Oceanic and super-deep continental diamonds share a transition zone origin and mantle plume transportation

Area of Science:

• Geochemistry
• Mineralogy
• Petrology

Background:

• Rare oceanic diamonds are thought to originate from the mantle transition zone, similar to super-deep continental diamonds.
• Oceanic diamonds exhibit a uniform, organic-like carbon isotope signature (δ¹³C -28 to -20‰).
• Super-deep continental diamonds show a wider range of carbon isotope signatures (δ¹³C -25‰ to +3.5‰), reflecting both organic and lithospheric mantle sources.

Purpose of the Study:

• To investigate the origin and carbon isotope signatures of oceanic diamonds.
• To compare the carbon isotope composition of oceanic diamonds with super-deep continental diamonds.
• To elucidate the role of subduction and mantle plumes in diamond formation and transport.

Main Methods:

• Analysis of carbon isotope ratios (δ¹³C) in oceanic and continental diamonds.
• Comparison of isotopic data with known diamond formation environments.
• Correlation of diamond occurrences with geological settings like large igneous provinces and ocean islands.

Main Results:

• Oceanic diamonds and the lighter cores of super-deep continental diamonds share a common organic δ¹³C signature, indicative of subducted carbon.
• The rims of super-deep continental diamonds possess δ¹³C values similar to peridotitic diamonds from the lithospheric mantle.
• Most oceanic diamonds, like lithospheric continental diamonds, are associated with mantle plume activity.

Conclusions:

• Subducted carbon is a primary source for transition zone diamonds found in both oceanic and continental settings.
• Mantle plumes play a crucial role in bringing transition zone diamonds to shallower depths.
• Continental lithosphere can impart distinct carbon isotope signatures to diamond rims during emplacement at shallower levels.