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Assessing origins of end-Triassic tholeiites from Eastern North America using hafnium isotopes
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  • Lynne J Elkins,
  • Christine Marie Meyzen,
  • Sara Callegaro,
  • Andrea Marzoli,
  • Michael Bizimis
Lynne J Elkins
University of Nebraska-Lincoln, University of Nebraska-Lincoln

Corresponding Author:lelkins@unl.edu

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Christine Marie Meyzen
Università degli Studi di Padova, Università degli Studi di Padova
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Sara Callegaro
University of Oslo, University of Oslo
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Andrea Marzoli
Dipartimento di Mineralogia e Petrologia, Universita' di Padova, Dipartimento di Mineralogia e Petrologia, Universita' di Padova
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Michael Bizimis
University of South Carolina, University of South Carolina
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The driving processes responsible for producing the Central Atlantic Magmatic Province, the Large Igneous Province associated with end-Triassic rifting of Pangea, remain largely debated. Because their compositions encompass most of the Central Atlantic basalt spectrum, tholeiites from southern Eastern North America are considered pivotal for identifying magma origins. New 176Hf/177Hf measurements for 201 Ma Eastern North American tholeiites dominantly record a local petrogenetic history. Their εHf ratios, corrected to an emplacement age of 201 Ma (-7.85 to +5.86), form a positive but shallowly sloped array slightly deviating from the terrestrial array on a εHf vs. εNd diagram. Comparison of 176Hf/177Hf to other isotope ratios and trace elements helps to rule out several petrogenetic scenarios, particularly mixing of melts from global depleted or enriched mantle components. In contrast, partial melting of subduction-metasomatized mantle can explain the parental magma composition for southern Eastern North America. Such metasomatism likely occurred during Paleozoic subduction around Pangea and may have been dominated by sediment-derived fluid reactions. The observed 176Hf/177Hf vs. 143Nd/144Nd array may reflect subsequent assimilation of lower continental crust, perhaps together with limited direct melting of recycled continental crust in the asthenosphere. The proposed recycling scenario does not specifically support or preclude a mantle plume origin for the Central Atlantic Magmatic Province, but instead points toward the presence of a distinct local mantle source and crustal assimilation processes during magma transport. Detailed understanding of these local effects is needed in order to more accurately understand the origins of Large Igneous Provinces.
Jun 2020Published in Geochemistry, Geophysics, Geosystems volume 21 issue 6. 10.1029/2020GC008999