جستجوی مقالات مرتبط با کلیدواژه « زمین درز سیستان » در نشریات گروه « زمین شناسی »

Based on geological classification of Iran, they are belong to the Sistan Suture zone (SSZ). These dykes have different trends but usually northwest-southeast trend, with a several kilometers at the length and an average five meters the width. They are usually folding and often have sharp border with the host rocks, and a lot of to different make of metamorphosed surrounding rocks. They are mainly diorite to granodiorite and similar extrusive in composition, and have been formed of mainly Plagioclase, biotite, hornblende and varying amounts of quartz minerals. These dyke have usually Porphyry to microgranular textures. Based on geochemical data they are calk-alkaline, high potassium calk-alkaline and meta-aluminous to peraluminous. They are enrichment from Zr, Rb, Sr, Br elements and depleted from V, Ni, Co elements compared to Chondrite references. These dykes are enriched from light rare earth element (LREE) to High rare earth elements (HREE), compared to Chondrite and primitive mantle. Eu/Eu* ratio changes between 0.99-1.2. Tectonomagmic and petrogenesis diagrams shows that they are belonging to subduction and late post collision zones. They have an amphibolite sources and geochemically formation similar to Zahedan granitoid environment. Therefore, it seems that the magma forming these dykes, similar to the Zahedan granite, was formed from the mantle wedge above the subduction plate of the Neotethys ocean under Central Iran plate after to shortly after the collision.

In Tighanab area at southeast of Sarbisheh, the intrusion of quartzdioritic subvolcanic bodies into the Paleocene- Eocene limestone and sandstone led to the skarn formation. Plagioclase, hornblende (magnesiohornblende) and quartz are the main minerals in the subvolcanic rocks. Base on microprobe analyses, the composition of plagioclases with 15-45% anorthite content varies from andesine to oligoclase. The pressure during mineral crystallization of the Tighanab quartzdiorite porphyry is about 5.27kbar and its average temperature, on the basis of thermometry with coexisting hornblende and plagioclase, was obtained about788ºC. The Tighanab exo- skarn are characterized by the presence of garnet, epidote, pyroxene (diopside), calcite, chlorite, quartz, magnetite, pyrite, hematite and gypsum. The studied garnets belong to the calcic category and are of the andradite- grossular solid solution type. The composition of andradite varies slightly whereas the grossular constituents, to some extent, are uniform. The occurrence of andradite as well as its compositional changes represents high oxygen fugacity and Fe3+/Al ratio changes respectively, during the garnet crystallization. The presence of andradite, diopside- rich pyroxene and the over abundance of garnet relative to pyroxene in the studied skarn indicates oxidant conditions and correspond with the results of amphibole chemistry study in generating skarn quartz diorite porphyry. The lack of wollastonite in exo- skarn can be indication of garnet clinopyroxene crystallization at temperatures below 550 °C by metasomatizing solutions.

Garagheh granitoid is located in the northwest Zahedan batholite and is exposed in Zahedan-Saravan granitoid belt and Sistan suture zone. This granitoid is composed of granite (synogranite, monzogranite) and granodiorite. These rocks have mainly consist of plagioclase, orthoclase, microcline, quartz, biotite and hornbelend with granoular texture. This pluton cut by microdioritic dykes. Garagheh granitoid have metapellitic enclaves with enrich from quartz and mica minerals with granoular texture. This granitoid is calc-alkaline, metalluminous, with (I) and slightly to S typs, enrichment from in LREE and LILE and depleted from in HREE and HFSE. Tectono magmatic diagrams show Garagheh granitoid is related to active continental environments. Positive anomalies in K and Cs elements and negative anomalies in Zr, Sr, and Ti elements show patterns similar to the subduction environment. Based on the Sr/Y versus Y and FeOt+MgO+TiO2+ Al2O3 versus Al2O3/FeOt+MgO+TiO2 digrams, it is thought that the constituent magma of this pluton is similar to the Zahedan granite due to the melting of amphibolite source, that resulted during closure of the Neothytean ocean east of Iran, located between the Lut and Helmand plates, during the Eocene-Oligocene to Miocene times.

Tahlab ophiolite is located at the Southeastern of Taftan volcano and the Sistan suture zone. This ophiolite (Upper Cretaceous) exposed in the Flysch zone (Eocene). Harzburgites and gabbro's rocks are main part of this ophiolite that studied in this article. Ultramafic rocks have olivine and pyroxene minerals.  Mafic rocks have plagioclase, pyroxene and olivine minerals. Serpentine and chlorite have secondary minerals. They are dominant granular, ophitic and sub-ophitic textures. All of REE elements in spider diagrams compared to enrichment mantle have low depletion in HREE and low enrichment to LREE, relatively flat slope, and more similar to E-MORB. Transition elements diagrams (V, Co, Cr, Ni) in against to La / Ce ratio show that differentiation of olivine mineral. High Mg number in the samples (42.91 to 86.02) shows that magma resulted from partial melting from mantle. Also (La/Sm) N in the samples are between 1.37 to 0.34 that show they are mantle source.  Tectonomagmatic diagrams shows Tahlab ophiolite has belonging to extensional oceanic intraplate, so it seems this ophiolite formed by subduction of Neothytean oceanic during Cretaceous between Lut and Afghan blocks.

Large benthic foraminiferas in Paleogene of Tethyan basin widley distributed that still remain poorly identified in the eastern Tethys specially in the southeastern of Iran. Based on systematic determination of LBFs 12 genera and 24 species in the Late Paleocene-Early Eocene interval are known that are Ranikothalia, Discocyclina, Miscellanites, Miscellanea, Kathina, Idalina, Assilina, Vania, Glomalveolina, Daviesina and Lockhartia. The base of SBZ3 biozone is defined by the first Occurence of Miscellanea juliettae, Miscellanites minutus, Miscellanites primitivus, Vania anatolica, Glomalveolina primaeva, Glomalveolina telemetensis, Glomalveolina dachelensis, Discocyclina seunesi, Ranikothalia sindensis, Ranikothalia tubleri, Kathina selveri. With respect to its high abundance and limited biostratigraphic range of above mentioned species (except Ranikothalia sindensis  and  Kathina selveri) can be taken as an index fossils of SBZ3. The base of SBZ4 biozone is defined by the first appearance of Discocyclina ranikotensis, Daviesins langhami, Miscellanea miscella which among them Ranikothalia  sindensis, Miscellanea miscella and Daviesina langhami appear in high abundance and widley distributed. It is mentioned that Miscellanites primitivus, in the studied section,is continued to SBZ5/6.SBZ5/6 biozone is defined  by Lockhartia haemei, Ranikothalia nuttalli, Ranikothalia sp., Assilina dandotica, Discocyclina dispansa and Discocyclina sella. Species of   Ranikothalia nuttalli, Assilina dandotica and Ranikothalia sindensis has high abundance and wide distributions. it is mentioned that in the some part of the eastern Tethys such as Tibet Daviesina genus has disappeared in the SBZ5/6 whilst in the studied sections has high abundance although  Alveolina vredenburgi  is not seen and Miscellanea miscella has low distribution regard to SBZ4. In the studied section, Earliest Eocene Large Benthic Foraminifera (SBZ5/6) predominantly consists of Ranikothalia and Miscellanea while the new Foraminifera assemblage that’s appear in the other locations (such as Assilina, Alveolina and Discocyclina) are less important and Nummulites are absent. In continuation of Early Eocene, gradual diversity of species of Discocyclina، Operculina and Assillina has occurred, whilst Ranikothalia is disappeared and Miscellanea  in the end of SBZ5/6 is less important. Similarity Larger Benthic Foraminifera assemblage in the other part of eastern Tethys especially India and Pakistan are recorded. Therefore this assemblage in the eastern Tethys are different from western Tethys.

The Tighanab area is located in the Southern Khorasan province and 104km south-east of Sarbisheh, in the eastern part of Sistan suture zone (Tirrul et al., 1983). The Sistan suture zone has formed as a result of collision between the Lut and Afghan blokcs and its closure time is related to upper Cretaceous era (Bröcker et al., 2013). Eocene-Oligocene magmatism in eastern Iran (Lut-Sistan) crop out as volcanic rocks, pyroclastic and subvolcanic rocks (Pang et al., 2013) which have caused skarn mineralization in some parts. The relationship between skarn mineralization and adakites has been discussed by various researchers (Lei et al., 2018). Skarn deposits and their associated Cenozoic plutonic rocks in Iran, have outcrops in northwest, central and southeast of the Urumiyeh-Dokhtar magmatic belt, Sabzevar-Dorouneh magmatic belt and the eastern Iran magmatic belt (Sepidbar et al., 2017). The Tighanab subvolcanic bodies play an important role in skarn mineralization.This research study is carried out for studying petrography, geochemistry and tectonic setting of subvolcanic bodies and their role in skarn mineralization since geochemistry and petrology of the mentioned masses have not been studied.

This research is based on field observations, thin sections, polished thin section studies and chemical analysis of samples. In this regard, 90 thin sections were prepared and studied by microscope. Then, 11 samples of subvolcanic rocks with the least alteration were selected. Then they were crushed and powdered. Next, they were analyzed by the ICP-ES method for major elements and the ICP-MS method for trace and rare earth elements. The magnetic susceptibility of the samples was measured by SM20 magnetic sensitivity device at university of Birjand.

The study area is located in the eastern part of the Sistan suture zone and the Mahirud geological map (1:100000). Quartzdioritic subvolcanic rocks intruded the Paleocene-Eocene limestone and sandstone and formed iron skarn mineralization. The main textures in quartz diorite porphyry are porphyry with microgranular groundmass and poikilitic. Plagioclase, hornblende and quartz are the main constitutes of these rocks. Plagioclase phenocrysts have polysynthetic twinnig, zoning and resorption rim and are andesine and rarely oligoclase based on extinction angle. Different geochemical diagrams show correlation between the Tighanab igneous rocks and intrusions associated with iron skarns. Geochemical features as mean of SiO 2 (64.48%), Al 2 O 3 (16.68%), Sr(470ppm), Y(8.9ppm), Sr/Y(55.58), Yb(0.89ppm) and poor negative anomaly of Eu are representative of high silica adakitic features for these rocks. The amount of Mg#(55.48-68.1), Sr/Y(mean55.58), Th/La(mean0.32), La/Yb N .(4.2) and Th(mean1.8ppm) indicate oceanic crust melting with garnet-amphibolite composition to generation of adakitic magma.

Field evidence, mineralogy, and magnetic susceptibility measurements show that granitoids of the Tighanab area belong to the magnetite series. Based on tectonic discrimination diagrams, the intermediate samples of the Tighanab area are located in the range of VAG and VAG + Syn-COLG. The studied rocks show depletion of HFSE such as Ti, P, Nb, Yb, Y and enrichment in LILE that indicates their association with the subduction environment. Negative anomaly of HFSE may be a result of contamination of magma by crustal materials during ascent and emplacement in subduction zones. Comparison of some major and trace elements of Tighanab samples with adakites indicated that these rocks have high silica adakitic nature. Geochemical evidence shows that the studied rocks are similar to the rocks associated with iron skarns. Some geochemical characteristics such as HREE and HFSE depletion, high Sr, Sr/Y and (Gd/Yb) N >1 and poor negative anomaly of Eu in the studied samples, indicate that the adakitic magma has been formed at pressures above the plagioclase stability. The geochemical characteristics of the studied samples, such as low Y and high Sr/Y ratio, indicate the presence of garnet in the origin of these rocks (Mao et al., 2018). Trace and rare element diagrams show that adikatic magma of the Tighanab area subvolcanic rocks have been produced by melting of the oceanic slab. Adakitic rocks of the Tighanab area have been formed from a source with 10 to 25% garnet amphibolites composition.

Siahjangal ophiolite is located in the North and Northeastern part of Taftan volcano in the Sistan Suture Zone (SSZ). This ophiolite (Upper Cretaceous) is exposed in the Flysch rocks (Eocene). Harzburgite, lherzolite, serpentine, spilite and gabbro are major rocks in this ophiolite. Ultramafic units have olivine, orthopyroxene and clinopyroxene minerals. Mafic units have clinopyroxene and plagioclase. Ultramafic rocks have mainly granular and gabbro rocks have ophitic, sub-ophitic and granular textures. Geochemical verities of major, minor and rare earth elements in the Siahjangal ophiolite revealed that the ultrabasic and basic rocks were formed due to partial melting than crystal differentiation. REE elements diagrams normalized to the Chondrite and MORB and their comparison with the normal and enriched MORBs, chemical differentiation diagrams, the ratios of accessory elements and changes of Zr, Nb, Y, U, Ti elements against Zr / Nb ratio all indicates the similarity to N-MORB. Transition elements diagrams (V, Co, Cr, Ni) against La / Ce ratio and the ratio of (La / Yb) N, La / Yb, La / Ce versus (La / Sm) N, show that these ratios compared with N-MORB and E-MORB represent enrichment and geochemical similarities to N-MORB. Tectonomagmatic diagrams show Siahjangal ophiolite belongs to supra-subduction zone.

Deformed rock units in Tutak and Mahirud regions in northern part of Sistan suture zone include ophiolite, igneous and sedimentary rocks. In this research, based on microstructures and by using Rf /Ф and shear strain methods, finite strain and vorticity analyses were carried out on both sections. The estimated values of mean strain ellipsoid shape (K-value) for both A and B sections are 0.67 and 0.78 respectively, which show flattening strain shape on the modified Flinn diagram and reveal a transpressional regime in the study area. The mean kinematic vorticity evaluated amounts for both A and B sections are 0.51 and 0.71 respectively.
Likewise, the relative contributions of the pure shear component with respect to the simple shear component are 66 to 34 percent for section A; whereas both pure and simple shear components for section B are 50 percent. These results confirm pervious study in this area which mentioned the amount of simple shear components decreased to the termination (to the north) of suture zone.

The Rigmalak granitoid is located East of Taftan volcano, southeast of Zahedan, in Sistan Suture Zone.This pluton (Oligo-Miocene) has intruded into Eocene Flysch deposidt and cause low metamorphism in the borders. This pluton is composed of granite, synogranite, monzogranite, granodiorite, tonalite, pegmatitie and diorite in composition. The main minerals in this pluton are quartz, plagioclase, orthoclase, biotite and hornbelande and they are mainly granoular to pegmatitic in texlures. Presence of biotite and hornbelends minerals in this granitoides show that it is simillar to Zahedan granitoid and it is belonging to I type granite.  Geochemical studies show that these rocks have calcalkaline to low alkaline magmatic series and metaluminous, I type, enrichment from LREE and LILE and depleted from HREE and HFSE. Major, rare and trace elements digramas of shows crystal defferintation is important role the formation pluton. Digrams normalized to chondorite and primitive mantle show that rocks formed this pluton are enriched in LREE to HREE and dominantly simillar and parall trends. Also, Zr and Th elements show positive anomalyes and Sr, Nb and Ti negative anomalyes, similar to subduction zones.Tectono magmatic diagrams show Rigmalak granitoid rocks related to syncollision to low post collision environments. Geochemical evidence of Rigmalak samples showed that crystal differentiation was not the only effective process in the formation of magma but may be several phases or melting of a phase with different degrees also may happened in the region. It seems that the formation of this granitoid in the Sistan suture zone is related to the collisions between Lut and Afghan blocks.

Miscellaneidae are Paleogene larger index microfossils (Middle Paleocene–Early Eocene) that are important for biozonation of shallow marine deposits. These large benthic foraminifera have distinct architecture and ornamentation schemes which differentiated them form Nummulitidae and Rotalidae families. Miscellaneidae have different taxa that essentially are usefulness for biostratigraphic and palaeobiogeographic investigations. For biostratigraphic studies, age and systematic determinations of miscellaneidae, Middle Paleocene–lower Eocene deposits of two outcrop sections are investigated in the Padagi village in the north of Zahedan. These stratigraphic sections mainly consist of alternation of marls, marly limestones and limestones with 237.5 m thickness for PE section and 222.5 m thickness for PEP section. Study of different Misellaneidae genera led to identifications of Miscellanea miscella, Miscellanea juliettae, Miscellanites primitives and Miscellanites minutus that shows standard biozone SBZ3–-SBZ6 and therefore suggested Late Paleocene–-Early Eocene age. Moreover, global distribution patterns of older species of Miscellaneidae represents that these species belong to the eastern Tethys basin.

Ardakol fault with the length of 125 km and dextral strike-slip mechanism is located in the northern part of Sistan suture zone. This fault caused an earthquake with the magnitude of 7/3 Mw in the region on 10/05/1997 and caused the longest coseismic rupture associated with earthquakes in recent Iranian centuries. Comparison of seismic moment, geological and geodetic values shows that the changes in moment ratio are directly related to the length of the fault, as the length of the fault increases, the moment increases as well, and as a result it releases higher levels of energy. The study of the moment and fractional changes for the Ardakul fault shows that the energy released rate in the northern part is higher than that of the southern section, which means that in the northern parts, more earthquakes occur and therefore the number of active faults is larger. In general, the seismic moment of the Ardakol fault is decreasing from north to south and as a result, more energy is stored in the South or deformation in the southern part, so, southern parts are in danger of more earthquakes.

The Heydarabad ophiolitic mélange is hosted in the Sistan suture zone, which marks the boundary between the Lut and the Afghan continental blocks and comprises of mantle peridotites and crustal sequence. The studied mantle peridotites are dominated by harzburgite and clinopyroxene-rich harzburgite that formed in mid-ocean ridge (MOR) setting. These mantle peridotites, due to the effect of hydrothermal solutions, have been altered. Moreover, iron-copper mineralization developed by the influence of hydrothermal fluids moving through the fractures and the faults. The textures and structures of mineralization formed as open space filling, disseminated, vein-veinlet and replacement. Two important stages could be recognized for the mineralization in this area. The first stage includes processes, which caused the development of sulphide mineralization in the mantle peridotites. The second stage is related to oxide fluids, which led to magnetite mineralization.Based on detailed electron microprobe study, olivine, orthopyroxene, clinopyroxene and spinel are the essential rock forming-minerals of the rocks under study. Most of the olivines from the mantle peridotites are serpentinized but some, with forsterite composition, are fresh. The composition of the ortho- and clinopyroxenes is enstatite and diopside respectively and the spinels are classified as Al-rich Cr-spinel type.

The Gapdan granitoid is located in the southwestern margin of Zahedan granitoid and in the Sistan suture zone. The granitoid under study is composed of granite, monzogranite, granodiorite, pegmatite and diorite. These rocks consist mainly quartz, plagioclase, orthoclase, biotite and hornblende with granular and pegmatite textures. This pluton has intersected by andesitic to dacitic dykes with similar mineralogy with those of the Gapdan granitoid, but they have microlitic and microlitic porphyry textures indicating their formation at a shallow depth and sub-volcanic conditions. The Gapdan granitoid is characterized by metapelitic enclaves with dark-colored and irregular edges with their host pluton and are often enriched in quartz and mica minerals and usually granular texture. Geochemical studies show that the study rocks have calcalkaline to low alkaline magmatic series and metaluminous, I type, LREE and LILE enrichment and depleted in HREE and HFSE. These geochemical characteristics share with those of continental arcs. The amount of Nb / Ce (ave. 0.27) and Nb / La (ave. 0.58) ratios indicate the effect of crustal on the evolution of the Gapdan granite. Tectono magmatic diagrams show the Gapdan granitoid rocks related to syncollision to low post collision environments. According to geochemical data, the study granitoid rocks possibly originated by the rising residual melts from partial melting of oceanic crust (Neo-Tethys) during the collision between the Lut and the Sistan blocks (particularly the Sistan oceanic crust and the mantle wedge overlying it). The continental crust (Flysch and greywake metamorphosed deposit) has been affected the contamination of magma and its formation in post collisional tectonic regimes. Therefore, the Gapdan granitoid may be considered as a hybrid granite type.

Khunik Duplexes located at 18 kilometers south of the city of Qayen and terms of tectonic located in the northern part of Sistan suture zone. Khunik duplex performance in a strike-slip fault with a length of 6 km and a geometric mechanism N150 / 73NE and Reak24NW formed. Based on the perceptions and learn measure used, duplex of Khunik of three horses (Horse) formed from the northeast to the southwest on each pushed (due to shrinkage young horses). Interpretations of existing faults around and on duplex (N51 / 13) and folds around the duplex (N36 / 1), to stress the duplex, which represents a regional NE-SW West. Folds study area have thrust to the North East that is consistent with the thrust duplex Khunik (according to the hinterland and foreland and orientation are duplex). The shortening rate based on parameters the amount of 57% (196.5 m) on the duplex of Khunik shows a better correlation with the value obtained from laboratory modeling. According to data obtained from the model break back duplex Khunik follow.

IntroductionBasaltic volcanoes are one of the volcanisms that have occurred in different parts of the world. The study of these lavas is important for petrologists, because they are seen in different tectonic settings and therefore diverse mechanisms affect their formation (Chen et al., 2007). Young volcanic rocks such as Quaternary basalts are one of latest products of magmatism in Iran that are related to deep fractures and active faults in Quaternary (Emami, 2000). The study area is located at 140km east of Birjand at Gazik 1:100000 geological map (Guillou et al., 1981) and have 60̊ 11' to 60̊ 15 '27" eastward longitude and 32̊ 33' 24" to 32̊ 39' 10" northward latitude. On the basis of structural subdivisions of Iran, this area is located in the northern part of the Sistan suture zone (Tirrul et al., 1983). Because of the importance of basaltic rocks in Sistan suture, this research is done with the aim of investigating the petrography and mineralogy of basaltic lavas, the nature of basaltic and intermediate magmatism and finally determination of tectonomagmatic regime.
Materials and methodsAfter field studies and sampling, 85 thin sections were prepared and carefully studied. Then ten samples with the lowest alteration were analyzed for major elements by inductively coupled plasma (ICP) technologies and trace elements were analyzed using inductively coupled plasma mass spectrometry (ICP-MS), following a lithium metaborate/tetraborate fusion and nitric acid total digestion at the Acme laboratories, Vancouver, Canada. Electron probe micro analyses of clinopyroxene and olivine were done at the Iranian mineral processing research center (IMPRC) by Cameca SX100 machine. X-ray diffraction analysis of minerals was done at the X-ray laboratory of the University of Birjand.
ResultsIn 60km south of GaziK at the east of the southern Khorasan province and the northern part of the Sistan suture zone, volcanic rocks with intermediate (Oligomiocene) and basic (Quaternary) compositions outcropped above ophiolitic units. Electron probe micro analyzer (EMPA) data indicated that clinopyroxene in basalt is diopside and olivine from chrysolite type with Mg# around 81-82 percent. The whole rocks geochemical data prove calc-alkaline and alkaline nature for andesites and basalts, respectively. Trace element patterns, especially for andesites show enrichment in Ba, K, Cs, Sr and Th, depletion in P, Nb, Ti and enrichment in LREE relative to HREE. Electron probe micro analyses of clinopyroxene in olivine basalt support alkaline nature and within plate tectonic setting for this rock. Thermobarometry of clinopyroxene in olivine basalt record crystallization conditions about 1200 oC and 6-10kbars.
DiscussionThe origin of intraplate volcanism is diverse and not always well understood. Most intraplate volcanos have been attributed to (i) mantle plumes and hot spots, (ii) continental rift, (iii) back-arc extension and (iv) lithosphere delamination and thinning (Chen et al., 2007). Although volcanism at intraplate settings is less common than along mid-ocean ridges and subduction zones, it is of significant importance for both preventing geological hazards and understanding mantle geochemistry. It is believed that alkaline oceanic island basalts (OIB) are only derived from the asthenospheric mantle (Alici et al., 2002). However, the intracontinental alkaline magmas can be produced by partial melting of metasomatized mantle enriched in LREE and LILE (Upadhyay et al., 2006).
On the basis of trace element diagrams, Ratouk basaltic rocks placed within plate volcanic zone (WPVZ) and andesitic samples have been located within the active continental margin (ACM).
The studies that took place about young basaltic volcanism (Alishahi, 2012; Mollashahi et al., 2011; Ghasempour et al., 2011; Pang et al., 2012; Walker et al., 2009) have shown that the mechanisms of their occurrence are similar such that all of them have been formed in intraplate extensional environments and active fault zone and originated from enriched mantle or asthenosphere. Lithospheric thickness maps derived from the speed of shear waves show that the lithosphere is thin in east of Iran and volcanic activity has occurred along strike-slip faults (Walker et al., 2009). Therefore, according to other similar basaltic eruptions that have occurred in the Sistan suture zone, we can say that all of them are from the same origin and as a result of deep fractures within continental plates that provide conditions for the eruption of basaltic magma.
Andesitic units in the Ratouk area are located within the active continental margin and show similar characteristics to rocks of the Subduction Zone in terms of composition.
AcknowledgementsThe authors would like to thank reviewers for the constructive comments which greatly contributed to the improvement of the manuscript.

The Beshgaz manganese-bearing veins are located in ~45 km northeast of Birdjand, South-Khorasan, and east of Iran. These veins with 0.1-1.5 m thickness and 4-7 m length are engulfed discordantly within Paleocene (Eocene-Oligocene) volcanic-pyroclastic rocks. The host of Mn-bearing veins are dacite to rhyo-dacite tuff, lapilli tuff with andesitic and andsi-basaltic fragments in shear zones. The Mn grade reaches up to 45% in the vein/veinlets. The major Mn ore minerals are pyrolusite, cryptomelane, and psilomelane. Ore minerals showing colloform and open-space filling textures. Amorphous silica is the principal gangue mineral in the Mn ores and the SiO2 content of these veins vary from 2.41 in Mn-bearing veins to 20.98 % in silicic zone. Based on mineralographic and geochemical data, the Mn ores were preliminarily precipitated as amorphous Mn-oxide and hydroxide gels, and gradually psilomelane and then pyrolusite were developed in expense of the primary amorphous minerals. The average ratio of Mn/Fe in Beshgaz manganese-bearing veins is 26.31 and positive correlation of manages with Ba, Sr, U, and Zn in Mn-bearing veins indicate that these veins have formed as epigenetic by hydrothermal fluids.

The Boushad shear zone (BSZ) is situated in the south of Birjand with at least 45 km length, about 9.2 Km width and strike N90E. The parts of the ophiolite mélange shear zone south of Birjand have changed by this shear zone. The earliest deformation, a polyphasesynmetamorphic deformation which occurred entirely in ductile conditions, D1 and D2 deformation phases are related to this deformation. The D3 deformation affected the area after a period of sedimentation and erosion, Tension gash veins are formed simultaneously. The Strike-slip faults, thrust faults and fault related folds were classified as structures related to the D4 tectonic event, the most recent phase of conflict in the region N055 ±10E is formed. Degree of convergence of the shear zone is R = 0.3, that indicating the formation of a dextral Transpression (Slightly oblique-convergent).

The Takht- e baz granitoid in the northwest of Birjand is cropped out in the vicinity of pyroclastic units composing of tuff، marly tuff and breccia. Petrography and major elements analysis show that this intrusion is alkali granite to granite in nature. Common textures in these rocks are granular، graphic، myrmekite، granophyric and perthitic. Potasium feldspars (perthitic orthoclase and microcline)، quartz and sodic plagioclases are essential minerals. Biotite as the only mafic mineral and zircon، titanite and Fe-oxide are the accessory minerals of these rocks. Biotite is altered to chlorite، and feldspars to sericite، calcite and clay minerals. Age dating with zircon uranium-lead method indicated that the alkali granite is 55. 7 ± 0. 6 Ma (early Eocene) old. Chemically، the rock suite is characterized by high total alkali، Fe/Mg، Ga/Al، Hf، REE (except for Eu)، SiO2 and Zr and low contents of Ba، CaO، MgO، P2O5 and Sr. These features along with various geochemical discrimination diagrams suggest that the Takht-e baz granitoid is post-collisional A-type (A2-type). This suite may be derived from melting of continental crust in an extensional setting after collision of the Lut and the Afgan continental blocks in the east of Iran.

Sistan suture zone ophiolitic rocks are remnants of Tethyan oceanic lithosphere between Lut and Afghan continental blocks. This oceanic basin has been existed at least during the Cretaceous. Mineral chemistry from crustal sequence ultramafic-mafic associations and petrographical evidences from parts of these ophiolitic complexes (the ophiolitic rocks located between the south of Birjand and Tchehel Kureh ophiolites) suggest distinct geodynamic setting for the formation of oceanic lithosphere. Plutonic rocks from crustal sequence mainly include ultramafic cumulates (dunite and pyroxenite)، cumulate gabbro، gabbronorite and isotropic gabbro. The crystallization trend in these rocks is variable including earlier crystallization of pyroxene relative to plagioclase and vice versa which implies SSZ (supra-subduction zone) and MORB (Mid-Oceanic Ridge Basalt) - type trends، respectively. The composition of plagioclase in cumulate gabbros and gabbronorite is bytownite and anorthite، respectively. Moreover، the contents of compatible and incompatible elements of clinopyroxene and orthopyroxene in ultramafic cumulates، cumulate gabbros and gabbronorite represent significant differences. The chemical composition of these minerals and crystallization trends indicate that pyroxenites-gabbronorite and troctolite-cumulate gabbros-isotropic gabbros have been formed from two different magma series with SSZ and MORB affinities، respectively. In the study area، it seems that the MORB-type magmatism resulted from partial melting beneath mid ocean ridge produced a depleted mantle. Subsequently، consequence of intra-oceanic subduction the MORB mantle has been suffered higher depletion due to fluid-induced melting in supra subduction zone setting and produced SSZ-type magmatism.

Tertiary volcanism in east and northeast of Nehbandan, eastern Iran, includes mostly basic-intermediate associations. They are characterized by sodic (1

Keywords: Calcalkaline basalt, Low, K tholeiite, Subduction zone magmatism, Sistan suture zone}