The Late Cretaceous alkaline magmatism in the SE Brazilian coast: new paleomagnetic data and age constraints

Author(s)

Ernesto, Marcia ; Raposo, Maria Irene Bartolomeu

• Document type: Journal article
• Source: BRAZILIAN JOURNAL OF GEOLOGY; v. 53, n. 2, p. 10-pg., 2023-01-01.

Abstract

Alkaline dikes from the Santos-Rio de Janeiro coast, SE Brazil, mainly from Sao Sebastiao and Buzios islands, yielded a Late Cretaceous paleomagnetic pole (SR) located at 319.7 degrees E 81.2 degrees S (N = 44, A95 = 3.0 degrees, k = 44). This pole includes some sites of alkaline stocks from Sao Sebastiao Island of the same age and supersedes the previous pole for this island. To match the available radiometric ages and the prevailing normal polarity remanence of the rocks with the geomagnetic polarity time scale, the SR pole is placed at 84 Myr. Another group of alkaline rocks, dikes located mainly in Rio de Janeiro, was assigned an age of less than 70 Myr. The ages of the Polos de Caldas, Itatiaia, and Passa Qua-tro paleomagnetic poles are also discussed based on available radiometric data. Assuming a rigid plate, the SR pole indicates the southward movement of about 7 degrees with virtually no rotation between 100 and 84 Myr. From approximately 84 to 70 Myr, a clockwise rotation of 8 degrees is postulated, with slight variation in latitude. (AU)