Paleomagnetic study of the 1112 Ma Huanchaca mafic sills (SW Amazonian Craton, Brazil) and the paleogeographic implications for Rodinia supercontinent

Abstract

During the Stenian Period (1200–1000 Ma) Rodinia was being formed, and the Amazonian Craton, presently in northern South America, was an important piece in this scenario. Recently a megacontinent named Umkondia composed by Amazonia/West Africa, Congo/São Francisco, Kalahari and India was proposed to have existed at 1100 Ma. We present a paleomagnetic study on the well-dated (U-Pb, baddeleyite) 1112 Ma mafic sills from the Huanchaca Intrusive Suite, western Mato Grosso State (Amazonian Craton) in order to test the proposed configuration of Umkondia. Alternating field (AF) and thermal stepwise demagnetization revealed northwestern characteristic remanent magnetization (ChRM) directions with low positive inclinations (mean: Dm = 303.2°, Im = 12.2°, N = 10, α95 = 14.5°, K = 12.0). A paleomagnetic pole was calculated for the Huanchaca sills (HU − 225.7°E, 30.1°N, A95 = 9.9°) which is classified with reliability index R = 5. Magnetic mineralogy experiments show that ChRM is carried by Pseudo single domain (PSD) magnetite. The Huanchaca paleopole favors the existence of the Umkondia megacontinent at 1100 Ma, which latter collided with Laurentia forming the Rodinia supercontinent around 1000–900 Ma.