The role of plate tectonics in the deep carbon cycle is crucial for understanding Earth’s climate, planetary life, and atmospheric CO2 over geological time; however, knowledge of carbon sources and sinks is dependent on reconstructed plate tectonic histories. Intra-oceanic subduction (i.e. subduction of an oceanic plate beneath another oceanic plate) is a recognized knowledge gap in plate tectonic reconstructions, especially within Pacific-Panthalassa, because continuous recycling of oceanic plates into the mantle leaves fewer geological traces. We examine the role of unassessed intra-oceanic subduction on paleoclimate reconstructions since the Mesozoic. We compare two global plate reconstructions: ”Tomopac” version 1, which integrates tomography and other constraints to enhance intra-oceanic subduction histories within Pacific-Panthalassa; and a widely-used model that implements less intra-oceanic subduction (Matthews et al., 2016). We model global seafloor ages, estimate total and areal subducted carbon since 200 Ma, and input subduction histories into the COPSE biogeochemical model (Lenton et al., 2021) to compare predicted global atmospheric CO2 and mean surface temperature histories. Tomopac with more intra-oceanic subduction shows a ~5% increase in global subduction zone lengths but a ~8% decrease in global subducted area and slab flux since 200 Myr. Overall, contrasted intra-oceanic subduction histories since 200 Ma alter estimates of subducted carbon by ~15-20%. Incorporating previously unassessed intra-oceanic subduction from Tomopac in COPSE reduces global mean surface temperatures up to 2°C and reduces atmospheric CO2 up to 300 ppm from 200 Ma to present, highlighting the importance of recognizing intra-oceanic subduction in modulating Earth’s long-term paleoclimate.

The Gulf of Mexico (GoM) is one of the most extensively studied offshore regions, but its Mesozoic evolution remains uncertain. The presence of a thick sedimentary cover and Jurassic salt poses challenges for geophysical imaging, hindering our understanding of the Mesozoic depositional history and crustal architecture evolution. Current tectonic models with rigid plates fail to capture key aspects of GoM evolution. This study introduces a new deformable plate model with optimised focused deformation designed to dynamically adjust stretching factors (SF) during rift evolution. Our model, which calculates crustal thickness and tectonic subsidence (TS) through time and accounts for stretching and thermal subsidence, can explain the depositional history of the pre-salt section and crustal architecture evolution of the GoM. Our model produces a predicted present-day crustal thickness with a root mean square error of 5.6 km with the GEMMA crustal thickness model. The resultant TS of ~1.5 km before the Yucatán block drifted, provides routes for the deposition of red beds through the paleo drainage systems of the northern GoM as successor basin infilling. The model explains ~40 Myrs of missing sedimentary strata, which we attribute to rapid subsidence in the central GoM, shifting red beds deposition beneath the Jurassic salt formations. Extension rate and SF calculations reveal a transition from a magma-rich to a hyperextended margin, with possible mantle exhumation. Our model can be useful in understanding the extent of other Jurassic deposits in the GoM basin and offers a robust framework for comprehending global passive rift margin evolution.

The tempo of subduction-related magmatic activity over geological time is episodic. Despite intense study and their importance in crustal addition, the fundamental driver of these episodes remains unclear. We demonstrate quantitatively a first order relationship between arc magmatic activity and subduction flux. The volume of oceanic lithosphere entering the mantle is the key parameter that regulates the proportion of H2O entering the sub-arc. New estimates of subduction zone H2O budgets over the last 150 million-years indicate a three- to five-fold increase in the proportion of H2O entering the sub-arc during the most recent global pulse of magmatism. Step changes in H2O flux enable proportionally greater partial melting in the sub-arc. Similar magmatic pulses in the ancient Earth could be related to variability in subduction flux associated with supercontinent cycles.