Heterogeneous Earth's mantle drilled at an embryonic ocean

Area of Science:

• Geology
• Geophysics
• Geochemistry

Background:

• Mantle processes are fundamental to plate tectonics and biogeochemical cycles.
• In-situ mantle sampling is limited due to burial beneath crust and sediments.

Purpose of the Study:

• To characterize the lithological features of mantle sections from an embryonic ocean in the Tyrrhenian Sea.
• To investigate the implications of these features for understanding mantle behavior in magma-poor rifts.

Main Methods:

• Drilling and lithological analysis of mantle sections from the International Ocean Discovery Program (IODP) expedition.
• Comparison of findings with mantle sections from Mid-Ocean Ridges (MORs) and passive margins.

Main Results:

• Discovery of exceptionally heterogeneous and fertile mantle lithologies, including lherzolites, harzburgites, dunites, and pyroxenites.
• Evidence of significant mantle refertilization, indicated by plagioclase- and clinopyroxene-rich layers, hydrous magmatic veins, and mafic intrusions.
• Delayed inception of magmatic crust formation.

Conclusions:

• Magma-poor rifts do not necessitate a chemically depleted mantle.
• Deep lithospheric processes, such as refertilization and prolonged thinning, can delay melt focusing and the establishment of spreading centers.