thumbnail

K-Ar ages and the opening of the South Atlantic Ocean: Basaltic rock from the Brazilian margin

Marine Geology
By: , , and 
https://doi.org/10.1016/0025-3227(83)90002-6

Metrics

44
Crossref references
Web analytics dashboard Metrics definitions

Links

Abstract

New K-Ar ages for 13 samples of basalt, gabbro, wehrlite, and trachyandesite drilled from the Brazilian continental shelf and coastline yield information about the timing of the opening of the South Atlantic and the nature of the crust seaward from the Brazil margin. The oldest basalt is 138.1 ± 3.5m.y. old and from offshore at 24.5°S; it represents Serra Geral flood basalt on attenuated crust in the Santos basin. Basalts from the coastline at 19.5°S are mixed with terrigenous graben sediments, and their ages confirm that rifting was underway before 130 m.y. Offshore sites in the Campos basin, ∼22°–23°S, 41°W, have basalt ranging from 124 to 112 m.y. in age and mostly continental flood basalt in composition. One 112-m.y. basalt, however, is MORB-like and could therefore represent oceanic lithosphere mixed with continental crust about 50 km from the shoreline at ∼22.5°S. Other samples reveal compositionally varied intraplate, passive-margin magmatism occurring 75-43 m.y. ago. They correlate with profuse contemporary alkalic magmatism on the southeastern Brazil coast and probably represent reactivation of zones of “weakness” (i.e., fracture zone-lineaments).

    Suggested Citation

    Fodor, R., McKee, E., and Asmus, H., 1983, K-Ar ages and the opening of the South Atlantic Ocean: Basaltic rock from the Brazilian margin: Marine Geology, v. 54, no. 1-2, p. M1-M8, https://doi.org/10.1016/0025-3227(83)90002-6.

    Study Area

    Publication type Article
    Publication Subtype Journal Article
    Title K-Ar ages and the opening of the South Atlantic Ocean: Basaltic rock from the Brazilian margin
    Series title Marine Geology
    DOI 10.1016/0025-3227(83)90002-6
    Volume 54
    Issue 1-2
    Year Published 1983
    Language English
    Publisher Elsevier
    Description 8 p.
    First page M1
    Last page M8
    Country Brazil
    Additional publication details