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THE FIELD OF STABILITY OF BLUE JADEITE: A NEW OCCURRENCE OF JADEITITE AT SORKHAN, IRAN, AS A CASE STUDY

Roland Oberhänsli^1,, Romain Bousquet¹, Hesam Moinzadeh², Mohssen Moazzen³ and Mohsen Arvin⁴

¹ Institute of Geosciences, Potsdam University, Karl Liebknecht Str. 27, D–14476 Potsdam, Germany
² Department of Geology, College of Arts and Sciences, Shahid Bahonar University, Kerman, 76176, Iran
³ Department of Geology, University of Tabriz, Tabriz, 51664, Iran
⁴ Department of Geology, College of Arts and Sciences, Shahid Bahonar University, Kerman, 76176, Iran

E-mail address: roob{at}geo.uni-potsdam.de

A new occurrence of "blue jade" is described. The jadeitite occurs as metasomatic veins in magnesite bodies within metaultramafic rocks in the Sorkhan area of southeastern Iran. The veins are composed of almost pure jadeite, 90 to 99.5 mol.% Jd, contain minor amounts of Ba-bearing K-feldspar, lawsonite and katophoritic amphibole, but unlike other occurrences of "blue" or "lavender jade", do not contain high amounts of Ti. The jadeitite veins formed at low-temperature – high-pressure conditions, around 1.6 GPa and 420°C. Such P–T conditions are characteristic of zones of cold subduction in which lawsonite blueschists to lawsonite eclogites typically form. Thermodynamic studies show that the mineral assemblage within the blue jade is strongly pressure- and temperature-dependent. Jadeitites containing two clinopyroxenes (jadeite and omphacite) are stable at high pressure (0.8 GPa) and low temperature (430°C) conditions, whereas blue jade with only one clinopyroxene (jadeite) forms at higher temperature or lower pressure. On the basis of these new calculations, P–T conditions of formation are re-examined for all occurrences of blue jade.

Keywords: blue jade, jadeitite, lawsonite, two-clinopyroxene stability, high-pressure petrology, Sorkhan, Iran.