Archean crustal fragments preserved within Paleoproterozoic orogenic belts provide important records of crustal growth, recycling and continental assembly. In the southern Minas-Bahia Orogenic System (SE-Brazil), the tectonic evolution of several Archean blocks and the Paleoproterozoic arc systems remains poorly constrained. One of these Archean domains is the Piedade Microcontinent, located between the Mineiro Belt and the Mantiqueira-Juiz de Fora Magmatic Arc System. This study integrates geological mapping, whole-rock geochemistry and Sm-Nd-Sr isotopes, and zircon U-Pb and Lu-Hf data to investigate its tectono-magmatic evolution and associated metavolcano-sedimentary sequences. The Archean basement records crustal growth between ca. 3.24 and 2.52 Ga and is characterized by predominantly juvenile isotopic signatures. Along the northwestern margin of the microcontinent, a previously unrecognized continental arc, herein named the Ressaquinha magmatic arc, developed between ca. 2.14 and 2.08 Ga. Geochemical and isotopic data indicate extensive reworking of older continental crust during arc magmatism. Collision between adjacent terranes occurred between ca. 2.08 and 2.05 Ga and was followed by late- to post-collisional bimodal magmatism represented by the São Bento dos Torres post-collisional suite. Detrital zircon data from metasedimentary rocks of the Barbacena metavolcano-sedimentary sequence yield maximum depositional ages between ca. 2.08 and 2.02 Ga and reveal contributions from the Archean basement, the Ressaquinha magmatic arc, the São Bento dos Torres post-collisional suite and juvenile adjacent terranes (i.e., Mineiro Belt and Mantiqueira-Juiz de Fora Magmatic Arc System). Together with the occurrence of associated mafic, alkaline and metaultramafic rocks, these data suggest that sedimentation began during the final stages of arc evolution and continued within a successor basin after final terrane amalgamation. These results redefine the northern limit of the Piedade Microcontinent, document a newly identified Paleoproterozoic continental arc and constrain the transition from arc magmatism to post-collisional basin development during assembly of the southern São Francisco Paleocontinent.
The assembly of the Grenville Province is often debated including the relationships between different crustal blocks and their origin, particularly within the Grenville Allochthonous Belt. Large-scale, LA-ICP-MS zircon U-Pb geochronology of graphite-bearing metasedimentary sequences across the Allochthonous Belt in the Western Grenville Province, Quebec, Canada, allow the investigation of the pre-Grenvillian tectonic architecture and basin economic potential. New detrital zircon data indicate that protoliths for the metasedimentary rocks within the Mont-Laurier and Morin terranes and within the Parent-Haute-Mauricie area were deposited at similar times (1290–1220 Ma), but could not have been deposited into the same basin system due to the general absence of Archean detrital zircon in the Parent-Haute-Mauricie area. Multi-dimensional scaling and cumulative age distribution analysis on new and compiled published detrital zircon dates from Quebec, Ontario and New York state identifies three types of detrital zircon distributions that correspond to three types of basins: Type 1, Extensional intracratonic basin with no singular major age peaks containing early Mesoproterozoic or older detritus (1460–3300 Ma); Type 2, Extensional intracratonic basin with dominant 1900–1800 Ma age peaks and lesser early Mesoproterozoic and older detritus (1460–3200 Ma); Type 3, Fore/Backarc basin with detritus more heavily weighted to younger detrital zircons and little to no Paleoproterozoic and older detritus. The connections between regions based on detrital zircon distribution types transcends traditional terrane and domain nomenclature, which is based on the last stage of orogenesis. Neither style of pre-Grenvillian plate margin configuration, the Laurentian-affinity nor the exotic model, are presently able to account for the distribution of metasedimentary rocks with and without Paleoproterozoic and older detritus. Detrital zircon analysis to constrain basin geodynamics coupled with detrital zircon distribution types can support resource exploration in orogenic belts, revealing a first-order control on graphite, Zn, and Cu endowment.
Mafic dyke swarms offer valuable insights into the geochronological, geochemical, mechanical and magnetic environments at the time of their formation. They also provide a key tool for reconstructing the assembly of cratons into their current and persisting configurations. Identifying and classifying dykes into swarms mark the critical first step in these investigations. Even in regions with limited outcrop, the strong magnetic signature of mafic dykes enables their identification and mapping.The relative position at 2000 Ma of the Amazon and West African cratons remains a subject of much debate, and the mafic dyke record offers a key part of the data needed to resolve this enigma, using their age but also their orientation. In the Amazon Craton, initial maps of mafic dyke distribution were created over 50 years ago, yet vast areas remain poorly documented. This paper introduces a significantly updated map of mafic dykes across the craton, combining new and recently published interpretations of regional airborne magnetic data. The map identifies over 3,200 dykes, revealing several orientation clusters that provide a minimum estimate for the number of dyke swarms in the region. While systematic dating of the swarms is still pending, and some previous studies have focussed on location rather than orientation as an indicator of dyke swarm affinity, this study reveals a long and complex history of mafic magmatism across the craton. We identify up to nine distinct dyke swarms based on their orientations, location and age, together with potential previously unrecognised swarms that occur across the craton.Comparisons of three swarms with similar ages (CAMP, Libiri/Avanaveroand Essakane/Sambarabougou/Käyser) that occur in the Amazon Craton and the West African Craton seem to share similar orientations using a 200 Ma plate reconstruction, suggesting that between 1790 Ma and 200 Ma the two cratons may well have been neighbours.The aim of this contribution is to map out large dyke swarms that can act as geochronological and orientational constraints, whilst recognising that this is very much a work in progress as new geochronological data can better constrain our efforts.
At approximately 550 Ma, a major biotic perturbation termed the Kotlin Crisis occurred, profoundly restructuring Earth’s earliest complex macroscopic communities. This event is widely regarded to have triggered a pronounced diversity decline across multiple groups, including the iconic Avalon–White Sea assemblages of macroscopic Ediacara-type organisms, Doushantuo-Pertatataka-type acanthomorphic acritarchs (DPAs), microalgae, and macroalgae. However, the severity of this crisis may have varied considerably among different fossil groups, and the magnitude of extinction across different biotic components may therefore warrant systematic reexamination. In this study, we report a macroalgal-dominated fossil assemblage (∼550–543 Ma) from the Dengying Formation in the Yangba Town, northern Sichuan Province, South China. A total of twelve genera and fifteen species of macroalgae were identified. The taxonomic composition of this assemblage are broadly comparable to those of the Miaohe biota from the uppermost Doushantuo Formation in the Yangtze Gorges area and the macroalgal assemblage from the middle Dengying Formation in the Maxi section, northern Huangling anticline. A statistical analysis of changes in the fossil richness of macroalgae across the Ediacaran–Cambrian of South China, incorporating this new macroalgal-dominated assemblage, reveals that macroalgae exhibited a certain degree of resilience during the Kotlin Crisis. This contrasts with other organismal groups, such as Avalon–White Sea assemblages, multicellular microalgae, and DPAs, all of which suffered considerably heavier losses during the same interval. The genus-level extinction proportion for the overall macroalgal flora around 550 Ma is estimated at approximately 35–44 %, yet this figure drops to as low as 13 %-16 % when the analysis is restricted to relatively shallow-water settings. Such marked disparities in extinction severity among different biotic components may provide critical clues for inferring the drivers of this extinction event. This highlights the necessity of incorporating responses of different fossil groups when evaluating causal mechanisms such as global anoxia, climatic perturbations or ecological interactions. Finally, our analysis reveals that the stratigraphic ranges of several key macroalgal taxa, including Enteromorphites, Doushantuophyton, Eoandromeda, and Sinospongia, extend beyond previous estimates, thereby complicating their biostratigraphic utility.
