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| 1 | 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显示文摘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 cumulate rocks were formed by crystal accumulation from a hydrous depleted basaltic melt with IAT affinity.This melt has been produced by moderate to high degree(~15%)of partial melting a depleted mantle source,which partially underwent metasomatic enrichment from subducted slab components in an intra-oceanic arc setting. | Fatemeh Rahmani Mohamad Ali Mackizadeh Moussa Noghreyan Claudio Marchesi Carlos J.Garrido | 2020 | Geoscience Frontiers2020，11，6： | 0 |
| 2 | The western Durkan Complex(Makran Accretionary Prism,SE Iran):A Late Cretaceous tectonically disrupted seamounts chain and its role in controlling deformation style显示文摘The Durkan Complex is a key tectonic element of the Makran accretionary prism(SE Iran)and it has been interpreted as representing a continental margin succession.We present here a multidisciplinary study of the western Durkan Complex,which is based on new geological,stratigraphic,biostratigraphic data,as well as geochemical data of the volcanic and meta-volcanic rocks forming this complex.Our data show that this complex consists of distinct tectonic slices showing both non-metamorphic and very low-grade metamorphic deformed successions.Stratigraphic and biostratigraphic data allow us to recognize three types of successions.Type-Ⅰis composed by a Coniacian-early Campanian pelagic succession with intercalation of pillow lavas and minor volcaniclastic rocks.Type-Ⅱsuccession includes a volcanic sequence passing to a volcano-sedimentary sequence with Cenomanian pelagic limestones,followed by a hemipelagic sequence.This succession is characterized by abundant mass-transport deposits.Type-Ⅲsuccession includes volcanic and volcano-sedimentary sequences,which are stratigraphically covered by a Cenomanian platform succession.The latter is locally followed by a hemipelagic sequence.The volcanic rocks in the different successions show alkaline geochemical affinity,suggesting an origin from an oceanic within-plate setting.Our new results indicate that the western Durkan Complex represents fragments of seamounts tectonically incorporated in the Makran accretionary wedge during the latest Late Cretaceous-Paleocene.We propose that incorporation of seamounts in the frontal prism caused a shortening of the whole convergent margin and possibly contributed to controlling the deformation style in the Makran Accretionary Wedge during Late Cretaceous-Paleocene times. | Edoardo Barbero Luca Pandolfi Morteza Delavari Asghar Dolati Emilio Saccani Rita Catanzariti Valeria Luciani Marco Chiari Michele Marroni | 2021 | Geoscience Frontiers2021，12，3： | 0 |
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