The possible subduction of continental material to depths greater than 200 km

• Published in: Nature (London) Vol. 407; no. 6805; pp. 734 - 736
• Main Authors: Ye, Kai, Cong, Bolin, Ye, Danian
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 12.10.2000; Nature Publishing Group
• Subjects: Crystalline rocks; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geology; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Lithosphere; Metamorphic rocks; Plate boundaries; Stone; Tectonics. Structural geology. Plate tectonics; Far East; China; chain silicates; eclogite; oxides; garnet; apatite; recrystallization; solid solution; exsolution; pyroxene; silicates; clinopyroxene; rutile; electron probe data; nesosilicates; metamorphic belts; metamorphic rocks; chemical analysis; high pressure; high-grade metamorphism; paragenesis; subduction; depth; Asia; phosphates; geologic barometry; plate convergence
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/35037566

Determining the depth to which continental lithosphere can be subducted into the mantle at convergent plate boundaries is of importance for understanding the long-term growth of supercontinents as well as the dynamic processes that shape such margins. Recent discoveries of coesite and diamond in regional ultrahigh-pressure (UHP) metamorphic rocks has demonstrated that continental material can be subducted to depths of at least 120 km (ref. 1), and subduction to depths of 150-300 km has been inferred from garnet peridotites in orogenic UHP belts based on several indirect observations. But continental subduction to such depths is difficult to trace directly in natural UHP metamorphic crustal rocks by conventional mineralogical and petrological methods because of extensive late-stage recrystallization and the lack of a suitable pressure indicator. It has been predicted from experimental work, however, that solid-state dissolution of pyroxene should occur in garnet at depths greater than 150 km (refs 6,7,8). Here we report the observation of high concentrations of clinopyroxene, rutile and apatite exsolutions in garnet within eclogites from Yangkou in the Sulu UHP metamorphic belt, China. We interpret these data as resulting from the high-pressure formation of pyroxene solid solutions in subducted continental material. Appropriate conditions for the Na2O concentrations and octahedral silicon observed in these samples are met at depths greater than 200 km.