The North Makran is the innermost structural domain of the Makran Accretionary Prism (SE Iran). It consists of an imbricated stack of south-verging tectonic units and chaotic complexes, which are (from north to south): 1) the northern ophiolites (e.g. Band-e-Zeyarat ophiolite); 2) the Bajgan and Durkan Complexes that are described as continental-derived metamorphic complexes; 3) the Coloured Mélange. The northern ophiolites are generally considered as generated in a back-arc basin developed since Early Cretaceous between the Bajgan-Durkan microcontinents and the Lut Block (McCall & Kidd., 1982; Hunziker et al., 2015). We present here preliminary petrological and stratigraphic data of the Band-e-Zeyarat ophiolites. This unit consists of an incomplete ophiolite sequence characterized by an intrusive complex (cumulate gabbros and dunite, isostropic gabbros, and minor diorites and plagiogranites) followed upward by a sheeted dike complex, which is capped by a volcano-sedimentary succession. This succession is characterized by pillow lavas passing upward to pillow breccias with decimetric slices of carbonatic sedimentary rocks, which gradually increase in abundance toward the top of the succession represented, in turn, by Barremian calcareous pelagic marls and limestones. Locally, the volcano-sedimentary succession is cut by dikes that feed some sills also intruded in the calcareous sedimentary rocks. New geochemical data on the volcanic and intrusive rocks indicate the occurrence of three distinct geochemical varieties: 1) rocks characterized by LREE depletion showing normal N-MORB affinity; 2) rocks showing slight enrichment in LREE and LILE, which are transitional between N-MORB and E-MORB; 3) rocks characterized by marked enrichment in LILE and LREE showing a clear E-MORB affinity. In contrast to most backarc basin magmatic rocks, the studied rocks show no subduction-derived chemical components. Rather, similar to rocks from many Iranian ophiolites, their enriched geochemistry suggests a formation from an enriched mantle source in subduction-unrelated oceanic basins or continental rift settings. Further geochemical, structural, and stratigraphic studies are necessary for providing robust constraints for the interpretation of the tectonic setting of formation of the Band-e-Zeyarat ophiolite.

Preliminary petrological and stratigraphic data on the Band-e-Zeyarat ophiolite (Makran accretionary wedge, SE Iran)

Saccani E.;Pandolfi L.;Marroni;
2018

Abstract

The North Makran is the innermost structural domain of the Makran Accretionary Prism (SE Iran). It consists of an imbricated stack of south-verging tectonic units and chaotic complexes, which are (from north to south): 1) the northern ophiolites (e.g. Band-e-Zeyarat ophiolite); 2) the Bajgan and Durkan Complexes that are described as continental-derived metamorphic complexes; 3) the Coloured Mélange. The northern ophiolites are generally considered as generated in a back-arc basin developed since Early Cretaceous between the Bajgan-Durkan microcontinents and the Lut Block (McCall & Kidd., 1982; Hunziker et al., 2015). We present here preliminary petrological and stratigraphic data of the Band-e-Zeyarat ophiolites. This unit consists of an incomplete ophiolite sequence characterized by an intrusive complex (cumulate gabbros and dunite, isostropic gabbros, and minor diorites and plagiogranites) followed upward by a sheeted dike complex, which is capped by a volcano-sedimentary succession. This succession is characterized by pillow lavas passing upward to pillow breccias with decimetric slices of carbonatic sedimentary rocks, which gradually increase in abundance toward the top of the succession represented, in turn, by Barremian calcareous pelagic marls and limestones. Locally, the volcano-sedimentary succession is cut by dikes that feed some sills also intruded in the calcareous sedimentary rocks. New geochemical data on the volcanic and intrusive rocks indicate the occurrence of three distinct geochemical varieties: 1) rocks characterized by LREE depletion showing normal N-MORB affinity; 2) rocks showing slight enrichment in LREE and LILE, which are transitional between N-MORB and E-MORB; 3) rocks characterized by marked enrichment in LILE and LREE showing a clear E-MORB affinity. In contrast to most backarc basin magmatic rocks, the studied rocks show no subduction-derived chemical components. Rather, similar to rocks from many Iranian ophiolites, their enriched geochemistry suggests a formation from an enriched mantle source in subduction-unrelated oceanic basins or continental rift settings. Further geochemical, structural, and stratigraphic studies are necessary for providing robust constraints for the interpretation of the tectonic setting of formation of the Band-e-Zeyarat ophiolite.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/950003
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