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Strongly serpentinized ultramafic rocks show complex geochemical variations in the Narman disrict, NE Turkey. All peridotites including dunite and harzburgite have H2O contents of 10-15 wt%, indicating that they are highly serpentinized. Major elements in the harzburgites are SiO2 (38,1-38,4 wt%), Fe2O3 (7,2-7,8 wt%), Al2O3 (0.4-0.7 wt%), and MgO (38,4-38,5 wt%). In contrast, the dunites have higher SiO2 (39,0 wt%) and MgO (39,1 wt%), and lower Al2O3 (0.03-03 wt%). Narman peridotites are characterized by high and homogeneous Mg# (91.2-91.3%) except for one dunite sample, is characterized by slightly lower Mg# (90.7%). In harzburgites, Al2O3 is concentrated mainly in pyroxenes, so that variation in Al2O3 reflects their degree of fertility. On average, dunites have lower CaO (0,1 wt%) contents than harzburgites (CaO = 0.2-0.5 wt%). The scattering of CaO relative to Al2O3 in harzburgites and dunites may by attributed to preferential Ca loss during serpentinization. Both Al2O3 and CaO are concentrated in clinopyroxene. The lower CaO concentrations in some peridotites has been attributed to either Ca loss during serpentinization and the presence of only minor amounts of clinopyroxene. However, the higher CaO content and the rough correlation observed between CaO and Al2O3 in the peridotites suggests the presence of the clinopyroxene in these rocks.
In terms of trace element geochemistry, the dunites and harzburgites are different. The trace elements in dunites are V (41 ppm), Sc (9 ppm), Ni (2073 ppm), and Co (105 ppm) on avarage. In contrast, the harzburgites are slightly enriched in the incompatible elements V (161 ppm) and Sc (10 ppm) but lower in Ni (2005 ppm) and Co (43 ppm) on avarage. Ni and Co are preferentially partitioned into olivine, whereas V and Sc are in clinopyroxene. Compatible trace element variations in the peridotites mainly reflect the modal proportion of olivine and clinopyroxene. Dunites are depleted in TiO2 (∼0.01 wt%), Zr (<0.5ppm), and Sr (<0.5-3,8 ppm) compared to the harzburgites. These moderately to highly incompatible elements preferentially partition into the liquid during partial melting. Within the peridotites, V and Sc are positively correlated with CaO and Al2O3. V and Sc partition preferentially into clinopyroxene, and their correlation with CaO and Al2O3, suggests the presence of clinopyroxene preserved in these rocks. The average composition of the peridotites plots at the most depleted end of the mantle fractionation array on a MgO/SiO2 vs. Al2O3/SiO2 diagram. This peridotites display low Al2O3/SiO2 (<0.02), similar to those of the most refractory peridotites such as the Izu-Bonin Mariana forearc peridotites and the Oman peridotites.
Chondrite-normalized REE patterns of the Narman peridotites roughly display flat, chondrite-normalized trends with absolute concentrations ranging from 0.2 to less than 1 times chondrite values and similar to those of Cyclops and Troodos ophiolites.
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