Comments on “Dehydration of hot oceanic slab at depth 30–50 km: key to formation of Irankuh-Emarat Pb-Zn MVT belt, Central Iran” by Mohammad Hassan Karimpour and Martiya Sadeghi

The Malayer-Esfahan Metallogenic belt (MEMB), southwestern Iran, contains numerous different types of the sediment-hosted Zn-Pb (±Ba±Ag), volcanic-sediment hosted Zn-Pb ± Ba, sideritic Fe-Mn-Pb (±Ba±Cu), and barite mineralizations. These deposits are hosted mostly in Jurassic shales and sandstones and in Early to Late Cretaceous carbonates and siltstones with minor volcanic rocks. In contrast to the orogenicrelated Mississippi Valley type (MVT) deposits, the MEMB deposits formed in an extensional back-arc environment and are characterized by their stratabound and stratiform orebodies. In these deposits, silicification and dolomitization (±sericitization) are the main wall-rock alteration styles. The presence of primary laminated sulfides, fine-grained disseminated sphalerite and galena in association with framboidal pyrite, sedimentary structures in sulfide laminae and bands, and the association of some tuffaceous and volcanic rocks with sulfide mineralizations, along with replacement ore textures in the MEMB deposits are not compatible with orogenic-related MVT model for these mineralizations. These characteristics in the Cretaceous MEMB deposits are more compatible with a sub-marine hydrothermal system with sub-seafloor replacement mineralization. Some deposits also share characteristics between Irish type and volcanogenic massive sulfide (VMS) deposits, called VSHMS in this paper. The main argument against the MVT model of Karimpour and Sadeghi (2018) is that this model is not acceptable for the MEMB deposits and could not explain metallogenic aspects of the Zn-Pb (±Ba±Ag) and other mineralizations in this belt.We thank prof. Stefano Albanese, chief editor of Journal of Geochemical Exploration, and two anonymous reviewers for their very useful and constructive comments. The authors are grateful to S. Rezaei for her help in creating the GIS data base of SH Zn-Pb deposits of Iran.Peer ReviewedPostprint (author's final draft

Mineral chemistry and Mossbauer spectroscopy of micas from granitic rocks of the Canadian Appalachians.

This thesis represents the results of a mineral chemical and crystal chemical investigation of trioctahedral and dioctahedral micas from the Paleozoic granitic rocks of the Dunnage, Gander, Avalon and Meguma tectonic zones of the Canadian Appalachians. The objectives of the thesis were: (1) to investigate the relationships between the composition of biotite and the tectonic origin of the host granitic rock. (2) to investigate the significance of quadrupole splitting distributions in the Mossbauer spectra of these Appalachian and other biotite specimens and (3) to investigate the cis and trans-octahedral Fe2+ Mossbauer spectral contributions of dioctahedral (muscovite) micas from the granitic rocks of the Gander zone in New Brunswick. These results of the study am presented as three manuscripts intended for submission to peer-reviewed journals. In the first manuscript, the author document the mineral chemistry of biotite occurring in granitic rocks of the Canadian Appalachians. The most significant variations are changes in total Al contents and Fe/(Fe+Mg) values. Using common oxygen geobarometers, the biotite from the granitic rocks of most zones plot on or above the NNO buffer, indicating moderate oxidizing conditions, whereas biotite from the Meguma zone plots between the QFM and NNO buffers implying fairly reducing conditions during crystallization. The composition of biotite in Appalachian granitic rocks reflects primarily the nature of the host magmas and cannot be readily used for interpreting the tectonic setting of these rocks. In the second manuscript, the methodology of quadrupole splitting distribution (QSD) analysis was used to describe the room temperature 57Fe Mossbauer spectra of 71 specimens of trioctahedral micas from the Paleozoic granitic rocks of the Canadian Appalachians, the granitic rocks of the Hepburn and Bishop intrusive suites of the Early Proterozoic Wopmay orogen, Northwest Territories, and the nepheline syenite of the Cretaceous Mont Saint-Hilaire alkaline intrusion, Quebec. To the author, the details of the crystallochemical controls of the observed QSDs in biotite are not well understood because of a lack of electronic structure calculations that link local distortion environments to quadrupole splitting values. Furthermore, several key crystal chemical parameters of the synthetic phlogopite-biotite-annite solid solution (e.g., Fe/(Fe+Mg), Fe3+/Fe total) do not correlate with any of the QSD features of natural biotites. The most strongly-correlated chemical parameter is found to be Altotal . Finally, in the third manuscript, QSD analysis of specimens of muscovite from granites of the Gander zone in New Brunswick shows that the Mossbauer spectra of these dioctahedral micas fall into two distinct groups. In the first group, two well-resolved octahedral Fe2+ spectral contributions occur whereas, in the second group, a single but broader octahedral Fe 2+ contribution occurs. Furthermore, spectra from the first group clearly show bimodal QSDs for Fe2+. In the second group, the spectra show broad unimodal QSDs for Fe2+. (Abstract shortened by UMI.

Mineral chemistry, thermobarometry and tectonomagmatic setting of Late-Cretaceous volcanic rocks from the Kojid area (south of Lahijan, northern Alborz)

The volcanic rocks of Kojid area (south of Lahijan) crop out in northern Alborz. They show mainly pillow structure with numerous cross-cutting dykes. Based on lithostratigraphic relationships and interpillow pelagic limestones, the volcanics are Late Cretaceous in age. The volcanics of Kojid area are predominantly basic in composition (olivine basalt and basalt) and minor more evolved suites such as trachyandesite and dacite. Olivine phenocrysts display forsterite (Fo) content of 63 to 83%. The phenocrystic and interstitial clinopyroxene crystals are augite to diopside in composition, with Na2O, Al2O3 and TiO2 contents of 0.24- 0.68, 2.3-6.53 and 1-5.1 wt.%, respectively. Furthermore, plagioclase is labradorite (An%= 51-68). The results of various geothermobarometric methods of clinopyroxene, plagioclase and olivine indicate good correlation with each other. Different thermometric calculations yielded temperatures in the range of 1100 to 1250 °C which are compatible with temperatures of basic melts. Moreover, clinopyroxene and plagioclase barometry of the phenocrysts (4 to 8 Kb) and interstitial phases

Geochemistry and Mineral Chemistry of Zeolites Bearing Basic Volcanic Rocks from the Boumehen-Roudehen Area, East of Tehran

Introduction The Upper Eocene basic volcanic rocks that have cropped out in Karaj formation in the Boumehen and Roudehen area in the east of Tehran are characterized by fibrous zeolites filling their vesicles, cavities and fractures creating amygdale texture. The study area is located structurally in the Central Alborz orogenic belt. The presence of large volumes of shoshonitic magma during the Middle to Late Eocene in southern–central Alborz implies that partial melting to produce shoshsonitic melts was not a local petrological event. Thus, their ages, formation processes, and interpretations are of regional tectonic significance. In this study, we present a detailed petrography, mineral chemistry, and whole-rock geochemistry of high-K (shoshonitic) basic rocks to understand the petrogenesis and source region and to deduce the nature of the tectonomagmatic regime of the Alborz. Materials and methods In this study, we present new major and trace element data for a selection of 4 of the least altered samples by a combination of X-ray fluorescence (XRF) and ICP-OES techniques at the Zarazma Mineral Studies Company. Mineral analyses were obtained by wavelength dispersive X-ray spectrometry on polished thin sections prepared from each rock sample described above for 12 elements using a Cameca SX-50 electron microprobe at the Istituto di Geologia e Geoingegneria Ambientale, C.N.R., University La Sapienza of Rome, Italy. Typical beam operating conditions were 15 kV and probe current of 15 nA. The accuracy of the analyses is 1% for major and 10% for minor elements. A total of 24 point analyses were collected. Results and Discussion The extent of alteration in the study rocks varies from slight to severe and shows porphyritic to glomeroporphyritic textures. Pyroxenes are generally subhedral to euhedral and occur as discrete crystals as well as aggregates. Olivine may occur only as relics filled with iddingsite, chlorite and calcite. Plagioclase is subhedral to euhedral and occurs both as pheocrysts and microliths in the glassy groundmass. The plagioclase crystals are variably sassuratised and sometimes replaced by zeolites. Microprobe data indicate a restricted range of chemical composition for pyroxene falling in diopside and augite fields of ternary pyroxene classification diagram (Morimoto, 1988). The plagioclase composistions have been plotted in the fields of labradorite and bytownite in the orthoclase–albite–anorthite ternary diagram (Deer et al., 1992). On the F1-F2 tectonic discrimination diagram of Nisbet and Pearce (1977), pyroxene compositions plot mainly in volcanic arc basalt field consistent with their whole rock geochemistry. Thermobarometry based on pyroxene composition (Soesoo, 1997) displays a range of temperatures from 1150 to 1250 0C and pressure from 3 to 8 kbar for its crystallization. Whole rock compositions show that the variations of SiO2 contents are narrow (47.08 – 47.47 wt%) and TiO2 (1.1 – 1.24 wt%). Relatively higher contents of K2O show a shoshonitic affinity in the K2O–SiO2 diagram (Peccerillo and Taylor 1976). Trace element and rare earth element (REE) distribution patterns for the basaltic samples normalized to the primitive mantle (McDonough et al., 1992) and chondrite values (Sun and McDonough, 1989) show similar patterns. The samples are all enriched in large-ion lithophile elements (LILEs), such as Rb, Ba, and K, and light rare earth elements (LREEs) ((La/Sm)N= 2.3–3.2) relative to the more immobile elements (e.g., Hf, Ti and Y). The plot of analyzed samples in a series of different tectonic discrimination diagrams shows that the Boumehen-Roudehen alkaline basalts are consistent with characteristics of subduction related (active continental margins) tectonic environments. In addition, enrichment in LILE and depletion in HFSE on spidergram create patterns which are very similar with the pattern of Andean counterparts indicating an arc setting. Acknowledgments Marcello Serracino is thanked for microprobe analyses. The authors are grateful to Journal Manager and reviewers who critically reviewed the manuscript and made valuable suggestions for its improvement. References Deer, W.A., Howie, R.A. and Zussman, J., 1992. An Introduction to the Rock Forming Minerals. Longman, London, 696 pp. McDonough, W.F., Sun, S.-S., Ringwood, A.E., Jagoutz, E. and Hofmann, A.W. 1992. Potassium, Rubidium and Cesium in the Earth and Moon and the evolution of the mantle of the Earth. Geochimica et Cosmochimica Acta, 56(3): 1001-1012. Morimoto, N., Fabries, J., Ferguson, A.K., Ginzburg, I.V., Ross, M., Seifert, F.A., Zussman, J., Aoki, K. and Gottardi, G., 1988. Nomenclature of pyroxenes. American Mineralogist, 73)9-10:( 1123–1133. Nisbet, E.G. and Pearce, J.A., 1977. Clinopyroxene composition in mafic lavas from different tectonic settings. Contributions to Mineralogy and Petrology, 63)2:(149-160. Peccerillo, A. and Taylor, S.R.,1976 . Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, Northern Turkey. Contributions to Mineralogy and Petrology, 58(1): 63-81. Soesoo, A. 1997. A multivariate statistical analysis of clinopyroxene composition: Empirical coordinates for the crystallisation PT- estimations. Journal of the Geological Society of Sweden, 119(1): 55-60. Sun, S.S. and McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts; implications for mantle composition and processes. In: A.D., Saunders and M.J., Norry (Editors), Magmatism in the ocean basins. Geological Society, London, Special Publications, 42. 313-345

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

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