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Integrated Ocean Drilling Program (IODP) Expedition 309/312 Hole 1256D, located in 15 Ma crust that formed at the East Pacific Rise during a period of superfast spreading (>200 mm/y), penetrated 1005 m into oceanic subbasement from the volcanic section to the upper portion of the plutonic complex (see the “Expedition 309/312 summary” chapter; Wilson et al., 2006). This data report presents the bulk rock trace element compositions of the basaltic rocks and gabbros recovered during the expedition. The analyzed samples represent a subset of shipboard samples that were analyzed onboard with inductively coupled plasma–atomic emission spectroscopy (ICP-AES) (shipboard AES samples) and a subset of samples collected and shared by a group of shipboard scientists (POOL samples). Shipboard AES samples were selected because they are the freshest and/or representative of rocks of each igneous unit. POOL samples were selected because they are representative of the various types of alterations and a few fresh alteration pairs (i.e., the fresh or less altered part and more altered part showing as alteration halos from the same sample).