On the enigmatic mid-Proterozoic: Single-lid versus plate tectonics

Hot, Wide, Continental Back-arcs Explain Earth’s Enigmatic mid-Proterozoic Magmatic and Metamorphic Record

“…wide-ranging P-T conditions) during the amalgamation of Columbia, presumably representing heterogeneity in ambient mantle temperature as well a network of both accretionary and collisional orogenic belts; 3) the onset of a sustained global subduction network between 2.5 and 2 Ga (Condie, 2021;Brown et al, 2022); 4) a potential mantle overturn event at ca. 2 Ga, perturbing the steady-state geological record (Condie et al, 2022); and 5) the dominance of accretionary orogenesis and lack of collisional orogenesis in the 1.7-1.1 Ga period (Roberts et al, 2022). Therefore, although the geochemical record features apparent dramatic shifts, we argue that changes in convergent margin geodynamics would have been pro-tracted transitions.…”

“…High metamorphic thermobaric ratios, the abundance of anorthosite magmatism, and granite composition indicative of high geothermal gradients have previously been speculated as a consequence of increased mantle heating below the mid-Proterozoic Columbia supercontinent (Cawood and Hawkesworth, 2014;Brown and Johnson, 2019;Tamblyn et al, 2022;Zou et al, 2023). Roberts et al (2022) questioned whether this additional mantle heating was necessary, and critically, highlighted that several of these 'indicators' of mantle heating appear in the geological record before the Columbia supercontinent fully amalgamated. Of note, granite compositions show a very distinct change at ca.…”

“…Therefore, although the geochemical record features apparent dramatic shifts, we argue that changes in convergent margin geodynamics would have been pro-tracted transitions. Roberts et al (2022) argued that the mid-Proterozoic was host to a transitional phase of geodynamics, influenced by both secular mantle cooling and the long tenure and impartial break-up of the Columbia supercontinent. Our present model builds on this argument -hot, wide, continental backarcs located along margins of the Columbia supercontinent provide a mechanism to generate the observed magmatic and metamorphic record of this period.…”

“…It has been proposed that many of these features can be explained by the combined influence of mantle heating due to supercontinental insulation (Brown and Johnson, 2018), a slowdown in plate motions (O'Neill et al, 2022), and a temporary return to a single-lid tectonic regime following an attempted start of plate tectonics in the Paleoproterozoic (Stern, 2020). However, Roberts et al (2022) questioned the necessity for supercontinental insulation and demonstrated that plate tectonics, albeit dominated by accretionary orogenesis, was active throughout the mid-Proterozoic. Although Roberts et al (2022) argued that the metamorphic and magmatic record resulted from transitional changes in geodynamics due to secular cooling of the mantle, they do not present a direct explanation for magmatic features such as the abundance of massif anorthosites, or an apparent increase in A-type granitic magmatism.…”

“…However, Roberts et al (2022) questioned the necessity for supercontinental insulation and demonstrated that plate tectonics, albeit dominated by accretionary orogenesis, was active throughout the mid-Proterozoic. Although Roberts et al (2022) argued that the metamorphic and magmatic record resulted from transitional changes in geodynamics due to secular cooling of the mantle, they do not present a direct explanation for magmatic features such as the abundance of massif anorthosites, or an apparent increase in A-type granitic magmatism. Here, we address these issues specifically.…”