february 1991 volume 33 ',:0

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FEBRUARY 1991

VOLUME 33 ',:0

Published by V. H. Winston & Son, Inc. Silver Spring, MD • Welwyn, England .,

in cooperation with

The American Geological I ns~t£¥8LOGIAN TUTi(t"~\JStl.::s.~\5l KIRJA::>TO Q21~

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INTERNATIONAL GEOLOGY REVIEW

18. Arth. 1. G., and Barker, E. 1976. Rare-euth partitioning between hornblende and dacitic liquid and implication for the genesis of trondhjemite.tonslitic magmas: Geology. Vo l. 4. pp. :534-536. 19. Bloomer. S. H., and Hawkins. J. W.. 1981. Petrology and geochemistry of boninite series volcanic rocks from the Mariana trench: Con· lrib. Minual. Petrol .• Vol. 91. pp. 361·311. 20. Clayton. R. N.• Onuma, N.• and Mayeda. T. K .• 1916. A c1assific:ltion of meteorites based on oxygen isotopes: Earth Pllll1et. Sci. Lett .• Vol. 30. pp. 10-18. 21. Crawford. A. 1.• 1980. Aclinoenstatite .bearing cumulative olivine pyroxenite from Howqua. Victoria: Conlrib. Mineral . Pelrol .• Vol. 15. pp.3S3-367. 22. Halliday. A. N .• FaJlick.A. E .• Did::in. A.P.. Mackenz.ie. A. B.• Stephens. W, E.• and Hildreth. W .• 1983. The isotopic and chemical evolution or Mount St. Helens: Earth Pltlllet. Sci. Lell.• Vol. 63. pp. 241 ·256. 23. Hofmeister, A. M .. 1983 , Effect of Hadean terrestrial magma ocean o n crust and mantle evolution: J. Geophys. Res .. Vol. 888. pp. 4963-4983. 24. Ito. E .• and Takahashi. E.• 1987, Meltine of peridotite at uppermost lower mantle condi· tions: NallUe. Vol. 338. pp. 524-517. 25. Kawakami. 5.. and Miz.utani. H.• 1984. Geoiogy and geochemistry o f Archean crust and implications for the early history of the Earth: J. Sci. Nagoya Univ.• VoL 32. pp. 49·94. 26. Kornprobst. 1.. Pineau, F.• Degiovanni. R .• and Dantria,I. M .• 1987. Primary igneous graphite in ultramafic xenoliths: 1. Petrology of the cumulate suite in alkali basalts near Tiuemt (Eggere, Algerim Sahara): J. Petrol .• Vol. 28. pp. 293·3 11. 27. Kuroda. N .. Shiraki. K .• and Urano. H .• 1988.

Ferropigeonite qU3J'tz dacites from Chichijima. Bonin Islands: late differentiates from boninite-forming magma: Conuib. Mineral. Petrol.• Vol. 100. pp. 129· 138. 28. Liu, L.. 1987. Effects of H2O on the phue behavior of the forsterite -enstatite system . t high pressures and temperalUres and implications for the Earth: Physics Earth Planet. Inler.• Vol. 49. pp. 142-167. 29. Moorbath, S .• Taylor. P. N .• and l ones, N. W .• 1986. Dating the oldest terrestrial rocks-fact or fiction: CMm. Geol .• Vol. 57. pp. 63 -86. 30. Myers. , . S .• 1988. Oldest known terrestrial anonhosite at Mount Narryer. Western Aus · tralia: Precambrian Res.• Vol. 38. pp. 309-323. 31. Nutrnan. A. P.• and Bridgewater. 0 .• 1986. Early Archean AmitsOq tonaliles and granites of the Isukasia area, Southwestern Greenland: de ... elopment of lhe oldest known sial: ConIrib . Mineral. Pelrol., Vol. 94, pp. 129-138. 32. Ohtani. E.. Chemical stratification of the mande formed by mehing in the early stage of the terrestrial e ... olution: Tectonophysics. Vol. 154. pp. 201-210. 33. Sasaki. S., and Nak3.l.awa. K .. 1986. Metal· silicate fractionation in lhe growing Earth : energ y source for the terrestrial magma ocean: J. Geophys. Res.• Vo l. 918. pp. 9231 -9238. 34. Walkcr. D. A .• and Cameron. W. E.. 1983. Boninite primary magmas: evidence from the Cape Vogel Peninsula. PNG: COnlrib. Mineral. Petrol.• Vol. 83, pp. 1150-11 58. 35. Wmen. P. H., 1989. Growth o f lhc continental crust: a planetary-mantle perspecti ... e: Tee · tonophysics. Vol. 161. pp. 165 · 199. 36. Wyllie. P. 1.• Huang. W. L., Stem. C. R., and Maaloe, S., 1976. Granitic magmas: possible and impossible sources, water contenu. and crystallization sequences: CllI1ad. J. Earlh Sci.• Vol. 13, pp. 1001-1019.

METAMORPHIC OLIVINES IN ULTRAMAFIC ROCKS OF THE OLONDA GREENSTONE BELT AND THE KOMATIITE IDENTIFICATION PROBLEM

I. S. Pdltlel', D. I. Frith . Khar,· N. A . Ashikhmina. Yw . Yo . Tomashpol'skiy. and N . G. Shirina (Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry (lGEM1. USSR Academy or Sciences, and Research Institute of Physicochemistry. Moscow) From: .. Metamorfiehesk iye 0 I iv iny ... u I'trabaz.itakh Olondinskogo z.elenoklUTlenno go peyasa i problem a identHibtsii komatiitov (Aldanskiy shchit)."ltvt:sliyaAN SSSR, seriya geologicheskaya. 1991. No.1. pp. 36-50.

t/

Olivine-carbonate-talc rocks from lIle Olonda greenstone belt contain intergrowths of tabular olivine crystals resembling spinifex texture. The olivine is un7.oned, fonns no skeleton crystal and is relati ... ely high in iron (Fa 13-25) and low in Ca and Cr. The equilibrium temper:nure in the system olivinc·chromite WIS 110-240°. typical of 10Il0ltempentu re oli... ine-talc assoc iations. In chemica1 composition. the uhramafic rocks o f Krasnaya Gorka from which the olivine·ta1c rocks were fonned. are similar to alpinotype ultramafics. The olivines are probably of metamorphic origin. The Krasnaya Gorka pluton appears to be lIle root of a mande plume that has been transCormed during the long history of tectonic evolution of lhe region.

Some unique talc-oli ... ine rocks are associated with sill-like ultramafic bodies in the OIonda greenstone belt of the Aldan shield. Siberia. The olivine forms elongated or tabul3J' idiomorphic crystals whose intergrowths morphologically resemble spinifex texture. This outward similarity has led some in... estigators to conclude thesc rocks are highly magnesian ultramafic extrusiveskomatiites [31 . This work is devoted to a detailed study of the talc-olivine rocks in cOMcction with the problem of identifying kom.tHtes.

The volcanogenic rocks are intruded by gabbroid and peridotite layered intrusi... es. relsite dikes and plagiogranite intrusions. Syn-rolding magnesian picritcs were emplaced during the Udokan stage of tectonomagmatic activation. All the rocks were metamorphosed under epidote-amphibolite to amphibolite racies conditions. The age of lhe "'01canogenic section has been dated as 2.96·2.91 Oa by the Sm-Nd and U-Ph isochron melhods. The tectonic history of the area includes several stages of folding and metamorphism before the end of the Early Proterozoic [5].

Geology and Petrogr.aphy oC the Ultramancs The ultramafic intrusions cutting the "'01canogenic section of the Olond. belt are subdi... ided into two groups on the basis or ,cologie position (Fig. 1). The fust includes thin lenticular bodies in the basin or the Tokko River. up to 150 x 1500 m in size. closely associated with the silicic upper partor the section. Some h ....e weU preserved magmatic zoning, with a chilled margin containing relicu of olivine phenocrysts placed by carbonate and a fairly well crystallized core. The rocks from the chilled

The OIonda greenstone belt. in the central part of the Olekma granite-greenstone region, is • narrow, complexly defonned syncline (4J. The section consists of a ...olcanogenic sequence including meta·extrusives of ultramafic (komatiitc) to intermediate·silicic (andesite-dacite) composition.

-Deceased. 160

161 Copyri,ht e 1991 by V. H. Winston &. Son,Inc. All ri,hu reserved.

INTERNATIONAL GEOLOGY REVIEW

1. S. PUKHTEL' ET AL .

TABLE 1. Compositions ofOli... ine·Carbonate·Talc Rocks

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developed along the content of the Krasnaya Gorka sills as a result of repeated metamorphism and schistification. Zone of schistification are most clearly manirested in the derormed northeastern part or the intrusive and gradually disappear toward its relatively well preserved central part Neverlheless, this one circumstance is no reason to claim that the olivines, and therefore the textures they constitute, are of metamorphic origin.

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TABLE 4. Chemical Composition ofOlivincs from Olivine·Carbonnte-Tale Schists

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