Rock magnetism of quartz and feldspars chemically separated from pelagic red clay: a new approach to provenance study

Abstract

Magnetic mineral inclusions in silicates are widespread in sediments as well as in igneous rocks. Because they are isolated from surrounding environment, they have potential to preserve original magnetic signature even in chemically altered sediments. Such inclusions may provide proxies to help differentiating the source of the host silicate. We measure magnetism of quartz and feldspars separated by chemical digestion of pelagic red clay. The samples are from the upper 15 m of sediments recovered at Integrated Ocean Drilling Program Site U1366 in the South Pacific Gyre. The quartz and feldspars account for 2.3-22.7 wt% of the samples. X-ray diffraction analyses detect both plagioclase feldspar and potassium feldspar. Plagioclase is albite-rich and abundant in the top ~ 7.4 m of the core. Potassium feldspar mainly occurs below ~ 10.4 m. The dominance of albite-rich plagioclase differs from a previous investigation of coarser fraction of sediments from the South Pacific. Saturation isothermal remanence (SIRM) intensities of the quartz and feldspars are 7.45 × 10 −4 to 1.98 × 10 −3 Am 2 /kg, accounting for less than 1.02% of the SIRM of the untreated bulk samples. The depth variations of the silicate mineralogy and the previously reported geochemical end-member contributions indicate that quartz and/or plagioclase above 8.26 m is likely to be Australian dust. In contrast, the relative abundance and the magnetic properties of quartz and feldspars vary below 10.42 m, without clear correlation with geochemical end-member contributions. We consider that these changes trace a subdivision of the volcanic component. Our results demonstrate that magnetism of inclusions can reveal additional information of mineral provenance, and chemical separation is an essential approach to reveal the environmental magnetic information carried by magnetic inclusions. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. remanence; IODP: Integrated Ocean Drilling Program. Authors' contributionsYU designed the study, conducted chemical separation, XRD analysis, and magnetic measurements of feldspars and quartz. TS conducted magnetic measurements of untreated samples. YU, TS, and TY interpreted the data. YU wrote the paper with input from TS and TY. All authors read and approved the final manuscript.

Magnetostratigraphic Evidence for Post-Depositional Distortion of Osmium Isotopic Records in Pelagic Clay and Its Implications for Mineral Flux Estimates

“…(Ohta et al, 2020), these numbers are converted to a quartz and feldspars ux of ~ 165-330 kg/m 2 /Myr. Typically, quartz and feldspars account for 10-20 wt.% of eolian dust(Blank et al 1985;Leinen et al 1994;Usui et al 2018), which is broadly consistent with our estimate of ~ 20-30 wt.% of the silicate. These numbers indicate > 500 kg/m 2 /Myr of eolian ux.…”

“…To quantify eolian dust content, we separated quartz and feldspars using the sodium pyrosulfate (Na 2 S 2 O 7 ) fusion method (Syers et al 1968;Clayton et al 1972;Blatt et al 1982;Stevens 1991;Usui et al 2018). Dry samples of ~ 1 g were rst treated with citrate-sodium dithionite solution buffered with sodium bicarbonate to remove poorly crystalline Fe-Mn oxyhydroxides (Rea and Janecek 1981).…”

Particle Size Specific Magnetic Properties Across the Norwegian‐Greenland Seas: Insights Into the Influence of Sediment Source and Texture on Bulk Magnetic Records

“…In these samples relatively fine PSD size ferrimagnetic grains are recognized in the silt fraction using Day Plots and FORC diagrams and are imaged as fine‐grained titanomagnetite inclusions within larger polycrystalline host grains (Hatfield et al, ). Silicate hosted ferrimagnetic inclusions have previously been recognized in marine sediment cores from the North Atlantic Ocean (Hatfield et al, ) and the Pacific and Indian Oceans (Chang et al, ; Usui et al, ). M rs /M s values are sensitive to magnetic domain state variations (e.g., Day et al, ; Dunlop, ; Néel, ) but also show a strong dependence with magnetite stoichiometry whereby greater titanium substitution yields higher M rs /M s values for samples of the same size (Day et al, ; Roberts et al, ).…”

Reductive dissolution of biogenic magnetite

“…Magnetite may also occur as inclusions within silicate minerals (Figs. 4k and 4l) and be protected from reductive dissolution (Chang et al 2016a;Zhang et al 2018;Usui et al 2018). This contributes to the relative loss and preferential dissolution of biogenic magnetite with respect to detrital magnetite.…”