Mafic magmatism triggered the Mesoproterozoic oxygenation event: Re-Os-PGE evidence from the Xiamaling Formation in North China and Velkerri Formation in North Australia

Abstract

It is widely recognized that oxygen levels may have transiently elevated around 1.4 Ga on Earth's surface. However, the specific drivers of this oxidation event remain unclear. This study presents new data on Re-Os and Sm-Nd isotopes, PGE concentrations, and major and trace elementsfor the Xiamaling Formation in the Yanliao Basin (North China Craton) and the formerly adjacent Velkerri Formation in the MacArthur Basin (North Australian Craton). The Re-Os isochron ages are 1388 ± 20 Ma and 1386 ± 7 Ma for Xiamaling and 1396 ± 41 Ma and 1384 ± 12 Ma for Velkerri, indicating nearly synchronous deposition. The initial ¹⁸⁷Os/¹⁸⁸Os ratios (0.14 ± 0.09 and 0.24 ± 0.02 for Xiamaling; 0.17 ± 0.28 and 0.21 ± 0.08 for Velkerri), which may reflect the seawater values at the time of deposition, are only slightly higher than mantle value (∼0.127). These low ratios are likely attributable to large-scale mafic magmatism. Positive ε_Nd(t) values further support global mafic magmatism during this period. Model calculations estimate ∼9 × 10⁶ t of mantle-derived Os to lower seawater ¹⁸⁷Os/¹⁸⁸Os from ∼0.5 to ∼0.2 over approximately 12 million years, requiring ∼3–9.7 × 10⁷ km³ of magmatism. Increased phosphorus and TOC content suggest that mafic rock weathering boosted oceanic phosphorus, promoting primary productivity and organic carbon burial, thereby driving the oxygenation event. Our findings demonstrate how Re-Os isotopes and PGE can provide crucial insights into the connection between deep magmatic processes and surface environmental changes, such as shifts in atmospheric oxygen levels.