Large Igneous Provinces: Versatile Drivers of Global Change

Reconstructing the tempo and emplacement mechanisms of large igneous provinces (LIPs) and establishing potential links to environmental change and biological crises requires detailed and targeted high-precision geochronology. Contact metamorphism during LIP intrusive magmatism can release large volumes of thermogenic gas, so determining the timing of these events relative to global climate change is crucial. The most reliable age information comes from U-Pb geochronology; however, LIP mafic igneous rocks do not commonly crystallize U-bearing minerals, such as zircon or baddeleyite. Recent work has shown that U-rich minerals can crystallize in fractionated melt pockets in intrusive components of LIPs after contamination of the melt by sedimentary rocks at emplacement level. Zircon and baddeleyite from these pockets make high-precision U-Pb geochronology of LIPs possible, but these unique mechanisms add other complexities.

Large igneous provinces (LIPs) can potentially cause cooling on tens- to thousand-year timescales via injection of sulfur aerosols to the troposphere, and on million-year timescales due to the increase of global weatherability. The ca. 719-Ma Franklin LIP preceded onset of the Sturtian Snowball Earth glaciation by less than two million years, consistent with CO2 drawdown due to weathering of Ca- and Mg-rich LIP basalts, which may have contributed to cooling past a critical runaway ice-albedo threshold. A relatively cool background climate state and Franklin LIP emplacement near a continental margin in the warm wet tropics may have been critical factors for pushing the Earth’s climate past the threshold of runaway glaciation.

Terrestrial ecosystems are integral components of global carbon budgets and modulators of Earth’s climate. Emplacement of large igneous provinces (LIPs) is implicated in almost every mass extinction and smaller biotic crises in Earth’s history, but the effects of these and other large-scale magmatic events on terrestrial ecosystems are poorly understood. Palynology, the study of fossilized pollen and spores, offer a means to robustly reconstruct the types and abundance of plants growing on the landscape and their response to Earth crises, permitting predictions of the response of terrestrial vegetation to future perturbations. We review existing palynological literature to explore the direct and cumulative impacts of large-scale magmatism, such as LIP-forming events, on terrestrial vegetation composition and dynamics over geological time.

Large igneous provinces (LIPs) are characterized by flood basalts and extensive magmatic plumbing systems. When sills and dykes are emplaced in sedimentary basins, the heat released can result in extensive contact metamorphism and gas generation. During the past 20 years, this process has been highlighted as potentially playing a key role in terms of proposed links between LIPs and global environmental changes. The geochemistry of the sedimentary rocks that the magma intrudes, and their potential to generate thermogenic gases such as CO2 and CH4 during heating, are critical controlling factors.

Evolution has not been a simple path. Since the first appearance of complex life, there have been several mass extinctions on Earth. This was exemplified by the most severe event during the Phanerozoic, the end-Permian mass extinction that occurred 252 million years ago and saw a loss of 90% and 70% of all marine and terrestrial species, respectively. Such mass extinctions have entirely reset ecosystems. Increasing evidence points to the massive eruption and crustal emplacement of magmas associated with large igneous provinces (LIPs) as key drivers of these events. Understanding how LIP events disrupted global biogeochemical cycles is of prime importance, especially as humans alter the atmosphere and biosphere today. We explore the cascading impacts of LIP events on global climate, oceans, and land—including runaway greenhouses, the release of toxic metals to the environment, the destruction of the ozone layer, and how global oceans are driven to anoxic and acidic states— all of which have parallels in the consequences of modern industrialisation.

Earth’s history has been punctuated by extraordinary magmatic events that produced large igneous provinces (LIPs). Many LIPs induced global changes, including millennial-scale warming, terrestrial and oceanic mass extinctions, oceanic anoxic events, and even glaciations. Research over the past 20 years has shown that shallow crustal degassing is an important factor contributing to the environmental impact of LIPs. Contact metamorphism in sedimentary basins can generate huge gas volumes, and operates as a function of magma volume and the architecture of LIP plumbing systems. Numerous open questions remain concerning the role of LIPs in triggering rapid and lasting changes, whose answers require collaboration across geoscientific disciplines. In this issue, we present the status of five key research themes and discuss potential ways forward to better understanding these large-scale phenomena.