M. Heidari; Ghasem Ghorbani; H. Shafaii Moghadam
Abstract
Abstract Forumad area is located in NW of Sabzevar, in NE of central Iran structural zone and in western part of Sabzevar ophiolite suite. The mantle section of Forumad ophiolite consists mainly of harzburgites, dunites, pyroxenitic dikes and choromititic lenses that contain brown to black Cr-spinels. ...
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Abstract Forumad area is located in NW of Sabzevar, in NE of central Iran structural zone and in western part of Sabzevar ophiolite suite. The mantle section of Forumad ophiolite consists mainly of harzburgites, dunites, pyroxenitic dikes and choromititic lenses that contain brown to black Cr-spinels. The content of Cr2O3 and Al2O3 of Cr-spinels in harzburgites are between 32.6-53.1 and 15.6-34.8 wt%, respectively, and their Cr# ([100 × Cr/(Cr + Al]) atomic ratio]) is between 39- 69%. Relationship between Cr# of Cr-spinels and Fo of coexisting olivine (Fo=91-92%) and low contents of TiO2 (
R Kohansal; M Ghorbani; S.M Pourmoafi; M Khalatbari Jafari; J Omrani; S Zolfaghari; S Soleimani
Abstract
Abstract The Forumadophiolitic rocks as a part of Iran marginal microcontinentophiolites have been situated in the western part of Sabzevarophiolite. Field study shows extrusive sequence in this area with Late Cretaceous in age. This sequence has included basaltic pillow lavas with radiolarian chert ...
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Abstract The Forumadophiolitic rocks as a part of Iran marginal microcontinentophiolites have been situated in the western part of Sabzevarophiolite. Field study shows extrusive sequence in this area with Late Cretaceous in age. This sequence has included basaltic pillow lavas with radiolarian chert related to Late Turonian-Santonian, in contrast to Coniacian- Late Campanian age, when this sequence has composed of basaltic pillow lavas in lower - middle part and various tuffs in upper part. Sheet flows, hyaloclasticbreccias and pelagic limestone are intercalations between lavas and tuffs.Abundantly, pillow lavas with phyric texture are most predominant feature contrast with sheet flows. Whereas enrichment of LILE and depletion of some HFSE (Nb, Ta) exhibit subduction environment (island arcs) for pillow lavas of Forumad, and different enrichment in LREE to HREE displays unhomogenous mantle in the generation of them; the presence of two magmatic nature in lavas (tholeiitic and calc-alkaline), their positions in tectonomagmatic diagrams and clear enrichment of Th element in Late Turonian –Santonian lavas which are generally exhibition of ophiolitic extrusive sequence in Forumad area have been generated in a supra-subduction environment and back-arc basin.
M Khalatbari Jafari; M Ghani
Abstract
In northwest Sabzevar the exposed extrusive sequence and supraophiolite series have interbedded pelagic limestone containing Late Cretaceous microfaunas. The extrusive sequence comprise of hyaloclastic breccia, tuff and sheet flow in lower part, aphyric and vesiculated pillow lava in middle part ...
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In northwest Sabzevar the exposed extrusive sequence and supraophiolite series have interbedded pelagic limestone containing Late Cretaceous microfaunas. The extrusive sequence comprise of hyaloclastic breccia, tuff and sheet flow in lower part, aphyric and vesiculated pillow lava in middle part and volcanic sedimentary rocks upwards. The supraophiolite series contain alternations of volcanogenic sediments, turbidites and lavas. The study of chemical analyses of the lavas of the upper part of extrusive sequence and the lavas of supraophiolite series indicate similar geochemical affinity. These lavas have calc alkaline character and show clear depletions of Nb and definite depletions of Zr and Ti in the patterns of spider diagrams. In tectonomagmatic diagrams, they plot in the realm of subduction zone suggesting their formation above the subducted slab. Slight changes of HREE in the patterns of spider diagram can be attributed to partial melting of depleted mantle wedge which influenced by subduction components (fluids- melt) released from subducted slab causing enrichments of LREE. In comparison, the sheet flow and pillow lave of the lower and middle parts of extrusive sequence have OIB character without depletion of Nb, Zr and Ti. The patterns of their spider diagrams show enrichment of LREE indicating low partial melting of garnet-bearing enriched mantle. It seems a period of extension or arc rifting or slab roll-back have occurred before the arc is well developed. These process formed back-arc basin located close to arc. In this stage, arc magmatism stopped and caused the mantle plumes rising. It seems that the extrusive sequence exposed in northwest Sabzevar formed in transitional zone between arc to back-arc in Late Cretaceous.
M Khalatbari Jafari; M Mirzaie; M. R Jannessary
Abstract
The plutonic crustal sequence of Garagoli-Bagjar, located in NE Sabzevar, is a part of ophiolitic association in the outer part of Central Iran microcontinent. This sequence comprises cumulative olivine gabbro, pyroxene gabbro, isotropic gabbro, foliated gabbro and diabasic sheeted dike complex, cross ...
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The plutonic crustal sequence of Garagoli-Bagjar, located in NE Sabzevar, is a part of ophiolitic association in the outer part of Central Iran microcontinent. This sequence comprises cumulative olivine gabbro, pyroxene gabbro, isotropic gabbro, foliated gabbro and diabasic sheeted dike complex, cross cut by the wherlitic intrusion, pegmatite gabbro and plagiogranite as small bodies, dikes and veins. This sequence is comparable to upper gabbroic part of the well known ophiolite complex. These rocks construct a large tectonic slics thrusted over the serpentinized peridotites and tectonically located under serpentinites. The cumulative gabbros change gradually to isotropic gabbro upwards and at the same time isotropic gabbro change generally to diabasic sheeted dike complex. The structural measurements of magmatic layering and strike of sheeted dikes, wherlitic intrusions, pegmatite gabbro and plagiogranite revealing E-W direction in the north of Qaragoli and N-S direction in SW Solymanieh might be comparable to the formation of plutoinc oceanic crust in fractures zone. The microscopic studies exhibit that mesocumulate to heteradcumulate textures are abundant which indicate the open magmatic chamber of the supra-subduction zones. The crystallization trends show diversity from olivine-plagioclase-clinopyroxene-orthopyroxene-amphibole trend (MORB like) to olivine-clinopyroxene-orthopyroxene-plagioclase-amphibole trend (as arc type). The study of the chemical analyses indicates diverse compositions and primitive mantle normalized spider diagrams show depletion of Nb with different enrichement of LREE. The low-Ti character, locations in arc related cumulate and non cumulate fields, island arc to MORB tectonomagmatic setting remark their supra-subduction origin which formed in Late Cretaceous.
M. Khalatbari Jafari; H. Sepehr
Abstract
The south Dehshir tectonized Ophiolite located at the extreme northern part of Sharbabak-Dehshir Ophiolite belt comprise of mantle peridotite and crustal sequence. The mantle peridotites are well serpentinized and consist of cpx- bearing harzburgite and lherzolite, cross cut by isolated diabasic dikes. ...
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The south Dehshir tectonized Ophiolite located at the extreme northern part of Sharbabak-Dehshir Ophiolite belt comprise of mantle peridotite and crustal sequence. The mantle peridotites are well serpentinized and consist of cpx- bearing harzburgite and lherzolite, cross cut by isolated diabasic dikes. There is no layered gabbro in the crustal sequence and that comprise of high level isotrope gabbro with cumulative character which gradually change to diabase sheeted dike complex on top of the sequence intruded by wherlitic intrusion, quartz diorite, pegmatite gabbro and plagiogranite- tronjemite. The volcanic sequence of this association consist of alternation of chert, radiolarite, pelagic limestone have Upper Cretaceous microfaunas at base and hyaloclastic breccia, hyaloclastite, tuff and pillow lava on top the sequence. The sheeted dike complex oriented in N- S direction with couples of inclinations toward either the east or the west. Listvenite and rodingite are the sporadic metasomatic rocks that expose inside the tectonized assemblage. A few dislocated amphibolites and calc-silicate blocks are tectonically exposed. Base of chemical analyses the crustal sequence show variety in composition and have tholeitic to calc-alkaline trends. In the tectonomagmatic diagrams, these rocks are often placed in the regions associated with the volcanic arcs and in some occasions they are plotted in the oceanic basin regions. The primitive mantle-normalized spider diagrams show depletion of Nb in most of analysis and depletion of Zr and Ti in some of them which indicating a supra- subduction origin. These types of patterns located in different levels and characterized by enrichment of LILE, might be related to diversity in mantle source and different degree of partial melting. The behavior of elements in different diagrams and comparation with the different tectonic setting, show that they tend located far from MORB type and near by the Arc type. The values of the elements such as Ba, Th, Nb, Yb, indicate the influence of the fluids releaved from the subducted slab on the mantle wedge. These geochemical characters and the expose of wherlitic intrusions and the small intrusions of quartz diorite-quartze monzodiorite indicate that the South Dehshir tectonized Ophiolite display a consistent sequence of events during their formation and evolution, includes birth, youth and maturity stages which is a natural consequence of the Supra- subduction zones. It seam that the Dehshir Ophiolite formed in a forearc basin with a distance from margin could be interpret with the downgoing of Neo-Tehytis in Late Cretaceous.
M. Khalatbari Jafari; M. Ghani
Abstract
The extrusive sequence exposed in the vicinity of Gez village located in the NW Sabzevar, comprises a diversity of rocks which could be divided in three main parts. The lower part contains abundance hyaloclastic breccia and tuff, and the middle part comprises vesicular pillow lava and the upper part ...
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The extrusive sequence exposed in the vicinity of Gez village located in the NW Sabzevar, comprises a diversity of rocks which could be divided in three main parts. The lower part contains abundance hyaloclastic breccia and tuff, and the middle part comprises vesicular pillow lava and the upper part has an alternation of sheet flow and volcanic-sedimentary rocks. The intercalations of pelagic limestone have Late Cretaceous microfouna. The abundant of hyaloclastic breccia-tuff, sheet flow and aphyric vesicular pillow lava versus phyric pillow lava indicate the formation of this sequence in the fast spreading rate. The supra-ophiolite volcanic-sedimentary rocks located in the Afchang area contain an alternation of turbidites with lava flow, phyric-aphyric lava, chert-radiolarite and pelagic limestone. The paleonthology studies of those revealed Late Cretaceous age, which suffer this idea that the supra-ophiolite serie formed in a trough juxtapose the Sabsevar oceanic crust at Late Cretaceous. Based an geochemical data, the sheet flow of lower part and the pillow lava of the middle part show OIB characters but the lava flows of the upper part of extrusive sequence and the phyric, aphyric and lava flow of supra-ophiolite serie are depleted in Nb and slightly depleted in Zr could be comparable with subduction volcanism. Study of the tectonomagmatic diagrams verifies the OIB and island arc tendency and seems that the generation of the magma of the lower and middle parts influenced by mantle plumes. The magmatic source of the upper part of extrusive sequence and supraophiolite lavas is depleted which have different enrichement from the subduction components (fluids-melt) released from subducted slab. The tectonomagmatic setting of extrusive sequence and supra-ophiolite series can be justified with the senario of general subduction of oceanic slab beneath the centeral Iran microcontinent during Upper Crtaceous, towards in a back-arc basin.
M. Khalatbari Jafari; H. Sepehr
Abstract
The Kahduiyeh tectonized Ophiolite exposed at the extreme northern part of Dehshir-Baft Ophiolite belt in the southern margin of centeral Iran microcontinent, comprise of mantle peridotites and crustal sequence. The serpentinized peridotites have cpx- bearing harzhburgite and lherzholite compositions ...
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The Kahduiyeh tectonized Ophiolite exposed at the extreme northern part of Dehshir-Baft Ophiolite belt in the southern margin of centeral Iran microcontinent, comprise of mantle peridotites and crustal sequence. The serpentinized peridotites have cpx- bearing harzhburgite and lherzholite compositions which cross cut by diabase isolated dikes. The plutonic part of crustal sequence consist isotropic gabbro, diabase sheeted dike complex, intruded by wherlitic intrusion, quartz diorite, pegmatite gabbro and plagiogranite-tronjemite. The volcanic sequence consist of the intercalation of the chert and radiolarite, pelagic limestone have the Upper Cretaceous micro faunas at base of sequence and hyaloclasic braccia, hyaloclastite, sheet flow, tuff and pillow lave on top of the sequence. Study of chemical analysis indicating a supra-subduction origin and enrichments for REE, Rb, Ba and Th might be affecting of slab-derived fluids. It seem that Kahduiyeh tectonized Ophiolite display a consistent sequence of events during their formation and evolution, includes birth, youth and maturity stages which is a natural consequence of ophiolite formation in the Supra-subduction zones.
