This README.txt file was generated on 07 March 2025 by Pamela Kempton ------------------- GENERAL INFORMATION ------------------- Title of Dataset: Mantle source evolution along the South Atlantic Transect (31?S) records a transition from HIMU plume component to depleted MORB Data associated with Kempton et al. (2025) Mantle source evolution along the South Atlantic Transect (31S) records a transition from HIMU plume component to depleted MORB. Geochemistry, Geophysics, Geosystems ------------------- ABSTRACT ------------------- Interactions between mantle plumes and mid-ocean ridges create considerable spatial variation in composition along ridge axes. What is less well known is the temporal variation in MORB compositions along single mantle flow lines. IODP Expeditions 390/393/390C/395E recovered basaltic basement from seven sites along such a flow line, the South Atlantic Transect (SAT), on the western flank of the Mid-Atlantic Ridge at ~ 31oS. SAT basalts ?49 Ma are tholeiitic with isotopic compositions similar to MORBs from the Mid-Atlantic Ridge between 25oS – 28oS. Basement from the oldest SAT site (U1556; 61.2 Ma) is more complex, consisting of three stratigraphic sequences (SSA, SSB and SSC) ranging from MORB-like at the bottom (SSC) to Ocean Island Basalt (OIB)-like at the top (SSA); their isotopic compositions are distinct relative to both younger SAT basalts and the EM1-type Tristan–Gough plume that dominates the region, being more akin to HIMU. The presence of previously unrecognized HIMU mantle in this region is due to one or more ridge jumps that occurred west of the Walvis Ridge at ~65 Ma. These ridge jumps relocated the spreading axis over a portion of the HIMU plume that had previously given rise to late-stage, off-axis HIMU magmatism adjacent to the Walvis Ridge. Upwelling beneath the spreading center progressively tapped a variably depleted source, reproducing it in reverse in the volcanic stratigraphy at Site U1556. Continued upwelling beneath the spreading center removed most of the HIMU plume material within ~12 Myr, the time of Site U1558 (49.2 Ma). ------------------- AUTHOR INFORMATION ------------------- Author Information First Author Contact Information Name: Pamela Kempton Institution: Department of Geology, Kansas State University, Address: Manhattan, KS 66506 USA Email: pkempton@ksu.edu Corresponding Author Contact Information Name: Pamela Kempton Institution: Department of Geology, Kansas State University, Address: Manhattan, KS 66506 USA Email: pkempton@ksu.edu Phone: 785-532-6724 Author Contact Information Name: R. M. Coggon Institution: University of Southampton, School of Ocean and Earth Science, National Oceanography Centre Address: Southampton, UK Email: r.m.coggon@soton.ac.uk Author Contact Information Name: I. Millar Institution: British Geological Survey Address: Keyworth, Nottinghamshire, UK Email: ilm@bgs.ac.uk Author Contact Information Name: T. M. Belgrano Institution: University College Dublin, School of Earth Sciences Address: Dublin, Ireland Email: tombelgrano@gmail.com Author Contact Information Name: E. Albers Institution: Woods Hole Oceanographic Institution Address: Woods Hole, MA, USA Email: ealbers@whoi.edu Author Contact Information Name: A. Michalik Institution: University of Southampton, School of Ocean and Earth Science, National Oceanography Centre Address: Southampton, UK Email: a.michalik@soton.ac.uk Author Contact Information Name: A. Milton Institution: University of Southampton, School of Ocean and Earth Science, National Oceanography Centre Address: Southampton, UK Email: jam1@soton.ac.uk Author Contact Information Name: A. D. Evans Institution: University of Southampton, School of Ocean and Earth Science, National Oceanography Centre Address: Southampton, UK Email: a.evans@soton.ac.uk Author Contact Information Name: R. N. Taylor Institution: University of Southampton, School of Ocean and Earth Science, National Oceanography Centre Address: Southampton, UK Email: rex@soton.ac.uk Author Contact Information Name: D. A. H. Teagle Institution: University of Southampton, School of Ocean and Earth Science, National Oceanography Centre Address: Southampton, UK Email: damon.teagle@southampton.ac.u --------------------- DATA & FILE OVERVIEW --------------------- # # Directory of Files in Dataset: List and define the different # files included in the dataset. This serves as its table of # contents. # Directory of Files A. Filename: #2025GC012175_Table_S1_Major_and_Trace_Element_Data_SAT_Basalts.xlsx and associated pdf #2025GC012175_Table_S1_Major_and_Trace_Element_Data_SAT_Basalts.pdf Short description: major and trace element concentration data for basalts from the South Atlantic Transect, IODP Exp 390/393 provided in original Excel format and an associated pdf B. Filename: #2025GC012175_Table_S2_Sr-Nd-Pb-Hf_Isotope_Data_SAT_Basalts.xlsx and associated pdf #2025GC012175_Table_S2_Sr-Nd-Pb-Hf_Isotope_Data_SAT_Basalts.pdf Short description: Sr-, Nd-, Pb-, and Hf-isotope data for basalts from the South Atlantic Transect, IODP Exp 390/393 provided in original Excel format and an associated pdf Filename: #2025GC012175_Table_S3_ Standards_for_Trace_Elements_by_ICPMS.pdf and associated pdf #2025GC012175_Table_S3_ Standards_for_Trace_Elements_by_ICPMS.pdf Short description: Standard data for trace element analyses of basalts from the South Atlantic Transect, IODP Exp 390/393 provided in original Excel format and an associated pdf File Naming Convention (if not included above): file names include (i) a 12-digit identifier (i.e., 2025GC012175) supplied by the journal publishing the paper (Geochemistry, Geophysics, Geosystems); (ii) a table reference number S1 to S3, where S refers to supplementary; (iii) and a brief description of the data in the file. # # Data Description: A data description, dictionary, or codebook # defines the variables and abbreviations used in a dataset. This # information can be included in the README file, in a separate # file, or as part of the data file. If it is in a separate file # or in the data file, explain where this information is located # and ensure that it is accessible without specialized software. # (We recommend using plain text files or tabular plain text CSV # files exported from spreadsheet software.) # ----------------------------------------- DATA DESCRIPTION FOR: #2025GC012175_Table_S1_Major_and_Trace_Element_Data_SAT_Basalts.xlsx and associated pdf #2025GC012175_Table_S1_Major_and_Trace_Element_Data_SAT_Basalts.pdf ----------------------------------------- The Excel workbook file consists of one spreadsheet: 1. Variables: SiO2, TiO2, Al2O3, FeO, MgO, MnO, CaO, Na2O, K2O, Mg#, Li, Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Pb, Th, U 2. Number of cases/columns: 22 samples. Sample naming convention follows the protocol established by the International Ocean Discovery Program (IODP) 3. Missing data codes: N/A 4. Variable List: All variables, except Mg#, are chemical elements or oxides and require no definition. Mg# calculated as molar Mg/(Mg+0.9Fe). Major element concentrations (SiO2, TiO2, Al2O3, FeO, MgO, MnO, CaO, Na2O, K2O) are in wt %. Trace element concentrations (Li, Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Pb, Th, U) are in ppm. ----------------------------------------- DATA DESCRIPTION FOR: #2025GC012175_Table_S2_Sr-Nd-Pb-Hf_Isotope_Data_SAT_Basalts.xlsx and associated pdf #2025GC012175_Table_S2_Sr-Nd-Pb-Hf_Isotope_Data_SAT_Basalts.pdf ----------------------------------------- The Excel workbook file consists of 1 spreadsheet 1. Variables (oxides): 87Sr/86Sr0, 87Rb/86Sr, 87Sr/86Sri, 143Nd/144Nd0, 147Sm/144Nd, 143Nd/144Ndi, epsilonNd, 206Pb/204Pb0, 207Pb/204Pb0, 208Pb/204Pb0, 238U/204Pb, 235U/204Pb,232Th/204Pb, 206Pb/204Pbi, 207Pb/204Pbi, 208Pb/204Pbi, 176H/177Hf0, 176Lu/177Hf, 176Hf/177Hfi, epsilonHf 2. Number of cases / rows: 26 separate analyses (22 samples, 4 duplicates) 3. Missing data codes: N/A 4. Variable List: variables are all standard isotopic ratios and require no definition ----------------------------------------- DATA DESCRIPTION FOR: #2025GC012175_Table_S3_Standards_for_Trace_Elements_by_ICPMS.xlsx and associated pdf #2025GC012175_Table_S3_Standards_for_Trace_Elements_by_ICPMS.pdf ----------------------------------------- The Excel workbook file consists of 1 spreadsheet 1. Variables (oxides Li, Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Pb, Th, U 2. Number of cases / rows: Two standards; data for each includes the recommended value, average of the measured values and the standard deviation (SD) on the average, 3. Missing data codes: N/A 4. Variable List: All variables are chemical elements or oxides and require no definition. Trace element concentrations (Li, Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Pb, Th, U) are in ppm. ----------------------------------------- ANALYTICAL METHODS ----------------------------------------- Trace element and Sr-Nd-Pb isotope analyses were carried out at the at the School of Ocean and Earth Science, University of Southampton, UK. In this study, we focused on core material that retained basaltic glass. Only at Site U1559 was it necessary to include a whole rock (WR) sample (393-U1559B-5R-1, 26-30 cm), because insufficient glass was recovered during coring. Analytical protocols for WR and glass samples were the same aside from powdering the WR prior to dissolution. Samples were crushed and handpicked under a binocular microscope to remove contaminants, such as altered glass and veins or vesicles variably filled with carbonate, zeolites, and clay minerals. Glass chips were ultrasonicated in ultra-pure milli-Q H2O for 1 hour, followed by 45 minutes in dilute (~1.5 M) HCl. After removal of the dilute acid using a micropipette, glass chips and WR powder underwent HF-HCl acid digestion. For trace element analysis, samples were subsequently diluted to 4000× dilution factor. Trace elements were analyzed using a Thermo Fisher Scientific X-Series 2 ICP-MS (Bremen, Germany). All samples, standards and blanks were spiked with internal standard elements Be, In and Re. Raw data were blank, interference and internally corrected and then calibrated using a suite of international rock standards comprising JB-2, BCR-2, JB-3, BIR-1, JGb-1, BHVO-2, AGV2 (using ‘preferred’ reference values extracted from the GeoREM database; Jochum et al., 2007; 2016). The long-term accuracy of this methodology is monitored using measurements of JA-2, prepared and analyzed as an unknown. For the elements reported here accuracy is within 1-7% of the reference values. Strontium, Nd, and Pb isotope ratios were analysed using a Thermo Scientific Neptune Plus multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). Following chemical purification by standard cation exchange column chemistry, Sr, Nd, and Pb aliquots were analysed via a Teledyne Aridus 3 desolvating nebuliser. Aliquots for Sr-isotope analysis nominally contained ~20 ppb Sr. The analytical protocol corrects for Kr and Rb interferences and performs a blank correction. Mass bias was exponentially corrected using 88Sr/86Sr of 8.37521. The NBS 987 Sr isotope reference standard was measured as an unknown using the same protocol. Over a 12-month period, the 87Sr/86Sr measured was 0.710243 ± 0.000017 (2SD), n=175; samples are reported relative to an accepted value for NBS 987 of 0.71024. For Nd-isotope analysis, 143Nd/144Nd compositions were corrected following a method adapted from Vance and Thirlwall (2002) through adjustment to a 146Nd/144Nd ratio of 0.7219 and a secondary normalisation to 142Nd/144Nd = 1.141876. Results for the JNdi-1 reference standard (Tanaka et al., 2000) measured as an unknown were 0.512115 with an external reproducibility of ±0.000009 (2SD) across 8 analysis sessions over 2 years. Given that our measured reference standard is identical to the accepted value for JNdi-1, sample data are reported without further normalization. Pb isotopes were corrected for instrumental mass fractionation using the SBL74 double spike method (Taylor et al., 2015). The Pb isotope reference standard NBS981 gave 206Pb/204Pb = 16.9400 ± 0.0023, 207Pb/204Pb = 15.4965 ± 0.0026 and 208Pb/204Pb = 36.7124 ± 0.0076 (>150 analyses during past 5 years). Samples are reported relative to accepted values for NBS 981 of 206Pb/204Pb = 16.9356, 207Pb/204Pb = 15.4891, 208Pb/204Pb = 36.7006 (Todt et al., 1996). Hafnium separation followed a procedure adapted from Münker et al. (2001). Hf fractions were analyzed on a Thermo Scientific Neptune Plus mass spectrometer operated in static multicollection mode at the National Environmental Isotope Facilty, Keyworth, UK. Correction for 176Yb on the 176Hf peak was made using reverse-mass-bias correction of the 176Yb/173Yb ratio empirically derived using Hf mass-bias corrected Yb-doped JMC475 solutions (Nowell and Parrish, 2001). 176Lu interference on the 176Hf peak was corrected by using the measured 175Lu and assuming 176Lu/175Lu = 0.02653. The column procedure used to separate Hf effectively removes most Yb and Lu, so these corrections are minimal. Data are reported relative to 179Hf/177Hf = 0.7325. The Hf standard solution JMC475 was analyzed during each analytical session and sample 176Hf/177Hf ratios are reported relative to a value of 0.282160 for this standard (Nowell and Parrish, 2001). Multiple analyses of JMC475 across the time of analysis gave mean 176Hf/177Hf values of 0.282148 ± 0.000002 (1-sigma, Session 1, n=10) and 0.282145 ± 0.000002 (1-sigma, Session 2, n=6). Major element glass compositions were determined by Cameca SX-100 electron microprobe analyser at the Faculty of Geosciences, University of Bremen, Germany. Glass was analyzed with an acceleration voltage of 15 kV, beam current of 40 nA, and a 15 ?m diameter spot size. Sodium was analyzed first, and monitoring of intensity showed that no Na loss occurred during analysis. Minerals and glasses from the Smithsonian Institution (Jarosewich et al., 1980) were used for calibration. Each glass composition is the average of six spot analyses. Analytical quality was monitored by repeat analysis of Smithsonian basalt glass reference materials VG-2 (NMNH 111240-52) and VG-A99 (NMNH 113498-1) (Jarosewich et al., 1980) and the USGS glasses BCR-2G and BHVO-2G (Jochum et al., 2005) alongside the samples. Concentrations of MnO were initially systematically underestimated by, on average, 19.3% relative to the reference materials, and this value was used to correct the sample values. Apart from this, all reference values were reproduced to within 1%, except for Na2O (2.5%) and K2O (2.9%). Precision expressed as relative standard deviation were better than 2.2%, except for MnO (6.0%), Na2O (3.4%), and K2O (4.3%). manuscript submitted to Geochemistry, Geophysics, Geosystems Confidential manuscript submitted to replace this text with name of AGU journal