Strontium isotope ratios and REE geochemistry in the Suwałki anorthosites, NE Poland

Geological Quarterly, 2000,44 (2): 1 83-1 86

Strontium isotope ratios and REE geochemistry in the Suwitlci anorthosites,

NE Poland

Wismicwska J. (2000) - Strontium isotopc ratios and REE gcochcmishy in the Suwalki anorthositcs, NE Poland. Gcol. Quart., 44 (2):

183-186. W a m w a .

Strontium isotopcratios for 14 samplcs of anorthositic rocks in the Suwalki Anorthwite Massif (SAM) range from 0.764875 to 0.705772.

T h c samc isotopic ratios calculated for 1.5 Ga (the U-Pb z i m age of he rapakivi-li kc p i k e s fmm adjacen t Mazury Complcx) rangc from 0.704583 to 0.705483. Thc m s p o n d i n g ar ^5W ,values for thc samc rocks range from 25.5 to 39.0. Thc pmnouncd Eu anomaly which charactcriscs thc REE distribution in thc anorikosttc plagioclasc is consistent with eady crystallization from basic magma

Kcy words: Suwalki Anorthosite Massif, strontium ntio, REE geochemistry.

Initial 8 7 ~ r / 8 8 ~ r ratios in igneous rocks are important in the recognition of magma sources. Data fiom basaltic achondrites with low RblSr ratios show that _the primordial value of ' ' ~ r t ~ ~ ~ r , about 4,6 bilion years ago was 0.699 (BABI - ba- saltic achondrite best initial) - a value of the primary strontium ratio for the whole solar system. With passing time, that initial '7~r18%r has changed due to the release of radiogenic 8 7 ~ r from Rb-bearing minerals (e.g., biotite, feldspars). The eadak crust bas a higher RbISr ratio then the upper mantle. If a magma source lay in the upper mantle or lower crust, and on its way up- wards, was not contaminated by foreign strontium, the 8 7 ~ r l s 6 ~ r ratio wouldremain low; the value wouldbe close to hat ofman- tle derived basalts. For a crustal source or in cases where crustal assimilation had occurred, the value of "~rJ86Sr would be higher (Faure and PuwelI, 1972).

The 14 samples of the anorthositic rocks _selected for nibid- iwn and sirontiurn determination were taken fiom several deep drill hoIes sited on magnetic anomalies in the SuwaUEi Anortho- site Massif (SAM) 20 km north h m Suwaki town (Fig. 1).

SAM is representative of a wide range of massif-type Anortho- site-Mangerite-Chamockite-Granite (AMCG) igneous com- plexes and is situated within the crystalline complex h o w n as ihe Mazury Complex,

The earliest geochronological studies of the SAM were pm- formed by Depciuch eta!. (1 975) using the K-Ar method. Later Jarmolowicz-Szulc (1 990) calculated a K-Ar age of 1347*93 Ma. This is probably areset age. Late granitoids in veins cutting the anorthosite complex may be responsible. U-Pb zircon stud- ies on granites (quartz rnonzonites fiom the GoMap core) ofthe Mazluy Complex (Claesson et al., 1995) and of the Kabeliai pluton in Lithuania (Sundblad et al., 1994) have yieled ca, 1500 Ma age. It is assumed that the granites sumunding the anorth*

site massif are genetically related to the anorthosites - as is o b served to be the case with AMCG complexes worldwide and in- cluding rapakivi granites, considered as anorogenic, related to active or reactivated deep crustal structures.

The Re-Os studies on magnetite and sulphide mineraliza- tion dispersed in the Suwalki anorthosites and norites (Stein et al., 1998; Morgan et al,, in press) have yielded a similar age of 1559-+37 Ma for the Jezioro Okqgle and Krzemianka deposits and 1556194 Ma for Udryh deposit, Initial values of ^{E ~ ,} were therefore cdculated for 1.5 Ga (Table 11,

Fig. 1. Goological map of the Sumtki Anorthosite Massif (after Kubicki and Ryka, 1982)

I - anorthosites, 2 - noritcs, 3 - gabbmorites and diorites, 4 -

granitoids, 5 - granitogncisses, 6 - gneisses; K, Jg U, Kz - drill holcs

METHODS

The anorthosites were initially examined unda the optical microscope to confirm that they had not been altered by second- ary processes. Major and trace element compositions were d&

termined by Atomic Absorbtion Speclmrnehy using the PU 9 100 X spectrometer at the Polish Geological Insti- tute (Warsaw) and REE were determined by hductively Cou- pled Plasma Mass Spectrometry at the University of Liege PeI- gium). The -ti= isotope determinations were carried out at the Isotope Laboratory of the Polish Academy of Sciences in Warsaw. Samples (I 00 mg) were dissolved in hydrofluoric and nitric acides and the Rb and Sr separated by chromatographic methods. The isotopic ratios were measured on a VE Sector 54 mass spectrometer using five collectors in dynamic mode.

Errors in Rb and Sr concentrations (determined by flame U S ) are &1 ppm. This errors may be ignored in the case of hgh (800-900 ppm) Sr samples. In the case of low Rb (2-7 ppm) samples, the error is of considerable significance. The measured Sr and Rb values were compared with measurements ofvarious international reference material, e.g. BM, TS, TB, and BE-N.

A11 8 7 ~ r / 8 6 ~ r ratios were normalised relative to a vaIue of ' ' ~ r $ ~ ~ r = 0.1 194, to correct for machine fiactiunation. Repli- cate analyses of the NBS SRM 987 standard gave an average 8 7 ~ r 1 8 6 ~ r ratio of 0.710255f 0.00002 1 over the period of this study.

The analysed anorthosite samples come h m four sites in the S w a W Massif - Krzemianka, Kazirni&wka, Jezioro Okugk and UdryA. All are only a few kilometres distance from one another. The anorthosites comprise relatively p m , me- dium- to coarse-grained feldspar (80-95% narmative plagioclase) with anorthite content of 45-55% on average, small amounts of quartz and K-feldspar and accessory pyroxene, amphbole, carbonate and _biotite.

The rocks are geochemically similar to other Proterozoic massif-type anorthosites elsewhere in the world, ^en&, those in the Grenville and Nain Provinces, Michicmau (Labrador), Morin (Quebec) and E g m d - O g n a , Rogaland Province (Nor- way). The anorthosites of Suwalki are enriched in N203

(1 8.5-29.9%), CaO (8.29-1 0.6%) and N a D and depleted in all other oxides mcept Si02 (-50%) and &O.The normative ratio of MAn-kAb i s 0.50-0.64. The rocks have relatively high concentrations of Sr (800-900 ppm), Ba (300-530 ppm), Fe (0.5-1 -0% F&

,

^{T i}

Fig. 2. Cbondritc-normalized REE pattcms o f plagioclascs scparatcd from anorthositen in drillcores Udryti 16 (U-16), Krzcmianka GO (K-hfl), and Iczioro Okagle IG 2 (J. Oh.-2) (Tablc 2)

Strontium isotope ratios and REE geochemistry in thc Suwalki anortRosites, NE Poland 185

Table 1 Isotopic data lor the Suwatki anorthosites*

*Analysw by R Bachlihski MG PAN

12 Kmcmianka60 1570.6 0.705136 0.0014

13 Kazirnicrbwka 1 2 160.6 0.705354 0.00 16 IS Jm. Okrqgle IG 2 1386.0 0.705772 0.00 17 16 Jm, O~&C 1G z 191 3.2 0.705093 0.00 15 17 Jm. Okrqgk IG 2 2245.2 0.705014 0.0016

18 U* 18 923.0 0.705 133 ROO IS

elements as Cr, Ni, CO, Cu (e-g. Ni and Cr ranging from 38-148 and 32-268 ppm, respectively). The total REB contents in the anorthosites are rather high, ranging from 1 1 to 58. Pure plagiocIase feldspar h m Udryli Knernimka and Jezioro Okrgle, analysed by ICP

MS

The REE are highly fractionated (LalYb~f= 25.1). The data lie within the range typical of plagioclase in massif-type anorthosites ( G r i m et al., 1974).

19 20 21 22 23 24 25 26

St Urbain

The low initial strontium ratios in the Suwalki anorthosites range from 0.704583 to 0.705483 (Table 1). They have been calculated h the measured ratios accounting for in ^situ decay of " ~ b since 1500 Ma- the age of the rapaluvi granites fnrm

the Maany Complex (Claesson et a/., 1995). As in most sam- ples, the RblSr ratio is very low, this correction is not very sig- nificant. The corresponding es, values range from 25.5-39.0 Udryf17

Udryfi7 U d m 4 Udryti7 Udry1il6 Udry6 16 Udryi 16 U d m 18

T a b l c 2 REE and some trace element compositions oi plagioclases from

anorthositcs From thrcc different areas of the Suwalki Anorthosite MsssiIX 1559.6

1867.7 1560.4 1865.3 1 127.0 1 134.0 1779.5 22 14.6

0.70 5 0

0

25 30 35 40 45 50 5 5

NORMATIVE An

0.705338 0.705 I 0 1 0.705436 0.705429 0.7048 75 5.704920 0.705071 0.704995

Constituents

Sr P P ~ CaO K20 FCZOI Ti02 ppm Ba Ba (ICP) Rb Y La Ce Nd

Sm Eu Gd Tb DY

Fig. 3. Aplot of Is,ratio vs, nwmativc %An for the Suwalkianorthosites; m-

60s for Labrcvillc, Morin, St. Urbain and Egegersund-Sogndal anorthositcs (af-

tcr Owcns et ah, 1994 and Demaiffc et aL, 1986) are also shown *Analyses by J.-C. Ducbesnc (University of LicgC) 0.0014

0.M)I 2 0.0012 0.001 5 0.001 6 0.001 6 0.0015 0.00 16

2.2 1 2.19 3.28

0.48 0.13 0.25

0.08 0.05 0.09

U d d 16

884 10,99

0.54 0.47 412 278 268 4.89

7.13 9.54 4.39 0.65 0.63 0.76 0.09 0.42 847

832 834 827 833 876 800 732

memian- ka 60

840 10.80

0.51 0.78 54 3 285 265

4.18 6.23 7.05 2.75 0.33 0.69 0.43 0.03 0.16

Jcz. Okpgk 1G 2

797 11.31

0.56 1.03 972 292 302

5.19 6.10 8.01 3.14 0.44 0.76 0.54 0.05 0.25 7

3 4 3 4 4 7 2

0.023319 0.010174 0.0 13533 0.010236 0.013548 0.014359 0.024688 0.007709

0.704836 0,704882 0.705 145 0.705209 0.704583 0.70461 1 0.704540 0.704829

29.78 30.42 34.17 35.08 26.18 26.58 25.56 29.68

Table 3 Isotope measuredg7~rla6~r ratio far massif-type anorthosites imm

Poland and some othcr places worldwide

(Table 1). An Is, vs. normative %An plot (Fig. 3.) shows the large variation in Is, (initial ratios) that exists between anorthosites from different massifs, e.g. Labreville, Morin, St.

Urbain (Grenville Province) and Egersund-Ogna (Norway).

The Suwalki data partIy overlap those of the Morin and Egersund anorthosites. The Pow isotopic stsontiurn ratios for the S u w a k anorthosites compare with those of many other massif-type igneous anorthosites in large AMCG complexes (Table 3).

CONCLUDING REMARKS

Localisation

SUWALKI Poland

M I C W A U Labrador

MORrN Qucboc

ROSELAND Virginia

EGERSUND-OGNA Norway

As the plagioclase-rich SuwaIki anorthosites usually have very low Rb/Sr ratios ranging from 0.008-0.02 approximately, it is impossible to obtain Rb-Sr jsochrons. However, initid ''~r186~r value can place some constraints on the genesis of the anorthosite parental magma.

The present " ~ r / s ' ~ r data fall into a narrow and low range.

Whether the parental magma originated directly from the man- tle at around E 500 Ma, or h r n the lower crust, is not opento IT%-

olution using only strontium initial ratios and REE patterns.

New Nd and 0 s isotope results obtained for the SuwaW anorthosites, norites, diorites and ore minerals may be of some help (Wismiewska et al., 1999). According to Demaiffe et al.

(1986), slrontium isotope data may indicate an upper mantle or- igin for the parental magma of the anorthosites and related norits and jotunites of the Rogaland anorthositic suite in Nor- way. Alternatively, an origin in the lower crust by melting ofju- venile basic components is possible.The new Sr-isotope data for the Suwalki AnorthositeMassifrare consistent with a fractional crystaIlization from a basic parental magma that originated by melting in the upper mantle or lower crust.

Rb bpml

4 4

9 7 N.D.

N.D N.D.

17 23

0'9 Ov4 Sr [ P P ~ I

- - - -

833 842

860 570 280

750 620

1250 730 I240 I330

425 677 797

AcknowIedgernents. This work has been supported by KBN grant nr, 6.20.93 16.00.0. Professor J-C. Duchesne of the Laboratory of Geology, Petrology and Geochemistry of the University of Likge (Belgium) is thanked for REE analyses by ICP MS. Strontitlm isotope analyses were carried out by R.BachlGsh h m the Isotope Laboratory of the Institute of Geological Sciences of the Polish Academy of Sciences in War-

saw, The manr~script was improved through the helpful com- ments and critical review of Professor J.Burchart from the Pol- ish Academy of Sciences and

Dr

*871B6~r

mcasd

0.7049 0.7058

0.7026 0.7039 0.7050

0.7054 5.7050 0.701 9 0.7058 0.7056 0.7054

0.7045 0.7051 0.7059

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