Slabs and Plumes Beneath South America Revealed by Whole-Mantle Tomography

South America is known as a long-lived and extensive subduction zone where the Nazca and Antarctic Plates are subducting beneath the South American Plate from the west. This subduction is considered to significantly influence the tectonics, seismicity, and volcanic activity in and around the continent. However, its relationship with the Mid-Atlantic Ridge on the other side of the continent remains poorly understood. The eruption mechanism of the Robledo caldera in the Andes of Argentina, which experienced a Volcanic Explosivity Index 7 eruption around 2300 BCE, is not well constrained either. To resolve these issues, we apply a global tomography method to reveal the 3-D P-wave velocity (VP) structure of the whole mantle beneath this region. We used ~7.2 million arrival times of 21,897 earthquakes recorded at 14,236 seismograph stations worldwide. The resulting $${V}_{P}$$ tomography clearly shows high-VP subducted slabs and low-VP anomalies above and below the slabs, which may reflect corner flow in the mantle wedge and subslab hot mantle upwelling (SHMU), respectively. A slab window is revealed beneath the Robledo caldera. Given the development of SHMU beneath this region, the huge eruption of the Robledo caldera might be powered by a mixture of the SHMU and magma in the mantle wedge through the slab window. Our tomography also suggests that the Mid-Atlantic Ridge had been opened due to hot mantle return flow associated with the subsidence of slab remnants into the lower mantle. Although such a mechanism was noted beneath North America, it is firstly confirmed in South America.