A palaeomagnetic and 40Ar/39Ar study of late precambrian sills in the SW part of the Amazonian craton: Amazonia in the Rodinia reconstruction

• Published in: Geophysical journal international 2009-07, Vol.178 (1), p.106-122
• Main Authors: Elming, S.-Å., D'Agrella-Filho, M. S., Page, L. M., Tohver, E., Trindade, R. I. F., Pacca, I. I. G., Geraldes, M. C., Teixeira, W.
• Format: Article
• Language: English
• Subjects: Magnetic fabrics and anisotropy; Palaeomagnetism applied to tectonics; Rock and mineral magnetism
• ISSN: 0956-540X; 1365-246X
• DOI: 10.1111/j.1365-246X.2009.04149.x

A new key palaeomagnetic pole (Plat. = 64.3°S, Plon. = 271.0°E, N = 14, A95 = 9.2°; Q = 5) is calculated from a primary magnetization isolated in early Neoproterozoic Aguapei basic sills and dykes hosted by 1.3–1.0 Ga sedimentary rocks from the southwestern part of the Amazon craton. The characteristic remanence carried by stable, pseudo-single domain titanomagnetite shows two antipodal polarities that pass a reversals test. Magnetic anisotropy for most sites shows fabric orientations that are typical of sills, with horizontal magnetic foliations concordant to the flat-lying bedding of the host sedimentary rocks. 40Ar/39Ar analyses for one of the sills reveal a well-defined plateau age at 981 ± 2 Myr. A tectonic reconstruction for Amazonia relative Laurentia based on this new pole ‘is consistent with’ a position of the present northwestern part of Amazonia attached with eastern Laurentia close to Greenland at ca. 981 Ma. On basis of palaeomagnetic and geological data, we propose a scenario where Amazonia moved northeastwards along the present southeast coast of Laurentia from ca. 1200 to 980 Ma. By 980 Ma, Amazonia is placed alongside Laurentia and Baltica, in a position similar to other reconstructions of Rodinia but with a significantly different orientation.