Ancient Laurentian detrital zircon in the closing Iapetus Ocean, Southern Uplands Terrane, Scotland

Early Paleozoic sandstones in the Southern Uplands terrane of Scotland were deposited during closure of the Iapetus Ocean between Laurentia and Avalonia. Their tectonic setting and sources are controversial, and different authors have supported subduction-accretion, extensional continental-margin development, or back-arc basin settings. We report new U-Pb detrital zircon ages from five Late Ordovician sandstones from the Northern Belt of the Southern Uplands and test models of their tectonic setting. The U-Pb zircon age distributions are dominated by peaks characteristic of sources in Laurentia and include grains as old as 3.6 Ga, older than any previously recorded in the British Caledonides SE of the Laurentian foreland. Discordant grains in one sample suggest derivation via erosion of metasedimentary rocks incorporated in the Grampian-Taconian orogen. Rare Neoproterozoic grains, previously interpreted as originating from a peri-Gondwanan terrane, may be derived from igneous rocks associated with Iapetan rifting. Only rare zircons are contemporary with the depositional ages. The results are difficult to reconcile with extensional continental-margin and back-arc models, but they support an active continental-margin subduction-accretion model. Close similarities with distributions from the Newfoundland Appalachians are consistent with sinistral transpression during closing of the Iapetus Ocean

Late cretaceous stratigraphy of the southeastern Chaco - Paraná basin (“norte basin” - Uruguay). The maastrichtian age of the calcretization process

In the last 40 years, successive revisions have been introduced to the lithostratigraphy of the Late Cretaceous of the Norte Basin, whose record is formed by predominantly siliciclastic continental fossiliferous sedimentary rocks. A factor that contributed to the terminology proliferation was the misplaced importance attributed to the epigenetic processes and products (calcretes and ferricretes, occasionally fossiliferous) affecting those siliciclastic rocks. Based on field work and lithological logs from a number of key areas, the validity of the original stratigraphic column showing, from base to top, the Guichón, Mercedes, Asencio and Queguay formations is supported. For those particular units, the lithostratigraphic scope given by the original definitions is correct and, with minimum adjustments, they should be restored for their practical usefulness as geological mapping units. An evolutionary scheme for the Late Cretaceous of the Norte Basin is herein presented, with the aim of contributing to a greater understanding of the succession of sedimentary and epigenetic processes. A Maastrichtian age is proposed for the carbonatic cementation and/or substitution that affected the Mercedes and Asencio formations, thus originating the Queguay Formation, based on absolute age of the calcite cement (~ 72 Ma; U-Pb), paleontological data, and the correlation established with similar events recorded in the Marília Formation on the Bauru Basin (Brazil)

Age And Origin Of The Neoproterozoic Brauna Kimberlites: Melt Generation Within The Metasomatized Base Of The São Francisco Craton, Brazil

The diamondiferous Brauna kimberlite field is situated in the northeast part of the São Francisco craton, Bahia State, Brazil, and ongoing exploration revealed three complex pipe-like bodies and nineteen dykes oriented along a N30W trend. Uranium-Pb perovskite age determinations of hypabyssal kimberlite material yielded a high-precision emplacement age of 642. ±. 6. Ma (2-sigma uncertainty). This age provides the first evidence for Neoproterozoic kimberlite magmatism in Brazil, and the Brauna kimberlites thus represent the oldest known primary source of diamonds in the São Francisco craton.Primary kimberlite mineralogy at Brauna comprises olivine, spinel, ilmenite, phlogopite, perovskite, apatite, as well as late-stage serpentine and carbonate. Furthermore, abundant olivine, Cr-diopside, and pyrope garnet xenocrysts are present. The most common xenoliths are wall-rock granodiorites, mantle eclogites and peridotites. The Brauna kimberlites do not fit into the classic subdivision of kimberlites and orangeites (formerly Group-II kimberlites) based on South African type occurrences. Their geochemical and isotopic signatures, with negative initial εNd values of -5.8 to -8.1 and variably enriched 87Sr/86Sr ratios (0.7045-0.7063), suggest that Brauna kimberlite magmas were derived from a mantle source region that was strongly metasomatized prior to kimberlite magmatism at ~642Ma. In particular, the incompatible element distribution suggests that Brauna kimberlite magmas originate from the metasomatized base of the São Francisco craton, with only minor input from the convecting upper mantle. The Brauna kimberlites mineralogically and geochemically resemble the slightly older "anomalous" mica kimberlites from Guaniamo in Venezuela (712±6Ma). This may suggest that both mica-rich kimberlite occurrences formed from similarly enriched subcratonic mantle lithosphere during Late Neoproterozoic extensional tectonics related to the breakup of the supercontinent Rodinia. © 2012 Elsevier B.V.3531935Araújo, A.L.N., Carlson, R.W., Gaspar, J.C., Bizzi, L.A., Petrology of kamafugites and kimberlites from the Alto Paranaíba Alkaline Province, Minas Gerais, Brazil (2001) Contributions to Mineralogy and Petrology, 142, pp. 163-177Barbosa, J.S.F., Sabaté, P., Archean and Paleoproterozoic crust of the São Francisco Craton, Bahia, Brazil: geodynamic features (2004) Precambrian Research, 133, pp. 1-27Bardet, M.G., Géologie du diamant (1977) Memoires Du BRGM, p. 177Beard, A.D., Downes, H., Hegner, E., Sablukov, S.M., Geochemistry and mineralogy of kimberlites from the Arkhangelsk Region, NW Russia: evidence for transitional kimberlite magma types (2000) Lithos, 51, pp. 47-73Becker, M., Le Roex, A.P., Geochemistry of South African on- and off craton, group I and group II kimberlites: petrogenesis and source region evolution (2006) Journal of Petrology, 47, pp. 673-703Becker, M., Le Roex, A.P., Geochemistry and petrogenesis of South African transitional kimberlites located on and off the Kaapvaal Craton (2007) South African Journal of Geology, 110, pp. 631-646Beyer, C., Berndt, J., Tappe, S., Klemme, S., Trace element partitioning between perovskite and kimberlite to carbonatite melt: New experimental constraints (2013) Chemical Geology, 353, pp. 133-140. , (this issue)Bizzi, L.A., Smith, C.R., Meyer, H.O.A., Armstrong, R., de Wit, M.J., Mesozoic kimberlites and related rocks in southwestern São Francisco craton, Brazil: a case for local mantle reservoirs and their interaction (1993) Special Publication 2/91, pp. 156-171. , H.O.A. Meyer, O.H. Leonardos (Eds.) Proceedings of the 5th International Kimberlite Conference, Araxá, Brasilia, DF: CPRMBizzi, L.A., Smith, B.C., De Wit, M.J., Macdonald, I., Armstrong, R.A., Isotope characteristics of the lithospheric mantle underlying the SW São Francisco craton margin, Brazil (1994) International Symposium on the Physics and Chemistry of the Upper Mantle, pp. 227-256. , Invited Lectures, São PauloBizzi, L.A., de Witt, M.J., Smith, C.B., McDonald, I., Armstrong, R.A., Heterogeneous enriched mantle materials and Dupal-type magmatism along SW margin of the São Francisco craton, Brazil (1995) Journal of Geodynamics, 20, pp. 469-491Carlson, R.W., Esperança, S., Svisero, D.P., Chemical and Os isotopic study of Cretaceous potassic rocks from southern Brazil (1996) Contributions to Mineralogy and Petrology, 125, pp. 393-405Carlson, R.W., Araujo, A.L.N., Junqueira-Brod, T.C., Gaspar, J.C., Brod, J.A., Petrinovic, I.A., Hollanda, M.H.B.M., Sichel, S., Chemical and isotopic relationships between peridotite xenoliths and mafic-ultrapotassic rocks from Southern Brazil (2007) Chemical Geology, 242, pp. 415-434Caro, G., Kopylova, M.G., Creaser, R.A., The hypabyssal 5034 kimberlite of the Gahcho Kue cluster, southeastern Slave craton, northwest territories, Canada: a granite-contaminated group-I kimberlite (2004) The Canadian Mineralogist, 42, pp. 183-207Chaves, M.L.S.C., Karfunkel, J., Hoppe, A., Hoover, D.B., Diamonds from the Espinhaço Range (Minas Gerais, Brazil) and their redistribution through the geologic record (2001) Journal of South American Earth Sciences, 14, pp. 277-289Clement, C.R., Skinner, M.W., Textural genetic classification of kimberlites (1979) Transactions of the Geological Society of South Africa, 88, pp. 403-410Costa, V.S., (1996), Estudos mineralógicos e químicos do kimberlito Batovi 6 (MT) em comparação com as intrusões Três Ranchos 4 (GO) e Limeira 1 (MG). Master Thesis. Geoscience Institute, University of Campinas, Campinas, São Paulo, BrazilCosta, F.G., Oliveira, E.P., McNaughton, N., The Fazenda Gavião granodiorite and associated potassic plutons as evidence for Palaeoproterozoic arc-continent collision in the Rio Itapicuru greenstone belt, Brazil (2011) Journal of South American Earth Sciences, 32, pp. 127-141Cruz Filho, B.E., Conceição, H., Rios, D.C., Rosa, M.L.S., Marinho, M.M., Geologia, petrografia e litogeoquimica do batólito trondhjemítico Nordestina, Núcleo Serrinha, Nordeste da Bahia (2003) Revista Brasileira de Geociencias, 33, pp. 175-186Cruz Filho, B.E., Conceição, H., Rosa, M.L.S., Rios, D.C., Macambira, M.J.B., Marinho, M.M., Geocronologia e assinatura isotópica (Rb-Sr e Sm-Nd) do batólito trondhjemítico Nordestina, Núcleo Serrinha, nordeste do estado da Bahia (2005) Revista Brasileira de Geociencias, 35, pp. 1-8. , 4-suplementoDawson, J.P., (1980) Kimberlite and their Xenoliths, , Springer, New York, 250 ppDonatti-Filho, J.P., Oliveira, E.P., Pisani, J.R.T., Ochika, F.P., Geochemistry and mineralogy of kimberlites from the Brauna Kimberlite Province, São Francisco Craton, NE Brazil (2008) 9o Int Kimberlite Conf Ext Abstr, Frankfut, Germany, 9IKC-A-00316Donatti-Filho, J.P., Oliveira, E.P., McNaughton, N., Age constraints for the Serrinha Block lithosphere based on inherited zircons from the Neoproterozoic Brauna Kimberlite field, São Francisco Craton, Bahia, Brazil (2010) 45° Congr. Bras. Geol., Abstr, Belém, BrazilDownes, P.J., Wartho, J., Griffin, B.J., Magmatic evolution and ascent history of the Aries micaceous kimberlite, Central Kimberley Basin, Western Australia: evidence from zoned phlogopite phenocrysts, and UV laser 40Ar/39Ar analysis of phlogopite-biotite (2006) Journal of Petrology, 47, pp. 1751-1783Fipke, C.E., Gurney, J.J., Moore, R.O., Diamond exploration techniques emphasising indicator mineral geochemistry and Canadian examples (1995) Bulletin 423, , 86 pp. Geological Survey of CanadaFraser, K.J., Hawkesworth, C.J., Erlank, A.J., Mitchell, R.H., Scott-Smith, B.H., Sr, Nd and Pb isotope and minor element geochemistry of lamproites and kimberlites (1985) Earth and Planetary Science Letters, 76, pp. 57-70Gaffney, A.M., Blichert-Toft, J., Nelson, B.K., Bizarro, M., Rosin, M., Albarède, F., Constraints on source-forming processes of West Greenland kimberlites inferred from Hf-Nd isotope systematic (2007) Geochimica et Cosmochimica Acta, 71, pp. 2820-2836Gibson, S.A., Thompson, R.N., Leonardos, O.K., Dickin, A.P., Mitchell, J.G., The Late Cretaceous impact of the Trindade mantle plume - evidence from large-volume, mafic, potassic magmatism in SE Brazil (1995) Journal of Petrology, 36, pp. 189-229Gibson, S.A., Thompson, R.N., Dickin, A.P., Leonardos, O.H., High-Ti and low-Ti mafic potassic magmas: key to plume-lithosphere interactions and continental flood-basalt genesis (1996) Earth and Planetary Science Letters, 141, pp. 325-341Gioia, S.M.C.L., Pimentel, M.M., The Sm-Nd isotopic method in the geochronology laboratory of the University of Brasília (2000) Anais da Academia Brasileira de Ciências, 2, p. 72Grütter, H.S., Gurney, J.J., Menzies, A.H., Winter, F., An updated classification scheme for mantle-derived garnet, for use by diamond explorers (2004) Lithos, 77, pp. 844-857Guarino, V., Wu, F.-Y., Lustrino, M., Melluso, L., Brotzu, P., Gomes, C., Ruberti, E., Svisero, D.P., U-Pb ages, Sr-Nd - isotope geochemistry and petrogenesis of kimberlites, kamafugites and phlogopite-picrites of the Alto Paranaíba Igneous Province, Brazil (2013) Chemical Geology, 353, pp. 66-83. , (this issue)Gurney, J.J., Zweistra, P., The interpretation of the major element compositions of the mantle minerals in diamond exploration (1995) Journal of Geochemical Exploration, 53, pp. 293-309Hawkesworth, C.J., Blake, S., Evans, P., Hughes, R., Macdonald, R., Thomas, L.E., Turner, S.P., Zellmer, G., Time scales of crystal fractionation in magma chambers - integrating physical, isotopic and geochemical perspectives (2000) Journal of Petrology, 41, pp. 991-1006Heaman, L.M., Kjarsgaard, B.A., Timing of eastern North American kimberlite magmatism: continental extension of the Great Meteor hotspot track? (2000) Earth and Planetary Science Letters, 178, pp. 253-268Jakubec, J., Kimberlite emplacement models - the implications for mining projects (2008) Journal of Volcanology and Geothermal Research, 174, pp. 20-28Kaminsky, F.V., Sablukov, S.M., Sablukova, L.I., Channer, D.M.D., Neoproterozoic 'anomalous' kimberlites of Guaniamo, Venezuela: mica kimberlites of 'isotopic transitional' type (2004) Lithos, 76, pp. 565-590Kjarsgaard, B.A., Pearson, D.G., Tappe, S., Nowell, G.M., Dowall, D., Geochemistry of hypabyssal kimberlites from Lac de Gras, Canada: comparisons to a global database and applications to the parent magma problem (2009) Lithos, 112, pp. 236-248Kopylova, M.G., Matveev, S., Raudsepp, M., Searching for parental kimberlite melt (2007) Geochimica et Cosmochimica Acta, 71, pp. 3616-3629Lapin, A.V., Tolstov, A.V., Vasilenko, V.B., Petrogeochemical characteristics of the kimberlites from the Middle Markha Region with application to the problem of the geochemical heterogeneity of kimberlites (2007) Geochemistry International, 45, pp. 1197-1209Le Roex, A.P., Bell, D.R., Davis, P., Petrogenesis of group I kimberlites from Kimberley, South Africa: evidence from bulk-rock geochemistry (2003) Journal of Petrology, 44, pp. 2261-2286Li, Z.X., Bogdanova, S.V., Collins, A.S., Davidson, A., De Waele, B., Ernst, R.E., Fitzsimons, I.C.W., Vernikovsky, V., Assembly, configuration, and break-up history of Rodinia: a synthesis (2008) Precambrian Research, 160, pp. 179-210Lorenz, V., Kurszlaukis, S., Root zone processes in the phreatomagmatic pipe emplacement model and consequences for the evolution of maar-diatreme volcanoes (2007) Journal of Volcanology and Geothermal Research, 159, pp. 4-32Makhotkin, I.L., Gibson, S.A., Thompson, R.N., Zhuralev, D.Z., Zherdev, P.U., Late Devonian diamondiferous kimberlite and alkaline picrite (proto-kimberlite?) - magmatism in the Arkhangelsk region, NW Russia (2000) Journal of Petrology, 41, pp. 201-227Malarkey, J., Pearson, D.G., Kjarsgaard, B.A., Davidson, J.P., Nowell, G.M., Ottley, C.J., Stammer, J., From source to crust: tracing magmatic evolution in a kimberlite and a melilitite using microsample geochemistry (2010) Earth and Planetary Science Letters, 299, pp. 80-90McDonough, W.F., Sun, S.S., The composition of the Earth (1995) Chemical Geology, 120, pp. 223-253Mello, E.F., Xavier, R.P., McNaughton, N.J., Hagemann, S.G., Fletcher, I., Snee, L., Age constraints on felsic intrusions, metamorphism and gold mineralization in the Paleoproterozoic Rio Itapicuru greenstone belt, NE Bahia State, Brazil (2006) Mineralium Deposita, 40, pp. 849-866Melluso, L., Lustrino, M., Ruberti, E., Brotzu, P., Gomes, C.B., Morbidelli, L., Morra, V., d'Amelio, F., Major- and trace-element composition of olivine, perovskite, clinopyroxene, Cr-Fe-Ti oxides, phlogopites and host kamafugites and kimberlites, Alto Paranaíbá, Brazil (2008) The Canadian Mineralogist, 46, pp. 19-40Mitchell, R.H., The alleged kimberlite-carbonatite relationship: additional contrary mineralogical evidence (1979) American Journal of Science, 279, pp. 570-589Mitchell, R.H., (1995) Kimberlites, Orangeites, and Related Rocks, , Plenum Press, New York, 410 ppMitchell, R.H., Potassic magmas derived from metasomatized lithospheric mantle: nomenclature and relevance to explanation for diamond bearing rocks (2006) Journal of the Geological Society of India, 67, pp. 317-327Mitchell, R.H., Bergman, S.C., (1991) Petrology of Lamproites, , Plenum Press, New York, 447 ppMitchell, R.H., Tappe, S., Discussion of "Kimberlites and aillikites as probes of the continental lithospheric mantle", by D. Francis and M. Patterson (Lithos v. 109, p. 72-80) (2010) Lithos, 115, pp. 288-292Navarro, M.S., Andrade, S., Ulbrich, H., Gomes, C.B., Girardi, V.A.G., The direct determination of rare earth elements in basaltic and related rocks using ICP-MS: testing the efficiency of microwave oven sample decomposition procedures (2008) Geostandards & Geoanalytical Research, 32, pp. 167-180Nelson, D.R., Isotopic characteristics and petrogenesis of the lamproites and kimberlites of central West Greenland (1989) Lithos, 22, pp. 265-274Nielsen, T.F.D., Jensen, S.M., Secher, K., Sand, K.K., Distribution of kimberlite and aillikite in the Diamond Province of southern West Greenland: a regional perspective based on groundmass mineral chemistry and bulk compositions (2009) Lithos, 112, pp. 358-371Nowell, G.M., Pearson, D.G., Bell, D.R., Carlson, R.W., Smith, C.B., Kempton, P.D., Noble, S.R., Hf isotope systematics of kimberlites and their megacrysts: new constraints on their source regions (2004) Journal of Petrology, 45, pp. 1583-1612Oliveira, E.P., Carvalho, M.J., McNaughton, N.J., Evolução do segmento norte do orógeno Itabuna-Salvador-Curaçá: cronologia da acresção de arcos, colisão continental e escape de terrenos (2004) Geologia USP, Série Científica, 4, pp. 41-53Oliveira, E.P., McNaughton, N.J., Armstrong, R., Mesoarchaean to Palaeoproterozoic growth of the northern segment of the Itabuna-Salvador-Curaçá orogen, São Francisco craton, Brazil (2010) Geol. Soc. London, Spec. Publ., 338, pp. 263-286. , T.M. Kusky, M.-G. Zhai, W. Xiao (Eds.) The Evolving Continents: Understanding Processes of Continental GrowthOliveira, E.P., Souza, Z.S., McNaughton, N.J., Lafon, J.-M., Costa, F.G., Figueiredo, A.M., The Rio Capim volcanic-plutonic-sedimentary belt, São Francisco craton, Brazil: geological, geochemical and isotopic evidence for oceanic arc accretion during Palaeoproterozoic continental collision (2011) Gondwana Research, 19, pp. 735-750Peate, D.W., Hawkesworth, C.J., Lithospheric to asthenospheric transition in low-Ti flood basalts from southern Parana, Brazil (1996) Chemical Geology, 127, pp. 1-24Peate, D.W., Hawkesworth, C.J., Mantovani, M.S.M., Rogers, N.W., Turner, A.P., Petrogenesis and stratigraphy of the high Ti/Y Urubici magma type in the Paraná flood basalt Province and implications for the nature of "Dupal"-type mantle in the South Atlantic region (1999) Journal of Petrology, 40, pp. 451-473Pisani, J.R.T., Tainton, K.M., Allan, A.F., Silva, S.B., Miranda, J.V., Geology and exploration of the Brauna Diamantíferous Kimberlites, Serrinha Block, Bahia, Brazil (2001) Revista Brasileira de Geociencias, 31, pp. 663-664Ramsey, R.R., Tompkins, L.A., The geology, heavy mineral concentrate mineralogy, and diamond prospectivity of Boa Esperanca and Cana Verde pipes, Corrego D'anta, Minas Gerais, Brazilin kimberlites, related rocks and mantle xenoliths (1994) Companhia de Pesquisa de Recursos Minerais - CPRM, 2, pp. 329-345. , Proceedings of the 5th International Kimberlite ConferenceRao, N.V.C., Lehmann, B., Mainkar, D., Belyatsky, B., Petrogenesis of the end-Cretaceous diamondiferous Behradih orangeite pipe: implication for mantle plume-lithosphere interaction in the Bastar craton, Central India (2011) Contributions to Mineralogy and Petrology, 161, pp. 721-742Rao, N.V.C., Wu, F.-Y., Mitchell, R.H., Li, Q.-L., Lehmann, B., Mesoproterozoic U-Pb ages, trace elements and Sr-Nd isotopic composition of perovskite from kimberlites of the Eastern Dharwar craton, southern India: Distinct mantle sources and a widespread 1.1 Ga tectonomagmatic event (2013) Chemical Geology, 353, pp. 49-65. , (this issue)Rios, D.C., Conceição, H., Davis, D.W., Plá Cid, J., Rosa, M.L.S., Macambira, M.J.B., McReath, I., Davis, W.J., Paleoproterozoic potassic-ultrapotassic magmatism: Morro do Afonso sienite pluton, Bahia, Brazil (2007) Precambrian Research, 154, pp. 1-30Santos, J.O.S., Potter, P.E., Reis, N.J., Hartmann, L.A., Fletcher, I.R., McNaughton, N.J., Age, source, and regional stratigraphy of the Roraima Supergroup and Roraima-like outliers in northern South America based on U-Pb geochronology (2003) GSA Bulletin, 115, pp. 331-348Schulze, D.J., Origins of chromian and aluminous spinel macrocrysts from kimberlites in southern Africa (2001) The Canadian Mineralogist, 39, pp. 361-376Schulze, D.J., A classification scheme for mantle-derived garnet in kimberlite: a tool for investigating the mantle and exploring for diamonds (2003) Lithos, 71, pp. 195-213Scott Smith, B.H., Canadian kimberlites: geological characteristics relevant to emplacement (2008) Journal of Volcanology and Geothermal Research, 174, pp. 9-19Silva, M.G., Coelho, C.E.S., Teixeira, J.B.G., Alves da Silva, F.C., Silva, R.A., Souza, J.A.B., The Rio Itapicuru greenstone belt, Bahia, Brazil: geologic evolution and review of gold mineralization (2001) Mineralium Deposita, 36, pp. 345-357Skinner, E.M.W., Proc. 4th Int. Kimberlite Conf. Kimberlites and Related Rocks (1989) Geol. Soc. Austrl. Spl. Publ., 14, pp. 528-544. , J. Ross, A.L. Jaques, J. Ferguson, D.H. Green, S.Y. O'Reilly, R.V. Danchin, A.J.A. Jause (Eds.)Skinner, E.M.W., Marsh, J.S., Distinct kimberlite pipe classes with contrasting eruption processes (2004) Lithos, 76, pp. 183-200Skinner, E.M.W., Smith, C.B., Viljoen, K.S., Clark, T.C., The petrography, tectonic setting and emplacement ages of kimberlites in the south western border region of the Kaapvaal Craton, Prieska area, South Africa (1992) Companhia de Pesquisa de Recursos Minerais, Rio de Janeiro, pp. 80-97. , H.O.A. Meyer, O.H. Leonardos (Eds.) Kimberlites, Related Rocks and Mantle XenolithsSmith, C.B., Pb, Sr and Nd isotopic evidence for sources of southern African Cretaceous kimberlites (1983) Nature, 304, pp. 51-54Smith, C.B., Gurney, J.J., Skinner, E.M.W., Clement, C.R., Ebrahim, N., Geochemical character of the southern African kimberlites: a new approach based on isotopic constraints (1985) Transactions Geological Society of South Africa, 88, pp. 267-280Sobolev, N.V., (1977) Deep-Seated Inclusions in Kimberlites and the Problem of the Composition of the Upper Mantle. (English Translation of Russian Edition, 1974. Izdatel'stvo Mauka), , American Geophysical Union, Washington, 279 ppSobolev, N.V., Lavrent'ev, Y., Pokilenko, N.P., Usova, L.V., Chrome-rich garnets from the kimberlites of Yakutia and their paragenesis (1973) Contributions to Mineralogy and Petrology, 40, pp. 39-52Souza, J.D., Kosin, M., Melo, R., Oliveira, E.P., Carvalho, M.J., Leite, C.M.M., Guia de excursão - Geologia do segmento norte do orógeno Itabuna-Salvador-Curaçá (2003) Revista Brasileira de Geociencias, 33, pp. 27-32. , (Suplemento)Sun, S.S., McDonough, W.F., Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes (1989) Geol. Soc. Spec. Publ., 42, pp. 313-345. , A.D. Saunders, M.J. Norry (Eds.) Magmatism in the Ocean BasinsSvisero, D.P., Distribution and origin of diamonds in Brazil: an overview (1995) Journal of Geodynamics, 20, pp. 493-514Tappe, S., Simonetti, A., Combined U-Pb geochronology and Sr-Nd isotope analysis of the Ice River perovskite standard, with implications for kimberlite and alkaline rock petrogenesis (2012) Chemical Geology, pp. 10-17Tappe, S., Foley, S.F., Jenner, G.A., Kjarsgaard, B.A., Integrating ultramafic lamprophyres into the IUGS classification of igneous rocks: rational and implications (2005) Journal of Petrology, 46, pp. 1893-1900Tappe, S., Foley, S.F., Jenner, G.A., Heaman, L.M., Kjarsgaard, B.A., Romer, R.L., Stracke, A., Hoefs, J., Genesis of ultramafic lamprophyres and carbonatites at Aillik Bay, Labrador: a consequence of incipient lithospheric thinning beneath the North Atlantic craton (2006) Journal of Petrology, 47, pp. 1261-1315Tappe, S., Foley, S.F., Stracke, A., Romer, R.L., Kjarsgaard, B.A., Heaman, L.M., Joyce, N., Craton reactivation on the Labrador Sea margins: 40Ar/39Ar age and Sr-Nd-Hf-Pb isotope constraints from alkaline and carbonatite intrusives (2007) Earth and Planetary Science Letters, 256, pp. 433-454Tappe, S., Foley, S.F., Kjarsgaard, B.A., Romer, R.L., Heaman, L.M., Stracke, A., Jenner, G.A., Between carbonatite and lamproite - diamondiferous Torngat ultramafic lamprophyres formed by carbonate-fluxed melting of cratonic MARID-type metasomes (2008) Geochimica et Cosmochimica Acta, 72, pp. 3258-3286Tappe, S., Steenfelt, A., Heaman, L.M., Simonetti, A., The newly discovered Jurassic Tikiusaaq carbonatite-aillikite occurrence, West Greenlan

Evaluating baddeleyite oxygen isotope analysis by secondary ion mass spectrometry (SIMS)

Two baddeleyite megacrysts were evaluated as potential reference materials (RMs) for SIMS oxygen isotope analysis, and utilized to understand and calibrate instrumental mass fractionation (IMF). A baddeleyite crystal (S0045) from the Phalaborwa carbonatite, South Africa has a mean δ18OVSMOW=+4.6 ± 0.3‰(range 0.75‰) measured using laser fluorination gas source mass spectrometry (LF-GMS) and one (S0069) from the Mogok metamorphic belt, Myanmar has δ18OVSMOW=+22.2 ± 0.4‰ (range 0.89‰). SIMS standardization utilizing these inherently heterogeneous RMs is possible by analyzing a number of crystal fragments and utilizing one of them lying at the median of the range. Metamictization, lattice orientation, and chemical composition do not appear to be significant (< 0.5‰) variables in matrix matching of RMs and unknowns. Propagation of errors while utilizing the imperfect RMs results in 10 μm diameter spot uncertainties of about±0.3‰ (2σ). SIMS oxygen isotope analysis of co-crystalline zircon and baddeleyite from the 2.2 Ga Duck Lake sill (DLS) in the Northwest Territories, Canada, yield predominant δ18OVSMOW modes of +6.0‰ and +3.2‰, respectively. This difference is consistent with preserving high-temperature isotopic equilibrium between zircon and baddeleyite. DLS baddeleyite δ18O data as a whole are negatively skewed (to 0.0‰), and interpreted to reflect low temperature, open-system behaviour. Zircon δ18O are less affected, but also show hints of the same influences of secondary alteration and oxygen isotope exchange

Timing and origin of magmatism in the Sverdrup Basin, Northern Canada—Implications for lithospheric evolution in the High Arctic Large Igneous Province (HALIP)

Cretaceous magmatism in the Sverdrup Basin of Arctic Canada is widely considered to be part of the circum-Arctic High Arctic Large Igneous Province (HALIP). Recent studies have questioned: (i) plume involvement in the HALIP, and (ii) whether the younger magmatic events constitute the same large igneous province. We present an integrated geochemical and geochronological study to better constrain the initiation and evolution of magma genesis in the Canadian HALIP. Six new U–Pb and four 40Ar/39Ar ages of mafic lavas and intrusive sheets range from 120.9 ± 0.9 Ma to 78.4 ± 0.1 Ma, which is within the published timespan of the HALIP. The U–Pb ages are the first analyzed from the mafic intrusions of Axel Heiberg and Ellesmere Islands. The new geochronology, combined with all recently (post-2000) published ages, detail a >50 Myr duration of magmatism (128 to 77 Ma) with three main pulses. Tholeiites dominate the first 25 Myr while the latter 25 Myr consisted of coeval emplacement of alkali and tholeiitic basalts. Rare-earth-element inversion models reveal that the alkalic and tholeiitic magmas were generated beneath a bimodal lithospheric ‘lid’ thickness of 65 ± 5 and 45 ± 4 km, respectively. Whole-rock Sr–Nd isotope ratios indicate that both magma types are derived from a similar source dominated by convecting mantle. Further, these two magma types were spatially segregated by the tectonic domains of the Sverdrup Basin. We suggest that the early 128–120 Ma tholeiitic event is primarily plume-generated and correlates across the circum-Arctic with the other HALIP tholeiites. The younger magmatism, with coeval alkalic and tholeiitic magmas erupting over 25 Myr, is likely not plume-generated and may be explained by alternating modes of edge-driven mantle convection as the primary control on magma genesis. A distal plume would intensify magma production by edge-driven convection, but its influence would be secondary