Diamonds recovered from peridotite o
Source: Acta Petrologica Sinica   Publish Time: 2015-05-08 15:20   203 Views   Size:  16px  14px  12px

Diamonds recovered from peridotite of Purang ophiolite in Yarlung-Zangbo suture of Tibet: A proposal for a new type of diamond occurrence

 

Abstract: After the discovery of diamonds and other unusual minerals in peridotites and chromitites of the Luobusa ophiolite, Tibet, it became important to determine if this was an isolated occurrence or if the same minerals occur in other ophiolites of the Yarlung-Zangbo suture zone. Here, we report the discovery of a similar collection of minerals in mantle peridotites of the Purang ophiolite, which lies in the westernmost part of the Yarlung-Zangbo suture, more than 1000km from the Luobusa massif. The Purang ophiolite consists mainly of harzburgite, lherzolite and dunite, probably of MOR type, which were modified in a SSZ environment. Many grains of diamond and some unusual minerals, such as moissanite, were recovered by standard mineral separation techniques from a 657kg sample of harzburgite. The presence of native Cr, Fe and Zn, together with the moissanite, indicates a strongly reducing environment. This discovery confirms that the Luobusa massif is not unique in the Yarlung-Zangbo suture. Based on the presence of similar minerals in the Ray-Iz ophiolite of the Polar Urals, and reports of diamonds in Alpine-type mantle peridotites, we suggest that diamonds and highly reduced minerals may be common in ophiolitic peridotites. These occurrences indicate a completely new environment for diamond formation, which can be regarded as ophiolite-type diamond, distinct from the other two well known types, i.e. kimberlitic diamonds and ultrahigh pressure metamorphic diamonds.

 

Yang JS, Xu XZ, Li Y, Li JY, Ba DZ, Rong H and Zhang ZM. 2011. Diamonds recovered from peridotite of the Purang ophiolite in the Yarlung-Zangbo suture of Tibet: A proposal for a new type of diamond occurrence. Acta Petrologica Sinica, 27(11): 3171-3178 (in Chinese with English abstract) [pdf]