Potassium isotopic composition of low-temperature altered oceanic crust and its impact on the global K cycle

High precision analysis of stable potassium (K) isotopes by the collision cell MC-ICP-MS “Sapphire” and a correction method for concentration mismatch

“…37–40 This improved precision has quickly led to discoveries of natural 41 K/ 39 K variations in many terrestrial and extraterrestrial samples that were not resolvable in the past, shedding new light on a wide range of critical processes ranging from formation of the moon to silicate weathering. 41–60 The current understanding of stable K isotopes has been summarized in a recent review. 61 Despite being possible, MC-ICP-MS analysis of K isotopes faces major challenges associated with intense Ar-related interferences arising directly from the argon plasma, for example, argon hydride ( 40 ArH + ) on 41 K + .…”

An efficient method for high-precision potassium isotope analysis in carbonate materials

“…Its original protocol by Chen et al 43 has been extensively applied to extract K from $10-100 mg silicates for isotopic analysis. 12,13,17,20,48 However, it is not suitable for low-K carbonates due to remarkably high Ca and/or Mg in the matrix. Such matrices will cause signicant elemental peak shis, leading to unsatisfactory K separation.…”

“…Seawater composition reects chemical exchanges between the lithosphere, hydrosphere, atmosphere, and biosphere. 1 Among all elements investigated, K and its stable isotopes ( 39 K and 41 K) in seawater have been given particular attention, not only due to K being an essential nutrient for life, [2][3][4][5][6] but also because K, a major cation in both Earth's crust (1.81%) 7 and seawater ($400 mg g À1 ), 8 actively involves in various uid-rock interactions between lithosphere and hydrosphere (e.g., silicate weathering; [9][10][11][12][13] reverse weathering; [14][15][16][17] hydrothermal alterations [18][19][20][21][22] ). Recent high-precision measurements of potassium isotopes by multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) have revealed signicant 41 K/ 39 K variations in terrestrial samples, and a signicantly higher d 41 K value in seawater ($0.12&) 23,24 relative to the bulk silicate Earth (BSE) ($À0.43&).…”

High-Temperature Inter-Mineral Potassium Isotope Fractionation: Implications for K–Ca–Ar Chronology

“…The high-precision measurements of K isotopes can be traced back to the 1990s, when an extensive survey of geological samples by Humayun and Clayton found no measurable K isotopic difference on Earth. However, with the development of multiple-collector inductively coupled-plasma mass-spectrometry (MC-ICP-MS), the measurements of K isotopes have been significantly improved, and considerable isotopic variations of K have been observed in bulk igneous and sedimentary rocks, clay, evaporite minerals, and seawater samples. − The K isotopic variations observed on Earth have been mostly attributed to low-temperature geochemical processes such as continental weathering, hydrothermal alteration, and authigenic clay formation. ,− However, it is still unknown whether there is any significant inter-mineral K isotope fractionation during high-temperature igneous processes. Any inter-mineral fractionation of K isotopes is important for the accuracy of K–Ca–Ar dating because current calculations assume a constant 40 K abundance across different samples and minerals (cf.…”