessories. Hornblende is clearly oriented along the earlier lineation which is parallel to the dip. The homoaxial replacement of hornblende by colour- less twinned cummingtonite, observed along ca. 10 m-thick subconcordant zones within the andesite unit, suggests a local rise in temperature in these zones. The formation of carbonate (ankerite) near the lower contact with ferrobasalts is related to the circulation of carbon dioxide solutions in the tec- tonically active contact zone. In a ca. 1.0 m-thick zone near the upper contact with the quartz arenite unit, the garnet poikiloblasts with numerous unde- formed rounded quartz inclusions are ﬂattened in the schistosity plane. Also in this zone, large hornblende poikiloblasts are oriented across earlier lineation along the late subhorizontal lineation

which is parallel to the Ac-axes of late shear zones. Fine (up to 2.0 mm) granoblastic quartz veinlets and chlorite rosettes, concordant with schistosity, are observed here. In amygdaloidal andesites, amygdales are ﬁlled with milky quartz as well as quartz-plagioclase or quartz–chlorite–carbonate aggregates. Plagioclase plates, up to 1.0 cm in length, that occasionally form stellate aggregates Fig. 5. Stratigraphic columns for andesite-quartz arenite asso- are characteristic of glomeroporphyritic andesites. ciation in sections A and B. Sample numbers appear to the left of the columns. 3.1.3. Geochemistry The Hisovaara andesites belong to the tholeiitic magma clan using the scheme of Jensen (1976). With respect to major element geochemistry, the Hisovaara andesites are tholeiitic andesites similar to those of the Blake River Group in the Abitibi greenstone belt (Xie, 1996). Based on the ﬁeld appearance of the unit in general and the low LOI values, we expected to see little evidence for alteration. Two pairs of andesite samples (94-PCT-002 & 004 and 94-PCT-022 & 023) were taken, with one of each pair from within a few cm of the quartz arenite and the other member of the pair from 1–2 m beneath the contact. When major element data for the andesites are compared, we observe with increasing proximity to the contact: addition of Fe+3, K, and P, loss of Mg and Fig. 6. The basal contact of the quartz arenite with the +2 underlying andesite at location B. The lighter coloured quartz Na and variable behaviour of Si, Fe , Al, Na and arenite lies above the lighter (about 7.5 cm long) and the Ca. Spidergrams of trace element geochemistry weathered andesite beneath the lighter. (Fig. 7) display a fractionated pattern with nega- 322 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340

tive anomalies for TiO2, Ta and Nb typical of tion of the HREE. Precambrian weathering of island arc volcanism. The negative Hf anomalies basaltic rocks (Kimberley and Grandstaff, 1986) in some samples are due to incomplete sample results in Na depletion, variable behaviour of the dissolution verified by comparing Zr values ob- heavier alkalies (K,Rb, Cs) and the alkaline earths tained by XRF with those obtained by ICP-MS (Ca, Mg). Fe shows an upward decrease into the and corroborated by complete dissolution of simi- paleosol but this pattern can be disturbed by lar samples using the closed beaker technique downward percolation of Fe-bearing ground- (Jenner, 1996). water. These authors also report depletion of the REE data for these sample pairs are plotted in LREE in weathering of the Kinojevis basalts in Fig. 8a and b. The LREE are quite variable for a the Abitibi subprovince. In general the behaviour suite of samples obtained within a stratigraphic of REE in weathering of mafic rocks seems some- section of a mesoscopically similar rock type a what variable (Braun et al., 1990; Marsh, 1991; few metres in thickness. In basaltic rocks within a Price et al., 1991). Leaching experiments indicate coherent unit, LREE variation is conventionally that incipient alteration tends to release REE with ascribed to fractionation of clinopyroxene9pla- behaviour controlled by groundwater parameters gioclase. No conventional igneous fractionation (flux, Eh, pH) and the secondary minerals pro- process will yield sample-to-sample variation in duced during alteration (Price et al., 1991). The Ce anomalies or crossing REE patterns. proximity of samples 94-PCT-004 and 94-PCT- Comparison of the samples immediately under- 022 to the quartz arenite contact and the presence lying the quartz arenite vs. those somewhat re- of mineralogical changes near the contact and the moved from the contact reveals: marked LREE similarity to the above studies of Precambrian and depletion, a negative Ce anomaly, some depletion younger basaltic weathering suggest that the of the HREE and loss of Rb and Cs (Figs. 7 and chemical changes we observe may be related to 8a, b). A sample of the regolith (Fig. 8c) shows weathering of andesite. If the alteration were due negative Ce and Eu anomalies and extreme deple- to recent weathering, this cannot explain the min-

Fig. 7. Spidergram (extended trace element diagram) using the normalizing factors of Wood et al. (1986) for the Hisovaara andesites. P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 323

eralogical differences in samples proximal to the quartz arenites, reddening of the fresh surface near the quartz arenite or the more intense alteration being in samples taken closest to the quartz arenites. Therefore weathering took place prior to quartz arenite deposition. 3.2. Quartz-arenite (unit Q) 3.2.1. Field description Quartz arenites associated with andesites were traced over several kilometres on the northern flank of the Hisovaara structure and were studied in detail at some localities (Fig. 2). Quartz arenite unit Q is subdivided into subunits Q1 and Q2. Lower subunit Q1, in contact with the andesite unit, was revealed at all the points shown on the map (Fig. 2). Upper subunit Q2 was found only on the northern shore of Lake Verkhneye in section B. Considerable variations in diverse textures and primary structures, apparent both laterally and vertically, are characteristic of unit Q. For example, subunit Q1 varies in thickness from 6–8 m (points C and D, Fig. 2) to 10–12 (points B, E, 913) and even 40 m in section A. Other differences are apparent in comparing sections A and B. In section A, white fine- to medium- grained thin-laminated quartz arenites rest with a sharp direct contact on glomeroporphyritic andesites (Fig. 9). Hummocky cross-bedding with characteristic low angles between cross-bedded units and erosion surfaces is observed in some out- crops, depressions being filled with micaceous (argillic) material (Fig. 10). Quartz clasts are predominantly sand sized, except sample 94-PCT-012 that includes small (B1.0 cm) quartz pebbles. The fairly high degree of rounding of fine quartz pebble material reflects the textural maturity of the rocks. The prevalent white colour of the rocks with a very small admixture of stained minerals indicates the high mineralogical maturity of these quartz arenites. One-centimetre-thick feldspar-rich laminae are preserved locally. Primary stratification is retained, despite a pressure-solution cleavage which cross-cuts bedding at a medium angle. Fig. 8. (A) Chondrite normalized REE profile for andesites The rocks are recrystallized strongly enough to 94-PCT-002 and 94-PCT-004 taken from beneath the quartz arenite at location A. (B) Chondrite normalized REE profile form metamorphic quartz veins, with the degree for andesites 94-PCT-022 and 94-PCT-023 taken from beneath of recrystallization increasing toward the upper the quartz arenite at location B. (C) Regolith. contact of subunit Q1. 324 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340

tion A. Here, a 10–20 cm-thick fine pebble quartz conglomerate horizon lies at its base and has a sharp contact with weathered glomeroporphyritic andesite. White, moderately rounded, flattened quartz pebbles, up to 3.0 cm in size along the long axis, are closely packed and supported by sand- sized mica and quartz matrix. These rocks gradu- ally pass upwards to fine pebble arenites. Poorly rounded, often angular pebbles measuring 1.0–1.5 cm are represented solely by white quartz. The grey quartz arenite matrix consists of unequally rounded commonly angular quartz grains, 1.0– Fig. 9. Unconformity between massive andesite (bottom of 2.0 mm in size, with the addition of biotite, which photo) and overlying quartz arenite. Lighter colour of andesite suggests the low textural and mineralogical matu- adjacent to the quartz arenite can be seen. Lens cap, 52 mm in rity of the rock. In this unit, which has an ex- diameter. posed thickness of ca. 7.0 m, trough bedding, most distinct in its lower half, is obvious. The In section B, both subunits are represented, upper contact between subunit Q1 and the andes- with subunit Q1 markedly differing in some char- ites of subunit A2 is not visible because it is acteristics from its stratigraphic analogue in sec- covered by Quaternary deposits.

Fig. 10. Map of quartz arenite exposures with hummocky cross-bedding (subunit Q1) in section A. P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 325

The second quartz-rich rock horizon (subunit occur as newly-formed grains or chains of mica, Q2) is up to 7.0 m thick. It rests with a sharp amphibole, garnet, kyanite, staurolite and chlorite contact on the weathered andesites of subunit A2. aggregates. Zircon, sphene and opaque ore miner- Subunit Q2 differs in some macroscopic features als occur as detrital accessories. from subunit Q1. It is characterized by: Pebbly quartz arenites are second in abundance 1. The yellowish, locally rusty colour of the rocks in the section. Unlike the quartz arenites de- caused by the presence of ﬁnely dispersed al- scribed above, they contain polycrystalline quartz tered iron sulphides. interpreted as vein quartz strongly elongated

2. Thin, locally deformed parallel lamination. along the Ac axis which is parallel to the mineral 3. A dominant sand size and smaller dimensions lineation and dip of the rocks. In cross section, of quartz grains and scarce thin (10–15 cm) normal to lineation, various shapes of quartz horizons containing fine (B1.0 cm) quartz pebbles (subrounded to angular, but generally pebbles (sample 94-PCT-015). poorly rounded) that vary in size from 0.2×1– 4. The presence of ca. 30 cm-thick horizons with 1×2 cm (over 5 cm along lineation) in these very fine-grained (B0.05 mm) quartz (sample cross-sections are easily observed in sawed slabs. 94-PCT-021). Individual quartz pebbles constitute thin centime- 5. The occurrence of thin (10–15 cm) muscovite- tre-scale laminae in quartz arenites that provide enriched horizons (sample 94-PCT-019) re- the matrix for coarser quartz. Trace minerals and sponsible for the graded nature of individual accessories are similar to those described above, beds of this subunit. but their quantities vary markedly. For example, Resting directly on subunit Q2 are 2.0–3.0 m of pebbly quartz arenites from section B contain carbonaceous rocks overlain by felsic rocks that more biotite, and at station 913 zircon is present represent rhyolitic ash flows. in large amounts (about 30 grains in one thin section). 3.2.1.1. Petrography. Highly siliceous rocks are In subunit Q2, two more rock types were seen divided based upon microscopy into several types in section B. In sample 94-PCT-021, fine that differ in the nature of clastic material, the equigranular quartz (grain sizeB0.05 mm) in degree of quartz recrystallization, and the rela- which individual coarser (1–2 mm) deformed de- tionships between quartz and other silicates etc. trital grains are observed. The quartz arenites pass Quartz arenites, the most abundant rock type upwards into thin-laminated muscovitic quartz of the unit, are bedded rocks in which quartz-rich arenites. This subunit includes chemical sediments beds alternate with beds that contain quartz and and tuffaceous material. other silicates. Ninety to ninety-five per cent of Several populations of zircon are found in the the rock consists of quartz grains varying from quartz-rich sedimentary rocks of the quartz 0.2 to 2–3 mm in diameter. Intense recrystalliza- arenite-andesite association at Hisovaara. The tion gives rise to the less common sutured polygo- transparent long-prismatic grains are probably nal boundaries of grains in quartz monocrystals metamorphic based upon similarity to metamor- and deformation that continues until lenticular phic zircons (cf. D.W. Davis, pers comm 1996) aggregates are formed. It is, therefore, impossible Rounded, transparent and dark metamict grains to estimate the degree of roundness of fine clastic are prominent among detrital zircons. Of great quartz. Two types of plagioclase are observed in interest are scarce poorly rounded, broken zircon the quartz arenites: (a) fine, poorly rounded clas- prisms that may indicate a fairly proximal source tic grains are commonly filled with grey dust-like of zircon. It is also important that both macro- opaque material along cleavage cracks, which is scopic and petrographic observations point to the presumably due to weathering; (b) newly-formed absence of lithic fragments in the quartz arenite plagioclase grains occur together with garnet and unit. Vein quartz pebbles and clastic zircons are amphibole in the form of fine chains that fill the most distinct indications of detritus whose interstices between quartz grains. Trace minerals textural maturity was presumably variable. A neg- 326 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340

Table 2 Mean chemical compositions of quartz-arenites from Hisovaara and other Archean regionsa

1234 5678

SiO2 94.494.5 92.13 95.97 87.02 88.65 92.11 93.45 TiO2 0.040.05 0.06 0.02 0.1 0.26 0.07 0.04 Al2O3 2.21 2.44 4.34 2.24 4.47 7.71 4.58 4.07 Fe2O3 1.581.4 1.07 0.79 1.95 0.7 1.09 0.55 MnO 0.020.02 0.01 0.01 0.08 0 0.01 0.02 MgO0.42 0.35 0.31 0.2 2.47 0.44 0.88 0.27 CaO 0.43 0.26 0.26 0.07 2.98 0.1 0.09 0.14

Na2O 0.760.46 0.98 0.04 0.07 0.36 0.24 0.17 K2O0.15 0.42 0.83 0.65 0.83 1.76 1.01 1.24 B P2O5 0.020.05 0.02 0.01 0.02 0.01 0.01 0.03 SiO2/Al203 42.738.8 21.2 42.8 19.5 11.5 20.1 23 K2O/Na2O0.2 0.9 0.8 16.2 11.9 4.9 4.21 7.3 Al2O3/Na2O 2.9 5.3 4.2 56 63.9 21.4 19.1 23.9 CIA 5263 62 71 n.d. 74 73 69 N 1049 1 22 3 8 49

a Recalculated to 100% on a volatile-free basis. (1–4) Quartz arenites from Hisovaara: quartz arenites, subunits Q1 (1) and Q2 (2); pebbly quartz arenites, subunits Q1 (3) and Q2 (4). (5–6) Quartz arenites, Keewaywin formation (5) and Keeyask Lake Formation (6), Sandy Lake greenstone belt Superior Province, Canada (Cortis, 1991). (7) Quartz arenites, Pongola supergroup, S. Africa (Wronkiewicz, Condie, 1989). (8) Quartz arenites, Yavanahalli belt, S. India (Argast and Donnelly, 1982).

ligible amount of plagioclase and the absence of Hisovaara quartz arenites contain more SiO2, lithic fragments suggest that in a quartz-feldspar- CaO and Na2O and less Al2O3 and K2O. Their lithic fragment sandstone provenance, the compo- SiO2/Al2O3 ratio is higher and K2O/Na2O ratio is sitions of the quartz-rich metasediments of the lower. The high CaO content of the quartz quartz arenite-andesite assemblage at Hisovaara arenites in the Keewaywin Formation is obviously lie on the ‘quartz-feldspar line’ near the quartz due to superimposed carbonatization (Cortis, apex (i.e. in field 1), suggestive of a cratonic 1991). The CIA value (CIA=[Al2O3/(Al2O3 + provenance (Dickinson, 1985). CaO+Na2O+K2O)]×100; Nesbitt and Young, 1982) estimated for this group is not given be- 3.2.1.2. Geochemistry. The major and rare earth cause in the calculations CaO represents Ca in a element geochemistry of quartz arenites and asso- silicate form (McLennan et al., 1990). Many sam- ciated rocks from the Hisovaara greenstone belt is ples collected in subunit Q1 show ultralow (B0.2) shown in Tables 2–4. Both field and microscopic K2O/Na2O ratios (Fig. 11). The above character- characteristics are used to define three groups: istics of the rocks described, emphasized by the quartz arenites Q1 and Q2 and pebbly quartz strong predominance of Na2O over K2O, indicate arenites Q1. Pebbly quartz arenite (sample 94- that the matrix of Hisovaara arenites, in which PCT-015) and mica quartz arenite (sample undecomposed plagioclase grains play a major 94PCT-019) from subunit Q2 were analysed sepa- role and the pelite component is less significant rately. In the above groups, some major compo- and chemically immature. The only exception is nents such as SiO2,Al2O3, FeO, Fe2O3, CaO, mica quartz arenite (sample 94-PCT-019) which is Na2O and K2O vary over a wide range. Variations abnormally poor in SiO2 and abnormally rich in in TiO2 and MgO content are less appreciable. We Al2O3 and K2O. compare the average compositions of the Hiso- The chemical indices of alteration (CIA; Nes- vaara quartz arenites with similar rocks from bitt and Young, 1982), calculated for the above other Archean regions (Table 2) but they have rock groups are much lower than those for quartz some distinctive characteristics. For example, arenites from other Archean regions. This indi- P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 327

Fig. 11. SiO2/Al2O3-K2O/Na2O plot for quartz arenites. cates the lower chemical maturity of quartz There are marked differences in REE distribu- arenites at Hisovaara. The lowest mean CIA value tion pattern between the groups studied. This of 52 was determined for the quartz arenites of primarily applies to the quartz arenites of sub- subunit Q1. A fairly unusual combination of low units Q1 and Q2. In subunit Q1, two types of chemical maturity and very high SiO2 content, samples are distinguished. Type 1 (samples 94- observed in the rocks discussed, is largely respon- PCT-005 and 011) is characterized by slightly sible for their trace element geochemistry. fractionated REE distribution (LaN/YbN =2.78– Analysis of REE content and REE distribution 4.32), ﬂat HREE distribution (GdN/YbN =0.9– patterns has revealed some distinctive features of sedimentary rocks at Hisovaara. First of all, it should be noted that their SREE values are much lower than those of Pongola quartzose sandstones (Fig. 12). Extremely small quantities of rare earths (SREE=4.46–15.20 ppm) were determined for the quartz arenites of subunit Q1. The pebbly arenites of both subunits and the quartz arenites of subunit Q2 contain REE in much greater quantities. The REE content of mica quartz arenite in sample 94-PCT-019 is abnormally high (SREE= 96.76 ppm). This supports the conclusion that REE dominantly form part of micas, i.e. the argillic matrix of quartz arenites (Wronkiewicz and Condie, 1989). All rock samples show a nega- Fig. 12. Chondrite-normalized generalized REE diagrams for tive Eu anomaly Eu* (Eu*=Eu /(Sm ,Gd )1/2) quartz-rich sedimentary rocks at Hisovaara and Pongola n n n (Wronkiewicz and Condie, 1989). Hisovaara rocks are value of 0.67 (Taylor, 1979). About 80% of markedly depleted in REE. Both groups are similar to typical Archean sedimentary rocks have Eu*]0.85 post-Archean REE distribution pattern with a negative Eu (McLennan et al., 1984, 1990). anomaly. 328 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340

Fig. 13. Chondrite normalized REE proﬁles for Hisovaara quartz arenites. (A) Unit Q1 type 1; (B) unit Q1, type 2; (C) unit Q2 fractionated REE patterns; and (D) pebbly quartz arenites.

1.02), a higher Eu/Eu* value (0.75) and a mini- ples 94-PCT-019 and 021 show maximum REE S S mum REE value (4.46–6.41 ppm) (Fig. 13A). (LaN/YbN =24.57 and 25.43) and REE (GdN/ Type 2 (samples 94-PCT-007, 008 and 010) is YbN =3.08 and 2.76) fractionation, but they dif- characterized by a higher LaN/YbN ratio (8.82– fer markedly in Eu/Eu* ratio (0.82 and 0.59, 12.15), more fractionated SREE distribution respectively) (Fig. 13C). In both subunits, pebbly

(GdN/YbN =1.74–2.0), lower Eu/Eu* values quartz arenites generally have more persistent (0.59–0.74) and higher SREE values (10.23– REE and SREE fractionation patterns, but their 15.20 ppm) (Fig. 13B). Subunit Q2 shows even Eu/Eu* values vary substantially (0.53–0.80) (Fig. more diverse REE characteristics. For example, 13D). Sample 94-PCCT-017 from altered felsic sample 94-PCT-016 is fairly similar in REE frac- tuff differs greatly in REE distribution from the tionation pattern (LaN/YbN =3.91, GdN/YbN = rocks described. It has a slightly fractionated 0.92) to samples of type 1 from subunit Q1. (LaN/YbN =2.46) REE distribution, marked S However, its higher REE value is observed to- REE enrichment (GdN/YbN =0.76) and a pro- gether with a far more intense negative Eu nounced positive Eu anomaly (Eu/Eu*=2.00) anomaly (Eu/Eu*=0.59) (Fig. 9A). Samples 018 (Fig. 13C). and 020 occupy an intermediate position in terms In the GdN/YbN –Eu/Eu* diagram (McLennan of REE characteristics between types 1 and 2 in and Taylor, 1991), Hisovaara quartz-rich sand- subunit Q1 (LaN/YbN =8.29–8.51, GdN/YbN = stones plot outside the Archean sedimentary rock 1.20–1.49, Eu/Eu*=0.70–0.73) (Fig. 13B). Sam- ﬁeld because they have a stronger negative Eu P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 329 anomaly. Partial overlap with the Archean sedi- sample 94-PCT-013 with an abnormally small mentary rock ﬁeld is observed in the low GdN/ amount of U (0.49 ppm) and, correspondingly, an

YbN range (Fig. 14A). abnormally high (15.1) Th/U ratio. The quartz Th and U content varies between and within arenites of subunit Q2 are markedly richer in both the rock groups differentiated (Fig. 14). In sub- elements (U=1.58 ppm and Th=7.28 ppm) than unit Q1, quartz arenites contain less U (average U the quartz arenites of subunit Q1. Th/U values content is 1.02 ppm) and especially Th (average vary from 2.7 to 15.1, extremely high values being Th content is 3.62 ppm) than pebbly arenites due to either extremely low U content (sample (U=1.57 ppm, Th=8.95 ppm). One exception is 013) or abnormally high Th content (sample 94- PCT-021). Generally speaking, in Th versus Th/U coordinates (McLennan and Taylor, 1991) the Hisovaara quartzose sandstones plot completely within the Archean sedimentary rock ﬁeld. Th and U distribution seems to be largely controlled by the distribution of heavy minerals, primarily zircon, indicated by the fact that anomalous quantities of some trace elements (Zr=933 ppm; Th=338 ppm; Y=57 ppm and Pb=72 ppm) that can only be explained by the accumulation of relatively abundant zircon as found in sample 913 (Kozhevnikov, 1992).

3.2.1.3. Interpretation. The above geological, petrographic and geochemical data on the quartz arenite unit can be discussed from two aspects. One aspect is related to the source of both quartz and the other detrital components which constitute the unit. The other aspect is the reconstruc- tion of the depositional environment and depositional mechanism of these rocks that are the oldest sedimentary rocks in the Hisovaara greenstone belt. With respect to the provenance of the quartz arenites, identiﬁcation of class types is the most informative data set. Hisovaara rocks contain no lithic fragments that directly indicate possible sources. Therefore, data on the geochemistry of immobile elements such as REE, major element chemistry, abundance of quartz pebbles and some textural characteristics of the rocks discussed are critical. Vein quartz, normally present in addition to Fig. 14. GdN/YbN-Eu/Eu* (A) and Th-Th/U (B) plot for quartz-rich rocks. Same symbols as in Fig. 8. Negative Eu other types of rock fragments, has been reported anomalies are markedly higher in Hisovaara rocks than in from practically all Archean quartz-rich sediments Archean and a large part of Proterozoic rocks. In the Th-Th/ (Eriksson, 1980; Srinivasan and Ojakangas, 1986; U coordinates, they are, in fact, completely delineated by Archean rocks. In Proterozoic rocks, Th/U ratio is generally Bhattacharyya et al., 1988; Wronkiewicz and lower. Archean and Proterozoic rock ﬁelds are given after Condie, 1989; Cortis, 1991, etc.). Several rock McLennan and Taylor, 1991; Fig. 7c, d and Fig. 8c, d. types can be proposed as hypothetical sources. 330 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340

Geochemical, mineralogical and other data place sible, in principle, in sample 94-PCT-017 which a limit on some sources that are probable in has slightly fractionated REE distribution and a principle. It should be noted that when using REE strong positive Eu anomaly. geochemistry to constrain source(s) of the clastic Weathering of quartz-rich amygdaloidal andes- material in the quartz arenites, we assume that: ites could provide a source of quartz. It could 1. Quartz-rich clastic rocks adequately reﬂect accumulate in some settings, e.g. a nearshore source area geochemistry. This follows from beach zone. However, the possible mechanism for ﬂat REE distribution patterns in quartz sands such complete andesite decomposition, needed to normalized in terms of the REE content of explain the complete absence of lithic fragments, associated muds in both present-day passive remains obscure. Furthermore, weakly positive margin environments (Biscay, Ganges) and ac- Eu anomalies in andesites do not favour this tive continental margin settings such as back- option. arc basins (Japan) and continental arcs (Java) Quartz-rich metasomatic rocks could be a (McLennan et al., 1990). source of quartz, as observed, for example, in 2. The low SREE content of Hisovaara rocks is some Proterozoic rocks in Karelia (Kozhevnikov presumably due to the diluting effect of and Golubev, 1995). Fragments of metasomatic quartz. This phenomenon was used to explain rocks, fuchsite schists, tourmaline quartz arenites small quantities of SREE in Archean quartz and other rocks are found in some Archean belts arenites (McLennan et al., 1984; Wronkiewicz (Luukkonen, 1988; Cortis, 1991; Kozhevnikov, and Condie, 1989) and the commonly ob- 1992). Metasomatic quartz rocks usually contain served low REE content of modern sands in no plagioclase, and the rocks consist of a quartz- comparison to that of associated muds, in mica association, Ca and Na being completely which La/Yb, La/Sm and Gd/Yb ratios being removed. The presence of plagioclase in the detri- either unchanged or slightly disturbed tal material of quartz arenites at Hisovaara and (McLennan et al., 1990). their low CIA value does not seem to favour a 3. The role of vein quartz in the REE distribu- metasomatic source. The REE distribution pat-

tion pattern, i.e. LaN/YbN,LaN/SmN,GdN/ tern of most of the samples analysed indicates YbN and Eu/Eu* values, is presently that the major constituent of the source was rep- impossible to assess properly because there are resented by felsic rocks, which is reﬂected in no data on these parameters for the vein LREE enrichment, fractionated HREE distribu- quartz of Hisovaara rocks. The relevant evi- tion and a negative Eu anomaly. Their sodic dence, in the literature, is scanty (Siddaiah et nature, which is retained even during partial al., 1994). Therefore, such an assessment is of weathering, suggests that they could be tonalite- limited value. type granitoids or felsic volcanics of a sodic series.

4. Low CIA, low K2O/Na2O and Al2O3/Na2O Judging by the presence of at least two types of and high SiO2/Al2O3 values observed in the detrital zircon in the samples analysed, the felsic Hisovaara quartz arenites indicate that the source is assumed to be complex. Some problems initial geochemical parameters of the felsic that arise when the ‘quartz budget’ in quartz-rich source area(s) are retained better here than in sediments is estimated using a granitoid destruc- similar rocks from other regions. tion mechanism (Pettijohn et al., 1972) can be The chemical-exhalative mechanism for devel- overcome by assuming that hypabbysal subvol- opment of a high SiO2 concentration in a hypo- canic bodies, typically containing abundant vein thetical source of clastic quartz cannot really be quartz, were destroyed. applied to Hisovaara rocks because of their dis- To assess the possible source(s) of the material, tinct negative Eu anomaly which is sharply posi- which comprises subunit Q, calculations were tive in chemically precipitated rocks (Bavinton made using the REE content of the rocks. The and Taylor, 1980; Siddaiah et al., 1994). An ad- amount of REE in the tonalites, rhyolites and mixture of chemically precipitated material is pos- komatiites of the lower mafic assemblage was P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 331 employed as end members. Komatiites were in- drained basin is a possible environment. It seems cluded in calculations for several reasons. Firstly, to be the type of setting in which clastic (e.g. pebbly) it has been found earlier that the Cr content of quartz material could be abraded for a short time subunit Q1 varies over a very broad range from 42 and the multiple intense scour of deposits, accom- to 581 ppm (Kozhevnikov and Travina, 1993). panied by the formation of quartz sands and coarse Secondly, thin (maximum 15 cm) Cr-enriched gravel, could occur. The proximity of source(s) of metasandstone horizons that contain finely dis- clastic material and its very rapid transport without persed metamorphic fuchsite were observed in long abrasion is indicated by: quartz arenites at several levels above quartz 1. The textural immaturity of pebble-sized clasts. arenite subunit Q, which testifies to the presence 2. The occurrence of unrounded, euhedral zircon and weathering of an ultramafic source fragments. (Kozhevnikov, 1992). Thirdly, flat HREE distribu- Some characteristics of the quartz arenite accumu- tion and slight LREE enrichment at low LaN/YbN lation field can be reconstructed by summarizing and a strong negative Eu anomaly require the use the above evidence. Judging by the bedding pat- of an additional component for interpretation. This terns in quartz-rich and associated rocks, they were component must have characteristics most similar deposited in a marine setting. In section A quartz to those of the komatiites in the lower mafic arenites, hummocky cross bedding could be formed association. in a shelf zone affected by contour currents and Table 5 shows the chondrite-normalized REE storm waves at a depth up to 90 m, i.e. above the content of the rocks that hypothetically form the storm wave base (Duke, 1985). Other possible end members of possible sources (tonalites, komati- environments for the occurrence of hummocky ites and rhyolites), for a series of quartz-rich cross stratification are known [flash-flood braided samples from subunits Q1 and Q2 and in estimated delta (Hjellbakk, 1993), eolian systems Langford mixtures diluted with quartz containing negligible (1989), and antidunes in a fluvial channel (Rust and REEs. Estimated normalized REE values are sim- Gibling (1990))]. The angularity of quartz pebbles ilar to those observed in the Hisovaara quartz is presumably due to limited transport distances. arenites. Their distribution curves are similar, too Furthermore, the transition to overlying sulfidic (Fig. 15). This suggests that such REE distribution, argillites, could represent basin deepening e.g. e.g. those observed in samples from unit Q1, could Hoffman, 1987) or development of lagoonal condi- be indicated by the deposition of the products of tions. This transition could be rapid enough for the destruction of a bimodal source with various ratios burial of texturally immature quartz-rich rocks. of felsic to ultramafic components. Tonalite de- The trough cross-bedding, observed in the quartz- struction products were deposited dominantly rich sandstones of section B, could form in small within individual thin horizons (sample 94-PCT- channels near the shoreline (Mueller and Dimroth, 007). In the course of subunit Q2 formation, the 1985). Association of these rocks with subaerial role of a felsic source increased steadily, the degree andesites and rhyolites favours such a setting. of quartz dilution being possibly lower. The two andesite units (Fig. 5) differ in texture, Intense weathering of tonalites and ultramafic but are identical geochemically, thus indicating rocks must have followed the uplift and deep similar magma-generating conditions. This points erosion of the roots of the greenstone belts domi- to a short time interval between the two episodes nated by the rocks of the mafic assemblage, includ- of andesite volcanism, the succession of processes ing komatiites and hypabbyssal tonalitic plutons being: andesite volcanism — a non-depositional saturated with vein quartz. In this case, conditions interval — the formation of a thin weathered favourable for the concentration of the most resis- crust-rapid transport and deposition of quartz rich tant rock destruction products, e.g. quartz, heavy sedimentary rocks. Addition of tuffaceous material minerals and partly plagioclase, must have been to subunit Q2 indicates that sedimentation associ- formed locally. A river channel in a deeply eroded ated with the completion of andesite volcanism mountain system or in any other small, seasonally continued as well as rhyolite volcanism. 332 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 16.40 67.00 6.24 576-4 003 renites from the subunit 0.44 0.44 0.01 0.01 94-PCT- 014 003 B t 3.44 2.02 1.90 1.10 1.42 0.64 0.31 0.35 0.26 0.17 n.d. 0.15 0.430.07 0.38 0.15 0.90 0.95 0.51 0.23 0.02 1.22 0.12 0.11 0.27 0.05 0.02 0.010.50 0.07 0.01 0.07 2.62 3.33 26.40 1.43 3.15 2.62 2.75 99.84 99.76 99.68 022 94-PCT- 92-36 94-PCT- 2.92 0.10 153 1.04 0.01 0.03 0.91 0.04 0.40 0.18 0.15 0.01 0.300.07 0.30 0.60 0.20 4.03 4.46 99.89 94-PCT- 023 33 34 35 36 37 105 0.78 0.44 15.0 012 B t 0.63 0.05 0.22 32 B eridotitic komatlite 2. (37) Tonalite. t d (32) near contact with quartz-rich subunit Q1. (33–35) Andesites from (28–29) Amygdaloidal (28) and homogeneous (29) andesite fom the lower 2.99 2.82 0.01 0.02 8.08 3.00 5.13 8.73 3.01 45.83 004 002 B t 0.26 0.63 0.01 0.03 0.03 2.03 012 B t 87.52 88.42 91.80 91.94 92.06 92.64 93.48 94.30 0.01 0.05 96.98 578-2 577-2 92.39 94-PCT- 94-PCT- 831-1 B 0.01 94-PCT- 007 B 0.01 0.01 0.01 0.10 0.080.01 0.04 0.06 0.07 0.06 0.03 0.04 1.82 1.20 94-PCT- 94-PCT- 008 B B 94-PCT- 12.5 0.16 0.52 0.88 2.04 1.65 3.56 11.60 2.23 13.02 12.38 17.74 13.39 13.25 15.73 14.48 14.88 14.20 14.41 14.27 0.01 0.01 0.06 0.16 0.17 0.22 0.24 0.24 0.22 0.02 0.12 0.35 0.72 0.77 0.60 0.84 1.32 1.30 0.05 0.31 0.06 0.10 0.21 2.23 0.19 1.15 0.33 0.65 4.00 2.75 2.91 0.08 0.26 0.27 0.52 0.33 0.08 0.10 0.05 0.02 0.07 0.20 0.10 0.10 0.15 0.00 0.99 0.01 0.01 0.01 0.02 0.01 0.01 0.01 0.02 0.04 0.12 0.17 0.14 0.13 0.11 0.20 0.61 0.40 1.00 4.33 4.44 2.11 3.02 3.98 0.63 0.42 0.07 0.07 0.07 0.42 0.07 0.52 0.42 0.35 0.20 0.20 0.15 0.45 0.30 0.60 0.20 2.35 2.35 1.70 1.84 1.18n.d. 6.72 6.15 4.20 4.45 99.7071 99.77 70 99.85 99.52 99.94 99.74 99.78 99.52 100.37 99.65 99.53 99.87 100.08 99.96 95.44 77.76 78.30 66.00 57.88 57.98 56.72 57.10 56.40 57.00 56.02 60.42 37.75 93.80 94.40 96.08 96.48 24 25 26 27 28 29 30 31 B 100.03 99.95 100.19 100.16 100.03 99.80 99.95 99.77 99.71 6 7 8 9 10 11 12 13 14 15 16 17 18 0.44 0.01 0.02 0.01 1.94 2.76 6.71 2.70 3.28 9.82 18.67 0.28 0.14 0.42 0.05 0.05 0.16 0.57 0.02 0.06 0.89 0.10 0.180.50 1.75 6.19 0.06 2.21 2.80 16.25 0.01 0.25 0.07 0.07 3.28 73 11.33 55.75 40.69 8.20 7.33 53 99.77 28.51 016 021 019 24 017 94-PCT- B 169 B a . See Figs. 2–5 for locality locations. (1–10) Quartz arenites from the subunit Q1. (11–19) Pebbly quartz arenite from the subunit Q1. (20–23) Quartz a 3 0.01 0.12 0.04 0.07 0.02 0.05 0.15 0.04 0.32 1.51 2.42 5.17 5.98 5.47 4.33 3.45 5.15 4.01 5.17 0.08 5.88 0.082.31 0.02 0.02 0.02 46.00 99.76 O 2 B 018 2294-PCT- 23 94-PCT- 94-PCT- 011 010 PCT-05 0.84 0.08 n.d. 6.93 41.4 0.08 0.38 2.07 0.00 0.49 0.36 2.62 61 94-PCT- 020 21 99.62 92-16 094- 92-35 94-PCT- 92-37 92-38 94-PCT- 94-PCT- 3.11 2.84 2.07 1.70 0.07 0.20 0.40 0.50 0.10 0.10 0.29 0.24 0.93 11.80 0.27 0.28 0.20 0.07 0.03 0.02 0.04 0.62 0.07 0.03 1.00 0.43 1.15 1.01 0.50 1.15 0.02 0.03 0.01 0.01 0.80 0.65 0.40 0.25 0.05 0.02 1.12 0.40 0.85 0.30 1.00 0.42 0.42 0.14 n.d. n.d. 0.24 0.06 2.39 8.73 2.31 29.61 32.92 50 68 36 56 50 92.00 93.00 93.24 03.50 45.32 35.50 40.36 149 1.13 0.72 021 20 94-PCT- 94-PCT- 92-8 92-12 92-14 94-PCT- 2.09 0.05 0.01 0.59 0.20 1.79 1.39 2.23 2.56 0.71 0.35 1.18 1.47 1.49 1.45 1.37 11.51 0.83 0.07 0.41 0.04 0.08 0.25 0.16 0.23 0.170.76 0.07 0.19 0.11 0.76 011 0.58 0.18 0.28 0.56 0.11 0.21 0.03 0.35 0.10 0.23 0.09 0.66 0.15 0.15 0.33 0.19 0.22 0.06 0.29 0.14 2.361.291.00 2.03 1.16 0.58 1.28 0.29 0.04 1.22 0.161.55 0.570.50 0.100.01 0.68 0.72 1.14 – 0.93 – – 0.72 0.57 – 1.15 0.86 1.01 0.50 1.94 7.64 6.36 – 8.38 8.98 8.62 9.05 7.54 4.57 2.15 0.03 0.98 0.10 0.10 0.75 1.25 0.85 0.35 0.630.07 0.56 0.12 0.36 0.03 0.52 1.50 0.87 0.55 0.07 0.87 0.42 0.06 0.70 2.10 6.03 6.20 6.16 5.68 6.10 4.28 6.00 4.51 5.74 3.27 n.d.* n.d. 0.06 0.02 1.89 45.15 56.59 42.80 5.97 6.32 3.72 94.36 21.10 93.48 95.20 96.20 10.86 29.86 2.55 37 47 58 58 61 68 64 54 58 55 64 58 57 69 91.92 38.95 39.91 40.17 56.52 52.43 82.19 13.02 14.38 21.86 20.66 20.64 2941 35.68 34.29 913 19 92-10 12 3 4 5 3 3 O O O O O O 2 2 2 2 / 2 2 3 3 / 3 3 / / / / 3 5 5 2 2 O O 1.22 n.d. Not detected. t-Fe recalculated to Fe 2 2 2 2 O O 0 O O O Na Na Na Al Al Na 2 2 O OO 0.04 OO O 0.59 2 2 2 2 2 2 a O O 2 2 2 2 2 2 2 2 Fe Fe SiO CIA 66 Al Total 100.23 99.98 99.87 99.89 100.09 TiO Al SiO Al K L.O.1 P L.O.1 P H H K subunit A2; homogeneous unaltered (33) and altered (34) near contact with quartz-rich subunit Q2, coarse pyroclastic (35) from dark fragment. (36) P part of the andesite sequence (subunit Al). (30–32) Glomeroporphyritic andesites from the upper part of the subunit Al. Unaltered (30, 31) and altere Q2. (24) Pebbly quartz arenite from the subunit Q2. (25) Mica quartz arenite from the subunit Q2. (26) Altered rhyolite. (27) Altered luff-sandstone. FeO FeO MnO K MnO K CaO 0.30 MgONa 0.40 MgO Na CaO Total 100.08 99.78 CIA SiO SiO TiO Al Table 3 Whole-rock chemical analyses (wt%) from Hisovaara P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 333 0.75 1.79 5.22 3.56 1.58 1.03 0.53 2.99 0.23 0.22 24 94-PCT-014 37.97 0.81 2.12 4.40 1.46 0.72 3.91 0.28 0.24 23 14.45 97.04 0.58 7.4 5.3 8.03 5.7 6.0 3.9 7.0 1.99 1.03 1.89 1.91 1.76 2.04 1.63 5.0 0.88 1.01 0.92 0.37 0.53 0.59 4.41 7.46 4.91 2.97 3.02 3.53 3.17 1.93 6.14 1.71 1.78 3.00 4.59 4.050.62 4.889.33 0.57 4.00 7.39 0.80 4.60 8.46 0.49 10.62 4.85 0.59 14.59 4.55 0.73 6.35 3.14 3.18 1.50 0.82 1.92 2.12 2.09 0.72 1.785.2 0.49 15.1 1.78 4.80.931.47 2.220.302.05 4.8 1.260.47 4.571.50 1.95 n.d.0.22 3.781.57 0.43 n.d.0.24 7.5 2.11 n.d. n.d.2.96 1.64 1.89 2.14 1.22 0.28 n.d. 3.95 3.9 0.64 7.75 n.d. 3.67 0.90 1.18 0.70 0.17 3.85 0.62 0.26 3.09 3.65 1.66 0.24 0.70 1.37 4.45 1.72 0.25 0.62 1.67 3.35 0.24 0.64 4.72 3.93 0.24 1.51 0.75 0.21 3.41 6.54 1.80 0.59 5.42 1.54 1.56 6.89 24.64 4.09 4.24 9.73 14.63 7.53 5.19 4.31 8.17 7.16 6.14 6.67 4.16 3.73 6.74 6.08 4.72 1.170.210.910.13 0.670.61 0.110.12 0.520.33 0.060.04 0.68 0.260.34 0.16 0.050.06 0.55 0.14 0.07 0.02 1.12 0.34 0.18 0.16 0.06 0.04 0.89 0.18 0.11 0.02 0.93 0.56 0.25 0.15 0.11 0.04 0.65 0.32 0.08 0.04 0.33 0.39 0.85 0.06 0.06 0.19 0.17 0.74 0.02 0.11 0.19 0.03 0.11 0.37 0.06 0.50 0.08 41.47 124.19* 35.03* 42.01 66.04 107.19 35.4414.95 23.05 19.47 20.95 11.64 34.55 14.11 31.09 25.43 26.94 8.29 1794-PCT-017 568-2 18706 577-2 19 94-PCT-004 25.70 94-PCT-002 94-PCT-023 857 20 94-PCT-022 8.71 21 12.70 22 19.68 18.49 8.07 67891011 3.16 0.761.18 1.72 1.91 1.92 1.86 2.38 6.70 2.00 3.32 1.12 3.0 0.83 2.54 1.38 0.23 0.08 0.65 0.70 0.90 0.22 0.19 0.02 0.03 0.02 0.17 0.04 0.46 2.78 23.63 29.94 28.83 16 128.23 2.69 1.78 3.08 0.69 1.96 0.52 0.22 1.84 1.19 1.06 1.93 1.72 128 0.04 21.11 15 2.55 5.79 0.13 4.01 1.46 0.36 0.02 2.23 1.95 1.96 0.01 0.28 0.02 21.38 27.75 14 3.1 4.1 3.7 5.3 0.92 2.00 1.74 0.59 0.53 3.30 3.325.18 3.09 0.70 0.89 0.46 0.18 0.58 0.68 1.294.0 0.72 3.33.14 0.71 4.0 0.65 5.260.110.15 0.63 18.02 0.080.57 0.060.09 2.21 0.303.91 0.20 0.22 0.03 19.55 0.31 0.58 0.10 24.57 0.10 0.84 0.70 0.08 3.06 6.59 5.04 0.78 0.02 0.580.05 0.35 0.03 0.40 0.17 0.04 013 0.15 0.42 0.03 18.08 15.2012.15 10.87 11.58 10.23 8.82 716 12.66 13 94-PCT-016 94-PCT-015 94-PCT-019 94-PCT-024 94-PCT-010 94-PCT-008 94-PCT-007 2.7 2.21 5.97 6.30 9.82 6.21 2.61 1.02 0.90 2.163.620.70 2.34 2.97 1.78 4.10- 1.84 4.44 2.76 5.26 1.20 0.86 2.00 0.82 0.69 1.04 1.03 0.95 0.99 0.97 3.28 4.38 1.24 0.82 0.06 0.35 0.03 0.04 0.570.20 3.45 1.38 4.88 1.71 3.24 3.19 4.35 4.35 3.09 3.5 2.96 0.48 0.07 0.26 8.51 1.49 1.12 2.59 1.67 15.48 10.46 9.50 13.95 13.52 11.21 0.33 0.27 0.18 0.24 0.17 0.22 0.13 0.02 0.22 0.03 0.17 0.03 6.41 4.32 16.19 690 58.82 145 46 50.80 12.42 9.81 23.35 49.79 39.43 9.50 12 94-PCT-018 12345 94-PCT-011 94-PCT-005 94-PCT-012 94-PCT-013 94-PCT-003 94-PCT-001 94-PCT-021 94-PCT-020 N N N N N N REE without Tb, Dy, Ho and Tm; breccia (Fig. 13). Yb Sm Yb Sm / / / / / / S U Eu* 0.82 Eu* 0.75 0.74 0.59 0.67 0.75 U N N Yb Yb / / / / N N N N * REE 96.76 REE Gd UTh 0.81 1.90 1.52 Gd Eu Th Ce 43.54 Eu La ThEu 0.12 0.13 2.84 La U Th La Nd SmGd Tb Ho Er Yb Lu La 2.99 PrDyTmS 5.04 1.30 0.08 Table 4 Trace element geochemistry (ppm) of Hisovaara rocks La Ce 4.35 Pr 0.57 Nd 1.25 2.94 Sm EuTb Dy 0.06ErTmYb 0.12 0.11 0.06 0.14 0.08 0.10 0.05 0.13 0.10 0.02 GdHo 0.03Lu 0.05 0.03 0.33 0.03 S La 334 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 0.85 2.76 04 5.84 19.42 18.19 / 1.30 1.40 5.12 4.35 6 2.59 3.71 11.90 11.56 1.18 1.22 3.94 3.80 4.85 4.93 4.44 4.94 21.19 22.6512.83 68.25 12.49 70.63 38.03 38.93 es that result with various dilutions by 1; 1, diluted 5.6 times by quartz; (6) quartz = 1.58 5.40 3.41 4.57 1.33 e 11.02 19.52 1:4, diluted 1.1 times by quartz. = 2:3. diluted 3.7 times by quartz; (16) quartz arenite (94-PCT-021); (17) mixture = 1:1:1 diluted 3.1 times by quartz; (12) pebbly quartz arenite (94-PCT-012); (13) mixture of tonalite:rhyolite : 1:1:1 diluted 4.4 times by quartz; (8) quartz arenite (94-PCT-007); (9) contents in tonalite diluted 6.2 times by quartz; (10) : 09 / 6.20 5.87 4.14 4.24 7.87 8.26 14.08 14.59 11.10 2.060.94 1.90 1.11 1.62 0.87 1.48 1.02 2.69 1.34 2.68 1.56 4.45 2.40 4.33 2.49 3.08 1.42 3.04 3.18 3.26 10.82 10.16 3.77 3.13 2.60 2.56 4.42 4.41 7.60 7.62 5.78 2.07 1.92 1.38 1.58 2.76 2.70 3.62 4.78 2.24 3.32 4.01 3.09 3.11 4.00 4.00 4.05 4.08 4.10 1.18 1.13 1.18 1.02 1.57 1.59 2.36 2.26 1.18 2.000.74 1.68 0.79 1.78 0.67 1.64 0.81 1.78 0.80 1.93 0.78 2.16 0.62 2.08 0.83 2.55 0.53 2.41 0.84 2.76 0.59 2.79 0.85 3.08 0.82 67 10.33 10.04 6.82 6.58 14.89 14.11 24.27 24.92 19.85 12.15 11.11 2.61 0.84 3.86 1.03 0.66 2.61 0.82 0.92 0.72 03 / 4.06 2.64 1.03 1.18 2.61 5.43 3.94 92.21 14.31 1.4 diluted 3.6 times by quartz, 18-mica quartz arenite (94-PCT-019); (19) mixture of tonalite:rhyolite 9.83 6.34 4.70 4.10 0.66 6.30 8.82 29.92 4.32 5.61 5.63 3.94 1 34.47 69.50 3.42 3.28 40.80 23 45 49.43 117.9 4.58 4.60 15.91 22.40 1.75 1.76 = 2.18 7.86 5.39 5.56 11.00 11.06 19.09 19.77 15.15 15.12 17.84 17.29 52.28 53.88 2.48 1 8910111213141516171819 1.72 3.07 2.173.77 12.55 8.01 7.97 17.62 17.64 30.78 31.14 23.67 24.66 29.27 28.82 86.30 89.92 2.71 0.84 0.87 0.78 0.76 0.84 1.22 1.99 1.87 1.08 1.18 1.02 1.17 3.49 3.64 0.61 8.85 11.64 12.69 14.95 14.99 19.56 19.57 25.43 24.63 24.57 24.43 4.72 3.57 1.03 0.99 0.91 0.90 1.51 1.39 2.06 2.08 1.21 1.26 1.15 1.17 3.51 3.68 1.08 1.64 3.15 0.02 1.43 a Yb (1) Komatiite (s.576-4); (2) tonalite (s.831-1); (3) rhyolite (94-PCT-.024); (4) quartz arenite (94-PCT-.011); (5) mixture of komatiite: tonalit Eu* 0.45 0.81 0.86 0.75 Yb 8.82 Sm 0.58 3.11 5.26 3.2 diluted 2.4 times by quartz; (14) pebbly quartz arenite (94-PCT-015); (15) mixture of tonalite:rhyolite / / / / a Pr 8 Gd 3.87 9.20 12.43 1.08 1.17 Dy 0.71 quartz Table 5 Chondrite-normalized REE contents in komatiite, tonalite, rhyolite and in quartz-rich rocks from Hisovaara and calculated compositions of mixtur arenite (94-PCT-010); (7) mixture of komatiite: tonalite: rhyolite c of tonalite:rhyolite pebbly quartz arenite (94-PCT-003); (11) mixture of komatiite:tonalite:rhyolite Sm LaNd 2.98 26.32 49.87 12.51 Ce Eu La Er Eu Lu Yb Gd La P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 335

Fig. 15. Chondrite-normalized REE diagrams for tonalite, komatiite, rhyolite, some quartz-rich rock samples and rated mixtures at various degrees of quartz dilution. The normalized values given in Table 3 were used. Sample numbers in this ﬁgure are those used in Table 3.

Fairly aggressive acid rains, related to fumarolic providing an example of a combination of some activity between volcanic paroxysms, could well features characteristic of platformal settings with be responsible for the development of weathering those typical of environments that display an on andesites. active continental margin- or island-arc type of In summary, the Hisovaara quartz arenites are calcareous-alkaline volcanism. It is a rare case in associated with intermediate to felsic volcanics Archean greenstone belts. 336 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340

3.3. Felsic fragmental rocks (unit F) the matrix contains finer rained quartz, feldspar, biotite and sericite. 3.3.1. Field description This unit is composed of felsic pyroclastic rocks 3.3.3. Geochemistry and subordinate reworked equivalents The sole analysis of the rhyolitic unit done for (Kozhevnikov, 1992). In this section we provide the present study shows the unit to be a high silica the field evidence for interpretation of the deposi- rhyolite with potassium dominant over sodium tional environment of the unit. In the vicinity of (Table 3). In trace element terms, the unit displays location B, the sequence consists of metre scale a fractionated REE pattern similar to the FI units of tuff breccia and lapilli tuff with occa- rhyolites of Lesher et al. (1986). sional tuff intercalations. Primary textures and structures indicate the presence of both pumice and lithic fragments. Each unit is defined by 4. Summary and conclusions distinct size ranges of clasts, texture of pumice, a distinct phenocryst content and a regular succes- The Hisovaara quartz arenites represent a sion of size and density grading. Within individual mixed provenance involving contributions from units as defined above, reverse grading of pumice, TTG suite granitoids and a mafic to ultramafic normal grading of lithic fragments, sporadic ex- component with extensive weathering to explain amples of basal ground surge beds and thinly the lack of feldspar in the sandstones. Mature, laminated fine ash tuff beds occur which quartzose, shallow-water sandstones are not com- indicate the units represent ignimbrite deposition mon in Archean greenstones (Thurston and (Sparks et al., 1973). Evidence for welding con- Chivers, 1990; Lowe, 1994). The quartz-rich sand- sists of the presence of branching fumarolic struc- stones at Hisovaara are unusual in showing tures (cf. Thurston, 1980) and the presence of clearly the base of the sequence and evidence for flattened silicified pumice fragments concentrated weathering of the andesitic basement seen in field, toward the middle of the stratigraphic unit. The petrographic and geochemical evidence. Most silicified pumice ignores depositional unit Archean quartz-rich sandstones are associated boundaries and is thus interpreted as evidence of with platforms (De Kemp, 1987; Thurston and vapour phase recrystallization (Ross and Smith, Chivers, 1990) with one example of a cannibalized 1961) indicative of subaerial eruption and deposi- platform within a submarine fan environment tion. (Cortis, 1991). As an Archean quartz rich sand- At location A, in a few exposures, the quartz stone sequence, the Hisovaara quartz arenites are arenite is overlain by a few metres of a fragmental closely associated with subaerial arc andesites and aluminous metaconglomerate with granitoid and subaerial rhyolites at the south end of the belt possible metavolcanic clasts. This is overlain by similar to the ‘continental’ style assemblage type about a 100 m thickness of thin graded beds of of Thurston (1994). However, at the north end of sulfidic argillite and carbonate bearing silty the belt, the quartz arenites are succeeded upward sandstones. by conglomeratic rocks, argillites, and an overlying tholeiite unit with komatiites. This end of the 3.3.2. Petrography unit is then comparable to some of the Superior The rhyolites at location B consist of varying Province platformal quartz arenites in that proportions of quartz, plagioclase and minor quartz-rich sedimentation is followed by volcan- potassium feldspar with accessory biotite and ism (cf. De Kemp, 1987). Thus the Hisovaara sericite. Primary textures are completely obliter- quartz-rich sandstones demonstrate a relationship ated by metamorphic recrystallization but gross in an Archean setting between subaerial volcan- grain size variation seen mesoscopically is present ism in an arc setting and development of an in thin section. Silicified pumice fragments contain deepening basin and subsequent volcanism related irregular polycrystalline plates of quartz whereas to rifting. P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340 337

Post Archean quartz-rich sandstones are con- Acknowledgements ventionally considered to represent multiple passes through the sedimentary cycle (Pettijohn et This project is an outgrowth of the US–Rus- al., 1972, p. 298) with the interplay of climate, sia–Canada co-operative program during which relief, and provenance influencing the composi- the senior author visited Hisovaara with OGS tion of the sands (Basu, 1985). Recent work in the support. At that time the andesite-quartz arenite Orinoco basin has demonstrated the production assemblage was noted in the field as unusual. of single cycle quartz arenites in a regime of Subsequent field work was funded by the Geolog- intense chemical weathering (Johnsson et al., ical Institute of the Karelian Research centre, 1988). The process involves either long soil resi- Karelian Branch of the Russian Academy of Sci- dence times related to very low erosion and trans- ence in 1994 and 1996. We thank Dr Sergei I. port rates or storage of orogenically derived Rybakov, Director of the Geological Institute for sediments on alluvial plains enroute to the final his support of the project. This paper is published depositional site. In spite of the variety of mecha- with the permission of the Senior Manager Pre- nisms for production of quartz rich sandstones, cambrian Geoscience Section Ontario Geological we here use their presence in the Hisovaara green- Survey (Ontario Geological Survey, 1990). This stone belt to indirectly indicate the presence of project would not have been possible without granitoid rocks in the source area. A granitoid translation on the outcrop by Grigori N. Sokolov source area serves as a speculative indicator of at of the Institute and subsequent translation of least unroofing of plutons if not a possible cra- e-mails, letters and drafts of the paper. Dr K.I. tonizing or orogenic event. If the latter is the case, Heiskanen of the Institute is gratefully acknowl- the age constraints available in this greenstone edged for his thoughtful review of an early ver- belt suggest the possibility of a pre-2.7 Ga oro- sion of the manuscript. R.W. Ojakangas and J. genic event in the Baltic shield. Much additional Dostal as journal reviewers helped clarify many work is required to validate such a concept, but points and sharpen the presentation. Major ele- the tantalizing indication seen in this project will ment analyses were done in the chemical labora- perhaps point the way to further work on this tory of the Institute of Geology of the Karelian speculation. Research Centre (Saraphanova, R. Ph., Mokeeva, L.N., Punka G.P., and Pitka, N.V.) Field assis- tance was provided by E. Travina in 1994. Draft- 5. Geochemical methods ing has been done by O. Kozhenikova and S. Josey. Sample preparation and major element analysis by X-ray fluoresence were carried out at the Kare- lian Research Centre. The XRF analyses were References determined on fused glass discs after the method of Norrish and Hutton (1969). Trace elements Argast, S., Donnelly, T.W., 1982. Javanahalli quartzites. Evi- were determined in the Geoscience laboratories of dence for sedimentary mica and implications for the chem- the OGS at Sudbury. Rb, Sr, Ba, Cr, Ni, Zr and istry of Archean ocean water. In: Naqvi, S., Rogers, J.M. Y were determined by XRF on pressed powder (Eds.), Precambrian of South India. Geological Survey of India, Memoir 4, pp. 158–168. pellets. All other trace elements were determined Basu, A., 1985. Influence of climate and relief on compositions by ICP-MS following a mixed acid digestion in of sands released at source areas. In: Zuffa, G.G. (Ed.), open beakers (OGS, 1990). Results were checked Provenance of Arenites, NATO ASI series. D. Riedel for dissolution problems by comparison of XRF Publishing, London, pp. 1–18. determined Zr vs. ICP-MS values. Precision on Bavinton, A.O., Taylor, S.R., 1980. Rare earth element abundances in Archean metasediments from Kambalda, West- reference materials has been at the level of ern Australia. Geochim. Cosmochim. Acta 44, 639–648. B10% using these methods (cf. Tomlinson et al., Bhattacharyya, P.K., Bhattacharya, H.N., Mukherjee, A.D., 1998). 1988. The Chitradurga greenstone succession in South 338 P.C. Thurston, V.N. Kozhe6niko6 / Precambrian Research 101 (2000) 313–340

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