Heavy oxygen recycled into the lithospheric mantle

Area of Science:

• Geochemistry and Isotope Geology
• Mantle Petrology
• Volcanology

Background:

• Volcanic arc magmas carry geochemical and isotopic signatures reflecting mantle wedge metasomatism by subducted materials.
• Evaluating subduction metasomatism is challenging due to overprinting by crustal interactions during magma ascent.
• Continental crust recycling into the mantle remains a key question in Earth sciences.

Purpose of the Study:

• To provide unequivocal evidence for the recycling of continental crust components into the mantle.
• To investigate mantle domains that have reacted with melts derived from subducted continental crust.
• To establish an oxygen isotope benchmark for distinguishing mantle re-equilibration histories.

Main Methods:

• Analysis of veined peridotite xenoliths from Tallante monogenetic volcanoes.
• High-precision measurement of oxygen (¹⁸O/¹⁶O) and strontium (⁸⁷Sr/⁸⁶Sr) isotopes.
• Microtextural and mineralogical analysis of peridotite and felsic veins.

Main Results:

• Felsic veins and metasomatic aureoles in peridotite xenoliths exhibit the highest ¹⁸O/¹⁶O ratios globally for upper mantle materials.
• Anomalously high oxygen and strontium isotope compositions indicate the involvement of melts derived from subducted continental crust.
• Isotopic anomalies decrease away from veins, correlating with orthopyroxene formation and potentially influenced by diffusion.

Conclusions:

• Continental crust components are demonstrably recycled into the mantle wedge via Si-rich melts.
• The identified oxygen isotope variations serve as a benchmark for assessing the timing and extent of mantle metasomatism.
• This study refines our understanding of subduction zone processes and mantle-crust interactions.