Between carbonatite and lamproite—Diamondiferous Torngat ultramafic lamprophyres formed by carbonate-fluxed melting of cratonic MARID-type metasomes

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• 作者：Sebastian Tappe ; Stephen F. Foley ; Bruce A. Kjarsgaard ; Rolf L. Romer ; Larry M. Heaman ; Andreas Stracke ; George A. Jenner
• 关键词：coxa-basis articulation ; intrabasal joint ; marsupium ; feeding basket ; Peracarida
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：2008
• 出版时间：1 July 2008
• 年：2008
• 卷：72
• 期：13
• 页码：3258-3286
• 全文大小：3592 K

文摘

New U–Pb perovskite ages reveal that diamondiferous ultramafic lamprophyre magmas erupted through the Archean crust of northern Labrador and Quebec (eastern Canada) between ca. 610 and 565 Ma, a period of strong rifting activity throughout contiguous Laurentia and Baltica. The observed Torngat carbonate-rich aillikite/carbonatite and carbonate-poor mela-aillikite dyke varieties show a large spread in Sr–Nd–Hf–Pb isotope ratios with pronounced correlations between isotope systems. An isotopically depleted component is identified solely within aillikites (⁸⁷Sr/⁸⁶Sr_i = 0.70323–0.70377; εNd_i = +1.2–+1.8; εHf_i = +1.4–+3.5; ²⁰⁶Pb/²⁰⁴Pb_i = 18.2–18.5), whereas some aillikites and all mela-aillikites range to more enriched isotope signatures (⁸⁷Sr/⁸⁶Sr_i = 0.70388–0.70523; εNd_i = −0.5 to −3.9; εHf_i = −0.6 to −6.0; ²⁰⁶Pb/²⁰⁴Pb_i = 17.8–18.2). These contrasting isotopic characteristics of aillikites/carbonatites and mela-aillikites, along with subtle differences in their modal carbonate, SiO₂, Al₂O₃, Na₂O, Cs–Rb, and Zr–Hf contents, are consistent with two distinctive metasomatic assemblages of different age in the mantle magma source region.