Rare earth element (REE) abundances, Ni– Cr content and physico-chemical characteristics in different topsoils and bedrocks of Davarzan area, NE of Iran, were determined to understand the relationships of theses parameters in an ophiolitic region. Resulted data show that REE geochemistry could be a suitable proxy for parental materials of surface soils. The soils derived by serpentinite and peridotite rocks display REE properties similar to these ul t ra m afi c r oc k s . T h e y ha v e l ow l i g ht R EE (L R EE ), ne g at i ve Ce a n om a l y ( δ Ce = 0. 5 1 – 0 . 82 ) an d p os i t i ve Eu ano m aly (E u/E u⁎ = 1 .17– 1. 35 ). The RE E co nc ent ra tio ns of ultr am afi c- der i ved su rfa ce so il s ar e sig nifi ca nt ly hi gh e r th an pa ren ta l ro cks be ca us e of cla y mi ne ra l s. Th ere i s pos i tiv e co rr el at i on be tw ee n RE E co nt e nt a nd clay% and organic matter of these topsoils indicative of direct effect of such factors in REE abundances. The surface soils of low elevation samples in the studied area have been formed by weathering and transportation of different lithologies. Therefore, REE geochemistry is more sporadic and differs in various land uses. Agricultural surface soils have the highest organic matter and REE content ( ∑ REE N 100 ppm). Chondrite-normalized REE patterns of agricultural samples depict fractionated appearance with steep LREE and flat high REE (HREE) [(La/Yb)N = 15.31 –16.41]; while other samples have lower REE content ( ∑ REE = 31.89–58.3 ppm) and lower LREE/HREE. P-fertilizers are the major factor that produces REE enrichment in agricultural soils. Since these rocks are composed of mixed sources, there is no regular relation between REE content and other parameters such as organic matter and clay percentage. The concentrations of heavy metal elements such as Ni and Cr in surface soils of Davarzan area (693–1513 ppm) are higher than all threshold standards defined for environmental assessments. The Ni–Cr concentration increases with REE content in ultramafic-related topsoils; but the relation of REE content and heavy metal composition is more complicated and influenced by other factors in the low elevation soils with mixed parental materials.
کلید واژگان :Davarzan area, Rare earth elements, surface soils
ارزش ریالی : 600000 ریال
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