Basalt sills of the U reflector, Newfoundland Basin: A serendipitous dating technique

Publication Type  Journal Article
Year of Publication  2005
Authors  Karner, G. D.; Shillington, D. J.
Journal Title  Geology
Volume  33
Issue  12
Pages  985-988
Journal Date  Dec
ISBN Number  0091-7613
Accession Number  ISI:000233849100017
Key Words  newfoundland basin extension; early postrift magmatism; ocean drilling program; compaction; continental margins; volcanism

High core recovery at Ocean Drilling Program (ODP) Leg 210, Site 1276, provided a high-resolution porosity-depth relationship and an equally impressive age-depth model based on first and last occurrences of microfossils. Site 1276 was drilled over transitional crust in the Newfoundland nonvolcanic margin, offshore Canada, between known continental crust on the west and apparent oceanic crust on the east as identified by seafloor-spreading magnetic anomalies M3 to M0 (Barremian-Aptian, 129.8-124.8 Ma). At Site 1276, two diabase sills were drilled at depths equivalent to the U reflection, a bright reflection that overlies transitional crust interpreted from seismic reflection profiles throughout the Newfoundland Basin. The sills were emplaced within uppermost Aptian fine- to coarse-grained sediments, 100-200 m above basement as estimated from seismic reflection data. Magma emplacement occurred at shallow levels within the sediment column, as evidenced by: (1) the occurrence of vesicles in the sill, and (2) compaction-induced folding of calcite veins that were emplaced near vertically in the sediments and are assumed to be coeval with the intrusion. By calculating the degree of shortening of the calcite veins and determining the reconstructed porosity of the sediments during vein emplacement, the age of magma emplacement can be deduced. From the porosity-age curve, the age of sill emplacement is estimated to be 82.5-109.1 Ma, consistent with recent Ar-40/Ar-39 radiometric dating of the upper sill that gave ages of 105.95 +/- 1.78 Ma and 104.7 +/- 1.7 Ma. The source of magmatism responsible for the diabase sills is necessarily postrift, and the sills are temporally equivalent to alkali basalts dredged from the Newfoundland Seamounts. The simplest explanation for the Site 1276 diabases and the widespread distribution of the U reflection relates to the migration of the Azores, Madeira, and Canary plumes across the Newfoundland Basin between 80 and 120 Ma.


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URL  <Go to ISI>://000233849100017
DOI  Doi 10.1130/G21971.1