PETROGENESIS OF THE UAE CARBONATITES - GEOCHEMICAL AND ISOTOPIC SIGNATURES
δ18O and δ13C analysis shows an increase in the isotopic composition of the studied rocks in array from the primary (mantle) igneous carbonatite. However, excluding a few incompatible samples, 2nd group carbonatites exhibit a much higher isotopic enrichment than the 1st group. Moreover, variation trends of REE and trace elements in both groups are analogous, and some reveal similarity with carbonatites from Canary and Cape Verde islands.
These observations draw several important inferences: 1. UAE carbonatites have an oceanic origin and emplacement. 2. They were primarily originated from a silicate (alkaline) melt, and silicocarbonatites might represent a mix cognation between the two melt types. 3. The 2nd group “Calsiocarbonatite – Ferrocarbonatite” was initially produced from the 1st group “silicacarbonatite”. 4. A hot fluid enriched with heavier isotopic composition had affected these carbonatites, especially the 2nd group.
Finally, it is concluded that the UAE carbonatites might have formed in association with alkaline volcanic activities at an oceanic environment prior to the final obduction of the Semail ophiolite, during which they were exposed to metasomatism by a hot hydrothermal fluid.