ALBERT

Description: This dataset reports major and trace elements, Sr and Nd isotopic ratios, carbonate C and O isotopic ratios, and mineral chemistry of Eocene (~35 Ma) magmatic rocks from the Nangqian basin, Eastern Qiangtang, Central Tibet. Samples have microlithic to microphaneritic porphyritic textures. Trachydacites show K-feldspar, plagioclase and amphibole phenocrysts in a matrix of feldspar + amphibole + biotite + quartz + oxides; tranchyandesites show clinopyroxene, apatite and resorbed biotite phenocrysts in a matrix of feldspar + clinopyroxene + oxides. One intrusive outcrop of porphyritic syenite was also sampled, composed of clinopyroxene and biotite phenocrysts in a matrix of feldspar + clinopyroxene + biotite + apatite + oxides. Whole-rock major and trace elements were measured at ISTerre, University Grenoble Alpes. The SARM-CRPG in Nancy and SEDISOR in Brest performed the whole-rock Sr and Nd isotope analyses. In-situ major-element compositions of mineral phases were obtained using the JEOL JXA-8230 Electron Microprobe at ISTerre, University Grenoble Alpes. Stable isotope analysis of carbonates was carried out in the stable isotope laboratory of Geoscience Rennes, CNRS-University of Rennes I. These geochemical data suggest that the source of the Eocene magmas in Nangqian was a H2O- and CO2-enriched lithospheric mantle. A full discussion of the results can be found in the related article.

Description: Representative major element compositions (in wt%) of clinopyroxenes and phlogopites from Nangqian ultrapotassic rocks. In-situ major-element compositions of mineral phases were obtained using the JEOL JXA-8230 Electron Microprobe at ISTerre, University Grenoble Alpes. Analytical conditions were 15 kV accelerating voltage and 12 nA beam current. The ZAF procedure was applied to reduce the raw data. The microprobe was calibrated using natural and synthetic standards. An X-ray element map of a calcite-bearing aggregate was acquired using 15 kV accelerating voltage and 10 nA beam current.

Description: Whole-rock major and trace elements data, and whole-rock and carbonate isotope data, for the Nangqian potassic and ultrapotassic rocks. Whole-rock major and trace elements were measured at ISTerre, University Grenoble Alpes. For major elements, 50 mg of rock powder were digested in HF/HNO3 mixture at 90 during five days. Excess HF was neutralized using boric acid and solutions were diluted with 250 mL of Milli-Q water. Major element contents were measured by Inductively Coupled Plasma - Atomic Spectrometry (ICP-AES) in Grenoble using the method given in Chauvel et al. (2011, doi:10.1111/j.1751-908X.2010.00086.x). For trace elements, 100mg of rock powder were digested with a mixture of concentrated HF and HNO3 at 150 for at least two weeks in steer Spar bombs. Excess Hf was neutralized with HNO3, using cycles of acid addition/evaporation. 300 mg of a spike containing Be, Ge, In, Tm and Bi were added to an aliquot of the rock solution corresponding to 8 mg of the initial powder. The solutions were then evaporated, diluted with 2% HNO3 (+ 1 drop of HF), and analysed by Inductively Coupled Plasma - Mass Spectrometry. During measurement, the signal was calibrated using the reference material BR24 (Chauvel et al., 2011, doi:10.1111/j.1751-908X.2010.00086.x), which was run every 4 or 5 analyses. Quality of the analytical procedure was checked by analysing blanks, international reference materials (BHVO2, BEN, BCR2), duplicate solutions and multiple runs of solutions. Only elements with external reproducibility 〈 15% are given. The SARM-CRPG in Nancy and SEDISOR in Brest performed the whole-rock Sr and Nd isotope analyses. Results were normalized to values of 143Nd/144Nd = 0.512110 for JNd-I reference material and 0.511850 for LaJolla, and to 87Sr/86Sr = 0.710250 for the reference material NIST SRM 987. Blanks were 74 pg for Nd and 137 pg for Sr. ε-Nd(T) ratios were calculated using the CHUR isotopic composition of Bouvier et al. (2008, doi:10.1016/j.epsl.2008.06.010). Stable isotope analysis of carbonates was carried out in the stable isotope laboratory of Geoscience Rennes, CNRS-University of Rennes I. Carbonates in whole-rock powders were selectively dissolved at 50 with anhydrous phosphoric acid H3PO4. The released CO2 gases were collected using a cryogenic extraction line, and their isotopic compositions were analyzed by a VG Optima triple collector mass spectrometer. Results were normalized to the values of the laboratory in-house standard Prolabo Rennes and the international standard NBS18. The analytical uncertainty is ±0.2 for δ18O carb, and ±0.1 for δ13C carb.

Description: Deformed samples from the Yushu mélange, in the western Jinsha Suture, have been dated by 40Ar/39Ar isotopy on micas and/or amphibole. Rock samples were crushed using standard procedures. Individual grains were handpicked from the 0.5-1-millimeter fraction of the crushed samples. Samples were irradiated in three batches, IR24, IR26 and IR36, at McMaster Nuclear Reactor (Hamilton, Ontario, Canada - https://nuclear.mcmaster.ca/facilities-equipment/facility-list/mcmaster-nuclear-reactor/) in its 8E high neutron flux facility. IR24 IR26 and IR36 lasted 50.967h, 50h and 200.95h with global efficiencies (J/h) of 4.97 x 10-5, 8.25 x 10-5 h-1 and 1.03 x 10-4 h-1. The analytical procedure is described by Ruffet et al. (1991, 1995). The irradiation standard were sanidine TCRs (28.608 ± 0.033 Ma according to Renne et al., 2011) for irradiation IR24 and IR26 and amphibole Hb3gr (1081.0 ± 1.2 Ma according to Renne et al., 2011) for irradiation IR36. Blanks were performed routinely each first or third/fourth run, and are subtracted from the subsequent sample gas fractions. Errors of apparent ages are plotted at the 1σ level and do not include the errors on the 40Ar*/39ArK ratio and age of the monitor and decay constant. The errors on the 40Ar*/39ArK ratio and age of the monitor and decay constant are included in the final calculation of the error margins on the pseudo-plateau and plateau ages. 40Ar/39Ar ages are provided with 2σ errors. Analytical data and parameters used for calculations (e.g. isotopic ratios measured on pure K and Ca salts; mass discrimination; atmospheric argon ratios; J parameter; decay constants) and reference sources are available in Table "Parameters used for Ar-Ar data analysis".

Description: Deformed samples from the Yushu mélange, in the western Jinsha Suture, have been dated by U-Pb isotopy on zircons. This dataset presents U-Pb isotopy data obtained for these samples. The rock sample was crushed using standard procedures. The zircon grains were handpicked from the 80-200 micrometer non-magnetic fraction, placed on epoxy mounts and polished. Back-scattered electron images of the grains were acquired with a Hitachi S2500 Scanning Electron Microprobe at the Institut des Sciences de la Terre (ISTerre) of Grenoble (France). U-Pb zircon analyses were performed by in-situ LA-ICP-MS, using an ESI NWR193UC excimer laser coupled to a quadrupole Agilent 7700x ICP-MS at the GeOHeLiS analytical Platform (OSUR, Univ. Rennes). The diameter of the ablation spots varies from 20 to 30 µm, depending on the grain size. The repetition rate of the ablation was 3 Hz. Data were corrected for U-Pb and Th-Pb fractionation and for mass bias by repeated measurements of the standard GJ-1 (Jackson et al., 2004). Accuracy was monitored by analyses of the standard Plešovice (337.13 ± 0.37 Ma, Sláma et al., 2008), which produced a concordia age of 337.1 ± 2.1 Ma (N=18; MSWD=0.65) during the course of the analyses. Data reduction was carried out using the software Iolite v4 (Paton et al., 2010, 2011). The concordia ages and diagrams were generated using IsoplotR (Vermeesch, 2018). The full instrumental and analytical conditions can be found in Table "Operating conditions for the LA-ICP-MS equipment" and in Nosenzo et al. (2022).