5:15 PM - 6:30 PM
[SIT09-P08] Petrology and geochemistry of LREE-enriched fresh peridotite boulders from the basal part of the Fizh block, the northern Oman ophiolite
Keywords:fresh peridotite, incompatible trace elements, mantle metasomatism, Oman ophiolite
We found quite hard and fresh (LOI < 1.0) peridotite boulders at the southern basal zone of the Fizh block (e.g., Wadi Hayl). The texture is variable (mylonitic, porphyroclastic, equigranular, and coarse protogranular) and some porphyroclastic samples contain highly deformed fine-grained zones. It is difficult to determine the modal proportion of minerals due to the presence of fine-grained zone, but we can judge that they are mostly harzburgites and subordinately lherzolites, based on petrography of coarse-grained part of the samples and their whole-rock major-element compositions (SiO2 = 43.5-46.4 wt.%, Al2O3 = 0.38-1.10 wt.%, and CaO = 0.49-1.68 wt.%). Chondrite-normalized (the values showing with subscript CN hereafter) whole-rock REE concentrations show LREE-enriched U-shaped patterns, and the (La/Sm)CN and (La/Yb)CN are variable: 3.5-10.3 and 2.0-11.0, respectively. These values are quite high relative to the reported harzburgites (0.02-0.11 and 0.44-0.70; Godard et al., 2000) and fertile lherzolite (0.09-0.11 and 0.04-0.06; Takazawa et al., 2001: 0.28-1.15 and 0.09-0.53; Khedr et al., 2014) from other localities of the Oman ophiolite. The U-shaped REE pattern of ophiolitic peridotites has been interpreted as a result of secondary processes, such as serpentinization, ocean-floor alteration, or contamination of crustal materials during ophiolite obduction (Gruau et al., 1998). Low LOI value (< 1.0) of our samples denies the contribution of serpentinization and alteration to their enrichment of LREE, and indicates possible metasomatic addition of LREE to the mantle tectonite during/before ophiolite obduction (at high-temperature stage).