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

An important topic in ancient paleogeography is the Neoproterozoic Rodinia supercontinent (McMenamin and McMenamin, 1990). Although its existence is well-accepted, the cratonic blocks that composed it, their relative configurations and the time of final assembly are still intensively debated (Eyster et al., 2019, Jing et al., 2020, Jing et al., 2021, Sun et al., 2021, Evans, 2021).

There is general consensus that the Amazonian Craton was part of the Rodinia supercontinent during the early Neoproterozoic (e.g., Li et al., 2008). Geological evidence suggests that the Amazonian Craton collided with Laurentia along the 1200–900 Ma Sunsas and Grenville orogenic belts, developed along the (present day) southwestern Amazonian Craton and south to southeastern Laurentia, respectively (e.g., Brito Neves and Cordani, 1991, Sadowski and Bettencourt, 1996, among others). Most models of Rodinia shows the Amazonian Craton (together with Baltica) alongside the Appalachian-Labrador region of Laurentia (e.g., Li et al., 2008, Johansson, 2014, Cawood et al., 2016). However, the geodynamic processes that were involved in this collision is still intensively debated, mainly due to the scarcity of paleomagnetic poles for the Stenian/Tonian Periods, and this principally for the Amazonian Craton.

Based on the 1200 Ma Nova Floresta pole (Amazonian Craton), Tohver et al. (2002) suggested an oblique collision of Amazonia with Laurentia along the Grenvillian Llanos orogen, exposed today along the coast of Texas. Thereafter, Tohver et al., 2004a, Tohver et al., 2004b, Tohver et al., 2005a, Tohver et al., 2005b, Tohver et al., 2006), based on geological, geochronological and geophysical evidence proposed that Amazonia executed a transcurrent movement relative to Laurentia up to its collision with Baltica at 1000 Ma. Later, the 1150 Ma Fortuna Formation paleomagnetic pole corroborated this model (D’Agrella-Filho et al., 2008).

Alternatively, some authors proposed that the core of the Columbia supercontinent composed of Laurentia, Baltica, the Amazonian Craton and the West Africa Craton, maintained its integrity until 1270 Ma (e.g., Johansson, 2009, Johansson et al., 2022). When Baltica and the Amazonian-West Africa block broke away from Columbia, they performed a clockwise rotation to again dock with Laurentia during the formation of the Rodinia supercontinent at ca. 1000 Ma ago (e.g., Johansson, 2009, Evans, 2013, D’Agrella-Filho et al., 2016, Johansson et al., 2022). Cawood and Pisarevsky (2017) also proposed a clockwise rotation of Baltica relative to Laurentia. However, these authors consider that the Amazonian Craton has never belonged to Columbia (see also Pisarevsky et al., 2014), and suggest that it collided with Laurentia at ca. 1000–950 Ma, after the closure a large ocean (named the Mirovoi Ocean).

Recently, Choudhary et al. (2019) proposed the existence of a supercraton at 1100 Ma formed by Amazonia, West-Africa, Kalahari, Congo-São Francisco and India, named by them as Umkondia. Wang et al. (2021) regarded Umkondia as a megacontinent that was essential for continental assembly. In their reconstruction, a center plume situated in the (present day) northwestern margin of the Kalahari Craton was a magmatic center from which the ca. 1100 Ma Umkondo (Kalahari), Huila-Hepembe (Congo), Mahoba (India), Huanchaca (Amazonia) and Rio Perdido (Rio Apa block) dyke swarms radiated. This megacontinent is though to have collided with Laurentia to form Rodinia at ca. 1000–900 Ma (Choudhary et al., 2019, Wang et al., 2021).

In view of these contrasting models proposed for the collision of the Amazonian Craton with Laurentia during the assembly of Rodinia, determination of new robust paleomagnetic poles for Mesoproterozoic Amazonian geological units becomes essential to test the various models of Rodinia assembly. This work presents a new paleomagnetic pole for the well-dated 1112 Ma mafic sills from the Huanchaca Intrusive Suite (Mato Grosso State, Brazil).