Author Posting. © The Author, 2006. This is the author's version of the work. It is posted here by permission of Oxford University Press for personal use, not for redistribution. The definitive version was published in Journal of Petrology 47 (2006): 1051-1093, doi:10.1093/petrology/egl002.

A Detailed Geochemical Study of Island Arc Crust: The Talkeetna Arc Section, South-central Alaska

The Zagros fold-and-thrust belt of SW Iran is a young continental convergence zone, extending NW–SE from eastern Turkey through northern Iraq and the length of Iran to the Strait of Hormuz and into northern Oman. This belt reflects the shortening and off-scraping of thick sediments from the northern margin of the Arabian platform, essentially behaving as the accretionary prism for the Iranian convergent margin. Distribution of Upper Cretaceous ophiolites in the Zagros orogenic belt defines the northern limit of the evolving suture between Arabia and Eurasia and comprises two parallel belts: (1) Outer Zagros Ophiolitic Belt (OB) and (2) Inner Zagros Ophiolitic Belt (IB). These belts contain complete (if disrupted) ophiolites with well-preserved mantle and crustal sequences. Mantle sequences include tectonized harzburgite and rare ultramafic–mafic cumulates as well as isotropic gabbro lenses and isolated dykes within the harzburgite. Crustal sequences include rare gabbros (mostly in IB ophiolites), sheeted dyke complexes, pillowed lavas and felsic rocks. All Zagros ophiolites are overlain by Upper Cretaceous pelagic limestone. Limited radiometric dating indicates that the OB and IB formed at the same time during Late Cretaceous time. IB and OB components show strong suprasubduction zone affinities, from mantle harzburgite to lavas. This is shown by low whole-rock Al2O3 and CaO contents and spinel and orthopyroxene compositions of mantle peridotites as well as by the abundance of felsic rocks and the trace element characteristics of the lavas. Similarly ages, suprasubduction zone affinities and fore-arc setting suggest that the IB and OB once defined a single tract of fore-arc lithosphere that was disrupted by exhumation of subducted Sanandaj–Sirjan Zone metamorphic rocks. Our data for the OB and IB along with better-studied ophiolites in Cyprus, Turkey and Oman compel the conclusion that a broad and continuous tract of fore-arc lithosphere was created during Late Cretaceous time as the magmatic expression of a newly formed subduction zone developed along the SW margin of Eurasia.

/pdf/geodynamic-evolution-of-upper-cretaceous-zagros-ophiolites-1gno2ign5j.pdf

Geodynamic evolution of Upper Cretaceous Zagros ophiolites: formation of oceanic lithosphere above a nascent subduction zone

Volcanic activity focuses along plate boundaries. However, large volcanoes are also found in intraplate settings. For these volcanoes, geodynamic processes responsible for magma generation and structural controls on magma rise and extrusion need to be evaluated. We merge original (field and remote sensing) and available (geodetic, geophysical, and petrological) data to consider the tectono-magmatic relationships of three large intraplate volcanoes in the E-Anatolian-Iranian plateau; Sar'akhor (NE Iran), Damavand (Central Alborz) and Ararat (E Anatolia). In NE Iran, a Miocene-Pliocene NW-trending compression activated E-W dextral faults to the NW of Sar'akhor and N-S sinistral faults to the SE, creating an extruding wedge to the west of this volcano. Since Quaternary, NE-trending compression inverted fault movement, hindering further block extrusion and volcanism terminated. The adakitic composition of the Sar'akhor rocks suggests post-collisional melting of oceanic slab and/or mafic lower crust, possibly triggered by an asthenospheric rise after slab break-off or intramantle delamination. For the active Damavand and Ararat volcanoes, available data suggest magma generation due to rising hot asthenosphere, following lithospheric delamination or slab break-off in a transtensional environment. The features common to Sar'akhor, Damavand and Ararat allow proposing a model, where transtension focuses the rise of magma in intraplate settings overlying hot asthenosphere produced by delamination or slab break-off.

Structural control on volcanism in intraplate post collisional settings: late Cenozoic to Quaternary examples of Iran and Eastern Turkey

Eruptive rocks--their genesis, composition, classification, and their relation to ore-deposits; with a chapter on meteorites : Shand, S.J. London: Thomas Murby & Co. 1950. 479pp., illus., pls. 4th edition. 30s

This work applies a statistical methodology involving the calculation of success rates to evaluate a total of 28 tectonomagmatic discrimination diagrams: four bivariate (Ti/Y-Zr/Y; Zr-Zr/Y; Ti/1000-V; and Nb/Y-Ti/Y); six ternary (Zr-3Y-Ti/1000; MgO-Al2O3-FeOt, Th-Ta-Hf/3; 10MnO-15P2O5-TiO2; Zr/4-Y-2Nb; and La/10-Nb/8-Y/15); and three old (Score1-Score2; F1-F2; and F2-F3) and three sets of new discriminant function diagrams (each set consisting of five DF1-DF2 type diagrams proposed during 2004-2008). I established and used extensive geochemical databases of Miocene to Recent fresh rocks from island arcs, back arcs, continental rifts, ocean-islands, and mid-ocean ridges. Rock and magma types were inferred from a SINCLAS computer program. Although some of the existing bivariate and ternary diagrams did provide some useful information, none was found to be totally satisfactory, because success rates for pure individual tectonic settings typically varied from very low (1.1-41.6%) to only moderately high values (63.6-78.1%) and seldom exceeded them. Additionally, only "combined" tectonic settings were discriminated, or numerous samples plotted in overlap regions designated for two or more tectonic settings or even in areas outside any field. Furthermore, these old diagrams are generally characterized by erroneous statistical basis of closure problems or constant sum constraints in compositional data and by subjective boundaries drawn by eye. All such diagrams, therefore, should be abandoned and replaced by the new sets of discriminant function diagrams proposed during 2004-2010. These diagrams, especially those of 2006-2010 based on the correct statistical methodology and the boundaries drawn from probabilities, showed very high success rates (mostly between 83.4% and 99.2%) for basic and ultrabasic rocks from four tectonic settings and should consequently be adopted as the best sets of tectonomagmatic discrimination diagrams at present available for this purpose. Three case studies from Turkey (Kula, Eastern Pontides, and Lycian-Tauride) were also provided to illustrate the use of two new sets of discriminant function diagrams (2006-2008). For the Kula area, both sets of major- and trace-element based diagrams provided results consistent with a rift setting. For the Pontides area, trace-element based diagrams suggested an arc setting to be more likely, according to both basic and intermediate rocks. For the Lycian ophiolites, however, only the major-element based set of diagrams could be applied, and because of alteration effects, the tectonic inference between an arc or a MORB setting could not be decisive. A newer set of immobile element based, highly successful diagrams currently under preparation (2010) should provide a complementary set to the existing diagrams (2006-2008) for a better application of this important geochemical tool. Further work on these lines is still necessary to propose discrimination diagrams for other types of magmas such as those of intermediate silica compositions.

https://journals.tubitak.gov.tr/earth/issues/yer-10-19-2/yer-19-2-3-0901-6.pdf

Statistical evaluation of bivariate, ternary and discriminant function tectonomagmatic discrimination diagrams

The Nain ophiolite is a highly dismembered ophiolite complex cropping out at the north of the Nain town to the west of central Iran. The igneous rocks of this complex consist of both mantle and crustal suites and include serpentinized peridotites, peridotites, harzburgites associated with dunite and lherzolite, pegmatitic and isotropic gabbros, plagiogranites, sheeted dikes and pillow lavas. Several pyroxenite, wehrlite and rodingite dikes are present in the ultrabasic rocks. The sheeted dikes include subalkaline basalts, basaltic andesites and andesites. Their magma was of sub-alkaline (low potassium tholeiite) type and they are chemically similar to island arc tholeiitic basalts. The N-MORB-normalized incompatible elements for the sheeted dike samples indicate depletion in most of the high field strength elements (HFSE). The concentrations of the large ion lithophile elements (LILE) in these rocks are all greater than those in the N-MORB. Significant chemical characteristics of the these rocks are the positive anomaly for Th and negative anomaly of Nb that are considered to represent a subduction zone component. The chondrite-normalized rare earth element (REE) patterns of these rocks show HREE enrichment and LREE depletion [(LaN/SmN)ave = 0.63]. Their geochmistry also shows that the primary melt derived from high degrees of partial melting of a mantle source previously depleted with respect to the source of mid-ocean ridge basalts, and were subsequently enriched by aqueous fluids driven off subducted oceanic lithosphere in an arcbasin setting. We conclude that the Nain ophiolite is a supra-subduction zone type ophiolite.

Geochemistry of sheeted dikes in the nain ophiolite (central iran)

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.%), P2O5 (

https://digital.csic.es/bitstream/10261/216437/1/Garrido_C_GeoscienceFrontiers.pdf

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

Pliocene–Quaternary Adakite volcanism in the Isfahan area, Central Iranian magmatic belt

Late Miocene–Pliocene to Quaternary calc-alkaline lava flows and domes are exposed in southeast of Isfahan in the Urumieh Dokhtar magmatic belt in the Central Iran structural zone. These volcanic rocks have compositions ranging from basaltic andesites, andesites to dacites. Geochemical studies show these rocks are a medium to high K calc-alkaline suite and meta-aluminous. Major element variations are typical for calc-alkaline rocks. The volcanic rocks have SiO2 contents ranging between 53.8% and 65.3%. Harker diagrams clearly show that the dacitic rocks did not form from the basaltic andesites by normal differentiation processes. They show large ion lithophile elements- and light rare earth elements (LREE)-enriched normalized multielement patterns and negative Nb, Ti, Ta, and P. Condrite-normalized REE patterns display a steep decrease from LREE to light rare earth elements without any Eu anomaly. These characteristics are consistent with ratios obtained from subduction-related volcanic rocks and in collision setting. The melting of a heterogeneous source is possible mechanism for their magma genesis, which was enriched in incompatible elements situated at the upper continental lithospheric mantle or lower crust. The geochemical characteristics of these volcanic rocks suggested that these volcanic rocks evolved by contamination of a parental magma derived from metasomatized upper lithospheric mantle and crustal melts.

Geochemical constraints on the genesis of the volcanic rocks in the southeast of Isfahan area, Iran

Mineral chemistry of the ultramafic and mafic cumulates in the eastern part of the Sabzevar ophiolite (NE Iran): evidence for formation of high pressure cumulates in thickened arc crust

Moussa Noghreyan

Papers

Geochemistry of sheeted dikes in the nain ophiolite (central iran)

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

Pliocene–Quaternary Adakite volcanism in the Isfahan area, Central Iranian magmatic belt

Geochemical constraints on the genesis of the volcanic rocks in the southeast of Isfahan area, Iran

Mineral chemistry of the ultramafic and mafic cumulates in the eastern part of the Sabzevar ophiolite (NE Iran): evidence for formation of high pressure cumulates in thickened arc crust