A slab window in the south rim of the Parece-Vela Basin

Slab windows represent regions within the mantle that are largely devoid of slab material, facilitating direct communication between the mantle above and below the subducting slab. This unprecedented interaction disrupts the conventional material-energy exchange mechanisms between the subducted slab and mantle wedge, giving rise to anomalous heat flow, distinct magmatism, metamorphism, and geophysical features. Geochemical analyses of samples collected from the southern margin of the Parece-Vela Basin have illuminated the magmatic processes associated with a slab window. C20-3 is indicative of a hot and dry mantle upwelling that occurs through the slab window. On the other hand, C20-1 signifies an adakitic rock, which originates from the melting of oceanic crust at the periphery of the slab window. Slightly east of the slab window, C21-1 reveals evidence of a heated depleted mantle, influenced by the hot and dry mantle upwelling through the slab window. Additionally, a common Island Arc Basalt (IAB), denoted as C21-2, was also observed in the island arc region. Topographical data highlights the irregular distribution of numerous seamounts between the West Mariana Ridge and the Parece-Vela Basin spreading center. Seismological records reveal a preponderance of strike-slip earthquakes in the southern seamount region, alongside exceptionally high heat flow measurements at the northwest extremity of this area. The shape of the slab window can be roughly modeled by analyzing the distribution of earthquakes. Collectively, these observations lead us to postulate the existence of a slab window beneath the southern rim of the Parece-Vela Basin, likely attributed to the tearing of the subducting Pacific Plate along the strike-slip fault situated between the Ulithi and Fais Atolls.