Abstract
A bimineralic eclogite (JJG 41) shows clinopyroxene crystals of widely varying grain size (up to 6.0 cm) from which extensive lamellar and granular exsolution of garnet has occurred. The eclogite is rich in CaO and Al 2O 3, but poor in Na 2O; the initial clinopyroxene probably had 14.0 to 14.5 wt.% Al 2O 3 with tschermakite and jadeite contents of approximately 30% and 7% respectively. Considerable variation in chemical composition occurs within single clinopyroxene crystals and between different garnets (both granular and lamellar). Garnets show increasing grossular contents with progressive exsolution, and this is also associated with an increase of K' = Fe Mg Garnet/Fe/Mg clinopyroxene from approximately 1.8 to 5.5. These changes place much importance on declining temperature during exsolution. High pressure experimental work shows a wedge-shaped stability field for clinopyroxene (approximating the initial composition) below the solidus, and, assuming a magmatic derivation, gives an estimate of formation of an initial clinopyroxene + garnet assemblage of approximately 1400°C and 34–38 kb. It is suggested that the subsequent exsolution is largely related to cooling from these conditions towards the geotherm at initially constant depth.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
