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

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

Jul 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009geoji.178..106e&link_type=abstract

Geophysical Journal International, Volume 178, Issue 8, pp. 106-122.

Astronomy and Astrophysics

Astronomy

Magnetic Fabrics And Anisotropy, Palaeomagnetism Applied To Tectonics, Rock And Mineral Magnetism

Scientific paper

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.

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