Petrology and geochemistry of crustally contaminated komatiitic basalts from the Vetreny Belt, southeastern Baltic Shield: Evidence for an early Proterozoic mantle plume beneath rifted Archean continental lithosphere

New isotope and trace element data are presented for komatiitic basalts and a related peridotite Vinela Dike from the large Vetreny Belt in the southeastern Baltic Shield. The MgO contents of the erupted and intruded magmas are inferred to increase from 13 to 17% towards the center of the belt, which implies the respective increase in liquidus temperatures from 1370 to 1440°C. The elevated liquidus temperatures suggest that the source of the komatiite magmas had a substantially higher potential temperature (1630°C) than the ambient mantle (1480°C) and are regarded as evidence for the existence of a mantle plume underlying the region at ~2.45 Ga. Parental magmas to the lavas and the Vinela Dike were shown to have komatiite composition and were derived from a long-term LREE-depleted mantle source with [epsilon]Nd(T) of ca. +2.6. The evolution of these magmas en route to the surface was mainly controlled by 4-15% contamination with older felsic crustal rocks, which resulted in substantial changes in incompatible trace element and isotope ratios. The obtained Sm---Nd internal isochron ages of 2449 ± 35 and 2410 ± 34 Ma for the lavas, 2430 ± 174 Ma for the Vinela Dike, and a whole-rock Pb---Pb age of 2424 ± 178 Ma for the lavas together with a U---Pb zircon age of 2437 ± 3 Ma are identical to the reported U---Pb zircon and baddeleyite ages for numerous mafic-ultramafic layered intrusions in central and northern Karelia. From their chemical and isotope similarities, it is likely that these rocks had allied parental magmas. These magmas may have been emplaced in a continental rift setting during the interaction of a mantle plume and continental crust. Impinging of a plume head beneath the continental lithosphere resulted in its thinning, stretching, and rifting but failed to open a new ocean. This extensive magmatic event was responsible for a substantial contribution of early Proterozoic juvenile material to the Archean continental crust in the Baltic Shield.

[1]  M. Tatsumoto,et al.  Time Differences in the Formation of Meteorites as Determined from the Ratio of Lead-207 to Lead-206 , 1973, Science.

[2]  R. Cliff,et al.  Sm−Nd and Pb isotopic study of mafic rocks associated with early Proterozoic continental rifting: the Peröpohja schist belt in northern Finland , 1990 .

[3]  T. Green.  Experimental studies of trace-element partitioning applicable to igneous petrogenesis , 1994 .

[4]  S. Bogdanova,et al.  The ``Saamian'' of the Belomorian Mobile Belt: new geochronological constraints , 1993 .

[5]  B. Murton.  Tectonic controls on boninite genesis , 1989, Geological Society, London, Special Publications.

[6]  W. McDonough.  Constraints on the composition of the continental lithospheric mantle , 1990 .

[7]  N. Arndt,et al.  Crustally contaminated komatiites and basalts from Kambalda, Western Australia , 1986 .

[8]  S. Turchenko.  Precambrian metallogeny related to tectonics in the eastern part of the Baltic Shield , 1992 .

[9]  Y. Balashov,et al.  Isotope data on the age and genesis of layered basic-ultrabasic intrusions in the Kola Peninsula and northern Karelia, northeastern Baltic Shield , 1993 .

[10]  T. Skiöld,et al.  Age and geodynamic aspects of the oldest rocks in the Precambrian Belomorian Belt of the Baltic (Fennoscandian) Shield , 1996, Geological Society, London, Special Publications.

[11]  Walter H. F. Smith,et al.  An empirical thermal history of the Earth's upper mantle , 1994 .

[12]  A. Hofmann,et al.  Petrology of a 2.41 Ga remarkably fresh komatiitic basalt lava lake in Lion Hills, central Vetreny Belt, Baltic Shield , 1996 .

[13]  R. Hill.  Starting plumes and continental break-up , 1991 .

[14]  H. Huppert,et al.  Emplacement and cooling of komatiite lavas , 1984, Nature.

[15]  R. White,et al.  Mantle plumes and flood basalts , 1995 .

[16]  N. Arndt,et al.  Constraining the potential temperature of the Archaean mantle: A review of the evidence from komatiites , 1993 .

[17]  T. Krogh.  Improved accuracy of U-Pb zircon ages by the creation of more concordant systems using an air abrasion technique , 1982 .

[18]  R. Rudnick,et al.  Nature and composition of the continental crust: A lower crustal perspective , 1995 .

[19]  A. Hofmann,et al.  The Kostomuksha greenstone belt, NW Baltic Shield: remnant of a late Archaean oceanic plateau? , 1997 .

[20]  Derek York,et al.  Least squares fitting of a straight line with correlated errors , 1968 .

[21]  G. Wasserburg,et al.  Sm-Nd isotopic evolution of chondrites and achondrites. II , 1984 .

[22]  V. F. Smolkin,et al.  Early Proterozoic layered intrusions in the northeastern part of the Fennoscandian Shield , 1990 .

[23]  C. Hawkesworth,et al.  Lithosphere Remobilization during Paraná CFB Magmatism , 1988 .

[24]  M. Bickle,et al.  The Volume and Composition of Melt Generated by Extension of the Lithosphere , 1988 .

[25]  D. Abbott.  Plumes and hotspots as sources of greenstone belts , 1996 .

[26]  A. Saunders,et al.  Magmatism in the Ocean Basins , 1989 .

[27]  H. Huppert,et al.  Cooling and contamination of mafic and ultramafic magmas during ascent through continental crust , 1985 .

[28]  N. Arndt,et al.  Pb isotopic compositions of Archean komatiites and sulfides , 1990 .

[29]  E. Flueh,et al.  The crustal structure along the POLAR Profile from seismic refraction investigations , 1989 .

[30]  M. Thirlwall.  A triple-filament method for rapid and precise analysis of rare-earth elements by isotope dilution , 1982 .

[31]  W. Mooney,et al.  The structural and geochemical evolution of the continental crust: Support for the oceanic plateau model of continental growth , 1995 .

[32]  G. Manhès,et al.  Comparative uranium-thorium-lead and rubidium-strontium study of the Saint Sèverin amphoterite: consequences for early solar system chronology , 1978 .

[33]  Y. Amelin,et al.  Nd and Sr isotopic geochemistry of mafic layered intrusions in the eastern Baltic shield: implications for the evolution of Paleoproterozoic continental mafic magmas , 1996 .

[34]  S. Wilde,et al.  Timing of Late Archaean granulite facies metamorphism in the southwestern Yilgarn Craton of Western Australia: evidence from UPb ages of zircons fro mafic granulites , 1994 .

[35]  M. Timmerman,et al.  SmNd evidence for late Archaean crust formation in the Lapland-Kola Mobile Belt, Kola Peninsula, Russia and Norway , 1995 .

[36]  Albrecht W. Hofmann,et al.  Chemical differentiation of the Earth: the relationship between mantle, continental crust, and oceanic crust , 1988 .

[37]  F. Albarède,et al.  The REE content of some hydrothermal fluids , 1986 .

[38]  N. Machado,et al.  UPb isotopic geochemistry of komatiites and pyroxenes from the southern Abitibi greenstone belt, Canada , 1995 .

[39]  Anthony J. Martin,et al.  Uniquely fresh 2.7 Ga komatiites from the Belingwe greenstone belt, Zimbabwe , 1987 .

[40]  C. Hubert,et al.  Accretion of Archean oceanic plateau fragments in the Abitibi, greenstone belt, Canada , 1993 .

[41]  P. Beattie,et al.  Partition coefficients for olivine-melt and orthopyroxene-melt systems , 1991 .

[42]  A. Hofmann,et al.  Nb-Th-La in komatiites and basalts: constraints on komatiite petrogenesis and mantle evolution , 1991 .

[43]  R. Harmon,et al.  Mineralogy, Chemistry, and Genesis of the Boninite Series Volcanics, Chichijima, Bonin Islands, Japan , 1994 .

[44]  K. Ludwig.  ISOPLOT; a plotting and regression program for radiogenic-isotope data; version 2.53 , 1991 .

[45]  M. Richards,et al.  Numerical investigations of the mantle plume initiation model for flood basalt events , 1994 .

[46]  G. Wasserburg,et al.  Sm-Nd isotopic evolution of chondrites , 1980 .

[47]  M. Bau.  Rare-earth element mobility during hydrothermal and metamorphic fluid-rock interaction and the significance of the oxidation state of europium , 1991 .

[48]  C. Langmuir,et al.  Modelling of major elements in mantle-melt systems using trace element approaches , 1978 .

[49]  O. Bogatikov,et al.  Trace-element geochemistry of Archaean and Proterozoic rocks from eastern Karelia, U.S.S.R. , 1988 .

[50]  S. Hart,et al.  In search of a bulk-Earth composition , 1986 .

[51]  I. Krylov,et al.  Archaean rocks from southeastern Karelia (Karelian granite greenstone terrain) , 1993 .

[52]  D. McKenzie,et al.  Melt Generation by Plumes: A Study of Hawaiian Volcanism , 1991 .

[53]  C. Garbe-Schönberg.  SIMULTANEOUS DETERMINATION OF THIRTY‐SEVEN TRACE ELEMENTS IN TWENTY‐EIGHT INTERNATIONAL ROCK STANDARDS BY ICP‐MS , 1993 .

[54]  A. Glazner,et al.  Production of Isotopic Variability in Continental Basalts by Cryptic Crustal Contamination , 1992, Science.

[55]  I. Campbell,et al.  Zircon xenocrysts from the Kambalda volcanics: age constraints and direct evidence for older continental crust below the Kambalda-Norseman greenstones , 1986 .

[56]  G. Jenner,et al.  The Sm-Nd age of Kambalda volcanics is 500 Ma too old! , 1985 .

[57]  S. Goldstein,et al.  An open boundary between lower continental crust and mantle: its role in crust formation and crustal recycling , 1989 .

[58]  M. Richards,et al.  Flood Basalts and Hot-Spot Tracks: Plume Heads and Tails , 1989, Science.

[59]  P. Hooper,et al.  Evaluating crustal contamination in continental basalts: the isotopic composition of the Picture Gorge Basalt of the Columbia River Basalt Group , 1993 .

[60]  G. Gaál,et al.  An Outline of the precambrian evolution of the baltic shield , 1987 .

[61]  P. Hamilton,et al.  Rare-earth abundances in chondritic meteorites , 1978 .

[62]  W. McDonough,et al.  The composition of the Earth , 1995 .

[63]  C. Herzberg.  GENERATION OF PLUME MAGMAS THROUGH TIME : AN EXPERIMENTAL PERSPECTIVE , 1995 .

[64]  Y. Amelin,et al.  UPb geochronology of layered mafic intrusions in the eastern Baltic Shield: implications for the timing and duration of Paleoproterozoic continental rifting , 1995 .

[65]  G. Wasserburg,et al.  Sm-Nd age of the Stillwater complex and the mantle evolution curve for neodymium , 1979 .

[66]  P. Roeder,et al.  Olivine-liquid equilibrium , 1970 .

[67]  N. Arndt.  Komatiites: a dirty window to the Archean mantle , 1985 .

[68]  R. Gorbatschev,et al.  Frontiers in the Baltic Shield , 1993 .

[69]  F. Richter.  A Major Change in the Thermal State of the Earth at the Archean-Proterozoic Boundary: Consequences for the Nature and Preservation of Continental Lithosphere , 1988 .

[70]  P. Renne,et al.  Rapid Eruption of the Siberian Traps Flood Basalts at the Permo-Triassic Boundary , 1991, Science.

[71]  R. Hori,et al.  A model of ocean-crust accretion for the Superior province, Canada , 1993 .

[72]  N. Arndt,et al.  Pb and Nd isotopic study of two archean komatiitic flows from Alexo, Ontario , 1984 .

[73]  N. Arndt,et al.  The Geology of the Belingwe Greenstone Belt, Zimbabwe , 1993 .