The potential sources of Bauxite in PirMishi Tash, Semnan province, northern Iran

The Tash bauxite mine is located approximately 6 km northeast of Tash village and 40 km northwest of Shahroud city in Semnan Province with coordinates of 36° 32′ N to 36° 37′ N and 54° 41′ E to 54° 48′ E. The actions of the orogenic phase of the former Cimmerian as well as the chemical and physical factors have caused the erosion of the basalts in the Shemshak sedimentary basin, which has resulted in the simultaneous deposition of the Shemshak molasses‌ and bauxite in the Tash area. According to some geological evidence and the location of Elias rule, bauxites in the vicinity of Shemshak Formation shales, it is concluded that the clay minerals have played an important role in forming the bauxite deposits in this area. The results showed that the basalts were formed from the alkaline magma and then altered to clay minerals. The remaining immobile elements such as aluminum and residual iron formed the Tash bauxite deposit. The investigation of thin sections designates that the studied ore contains ooidal, plitomorphic, allogeneic pizolite, coloform, and compressive dissolution texture, which indicates the autochthonous origin. Pyrite, chalcopyrite, goethite, and hematite were also recognized. The mineralogical study, performed by the X-Ray diffraction method, led to the identification of minerals of anatase, boehmite, diaspore, chamosite, kaolinite, quartz, and hematite. Analysis of ore samples by the X-Ray fluorescence method and calculation of aggregation coefficient of trace elements and geochemical indicators along with geological evidence revealed the source rock could be from the mafic type

Mineral chemistry and petrogenesis of the Gurgur Mount volcanic rocks (Northeast Takab)

Andesitic and andesitic-basaltic lavas are widespread over most of the ground surface of the Gurgur area altered mostly by the hydrothermal solutions. The main rock forming minerals in these rocks are plagioclase, pyroxene and olivine affected by the hydrothermal solutions. The altered rocks do contain minerals including calcite, sericite and chlorite. Given the results obtained and the mineral chemistry studies, the clinopyroxenes formed in the area are, chemically, calkalkaline and of diopside-augite type formed in subvolcanic to near surface levels contemporaneous with magma ascending. Plagioclase minerals show zoning textures and lie within the two andesine and albite-oligoclase fields. These units, in terms of total rock chemistry, are classified as the calk-alkaline volcanic rocks formed in the continental arcs. On the other hand, on the trace elements chondrite-normalized diagrams and enriched mantle-normalized multi- element diagrams, the LREE enrichment relative to the HREE is observed. The LILE (i.e. Rb, K and Th) and the LREE (e.g. La, Ce and Nd) show an enrichment in comparison to the HFSE (Zr, Hf, Nb, Yb, Y and Sm). Given the Nd/Th (1.42-1.15), Zr/Nb (12.27-21.22), Ba/La (18.64-29.77) as well as LILE enrichment associated with depletion in Nb, Ta and Ti, an environment related to the subduction zones can be proposed for the area under study. Moreover, the similarity between the REE distribution pattern and the incompatible elements point to the genetic relationship between these rocks. Finally, on the base of the obtained data, it can be concluded that the volcanic rocks in the Gurgur Mountain were likely formed during the extended magmatism of the Urumieh-Dokhtar in the Cenozoic

Petrology and geochemistry of the Karaj Dam basement sill: Implications for geodynamic evolution of the Alborz magmatic belt

The northeastward subduction of the Neo-Tethyan oceanic lithosphere beneath the Iranian block pro- duced vast volcanic and plutonic rocks that now outcrop in central (Urumieh–Dokhtar magmatic assemblage) and north–northeastern Iran (Alborz Magmatic Belt), with peak magmatism occurring dur- ing the Eocene. The Karaj Dam basement sill (KDBS), situated in the Alborz Magmatic Belt, comprises gabbro, monzogabbro, monzodiorite, and monzonite with a shoshonitic affinity. These plutonic rocks are intruded into the Karaj Formation, which comprise pyroclastic rocks dating to the lower–upper Eocene. The geochemical and isotopic signatures of the KDBS rocks indicate that they are cogenetic and evolved through fractional crystallization. They are characterized by an enrichment in LREEs relative to HREEs, with negative Nb–Ta anomalies. Geochemical modeling using Sm/Yb versus La/Yb and La/Sm ratios sug- gests a low-degree of partial melting of a phlogopite–spinel peridotite source to generate the KDBS rocks. Their low ISr = 0.70453–0.70535, Nd (37.2 Ma) = 1.54–1.9, and TDM ages ranging from 0.65 to 0.86 Ga are consistent with the melting of a Cadomian enriched lithospheric mantle source, metasomatized by fluids derived from the subducted slab or sediments during magma generation. These interpretations are con- sistent with high ratios of 206 Pb/204 Pb = 18.43–18.67, 207 Pb/204 Pb = 15.59, and 208 Pb/204 Pb = 38.42–38.71, indicating the involvement of subducted sediments or continental crust. The sill is considered to have been emplaced in an environment of lithospheric extension due to the slab rollback in the lower Eocene. This extension led to localized upwelling of the asthenosphere, providing the heat required for partial melting of the subduction-contaminated subcontinental lithospheric mantle beneath the Alborz mag- matic belt. Then, the shoshonitic melt generates the entire spectrum of KDBS rocks through assimilation and fractional crystallization during the ascent of the magma

The paleozoic Jalal Abad mafic complex (Central Iran): Implication for the petrogenesis

The Jalal Abad magmatic rocks are located at the southeastern edge of the Kashmar-Kerman tectonic zone, which includes Cadomian magmatic rocks and sedimentary strata intruded by several Silurian alkaline plutons and associated dikes. They have typical alkaline kaersutite and alkaline to per-alkaline pyroxene and are characterized geochemically by enrichment in LREE, Nb and Ta, and high concentrations of incompatible trace elements, demonstrating alkaline features with typical ocean island basalt signatures. Chondrite-normalized REE and multi-element spider diagrams along with High 206Pb/204Pb ratios (18.46–19.83) for the Jalal Abad gabbro, diorite, and dibasic dikes indicate involvement of an OIB-like source during the formation of these rocks. Modeling of bulk–rock trace elements and Sr–Nd isotopes suggest that magmas were generated by a pair of HIMU-EM1- like mantle source, consistent with a plume mantle origin in a within-plate rift zone. The melting took place in garnet stability field and the fractional crystallization played a major role in magmatic evolution of the mantle-derived parental magma. The Jalal Abad mafic rocks have U–Pb zircon ages of 425.5 ± 8.6 Ma and along with other Ordovician to Silurian rocks in different parts of the Iranian plate are related to the extensional tectonic regime responsible for the rifting of Cadomian fragments from northern Gondwana and the opening of Paleo-Tethys. Our findings indicate that the rifting and seafloor spreading of Paleo-Tethys and the formation of its oceanic crust were intensely influenced by a mantle plume activity in the early Paleozoic

Zircon U–Pb ages and Sr–Nd–Pb–Hf isotopic compositions constrain the tectono-magmatic evolution of the Anomaly 21-A iron ore region, Bafq metallogenic province, Central Iran

The late Proterozoic - early Paleozoic tectono-magmatic evolution of Central Iran is considered to be a result of subduction of the Proto-Tethys Ocean and the amalgamation of Gondwana continental fragments. Here, we present whole-rock geochemistry, Sr-Nd-Pb isotopes and zircon U-Pb-Hf data for monzonite to quartz monzonite from deep drill core in the area of the Iron Anomaly 21-A, Bafq metallogenic province of Central Iran, to decipher the petrogenetic evolution of the mantle during late Proterozoic–early Paleozoic times. The plutonic rocks display enrichment in large-ion lithophile elements (Rb, Ba, K, and Cs), and depletion in high-field-strength elements (Nb, Ta, Ti), typical of continental arcs. Zircon U-Pb ages of the studied rocks are in the range of 474–512 Ma, which is consistent with the general consensus on the age of the Cadomian basement of Central Iran, and the culmination of subduction along northern Gondwana in the early Paleozoic. The isotopic signatures of the samples, e.g., (87Sr/86Sr)i = 0.706 to 0.718, εNd(t) = -3.3 to +1.8, (206Pb/204Pb)i = 18.87 to 20.32, (207Pb/204Pb)i = 15.72 to 15.84, (208Pb/204Pb)i = 40.74 to 42.32, and εHf(t) = -4.7 to +11.6, cover a compositional range of mantle-derived melts with variable degree of contamination by Neoproterozoic continental crust. A setting of back-arc continental rifting is envisaged for the late Neoproterozoic to early Paleozoic magmatism in the Bafq province

Origin of 1.8 Ga zircons in Post Eocene mafic dikes in the Roshtkhar area, NE Iran

<p>The Roshtkhar area is located in the Khaf-Kashmar-Bardaskan volcano-plutonic belt to the northeastern Iran along the regional E–W trending Dorouneh Fault, northeastern of the Lut Block. There are several outcrops of subvolcanic rocks occurring mainly as dikes in the area, which intruded into Cenozoic intrusive rocks. We present U–Pb dating of zircons from a diabase dike and syenite rock using LA-ICP-MS that yielded an age of 1778 ± 10 Ma for the dike, indicating this Cenozoic dike has zircon xenocrysts inherited from deeper sources; and 38.0 ± 0.5 Ma, indicating an Late Eocene crystallization age for the syenite. Geochemically, the dikes typical of high-K calc-alkaline to shoshonitic magmas. Petrographic observations and major and trace element variations suggest that diabase melts underwent variable fractionation of clinopyroxene, olivine, and Fe-Ti oxides and minor crustal contamination during the differentiation process. Primitive mantle-normalized multi-element diagrams display enrichment in LILE, such as Rb, Ba, Th, U, and Sr compared to HFSE, as well as negative anomalies of Nb, Ta, P, and Ti, suggesting derivation from subduction-modified mantle. Chondrite-normalized REE plots show moderately LREE enriched patterns (<3.83 La_N/Yb_N <8.27), and no significant Eu anomalies. Geochemical modelling using Sm/Yb <i>versus</i> La/Yb and La/Sm ratios suggests a low-degree of batch melting (~1–3%) of a phlogopite-spinel peridotite source to generate the mafic dikes. The geochemical signatures suggest that the Roshtkhar mafic dikes cannot be related directly to subduction and likely resulted from melting of upper mantle in an extensional setting where the heat flow was provided from deeper levels. These dikes presumably derived the zircon xenocrysts from the assimilation of upper crust of Gondwanian basement. Processes responsible for partial melting of metasomatized lithospheric mantle and post-collision magmatism in NE Iran was triggered by heating due to asthenospheric upwelling in an extensional setting.</p

Magmatic differentiation in the calc-alkaline Khalkhab–Neshveh pluton, Central Iran

Geochemical and isotopic data (Sr, Nd) are presented for the Khalkhab–Neshveh pluton, an E-W elongated body of quartz monzogabbro, quartz monzodiorite, granodiorite and granite in the Urumieh–Dokhtar magmatic arc of Central Iran. The plutonic rocks are medium- to high-K, metaluminous, and I-type, with 52–71 wt.% SiO2. The geochemistry shows smooth differentiation trends in which most major elements (except Al2O3, K2O and Na2O) are negatively correlated with SiO2; K2O, Ba, Rb, Ce, Nb, and Zr are positively correlated. Na2O, Sr, Eu and Y follow curves that are not considered to represent simple mixing between mafic and felsic magmas, but reflect crystal fractionation of clinopyroxene, plagioclase and hornblende. Initial 87Sr/86Sr ratios (∼0.7047) and εNdt values (∼+3.0) are essentially constant, and the large volume of quartz monzogabbros compared to granites, as well as the lack of mafic enclaves in more evolved rocks, are also indicative of crystal fractionation rather than mixing of magmas from different sources. Clinopyroxene fractionation was the main control in the evolution of the magmas up to 55% SiO2; hornblende took over from 55 wt.%, resulting in decreasing Dy/Yb with increasing silica content in the most siliceous rocks. Sr concentration increases up to 55% SiO2, and then decreases together with CaO, Al2O3, Na2O. Fractionation of opaque minerals and apatite throughout the sequence, and the continuous increase in K2O and Ba vs. SiO2 reflect the absence of significant fractionation of biotite and K-feldspar. Based on geochemical and isotope data, geophysics information and field studies, it seems that suturing of the Arabia and Iran plates caused the Khalkhab and Koush nousrat faults with left-lateral strike-slip in the Urumieh–Dokhtar region, and generated a purely tensional T space at 32° to the faults which was exploited by the emplacement of Khalkhab–Neshveh pluton