Geochemical evidence for Late Cretaceous marginal arc-to-backarc transition in the Sabzevar ophiolitic extrusive sequence,northeast Iran |
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| Institution: | 1. Uni Grenoble Alpes, ISTerre, F-38041 Grenoble, France;2. V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 37, Moscow, 119991, Russia;3. Geological Institute, Russian Academy of Sciences, Pyzhevsky per. 7, Moscow, 119017, Russia;1. ARC Centre of Excellence for Core to Crust Fluid Systems and GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia;2. Dipartimento di Scienze, Sez. Scienze Geologiche, Università Roma Tre, Largo S. L. Murialdo, 1, 00146 Roma, Italy;3. Département de Minéralogie, Université de Genève, Genève, Switzerland;4. Institut für Geowissenschaften, Goethe Universität, Frankfurt, Germany;5. Departamento de Geología, Centro de Investigación Científicay de Educación Superior de Ensenada (CICESE), Carretera Ensenada–Tijuana No. 3918, 22860 Ensenada, Baja California, Mexico;6. School of Earth Sciences, Damghan University, Damghan, Iran;7. Department of Geology, Imam Khomeini International University, Qazvin, Iran;1. Department of Geological Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey;2. Department of Geological Engineering, Bülent Ecevit University, 67100 Zonguldak, Turkey;3. Department of Earth Sciences, Sun Yat-Sen University, Guangzhou, PR China;4. Department of Geological Engineering, Recep Tayyip Erdoğan University, Rize, Turkey;5. Department of Earth and Environmental Sciences, Ludwig-Maximilians-University, Munich, Germany |
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| Abstract: | The ophiolitic extrusive sequence, exposed in an area north of Sabzevar, has three major parts: a lower part, with abundant breccia, hyaloclastic tuff, and sheet flow, a middle part with vesicular, aphyric pillow lava, and an upper part with a sequence of lava and volcanic-sedimentary rocks. Pelagic limestone interlayers contain Late Cretaceous (Maastrichtian–Late Maastrichtian) microfauna. The supra-ophiolitic series includes a sequence of turbidititic and volcanic-sedimentary rocks with lava flow, aphyric and phyric lava, and interlayers of pelagic limestone and radiolarian chert. Paleontological investigation of the pelagic limestone and radiolarite interlayers in this series gives a Late Cretaceous age, supporting the idea that the supra-ophiolitic series formed in a trough, synchronous with the Sabzevar oceanic crust during the Late Cretaceous. Geochemical data indicate a relationship between lava in the upper part of the extrusive sequence and lava in the supra-ophiolitic series. These lavas have a calc-alkaline to almost alkaline characteristic, and show a clear depletion in Nb and definite depletions in Zr and Ti in spider diagrams. Data from these rocks plot in the subduction zone field in tectonomagmatic diagrams. The concentration and position of the heavy rare earth elements in the spider diagrams, and their slight variation, can be attributed to partial melting of the depleted mantle wedge above the subducted slab, and enrichment in the LILE can be attributed to subduction components (fluid, melt) released from the subducting slab. In comparison, the sheet flow and pillow lava of the lower and middle parts of the extrusive sequence show OIB characteristics and high potassium magmatic and shoshonitic trends, and their spider diagram patterns show Nb, Zr, and Ti depletions. The enrichment in the LILE in the spider diagram patterns suggest a low rate of partial melting of an enriched, garnet-bearing mantle. It seems that the marginal arc basin, in which the Sabzevar ophiolite was forming, experienced lithospheric extension in response to slab rollback. This process, which formed a backarc basin, may have aborted the embryonic arc, stopped arc magmatism, and led to the rise of mantle diapirs. The extrusive ophiolite sequence, north of Sabzevar probably formed during the transition from a marginal arc basin to a backarc basin during the Late Cretaceous. |
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| Keywords: | Supra-ophiolitic Ophiolitic extrusive sequence Pillow lava Sheet flow Supra-subduction Marginal arc Backarc |
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