The Freetown Layered Complex (FLC) is a massive mafic layered intrusion cropping out along the Atlantic coast of Sierra Leone. The present combined geochemical and geochronological (⁴⁰Ar/³⁹Ar on plagioclase: 201.7±0.7 and 202.3±2.3 Ma; U-Pb on baddeleyite: 198.794 ± 0.048/0.071/0.22 Ma) study of the complex flags it as a high-Ti occurrence of the Central Atlantic Magmatic Province (CAMP). Sr-Nd-Pb-Os isotope data indicate that the FLC is unique with respect to previously studied CAMP occurrences, constituting a new isotopic end-member for this large igneous province (LIP). Notably, the contribution of ancient source(s) is required to explain its low ²⁰⁶Pb/²⁰⁴Pb and high ²⁰⁷Pb/²⁰⁴Pb. Though the internal isotopic variability of the FLC can be explained by modest assimilation (<10%) of lower crustal (granulitic) material, represented by a xenolith found within the complex itself, an atypical mantle source is required to account for its unusual Pb isotopic composition. We present the first Hf isotopic data measured to date for the CAMP, which, in the case of the FLC, show a restricted range in ¹⁷⁶Hf/¹⁷⁷Hf, overlapping the OIB and MORB fields on the terrestrial array, and can further be used to characterize the FLC isotopic end-member. We propose that the FLC formed by mixing of a predominantly asthenospheric parental magma with small volumes (1-3%) of geochemically highly enriched lamproitic melts derived from the sub-continental lithospheric mantle in a geodynamic context in which a Proterozoic mobile belt (Rokelide) bordered an Archean craton (Man). Within the CAMP, similar isotopic compositions, in particular low ²⁰⁶Pb/²⁰⁴Pb and high ²⁰⁷Pb/²⁰⁴Pb, are found only in regions that were once contiguous with Sierra Leone. A comparable involvement of enriched components stored within the cratonic lithosphere may be envisaged for the high-Ti magmatism in the CAMP and two other LIPs of the Southern Atlantic realm – Karoo and Paranà-Etendeka. These Gondwana magmatic provinces share with other mantle-derived magmas from the Southern Atlantic Ocean enriched isotopic signatures (DUPAL, LOMU, EM1) of much debated origin. The present mantle source model for the FLC, CAMP, and neighbouring LIPs suggests ancient enriched subcontinental lithospheric mantle as a plausible conveyor of such isotopic signatures in the Southern and Central Atlantic.

Anomalous mercury (Hg) contents recorded near the Permian‐Triassic boundary (PTB) are often linked to Siberian Traps Large Igneous Province (STLIP) volcanism and the Permian‐Triassic boundary mass extinction (PTBME). However, mounting evidence indicates that the relation between STLIP volcanism and Hg “anomalies” is not straightforward. This study focuses on the timing and provenance of volcanic fluxes around the PTBME in South China. We constrain carbon isotope (δ¹³C) and Hg concentration and isotope records by utilizing high‐precision U‐Pb zircon ages from two expanded deep‐water marine sections spanning the Late Permian to Early Triassic in the Nanpanjiang Basin. Results reveal two episodes of Hg enrichment. The oldest episode predates the onset of a large negative δ¹³C excursion, which is documented to be older than 252.07 ± 0.130 Ma. The second episode occurred between 251.822 ± 0.060 and 251.589 ± 0.062 Ma, coinciding with the nadir of the δ¹³C excursion. Volcanic ash geochemistry and Hg isotope compositions suggest that mercury was mainly sourced from subduction‐related volcanic arc magmatism in the Tethys region, which peaked between 251.668 ± 0.079 and 251.589 ± 0.052 Ma. These results are compatible with suggestions that regional arc volcanism contributed to the causes of the PTBME in South China and provide evidence that Hg anomalies close to the PTB are not a reliable stratigraphic marker for the PTB extinction event. This study demonstrates that relations between volcanism, environmental perturbations and mass extinction during the Permian‐Triassic transition are better resolved with the aid of high‐precision U‐Pb zircon ages.

Zircon petrochronology is widely used to quantify the age and duration of magma emplacement and differentiation. However, in highly differentiated magmas, such as those forming rare-metal granites, zircon may form at the magmatic–hydrothermal transition, and its primary crystallisation history, together with its secondary hydrothermal overprint, needs to be resolved and clarified. To resolve zircon formation in such evolved and mineralised granitic systems, we investigated heterogeneous zircons from the Beauvoir rare-metal granite (Massif Central, France). Most of the Beauvoir zircons are characterised by the presence of two distinct domains, designated as Zone 1 and Zone 2. Zone 1 occurs as rounded, Si- and Zr-rich domains, which are embedded in the interconnected Si- and Zr-poor Zone 2 domains that are also extremely P-, U-, F-, Ca-, Fe- and Mn-rich. Both of these zones are strongly damaged (metamict) by radioactive decay, mainly from their high U concentrations. Textures and chemical composition strongly suggest that Zone 1 corresponds to magmatic zircon that has been partly replaced by the Zone 2 material during the magmatic–hydrothermal transition. The crystallisation of Zone 1 zircon is preceded by the crystallisation of U-rich cores (∼6 wt % UO₂) containing UO₂ (uraninite) micro-inclusions, which are then surrounded by a Zone 1 homogeneous rim. These uraninite micro-inclusions resulted from the uranium migration in the metamict and amorphous precursor zircon. U-Pb dating of single zircon grains using chemical abrasion, isotope dilution thermal ionisation mass spectrometry (CA-ID-TIMS) techniques yielded a well-defined discordia line with an upper intercept at 312±2.9 (7.2) Ma (2σ) and a near-zero-age lower intercept. The discordancy reflects the continuous loss of radiogenic lead from a heavily damaged and aperiodic zircon lattice. On the other hand, ID-TIMS data from magmatic apatite of the Beauvoir granite yielded an age of 313.4±0.2 (1.3) Ma (2σ), so far, the most accurate and precise crystallisation age of the Beauvoir granite. Thus, we emphasise that although the study of zircon from highly differentiated systems provides strong insights into the magmatic–hydrothermal transition of these objects, their metamict nature prevents their use to precisely and accurately date the emplacement of rare-metal granite.