Abstract

Zeolite isograds delineating regionally extensive metamorphic mineral zones occur throughout most of the early Tertiary flood basalts in central East Greenland. Mineralogic zones defined by isograds are essentially uniform in thickness throughout the province, parallel paleotopographic surfaces, and transgress lava stratigraphy. The distribution of index zeolite minerals is consistent with a thermal gradient of ∼40 ± 5 °C/km and heat flow of 1.7 ± 0.5 heat flow units. Zeolite facies metamorphism occurred rapidly during and just after the bulk of volcanism (57–55 Ma) and prior to hydrothermal alteration associated with emplacement of the ca. 55 Ma Skaergaard intrusion and mafic dikes of the coastal dike swarm. Consequently, zeolite isograds are temporal markers for distinguishing synvolcanic and postvolcanic deformation events. Discordance between dips of zeolite isograds and lava flows suggests a pre-metamorphic (and probably synvolcanic) component to tilting of the lava pile. Later deformation, likely associated with dikes and faults near the continental margin, tilts the zeolite isograds ∼ 2.5°SE.

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