The Choiyoi Magmatic Province (CMP), a significant region of silicic magmatism in southwestern Pangea during the mid-Permian to Triassic periods, has long been a subject of intense debate regarding its origin. Understanding the formation of the CMP is crucial for advancing our knowledge of large igneous provinces (LIPs) and their relationship to global geodynamic processes. The CMP's vast extent and the volume of silicic magma produced represent a significant perturbation of the Earth's system, potentially linked to major tectonic events and climate change. Previous hypotheses for the CMP's origin have included mantle plumes, crustal melting, and various subduction-related processes. However, none of these explanations fully account for the unique characteristics of the CMP, such as its size, geochemical signature, and temporal relationship with regional tectonic events. This study addresses this knowledge gap by proposing a novel hypothesis: the CMP's formation was driven by a large-scale slab loss event, a process characterized by the rapid detachment of a subducting tectonic plate from the mantle wedge. This hypothesis builds upon recent advancements in seismic tomography, which has revealed the presence of remnants of ancient subducted slabs in the lower mantle. By integrating these geophysical observations with plate tectonic reconstructions, geochronological data, and geochemical analyses of the CMP's igneous rocks, we aim to provide strong evidence in support of the slab loss hypothesis and to shed new light on the geodynamic history of southwestern Pangea.

Extensive research on the CMP has yielded diverse interpretations of its origin. Some studies emphasized the role of mantle plumes in generating the large volume of magma. Others focused on crustal melting processes within the continental crust of southwestern Pangea. Still others proposed different types of subduction-related processes. These models, however, often fail to reconcile the observed geochemical characteristics of the CMP rocks or the spatial extent of the magmatism. The recent advancements in mantle tomography, providing high-resolution images of the Earth’s interior, and improved plate kinematic models have enabled a new approach. Studies utilizing these tools have identified ancient subduction zones and slab remnants in the Earth's mantle, revealing insights into past subduction processes and their potential connection to LIP formation. This study leverages this new body of knowledge to test the hypothesis that a large-scale slab loss event is responsible for the CMP's formation. The integration of geophysical, geochronological, and geochemical data provides a more comprehensive approach compared to previous studies that often relied on single data types, enhancing the robustness and reliability of the proposed interpretation.

The study employed a multidisciplinary approach, combining various geophysical, geological, and geochemical techniques. The researchers used Gplates 2.0 software to integrate geological data, tomographic slices, and plate kinematic models. The UU-P07 global tomography model was utilized to delineate the extent of a slab gap in the lower mantle beneath southwestern Pangea. The criteria for identifying the slab gap involved consideration of wave speed amplitudes in the tomography model, utilizing a threshold of 0.2% for slab boundaries as suggested by previous research. Vote maps, constructed using data from 26 global seismic tomography models, were employed to strengthen the identification of the lower mantle slab gap. These vote maps were created by analyzing both P-wave and S-wave velocities at depths between 1800 and 2800 km, encompassing the depths typically associated with late Paleozoic and Mesozoic subduction zones beneath southwestern Pangea. The geochemical analysis involved the compilation and filtering of existing geochemical data of Upper Carboniferous to Jurassic igneous rocks. This data was filtered based on SiO2 content (between 55 and 70%) and aluminum saturation index (ASI < 1.1) to create a focused dataset suitable for tectonic discrimination diagrams, following established methodologies. This filtered dataset was then used to plot the geochemical data on tectono-magmatic discrimination diagrams to identify the tectonic setting and the geochemical signatures linked to slab break-off events. The spatio-temporal distribution of magmatic events was analyzed by integrating the geochronological data with the reconstructed paleogeographic position of the slab gap. This integrated approach aimed to assess the coincidence between the timing and location of the slab break-off event and the CMP's emplacement.

The integration of geophysical data (seismic tomography), plate reconstructions, and geochemical data revealed a strong correlation between a large-scale slab gap (approximately 2800–3000 km wide) in the lower mantle beneath southwestern Pangea and the spatial extent of the Choiyoi Magmatic Province. The timing of the slab gap formation, based on the analysis of seismic tomography and plate reconstructions, aligns well with the age of the CMP magmatism (mid-Permian to Triassic). The geochemical analysis of the CMP igneous rocks showed a distinctive geochemical signature consistent with a slab break-off event. This signature involved specific trace element ratios and abundances that are not typically associated with other types of magmatic processes (e.g., mantle plume activity, within-plate volcanism). The geochronological data revealed a distinct mineralization event between ~285 and 250 Ma, coinciding with the CMP's emplacement, which further supports the link between slab break-off and ore deposit formation. The study's analysis of the CMP demonstrates that its formation was primarily driven by a massive slab break-off event. This differs from previously proposed mechanisms for LIP formation and stands in contrast to typical SLIPs, which are characterized by more abundant rhyolitic magmatism and distinct geochemical signatures. The CMP's abundance of intermediate (andesitic) rocks is unusual and offers further evidence of the unique setting of this LIP.

The findings demonstrate that the Choiyoi Magmatic Province (CMP) is the oldest geophysically constrained example of a large igneous province (LIP) formed by catastrophic slab loss. This significantly extends our understanding of the role of slab break-off in LIP formation, which was previously thought to be primarily a Cenozoic phenomenon. The remarkable coincidence between the location and timing of the identified slab gap and the CMP's magmatism strongly supports the causal link between slab break-off and the generation of this vast volume of silicic magma. The distinctive geochemical signature of the CMP, which deviates from typical LIP signatures, highlights the specific conditions associated with massive slab break-off. This event likely involved extensive melting in the mantle wedge, triggered by the release of pressure and the influx of volatiles from the detached slab. The study's findings challenge existing models of LIP formation and emphasize the importance of incorporating mantle dynamics and subduction processes into our understanding of large-scale igneous events.

This study provides compelling evidence that a large-scale slab loss event triggered the formation of the Choiyoi Magmatic Province. The integration of geophysical, geochronological, and geochemical data establishes this as the oldest geophysically constrained example of a slab break-off-related LIP. This finding significantly expands our understanding of the processes responsible for the formation of large igneous provinces throughout Earth’s history. Future research should focus on applying similar integrated approaches to other ancient LIPs to test the generality of the slab break-off hypothesis and explore the role of this process in the evolution of continental margins and ore deposits. Further numerical modeling incorporating plate kinematic data and seismic tomography should refine our understanding of the dynamics of massive slab break-off events and their influence on regional magmatism.

The study's reliance on existing geochemical and geochronological datasets presents a potential limitation. While the dataset was rigorously filtered, the availability of data across the entire CMP area may not be uniform. Future studies could benefit from additional field work and targeted sampling to improve data coverage and density. Additionally, the interpretation of the seismic tomography data relies on the resolution of existing models. Improvements in seismic tomography techniques and data acquisition may refine our understanding of the lower mantle structure and the precise extent of the slab gap. Lastly, while the correlation between the slab gap and the CMP is strong, it is an observational correlation. More sophisticated numerical modelling is necessary to conclusively demonstrate a cause-and-effect relationship between the slab break-off event and the CMP's formation.