Documentation of the Sirjan Orocline in the southeast Sanandaj-Sirjan Zone, Iran

At the southeastern part of the SanandajSirjan Zone of Iran, a group of structural elements outline a large-scale arc curvature around a vertical axis. This curvature comprises several elongated structural elements and their dividing faults, axialfold traces, layering, and foliation. The most frequent lithological units include Paleozoic metamorphic rocks, Mesozoic-Paleogene sedimentary rocks, and Mesozoic magmatic-ophiolitic complex disposed in several anticlines and synclines, forming a horseshoeshaped structure with a 240-km arc length and a 90-km wavelength. We name this structure the Sirjan Orocline, and characterize this structure here through field observations and satellite image analyses. The Sirjan Orocline formed during the late EoceneOligocene related to the most significant deformation event after regional metamorphism. The final form of this structural arc is affected by a younger tectonic event that compressed and transected this structure.

Saqez–Sardasht Goldfield,North Sanandaj-Sirjan Zone,Iran:A Tectono-Metallogenic Synthesis

The Sanandaj–Sirjan Zone(SSZ),as the metamorphic-magmatic core of the Zagros Orogen in southwestern Iran,contains several styles of gold deposit of Phanerozoic age.The northern SSZ includes an ENE-trending goldfield belt.This area that encompasses the main orogenic gold deposits,e.g.,Qolqoleh,Kervian,Qabaqhlujeh,and the Barika VMS goldfield,was chosen for this research to study the spatial and temporal relationships between gold mineralization and orogenic phases.Regarding the rock unit variations,metamorphism,magmatism and the settings of the structures,the study area is divided into four distinct tectonic blocks,separated by three main NW-trending thrust faults(suture lines)including,from NE to SW,the Tamugheh,the Ebrahim Hesar and the Zagros main thrust(ZMT)faults.The area between the Tamugheh and Ebrahim Hesar faults is a tectonized/uplifted basement of accretionary wedge-originated thrust slivers,hosting the above orogenic gold mineralizations.The other area between the here termed Ebrahim Hesar fault and the ZMT is an island-arc basin,proposed here as the Sardasht–Barika zone,including the only recognized massive sulfide gold district all over the SSZ,named Barika.The Barika goldfield was metamorphosed,deformed and enriched due to the islandarc collision to the Arabian continent,before the closure of Neotethys on the eastern flank.

A preliminary study of the anisotropy of magnetic susceptibility (AMS) of Boroujerd granitoids, Sanandaj-Sirjan Zone, West Iran

The Boroujerd pluton (ca 175 Ma) was emplaced in the Sanandaj-Sirjan zone (SSZ) active margin of Central Iran consists of monzogranite, granodiorite, and quartz-diorite. Microstructural studies show a continuum from magmatic to (sub) mylonitic deformations fabric. Intensity of deformation decreases from W-NW to E-SE. The over- all magnetic fabric of the pluton yields steep NW- SE striking foliations and sub-horizontal lineations plunging both to the northwest and south- east. These features imply that during intrusion of the pluton, a NW-SE trending stretching was dominant. This stretching is ascribed to the trans- pressive deformation of the overriding SSZ during northeastward subduction of the Neotethys under the Iranian plate. The NW-SE trending lineations of the Gousheh pluton (ca 35 Ma) suggest that the transpressive regime was ongoing from the Mesozoic to late Eocene.

Geochemistry and Petrogenesis of Intrusive Pluton in North of Golpayegan (Central Part of Sanandaj-Sirjan Zone)

Granitoid pluton in the north of Golpayegan is located in10 kmnorth of Golpayegan at SanandajSirjan zone. Dominant rocks of this region include granite, syenite, and gabbro. Granite type is granular with medium to coarse crystals and its mineralogical composition contains alkali feldspar + quartz + plagioclase + biotite + secondary minerals (opaque + sphene + apatite). Granite rocks have calc-alkaline and?metaluminous to peraluminous nature, relative enrichment of Rb over Sr, and relative enrichment of LILE over HFSE elements. These granites, which are type I, are derived from the melting of metagreywackes and their tectonic setting is of upper continental crust and post-orogenic setting. Gabbroic type is older than other types of the pluton and is granular with medium to fine crystal. Mineralogical composition of these rocks is plagioclase + pyroxene + amphibole + biotite + secondary minerals (opaque). Based on geochemical characteristics of tholeiitic and metaluminous nature, relative enrichment of Ba and Sr elements over Rb, relative enrichment of LILE elements over HFSE, negative anomaly of Nb, Ba, and Ta, and positive anomaly of Pb are observed. Origin of this type is probably from enriched mantle and in-plane tectonic setting.

Mineralogical Evidence for Regional Metamorphism Overprinted by Contact Metamorphism

The Soursat metamorphic complex （SMC） in northwestern Iran is part of the Sanandaj- Sirjan metamorphic belt. The complex is composed of different metamorphic and plutonic rocks, but is dominated by metapelites composed of garnet, staurolite, kyanite, fibrolite, cordierite, and andalusite. Porphyroblasts in schists have the same fabric, and three stages of schistosity are present. The internal schistosity （Sn） inclusion trails are also offset by conjugate sets of extensional schistosity （Sn＋l） and a second （Sn＋2） that crenulates （Sn＋l）. Polyphase metamorphisms are present in the complex. Garnet, staurolite, kyanite, and fibrolite assemblage preserves conditions during the M1 metamorphic event. This assemblage yields a P-t estimate of 645±11℃ and 6.5±0.5 kbar. Other samples of the central part of SMC contain cordierite and andalusite （M2） overgrowth that yields a P- t estimate of 532±33℃ and 2.1±1.1 kbar.

Mineral Chemistry and Geothermometry of Amphibole and Plagioclase in the Metabasites, Located at the Tanbour Metamorphic Complex in Southern Iran

Metabasite refers to metamorphosed basalts and other mafic igneous rocks (rich in iron and magnesium). When a mafic igneous rock is subjected to new pressure and temperature conditions during metamorphism, these chemical components will rearrange themselves to form new minerals. Metabasites can be found in many metamorphic belts including Sanandaj-Sirjan metamorphic belt of Iran. The study area is a Tanbour metamorphic complex in Eastern of Sirjan city, which is geologically located at the Sanandaj-Sirjan metamorphic belt in Southern Iran. Metabasite in this complex consists of greenschist, epidote amphibolite and amphibolite. Amphibole and plagioclase are the main minerals in the greenschist and amphibolite, and the a secondary mineral in some micaschist seen in the study area. The electron microprobe analysis was done on this mineralization in greenschist, epidote amphibolite and amphibolite, which showed that the amphiboles in greenschist was a member of the calcic group and Actinolite type, and the amphiboles in epidote amphibolite was a member of the calcic group and these amphiboles were tschermakite up to Ferro-Tschermakite + Ferro-Hornblende type. The amphibole in amphibolite is a member of the calcic group and this amphibole is Magnesio-Hornblende type. The plagioclases in the greenschist is pure albite (An 3.29 - 3.6), and in the epidote amphibolite is oligoclase (An 19.5 - 24.2), while in the amphibolites is oligoclase (An 16.9 - 26.6). The estimated P–T conditions are in favor of their metamorphism under epidote amphibolite (550°C and 8 kbar) and amphibolite (611°C - 652° Cand 10.5 kbar) facies.

Right Lateral Shear and Rotation in the Northeast of the Arabian-Iranian Collision Zone

Accommodation of continental convergence by crustal thickening and lateral transport is mainly featured as strike-slip faulting along the trends roughly orthogonai to the orientation of plate convergence. This style of faulting will affect seismicity of the involving areas which can be proved in low seismic zones by determining regional stress pattern using numerical methods. Accordingly, the stress distribution and deformation pattern of the South Sanandaj-Sirjan zone in the northeastern part of the Iranian-Arabian collision zone is investigated here using a three dimen-sional mechanical model. The modeled area is bounded between the Zagros thrust fault on the west and Dehshir-Baft fault in the east. The model is composed of three layers： the upper two layers represent the upper brittle and lower ductile crust of the collided continent and the lowest layer represents the lithospheric mantle. The upper crust behaves as an elastic material while the lower crust is considered as a non-Newtonian viscous fluid layer. The lithospheric mantle is taken as a low-viscosity material which is not allowed to move in any direction relative to the overlying layers. The Zagros thrust fault was treated with two different dip values saying 90° and 45° but Dehshir-Baft fault was modeled as a vertical fault and allowed to have a dextral movement regarding to the existing evidence. The driving mechanism applied to the western side of the model was chosen considering two different approaches including a kinematic approach （the Arabian-Eurasian convergence velocity; 35 mm/yr） and a dynamic approach （an external boundary force equal to 3.55E＋17 N）. The resulted stress field indicates an orogen-parallel component of right lateral shear along the Zagros fault implying a rotational deformation pattern within the modeled region that suggests a stress partitioning in the study area. The pattern also indicates a stress accumulation towards the south which could be a reason for the regional seismic quiescence between the two seismic Zagros thrust and Dehshir-Baft faults. Based on the present modeling results, it seems that high stress localization on the boundary faults can be a support of block structure approach or quasi-rigid blocks deformation within the study area. The resultant patterns of stress and displacement fields are generally totally comparable with plate boundary shear zones and have been proven by field data.

Metasomatic Stages and Scapolitization Effects on Chemical Composition of Pasveh Pluton,NW Iran

Pasveh gabbros are mafic component of a plutonic complex in the northwest Sanandaj- Sirjan Zone. These cumulative rocks are composed of plagioclase and calcic clinopyroxene （Cpx）, which yield unusually high CaO （〉19 wt.%） in whole-rock chemistry. Petrographical and geochemical data suggest that Pasveh gabbros can be divided into two groups： free scapolite and scapolite-bearing gabbros. The second group has higher Na20, K20, and P205 relative to free scapolite ones and is enriched in LIL （large ion lithophile） and HFS （high field strength） elements. Two stages of metasomatism affected the primary composition of mafic rocks. Firstly, high temperature reaction caused to invert primary high Ti clinopyroxene to low Ti cUnopyroxene＋high Ti amphibole. This reaction was extensive and included all gabbroic samples. Hydrothermal fluids involved in this process can be derived from dehydration reactions of country rocks or from other magmas incorporated in the formation of Pasveh complex pluton. The second metasomatic stage relates to scapolitization of limited parts of gabbroic rocks. An external saline fluid, which is composed of major NaCI and minor KCI and P205 components, impacted locally on Pasveh gabbros and formed the second metasomatic stage. Possible sources of Na and Cl are primary evaporites or brines, which were present in the host sediments of the gabbros. The carbonate-free nature of these hydrothermal fluids suggests that hydrothermal fluids responsible for the formation of scapolite in Pasveh gabbros are derived from marine evaporitic parentage.