Supporting Information for "A ~700-km-long Fossil Tonian Magmatic Arc Belt Hidden within the Yangtze Block’s Interior, South China" submitted to JGR-Solid Earth

Fossil magmatic arcs preserve important archives of juvenile magmatism, crustal growth and differentiation, thereby aiding in our understanding of continental evolutionary histories. However, some ancient fossil arcs are situated in continental interiors, where they are buried beneath thick cover sequences, making their identification challenging. In this study, we present a dataset of deep boreholes, geochronology, geochemistry, and geophysics to investigate the basement properties and evolution of the Sichuan Basin in the Yangtze Block, South China. These results provide evidence for a large Tonian (ca. 820–770 Ma) magmatic arc belt hidden within the interior of the Yangtze Block. Seven deep boreholes (~3600–6500 m) penetrating into basin basement, together with geochronology and 3D seismic reflection profiles, show extensive Tonian (ca. 820–770 Ma) rhyolite/granites overlain by Ediacaran sediments. Aeromagnetic data reveal a NE-SW-trending, ~700-km-long high positive magnetic anomaly belt (PMAB) across the central Sichuan Basin, indicating the presence of (ultra-) mafic rocks in lower crust. Correspondingly, the Tonian felsic rocks drilled within PMAB range were likely sourced from a juvenile and thickened lower crust based on petrogenetic and geochemical studies. Thus, we interpret the PMAB as a record of mantle-derived melts input, followed by their evolution into granitic melts within the crust. This process was associated with a Tonian arc magmatic front that was once occurred in the Yangtze Block’s interior. Our finding broadens the range of the Tonian continental arc system in the region, reaching at least 400–900 km landward from block’s northwestern margin. Such a broad orogenic system played a vital role in continental evolution, element recycling, and basin formation of the Yangtze Block.