Origin of the King's Trough Complex (North Atlantic): Interplay Between a Transient Plate Boundary and the Early Azores Mantle Plume

Abstract The King's Trough cuts into an area of thickened oceanic crust associated with the 45°N melting anomaly at the Mid‐Atlantic Ridge. Here we present a comprehensive geochemical data set and new 40 Ar/ 39 Ar age and bathymetric data from magmatic rocks from the King's Trough and the smaller Peake and Freen Deeps to the east and from the Gnitsevich Seamounts located to the west. The samples can be roughly divided into two groups: (a) Lavas dredged from the King's Trough (45.5–37.5 Ma) and Gnitsevich Seamounts (10–11 Ma) as well as cored rocks from the thickened oceanic crust, possessing mainly alkali basaltic, geochemically enriched compositions typical for ocean island basalts and (b) Lavas from the Peake and Freen Deeps exclusively showing depleted, normal MORB signatures. It is proposed that the current 45°N anomaly represents a remnant of the early Azores plume, which has also caused the regional thickening of the oceanic crust by plume‐ridge interaction. Following the jump of the plate boundary between the Eurasian and the Iberian/African plates to this region ∼37 Ma ago, the King's Trough opened from east to west as a graben structure by oblique extension, thereby cutting into the young plateau of thickened crust. The largest extension took place at its eastern end, outside of the area of plume‐influenced, thickened crust with the opening of the ultra‐deep Peake and Freen Deeps. The lavas obtained from these deeps have depleted geochemical signatures consistent with being derived from the regular upper mantle by decompression melting.