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improved upon and superseded here with an element-by-element refinement of secondary cali-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.