Global influence of mantle temperature and plate thickness on intraplate volcanism

Global mantle perturbations following the onset of modern plate tectonics

Plate tectonics drives the compositional diversity of Earth's convecting mantle through subduction of lithosphere. In this context, the role of evolving global geodynamics and plate (re)organization on the spatial and temporal distribution of compositional heterogeneities in the convecting mantle is poorly understood. Here, using the geochemical compositions of intracontinental basalts formed over the past billion years, we show that intracontinental basalts with subchondritic initial neodymium-144/neodymium-143 values become common only after 300 million years, broadly coeval with the global appearance of kimberlites with geochemically enriched isotopic signatures. These step changes in the sources of intraplate magmatism stem from a rapid increase in the supply of deeply subducted lithosphere during the protracted formation of Pangea following the widespread onset of "modern" (cold and deep) subduction in the late Neoproterozoic. We argue that the delay (~300 million years) in the appearance of enriched intraplate magmas reflects the time required for the sinking and (re)incorporation of slabs into the sources of mantle-derived magmas.

An ensemble-based strategy for robust predictive volcanic rock typing efficiency on a global-scale: A novel workflow driven by big data analytics

Laboratory measurements, paleontological data, and well-logs are often used to conduct mineralogical and chemical analyses to classify rock samples. Employing digital intelligence techniques may enhance the accuracy of classification predictions while simultaneously speeding up the whole classification process. We aim to develop a comprehensive approach for categorizing igneous rock types based on their global geochemical characteristics. Our strategy integrates advanced clustering, classification, data mining, and statistical methods employing worldwide geochemical data set of ~25,000 points from 15 igneous rock types. In this pioneering study, we employed hierarchical clustering, linear projection analysis, and multidimensional scaling to determine the frequency distribution and oxide content of igneous rock types globally. The study included eight classifiers: Logistic Regression (LR), Gradient Boosting (GB), Random Forest (RF), K-nearest Neighbors (KNN), Support Vector Machine (SVM), Artificial Neural Network (ANN), and two ensemble-based classifier models, EN-1 and EN-2. EN-1 consisted of LR, GB, and RF aggregates, whereas EN-2 comprised the predictions of all ML models used in our study. The accuracy of EN-2 was 99.2 %, EN-1 achieved 98 %, while ANN yielded 98.2 %. EN-2 provided the best performance with highest initial curve for longest time on the receiver operating characteristic (ROC) curve. Based on the ranking features, SiO2 was deemed most important followed by K2O and Na2O. Our findings indicate that the use of ensemble models enhances the accuracy and reliability of predictions by effectively capturing diverse patterns and correlations within the data. Consequently, this leads to more precise results in rock typing globally.

Lithospheric thickness records tectonic evolution by controlling metamorphic conditions

The lithosphere, as the outermost solid layer of our planet, preserves a progressively more fragmentary record of geological events and processes from Earth's history the further back in time one looks. Thus, the evolution of lithospheric thickness and its cascading impacts in Earth's tectonic system are presently unknown. Here, we track the lithospheric thickness history using machine learning based on global lithogeochemical data of basalt. Our results demonstrate that four marked lithospheric thinning events occurred during the Paleoarchean, early Paleoproterozoic, Neoproterozoic, and Phanerozoic with intermediate thickening scenarios. These events respectively correspond to supercontinent/supercraton breakup and assembly periods. Causality investigation further indicates that crustal metamorphic and deformation styles are the feedback of lithospheric thickness. Cross-correlation between lithospheric thickness and metamorphic thermal gradients records the transition from intraoceanic subduction systems to continental margin and intraoceanic in the Paleoarchean and Mesoarchean and a progressive emergence of large thick continents that allow supercontinent growth, which promoted assembly of the first supercontinent during the Neoarchean.

Influence of reef isostasy, dynamic topography, and glacial isostatic adjustment on sea-level records in Northeastern Australia

Understanding sea level during the peak of the Last Interglacial (125,000 yrs ago) is important for assessing future ice-sheet dynamics in response to climate change. The coasts and continental shelves of northeastern Australia (Queensland) preserve an extensive Last Interglacial record in the facies of coastal strandplains onland and fossil reefs offshore. However, there is a discrepancy, amounting to tens of meters, in the elevation of sea-level indicators between offshore and onshore sites. Here, we assess the influence of geophysical processes that may have changed the elevation of these sea-level indicators. We modeled sea-level change due to dynamic topography, glacial isostatic adjustment, and isostatic adjustment due to coral reef loading. We find that these processes caused relative sea-level changes on the order of, respectively, 10 m, 5 m, and 0.3 m. Of these geophysical processes, the dynamic topography predictions most closely match the tilting observed between onshore and offshore sea-level markers.

Destruction and regrowth of lithospheric mantle beneath large igneous provinces

Large igneous provinces (LIPs) are formed by enormous (i.e., frequently >106 km3) but short-lived magmatic events that have profound effects upon global geodynamic, tectonic, and environmental processes. Lithospheric structure is known to modulate mantle melting, yet its evolution during and after such dramatic periods of magmatism is poorly constrained. Using geochemical and seismological observations, we find that magmatism is associated with thin (i.e., ≲80 km) lithosphere and we reveal a striking positive correlation between the thickness of modern-day lithosphere beneath LIPs and time since eruption. Oceanic lithosphere rethickens to 125 km, while continental regions reach >190 km. Our results point to systematic destruction and subsequent regrowth of lithospheric mantle during and after LIP emplacement and recratonization of the continents following eruption. These insights have implications for the stability, age, and composition of ancient, thick, and chemically distinct lithospheric roots, the distribution of economic resources, and emissions of chemical species that force catastrophic environmental change.