Was There a Magmatic Slowdown in Siderian and Rhyacian PaleoProterozoic?

Cratonic sedimentation regimes in the ca. 2450–2000 Ma period: Relationship to a possible widespread magmatic slowdown on Earth?

Authors:

P.G. Eriksson and K.C. Condie

Abstract:

The ca. 2.45–2.0 Ga supracratonic record of six cratonic terranes (Superior Province, Hearne Domain, Fennoscandian crustal segment, and São Francisco, Pilbara and Kaapvaal cratons) is investigated. A less than ~2415–2420 basal unconformity appears pervasive, floored by basement lithologies for the three “Kenorland-related” terranes (Superior, Hearne and Fennoscandian) and by passive margin chemical sedimentary platform deposits for the apparently “non-amalgamated” cratons. Palaeosols are locally associated with this unconformity, and glacigenic lithologies, for all of the “non-amalgamated” cratons as well as for Superior. A relatively complete sedimentary record is recorded for the three Kenorland supercontinent terranes, including at least two glacial events, whereas hiatuses characterise the Pilbara and São Francisco cratons, with an incomplete record for Kaapvaal. Evidence for geodynamic reactivation at ca. 2.2 Ga includes widespread mafic dykes and volcanics, orogenies in Pilbara and São Francisco, glaciation in Kaapvaal and Pilbara, and significant transgressions thereafter on many of the cratonic terranes. While the overall ca. 2.45–2.2 Ga records studied here are at least compatible with the postulated global magmatic slowdown of Condie et al. (2009), distinct differences between the records associated with “Kenorland-related” and “non-amalgamated” cratons might reflect thermal subsidence and associated sedimentation accompanying the slowdown for the former group (where thermal blanketing likely played a role), while elevated freeboard and concomitant erosive regimes accompanied the inferred slowdown for the latter group.