Os Isotopes and the Origin of the Tasmanian Dolerites

New Os isotope data obtained for oxides separated from samples are thought to be in excess of 1 × 10 km (e.g. the of the Jurassic dolerites of Tasmania (Australia) are used to Deccan case noted above). In general, CFBs are not constrain the petrogenesis of the Ferrar continental flood basalt primary magmas and have compositions that differ from province. It is proposed here that the unradiogenic initial Os ratio typical mid-ocean ridge and ocean island basalts (MORB ( Os/Os = 0·145 ± 0·049 2 ) of these rocks is inconsistent and OIB, respectively). In short, many CFBs formed with petrogenetic models involving the assimilation of continental from enormous volumes of basaltic magma that appear crust by mantle-derived magmas. Instead, the results are more readily to have been generated over a restricted timespan, and explained by models in which the introduction of upper-crustal with compositions unlike those of their oceanic countermaterials into the mantle contaminates the source of these magmas parts. before melting. The increasing body of Os isotope data for mantleFor more than half a century CFBs have presented the derived rocks also provides new opportunities to assess whether any geological community with cause for much enthusiastic distinction between the roles of asthenospheric vs lithospheric mantle scientific debate. In referring to the likely compositions in the genesis of continental flood basalts might be possible. It is of flood basalt parental magmas (picritic vs basaltic), Cox concluded that, in the absence of an Os-rich phase with low (1980) made the perceptive observation: ‘In the rather Re/Os, the uncertainties in calculated initial ratios preclude the well-matched and evenly-balanced debate which has distinction between mantle sources in this particular case. taken place so far it is tempting to discern that the views of various authors are coloured by the flood basalt provinces they have been most concerned with or influenced by.’ This comment could equally well apply to

[1]  V. Courtillot,et al.  Age of the Deccan traps using 187Re–187Os systematics , 1999 .

[2]  R. Walker,et al.  THE Re-Os ISOTOPE SYSTEM IN COSMOCHEMISTRY AND HIGH-TEMPERATURE GEOCHEMISTRY , 1998 .

[3]  V. Bennett,et al.  The persistence of off-cratonic lithospheric mantle: Os isotopic systematics of variably metasomatised southeast Australian xenoliths , 1997 .

[4]  J. Birck,et al.  Re‐Os Isotopic Measurements at the Femtomole Level in Natural Samples , 1997 .

[5]  G. Wörner,et al.  Os, Sr, Nd, Pb, O isotope and trace element data from the Ferrar flood basalts, antarctica: evidence for an enriched subcontinental lithospheric source , 1996 .

[6]  R. Carlson,et al.  Chemical and Os isotopic study of Cretaceous potassic rocks from Southern Brazil , 1996 .

[7]  J. Luck,et al.  Os isotopes in orogenic lherzolite massifs and mantle heterogeneities , 1996 .

[8]  E. Hauri.  Major-element variability in the Hawaiian mantle plume , 1996, Nature.

[9]  I. Nicholls,et al.  Multistage evolution of Australian subcontinental mantle: Re-Os isotopic constraints from Victorian mantle xenoliths , 1996 .

[10]  O. Leonardos,et al.  Erratum to “High-Ti and low-Ti mafic potassic magmas: Key to plume—lithosphere interactions and continental flood-basalt genesis” [Earth Planet. Sci. Lett. 136 (1995) 149–165] , 1996 .

[11]  J. Encarnación,et al.  Synchronous emplacement of Ferrar and Karoo dolerites and the early breakup of Gondwana , 1996 .

[12]  D. DePaolo,et al.  Osmium isotope systematics of drilled lavas from Mauna Loa, Hawaii , 1996 .

[13]  R. Carlson,et al.  Osmium Recycling in Subduction Zones , 1996, Science.

[14]  M. Norman,et al.  Two mantle-plume components in Hawaiian picrites inferred from correlated Os–Pb isotopes , 1996, Nature.

[15]  O. Leonardos,et al.  High-Ti and low-Ti mafic potassic magmas: Key to plume-lithosphere interactions and continental flood-basalt genesis , 1995 .

[16]  P. H. Nixon,et al.  Stabilisation of Archaean lithospheric mantle: a Re-Os isotope study of peridotite xenoliths from th , 1995 .

[17]  R. Walker,et al.  Carius tube digestion for low-blank rhenium-osmium analysis , 1995 .

[18]  L. Reisberg,et al.  Os isotopic systematics of the MORB mantle: results from altered abyssal peridotites , 1995 .

[19]  H. Staudigel,et al.  Os isotope systematics of La Palma, Canary Islands: Evidence for recycled crust in the mantle source of HIMU ocean islands , 1995 .

[20]  L. Reisberg,et al.  Longevity of sub-continental mantle lithosphere from osmium isotope systematics in orogenic peridotite massifs , 1995, Nature.

[21]  J. Morgan,et al.  Rhenium-osmium concentration and isotope systematics in group IIAB iron meteorites , 1995 .

[22]  R. Carlson,et al.  ReOs, SmNd, and RbSr isotope evidence for thick Archaean lithospheric mantle beneath the Siberian craton modified by multistage metasomatism , 1995 .

[23]  R. Carlson,et al.  Os isotopic variation in basalts from Haleakala Volcano, Maui, Hawaii: A record of magmatic processes in oceanic mantle and crust , 1994 .

[24]  M. Roy‐Barman,et al.  187Os186Os ratios of mid-ocean ridge basalts and abyssal peridotites , 1994 .

[25]  J. Morgan,et al.  RE-OS ISOTOPIC EVIDENCE FOR AN ENRICHED-MANTLE SOURCE FOR THE NORIL'SK-TYPE, ORE-BEARING INTRUSIONS, SIBERIA , 1994 .

[26]  R. Carlson,et al.  Depletion and enrichment history of subcontinental lithospheric mantle: An Os, Sr, Nd and Pb isotopic study of ultramafic xenoliths from the northwestern Wyoming Craton , 1994 .

[27]  D. Wyman,et al.  Os isotope systematics in ocean island basalts , 1993 .

[28]  R. Carlson,et al.  Evidence from Re–Os isotopes for plume–lithosphere mixing in Karoo flood basalt genesis , 1992, Nature.

[29]  Ulrich R. Christensen,et al.  The role of lithospheric mantle in continental flood volcanism: Thermal and geochemical constraints , 1992 .

[30]  K. Gallagher,et al.  Dehydration melting and the generation of continental flood basalts , 1992, Nature.

[31]  W. J. Pegram,et al.  Osmium isotopic compositions from oceanic basalts , 1992 .

[32]  R. Carlson.  Physical and chemical evidence on the cause and source characteristics of flood basalt volcanism , 1991 .

[33]  J. D. Fassett,et al.  Re-Os isotope systematics of Ni-Cu sulfide ores, Sudbury Igneous Complex, Ontario: evidence for a major crustal component , 1991 .

[34]  L. Reisberg,et al.  The ReOs systematics of the Ronda Ultramafic Complex of southern Spain , 1991 .

[35]  R. Ellam,et al.  An interpretation of Karoo picrite basalts in terms of interaction between asthenospheric magmas and the mantle lithosphere , 1991 .

[36]  C. Hawkesworth,et al.  The petrogenesis of Mesozoic Gondwana low-Ti flood basalts , 1991 .

[37]  Candace E Martin.  Osmium isotopic characteristics of mantle-derived rocks , 1991 .

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

[39]  A. Chivas,et al.  Geochemical and Isotopic Constraints on the Origin of the Jurassic Dolerites of Tasmania , 1989 .

[40]  G. Faure,et al.  The geochemistry of Jurassic dolerites from Portal Peak, Antarctica , 1989 .

[41]  R. Carlson,et al.  Os, Sr, Nd, and Pb isotope systematics of southern African peridotite xenoliths: Implications for the chemical evolution of subcontinental mantle , 1989 .

[42]  R. White,et al.  Magmatism at rift zones: The generation of volcanic continental margins and flood basalts , 1989 .

[43]  P. Castillo.  The Dupal anomaly as a trace of the upwelling lower mantle , 1988, Nature.

[44]  S. Hart,et al.  Heterogeneous mantle domains: signatures, genesis and mixing chronologies , 1988 .

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

[46]  H. Wensink.  Comments on "Deccan flood basalts at the Cretaceous/Tertiary boundary?" by V. Courtillot, J. Besse, D. Vandamme, R. Montigny, J.-J. Jaeger and H. Cappetta , 1987 .

[47]  J. Jaeger,et al.  Deccan flood basalts at the Cretaceous/Tertiary boundary? , 1986 .

[48]  C. Hawkesworth,et al.  Evidence from the Parana of south Brazil for a continental contribution to Dupal basalts , 1986, Nature.

[49]  C. Officer,et al.  Terminal Cretaceous Environmental Events , 1985, Science.

[50]  L. Atalla,et al.  Trace Element and Strontium Isotope Constraints on the Origin and Evolution of Paraná Continental Flood Basalts of Santa Catarina State (Southern Brazil) , 1985 .

[51]  G. Faure,et al.  Petrogenesis of the Kirkpatrick Basalt, Solo Nunatak, northern Victoria Land, Antarctica, based on isotopic compositions of strontium, oxygen and sulfur , 1984 .

[52]  D. McKenzie,et al.  Mantle reservoirs and ocean island basalts , 1983, Nature.

[53]  G. Faure,et al.  Correlation of δ18O and initial87Sr/86Sr ratios in Kirkpatrick basalt on Mt. Falla, transantarctic mountains , 1981 .

[54]  K. Cox.  A Model for Flood Basalt Vulcanism , 1980 .

[55]  A. B. Ford,et al.  K—Ar age, composition, and origin of Mesozoic mafic rocks related to Ferrar Group, Pensacola Mountains, Antarctica , 1980 .

[56]  J. Minster,et al.  87Rb-87Sr chronology of enstatite meteorites , 1979 .

[57]  E. Williams.  Tasman Fold Belt System in Tasmania , 1978 .

[58]  K. G. Cox,et al.  Flood basalts, subduction and the break-up of Gondwanaland , 1978, Nature.

[59]  R. Steiger,et al.  Subcommission on geochronology: Convention on the use of decay constants in geo- and cosmochronology , 1977 .

[60]  I. Mcdougall,et al.  Reply: Palaeomagnetic and potassium-argon dating studies of the Tasmanian dolerites , 1977 .

[61]  G. Faure,et al.  Strontium isotope composition and petrogenesis of the Kirkpatrick basalt, Queen Alexandra Range, Antarctica , 1974 .

[62]  K. G. Cox,et al.  Geochemical and petrographic provinces in the karroo basalts of southern africa , 1967 .

[63]  I. Mcdougall,et al.  Thorium and uranium concentrations, and the isotopic composition of strontium in the differentiated Tasmanian dolentes , 1965 .

[64]  J. Chesley,et al.  Crust–mantle interaction in large igneous provinces: Implications from the Re–Os isotope systematics of the Columbia River flood basalts , 1998 .

[65]  J. Mahoney,et al.  Large igneous provinces: continental, oceanic, and planetary flood volcanism , 1997 .

[66]  A. Basu,et al.  Earth Processes: Reading the Isotopic Code: Basu/Earth Processes: Reading the Isotopic Code , 1996 .

[67]  M. Roy‐Barman,et al.  187Os/186Os in oceanic island basalts: tracing oceanic crust recycling in the mantle , 1995 .

[68]  K. Foland,et al.  A short interval of Jurassic continental flood basalt volcanism in Antarctica as demonstrated by 40Ar39Ar geochronology , 1994 .

[69]  M. Roy-Barman.  Mesure du rapport 187Os-186Os dans les basaltes et les péridotites : contribution à la systématique 187Re-187Os dans le manteau , 1993 .

[70]  S. Hart,et al.  ReOs isotope systematics of HIMU and EMII oceanic island basalts from the south Pacific Ocean , 1993 .

[71]  C. Hawkesworth,et al.  Coats Land dolerites and the generation of Antarctic continental flood basalts , 1992, Geological Society, London, Special Publications.

[72]  R. Pankhurst,et al.  Magmatism and the causes of continental break-up , 1992 .

[73]  W. McDonough,et al.  Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes , 1989, Geological Society, London, Special Publications.

[74]  J. Hergt.  The origin and evolution of the Tasmanian dolerites , 1987 .

[75]  S. Taylor,et al.  The continental crust: Its composition and evolution , 1985 .

[76]  S. Taylor.  The continental crust , 1985 .

[77]  B. Dupré,et al.  Subcontinental versus suboceanic mantle, II. NdSrPb isotopic comparison of continental tholeiites with mid-ocean ridge tholeiites, and the structure of the continental lithosphere , 1982 .

[78]  I. Mcdougall,et al.  Geochemical comparison of the mesozoic basaltic rocks of Antarctica, South Africa, South America and Tasmania , 1968 .