First report of felsic whiteschist in the ultrahigh-pressure metamorphic belt of Dabie Shan, China

We report the first occurrence of a talc-kyanite assemblage typical of whit eschists in felsic ultrahigh-pressure metamorphic rocks of Dabie Shan, Chin a. The whiteschist assemblage occurs in a leucocratic layer, less than half a meter thick, which crosscuts a coesite-bearing eclogite. Both its geolog ic setting and geochemistry suggest that the protolith was a felsic dyke, w hich suffered loss of some elements, in particular alkalies. The whiteschis t consists of quartz, minor epidote, kyanite, talc and omphacite. Common ac cessories are rutile, apatite and zircon. Epidote is zoned, and the core in cludes quartz pseudomorphs after coesite and contains up to 5 wt% REE. Kyan ite includes fresh omphacite with the highest jadeite content (X-Jd less th an or equal to 0.60) The host eclogite consists of omphacite (X-Jd = 0.44 t o 0.37 from core to rim), garnet, quartz, kyanite, epidote, phengite (Si le ss than or equal to 3.47 a.p.f.u.) and amphibole, and accessory rutile, apa tite, zircon and ilmenite. Fresh coesite occurs in epidote, and its polycry stalline quartz pseudomorphs are included in both omphacite and kyanite. Th e whiteschist and the host eclogite share the same tectonometamorphic evolu tion, and show three metamorphic stages: (I) coesite-eclogite-facies stage at P greater than or equal to 2.6-2.7 Gpa and T = 710 +/- 20 degrees C; (II ) early decompression stage at P greater than or equal to 1.5-2.0 Gpa and T = 650 +/- 30 degrees C; (III) late adiabatic decompression to P = 0.7 Gpa and T = 670 +/- 40 degrees C.