MULTI-ANVIL RE-EQUILIBRATION EXPERIMENTS OF A DABIE SHAN ULTRAHIGH-PRESSURE ECLOGITE WITHIN THE DIAMOND-STABILITY FIELDS

Citation
K. Okamoto et S. Maruyama, MULTI-ANVIL RE-EQUILIBRATION EXPERIMENTS OF A DABIE SHAN ULTRAHIGH-PRESSURE ECLOGITE WITHIN THE DIAMOND-STABILITY FIELDS, Island arc, 7(1-2), 1998, pp. 52-69
Citations number
48
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geosciences, Interdisciplinary
Journal title
ISSN journal
1038-4871
Volume
7
Issue
1-2
Year of publication
1998
Pages
52 - 69
Database
ISI
SICI code
1038-4871(1998)7:1-2<52:MREOAD>2.0.ZU;2-G
Abstract
An eclogite (UHP303) formed at similar to 700 degrees C and P > 4 GPa fi om the Dabie Shall ultrahigh-pressure (UHP) terrane and the same sa mple + 1.1 wt% K2O (UHK303) were used for re-equilibrium experimental studies at P = 2.6-3.2 GPa and T = 900-1000 degrees C, employing a pis ton cylinder apparatus, and at P = 3-7 GPa and T = 900-1200 degrees C, employing a 1000 toll uniaxial multi-anvil apparatus (SPI-1000). Run products of UHP303 are composed of garnet, sodic augite, with or witho ut a SiO2 phase and phengite. Textural evidence indicates that the sol idus lies between 900 and 1000 degrees C at 5 GPa, and above 1000 degr ees C at 3 and 7 GPa for UHP303. The solidus temperature decreases to 1000 degrees C at 3-5 GPa and below 900 degrees C at 5 GPa in UHK303. Composition of rock-forming minerals of all run products have determin ed and compared with these of stal ting materials. Gal nets of all run products have a relatively higher almandine + spessartine component ( alm + sps 24-30 mol%) and lower grossular component (12-16) with const ant pyrope component (58-61), compared to the stal ting gal net (grs 1 6-26, alm 21-26, pyp, 42-61). The stable Ca-Na pyroxenes are sodic aug ite rather than omphacite at T higher than 1000 degrees C in the P = 3 -7 GPa pressure range, and the Cpx compositional gap is completely clo sed. The K2O content of Ca-Na pyroxenes is a function of P and T, and serves as a potential barometer in the diamond-stability field. Sodium content in garnet is negligible. Using the proposed K2O content in Ca -Na pyroxene as a function of pressure, the maximum Kokchetav UHP cond ition is suggested to have been 7 GPa at T = 900 degrees C.