Potassium isotopic heterogeneity in subducting oceanic plates

Area of Science:

• Geochemistry
• Isotope Geochemistry
• Marine Geology

Background:

• Oceanic crust and sediments are major potassium (K) sinks and are subducted into the mantle.
• Previous K isotope studies were limited by analytical precision, hindering understanding of oceanic K cycling.
• High-precision K isotope analysis is crucial for deciphering variations in oceanic plates and the global K cycle.

Purpose of the Study:

• To investigate the K isotope composition (δ⁴¹K) of marine sediments and altered oceanic crust.
• To understand the role of subducting oceanic components in the oceanic K cycle.
• To reveal the processes controlling K isotope variations in seawater.

Main Methods:

• High-precision K isotope measurements using mass spectrometry.
• Analysis of 69 global sediment samples for δ⁴¹K.
• Analysis of 20 altered oceanic crust samples from ODP Site 801 for δ⁴¹K.

Main Results:

• Marine sediments exhibit a wide δ⁴¹K range (-1.3 to -0.02‰), indicating continental weathering and diagenetic alteration.
• Altered western Pacific oceanic crust shows δ⁴¹K values from -0.60 to -0.05‰, averaging -0.32‰.
• Submarine alteration of oceanic plates is a key process influencing seawater's high-δ⁴¹K signature.

Conclusions:

• Subducting oceanic crust and sediments are heterogeneous sources of K to the mantle.
• Submarine alteration significantly modifies the K isotope signature of oceanic plates.
• These findings provide critical insights into the complex oceanic potassium cycle.