Hybridization Melting Between Continent‐Derived Sediment and Depleted Peridotite in Subduction Zones. Issue 5 (7th May 2018) - Wang, Yu
Abstract: To better constrain the processes by which subducted continent‐derived sediment and the overlying mantle wedge react to produce hybrid magmas, we have performed a series of high‐pressure interaction experiments involving a phyllitic metasediment and a depleted peridotite (dunite) from the Mediterranean section of the Alpine‐Himalayan orogenic belt at 2–3 GPa. Two different experimental methods were compared, namely, the reaction of separate, juxtaposed peridotite and metasediment blocks (reaction experiments) and capsules in which the two rocks were included as an intimately mixed powder before the experiments (mixed experiments). In reaction experiments, only the metasediment partially melted, and a marked, thin reaction zone dominated by orthopyroxene formed between the dunite and phyllite blocks. In contrast, a hybrid melt phase was found in all mixed experiments. Trace element analyses indicated that Cs, Rb, Ba, Th, U, Nb, Ta, Zr, and Hf were strongly incompatible, together with marked light rare earth element/heavy rare earth element fractionation. The reaction with peridotite can significantly affect the mobility of medium rare earth element, heavy rare earth element, and transition elements during sediment‐mantle interaction, enriching them in hybrid melts. In addition, the nature of the sedimentary starting materials can considerably affect trace element behavior in resulting hybrid melts. There is a significant resemblance between the trace element distribution patterns of hybrid melts produced in our experiments and those of natural postcollisional potassium‐rich volcanic rocks from the eastern Mediterranean region. The experiments show that phlogopite is not necessarily required in the source to produce the SiO2 ‐richer end of the range of K‐rich magmas. Key Points: The involvement of peridotite significantly affects the mobility of MREE, HREE, and transition elements during interaction between subducted sediments and mantle The hybridization process may account for characteristic geochemical features observed in Mediterranean postcollisional potassium‐rich magmas Phlogopite is not necessarily required in the source to produce magmas with moderately high K2 O contents (3–5 wt%)