Petrology and geochemistry of mafic and ultramafic cumulate rocks from the eastern part of the Sabzevar ophiolite(NE Iran): Implications for their petrogenesis and tectonic setting  

作　　者：Fatemeh Rahmani Mohamad Ali Mackizadeh Moussa Noghreyan Claudio Marchesi Carlos J.Garrido 

机构地区：[1]Department of Geology,Faculty of Sciences,University of Isfahan,P.O.Box:81746-73441,Isfahan,Iran [2]Instituto Andaluz de Ciencias de La Tierra(IACT),CSIC-Universidad de Granada,Avenida de Las Palmeras 4,18100,Armilla,Granada,Spain [3]Departamento de Mineralogía y Petrología,Facultad de Ciencias,Universidad de Granada,Avenida Fuentenueva s/n,18002,Granada,Spain

出　　处：《Geoscience Frontiers》2020年第6期2347-2364,共18页地学前缘（英文版）

摘　　要：The Late Cretaceous Sabzevar ophiolite represents one of the largest and most complete fragments of Tethyan oceanic lithosphere in the NE Iran.It is mainly composed of serpentinized mantle peridotites slices;nonetheless,minor tectonic slices of all crustal sequence constituents are observed in this ophiolite.The crustal sequence contains a well-developed ultramafic and mafic cumulates section,comprising plagioclase-bearing wehrlite,olivine clinopyroxenite,olivine gabbronorite,gabbronorite,amphibole gabbronorite and quartz gabbronorite with adcumulate,mesocumulate,heteradcumulate and orthocumulate textures.The crystallization order for these rocks is olivine±chromian spinel→clinopyroxene→plagioclase→orthopyroxene→amphibole.The presence of primary magmatic amphiboles in the cumulate rocks shows that the parent magma evolved under hydrous conditions.Geochemically,the studied rock units are characterized by low TiO2(0.18-0.57 wt.%),P2 O5(<0.05 wt.%),K2 O(0.01-0.51 wt.%)and total alkali contents(0.12-3.04 wt.%).They indicate fractionated trends in the chondrite-normalized rare earth element(REE)plots and multi-element diagrams(spider diagrams).The general trend of the spider diagrams exhibit slight enrichment in large ion lithophile elements(LILEs)relative to high field strength elements(HFSEs)and positive anomalies in Sr,Pb and Eu and negative anomalies in Zr and Nb relative to the adjacent elements.The REE plots of these rocks display increasing trend from La to Sm,positive Eu anomaly(Eu/Eu*=1.06-1.54)and an almost flat pattern from medium REE(MREE)to heavy REE(HREE)region[(Gd/Yb)N=1-1.17].Moreover,clinopyroxenes from the cumulate rocks have low REE contents and show marked depletion in light REE(LREE)compared to MREE and HREE[(La/Sm)N=0.10-0.27 and(La/Yb)N=0.08-0.22].The composition of calculated melts in equilibrium with the clinopyroxenes from less evolved cumulate samples are closely similar to island arc tholeiitic(IAT)magmas.Modal mineralogy,geochemical features and REE modeling indicate that Sabzevar

关 键 词：PETROLOGY GEOCHEMISTRY Cumulate rocks Sabzevar ophiolite Supra-subduction zone Iran 

分 类 号：P587[天文地球—岩石学] P597.3[天文地球—地质学]