TRACE ELEMENTS IN OLIVINE AND THEIR PETROGENETIC IMPLICATION: THE CASE STUDY OF CANARY ISLANDS

摘要

Olivine is one of the most abundant mineral in the upper mantle and in crustal ultramafic rocks on Earth. It can also occur as xenocrystal in several types of lava. The ideal composition of olivine is (Mg,Fe)SiO_4 but it may contain trace elements such as Ni, Mn and Ca in solid solution. Although with some cautions, the presence and abundance of these trace elements can be used as a petrogenetic indicator. In particular, low Ca content (＜ 1000 ppm) and high F_O contents (＞ 90 mol%) are considered as diagnostic features for mantle olivine as well as for those found in boninite, kymberlite and in some Alaskan-type complexes. NiO and MnO versus the F_O content were also successfully used to discriminate the olivine formed in the mantle section of the ophiolite from those crystallized in the crustal sequence.