Data report: high downhole resolution portable X-ray fluorescence geochemistry of South Atlantic Transect basement cores, IODP Expeditions 390C, 395E, 390, and 393

This report presents portable X-ray fluorescence (pXRF) geochemistry for lavas with mid-ocean- ridge to ocean-island basalt–like compositions recovered from the western flank of the Mid- Atlantic Ridge across the South Atlantic Transect (SAT) during International Ocean Discovery Program (IODP) Expeditions 390C, 395E, 390, and 393. The Bruker Tracer 5 pXRF spectrometer proved an effective tool for rapid, high downhole resolution determination of select major, minor (K, Ca, Ti, Mn, and Fe), and trace (V, Cr, Ni, Cu, Zn, Rb, Sr, Y, and Zr) elements on split core surfaces. Initial shipboard calibrations reported in the Expedition 390/393 Proceedings are improved upon and superseded here with an element-by-element refinement of secondary cali- bration curves and a thorough assessment of instrument drift and matrix effects between rock powders and sawed surfaces. Matrix corrections for Zr, Ti, and Y were necessary to align the pXRF data with shipboard inductively coupled plasma–atomic emission spectroscopy (ICP-AES) results for one of the pXRF analytical campaigns. Additional Zr drift corrections further improved the Expedition 390 data compared to shipboard ICP-AES. Replicate analyses of rock surface standards demonstrate precision of ≤11% RSD (relative standard deviation) for most analytes, with poorer precision only for V and Rb (≤25% RSD). Although less precise than ICP methods, demonstrable accuracy, differentiation of background and alteration halo analyses, and typical downcore spacing of 0.5–1 m make these data sets a useful tool for addressing SAT objectives related to volcanostra- tigraphy and hydrothermal exchange.