Low paleolatitude of the Carajás Basin at ∼2.75 Ga: Paleomagnetic evidence from basaltic flows in Amazonia

Highlights

• First Neoarchean ∼2.75 Ga paleomagnetic data for the Amazonian craton.

• At least six magnetic reversals are identified suggesting an active geodynamo.

• Carajás block was part of the Superia supercraton in an equatorial position.

Abstract

Establishing the positions of continents during the initial stages of Earth's evolution is one of the most important challenges in geosciences today. This challenge is mainly due to the severe limitations in obtaining geological and/or geophysical data from early Earth time, particularly robust paleomagnetic data. Here, we report the first paleomagnetic data from an Archean block in the Amazonian craton, the Carajás Province, for ∼2.76–2.74 billion years ago (Ga), when extensive dominantly mafic volcanism (Parauapebas Formation) covered an area of ∼18,000 km². The paleomagnetic investigation was conducted on fresh drill cores drilled into the Carajás iron ore mine and cutting across the Parauapebas Formation. After rotating the drill core segments to geographic coordinates using the viscous magnetic component, two characteristic components, Carajás 1 and 2 (C1 and C2) were identified and further used to calculate paleomagnetic poles: C1 (∼2759 Ma; 40.5°E, −44.6°S, N = 5 A₉₅ = 6.5°, K = 18.5) and C2 (∼2749 Ma; 342.4°E, −54.3°S, N = 28, A₉₅ = 14.8°, K = 27.8). Pole C2 is based on a bigger number of sites, passes a reversal test and is considered robust. A baked contact test was attempted for this component, but it is not conclusive. Our results, integrated with geological evidence reveals that the Carajás block occupied low latitudes at the time, and could have been part of the Superia supercraton during the Neoarchean (∼2.75 Ga) at equatorial latitudes. Finally, a consistent succession of six magnetic reversal events was identified in the lava flow sequence from the Parauapebas Formation, pointing to an already dynamic geodynamo pre-2.7 Ga.

Introduction

During the Archean, the first continents were formed and their remnants are now dispersed around the world. At present, there are approximately thirty-five of these ancient fragments of crust preserved globally (e.g., Bleeker, 2003). These ancient cratons form the nucleus of the present-day continents, and are a ‘window’ back into the environments of the early Earth. The Archean cratons stabilized at different times worldwide from 3.1 to 2.5 Ga, with a peak in cratonization heralding the transition from a mafic to a more evolved intermediate composition (Bleeker, 2003, Cawood et al., 2018, Hawkesworth et al., 2020). Additionally, records of Earth's primitive atmosphere and oceans emerge in the earliest to latest Archean, and evidence of the earliest primitive life forms appears in rocks about these old times (e.g., Planavsky et al., 2021). Crust–mantle interactions also seem became significantly more prominent towards the end of the Archean, reflecting a significant change in mantle dynamics and plate tectonics during the Neoarchean (Halla et al., 2017, Gerya, 2019, Palin et al., 2020, Windley et al., 2021). Establishing the positions of continents at this time, when the continental configuration is yet poorly known and intensely debated, is one of the most important tasks in deciphering the geological evolution of the planet at its youth. The first-order question to answer is whether the Archean continental blocks were amalgamated into a single, large supercontinent, putatively named “Kenorland” (Williams et al., 1991), or whether they were dispersed into several smaller “supercratons” such as Superia, Zimgarn, Sclavia, and Vaalbara (e.g., Bleeker, 2003, Smirnov et al., 2013). In that sense, paleogeographic reconstructions are a key discriminant between these hypotheses, providing a clearer picture of the ancestral landmass(es) configuration. Unlike Proterozoic supercontinents (Rodinia and Columbia), the paleogeography for the late Archean cratons is not so clear, owing to the general paucity of paleomagnetic data from most cratons (Buchan et al., 2000, Pesonen et al., 2003). Nevertheless, particularly during the Neoarchean Era, the relative positions of cratons are becoming tractable by the increasing numbers of refined paleomagnetic data and geochronologic studies (e.g., de Kock et al., 2009, Denyszyn et al., 2013, Smirnov et al., 2013, Salminen et al., 2019, Liu et al., 2021).

South American cratons, such as São Francisco and Amazonian, have been absent from most of the Archean supercraton reconstructions. Recently, Salminen et al. (2019), based on paleomagnetic data and comparison of magmatic barcodes, demonstrated that the Uauá block, a fragment of the São Francisco craton, could have been part of a much larger supercraton named Supervaalbara by Gumsley (2017) constrained at 2.43 Ga. Meanwhile, the paleogeography of the Amazonian Craton (Fig. 1A), one of the largest cratonic areas in the world (∼5,600,000 km²; Almeida et al., 1981), remains a challenging task especially during Archean-Paleoproterozoic times, being one of the least studied Archean cratons (D’Agrella-Filho et al., 2016).

Here, we focus on the paleomagnetic record of an Archean block in the Amazonian craton, the Carajás Province (Fig. 1) for the ∼2.76–2.74 Ga interval, when extensive volcanism, dominantly mafic, covered an area of approximately 18,000 km² (Macambira, 2003). This volcanism produced the Parauapebas Formation, the lowermost unit of the Neoarchean volcanic-sedimentary sequence of the Grão-Pará Group (Vasquez et al., 2008, Martins et al., 2017). We report new paleomagnetic data for basaltic lava flows from two well-preserved deep drill cores sampled from the Carajás Basin in the northern Carajás Province. Our goal is to provide the first paleogeographic constraints for this Archean block, yielding a paleolatitude estimate for the block and discussing its affiliation to previously proposed Archean cratonic assemblies (e.g., Williams et al., 1991, Bleeker, 2003, Bleeker and Ernst, 2006, de Kock et al., 2009, Gumsley et al., 2017, Salminen et al., 2019, Liu et al., 2021). Furthermore, the thick sequence of basalts in the Carajás Basin has a good potential to provide evidence for geomagnetic reversals across the succession.