ThesisPDF Available

Chemistry and origin of garnet in the granitoids and metamorphic rocks in the south of Mashhad (Khajeh-Morad, Khalaj and Dehnow)

Authors:

Abstract and Figures

پیامبر خدا (صلی‌الله ‏علیه و ‏آله و سلّم) فرمودند: هر گاه مؤمن یک برگه که روى آن علمى نوشته شده باشد از خود برجاى گذارد، روز قیامت آن برگه پرده میان او و آتش می ‏شود و خداوند تبارک‌وتعالی به ازاى هر حرفى که روى آن نوشته شده، شهرى هفت برابر پهناورتر از دنیا به او میدهد. سلام علیکم؛ ایزد دانا را سپاس می‌گویم که بنده را یاری بخشید تا بتوانم در زمینه تحقق اهداف خویش، گام بردارم. برای پاسداشت و ترویج علم مقدس زمین‌شناسی، رساله دکتری خود را به همه فرهیختگان جامعه علمی زمین‌شناسی ایران تقدیم می‌نمایم. شایسته است انشالله همه بزرگواران امانت داری کامل علمی را رعایت بفرمایند. پیروزی و موفقیت شما را در تمامی امور زندگی آرزومندم. دکتر رامین صمدی
Content may be subject to copyright.
A preview of the PDF is not available
... Aydar and Gourgaud, 2002;Mirnejad et al., 2008;Patranabis-Deb et al., 2008) or have oscillatory compositional zoning (e.g. Day et al., 1992;Kano, 1983;Kawabata and Takafuji, 2005;Samadi, 2009Samadi, , 2014Samadi et al., 2014b). Garnets from aplite-pegmatite are often Fe-Mn rich, and exhibit pronounced core-to-rim decrease in Mn (e.g. ...
... Baldwin and Von Knorring, 1983;Gadas et al., 2013;Manning, 1983;Thöni et al., 2003;Whitworth, 1992), whereas garnets from granitoids are mostly Fe-rich and exhibit weak core-to-rim increase in Mn (e.g. Allan and Clarke, 1981;Day et al., 1992;Green and Ringwood, 1968;Harangi et al., 2001;Kawabata and Takafuji, 2005;Koepke et al., 2003;Mirnejad et al., 2008;Samadi, 2014;Samadi et al., 2014b;Spear and Kohn, 1996;Vielzeuf et al., 2005;Wang et al., 2003). Other chemical characteristics of magmatic, Li 97 177 188 213 187 136 96 107 104 93 107 128 Na 75 94 143 168 155 107 62 73 86 75 87 81 Ti 222 426 737 594 745 326 229 294 272 264 333 Xenocrystic garnets in igneous rocks are characterized by Mnnormal zoning with core-to-rim depletion in Mn, whereas magmatic garnets exhibit reversed zoning with core-to-rim enrichment in Mn (Allan and Clarke, 1981). ...
... The δ 18 O values of garnet in Khajeh Morad aplite and pegmatite garnet are similarly lower than those values for garnets from local metamorphic complex (e.g. schists from Dehnow and Khalaj areas in the northwest and (Samadi, 2014) and Dehnow (Samadi et al., 2014b) areas. δ 18 O of magma is calculated based on Δ quartz-magma = 1.1‰ of Kontak and Kyser (2009). ...
Article
Triassic monzogranites and granodiorites of the Khajeh Morad region in northeastern Iran are cut by two types of garnet-bearing intrusive veins: (1) aplite and (2) granitic pegmatite. The former is composed of quartz, feldspar, muscovite, with minor garnet, biotite, and ilmenite. The latter contains quartz, plagioclase (± quartz and muscovite inclusions), alkali feldspar, and muscovite, with minor amounts of garnet, tourmaline, beryl, columbite, and ilmenite. Garnet in both rock types has MnO > 12 wt% and CaO < ~2 wt% with spessartine-rich cores, and a core-to-rim increase in Fe, Mg, and Ca. Garnet cores are enriched in Y, REE, Zr, Nb, Ta, Hf, and U. The Y, HREE, and Mn concentrations show strong positive correlations in both types of garnet associations and decrease from core-to-rim. These core-to-rim elemental variations can be explained by increasing fluid content and H2O activity in magma, together with decreasing Mn contents of an evolved host melt. Aplite and pegmatite garnet δ18O values are nearly identical (~10.3‰, n=7, SD=0.09) and are similar to magmatic garnets in granitoids elsewhere. On the basis of calculated δ18O values for magma (~12.5 and 12.6‰) and quartz (~13.6‰, n=7, SD=0.08) as well as the major and trace element characteristics, we suggest that the Khajeh Morad garnets crystallized from a variably fractionated S-type monzogranitic magma.
Article
Introduction Granitoids are the main rock units in the continental crust. Study of granitoids reveals significant information on tectonic mantle and upper crust. Many researchers have investigated petrogenesis and origin of granitoids (e.g., Chappell and White, 2001; Barbarin, 1999; Frost et al., 2001). For example, Chappell and White (1992), Pitcher (1993) and Chappell et al., (1998) have divided granites into two major groups of: (1) I-type granites (high-temperature or Cordellerian granitoids, including low-K granitoid to high-Ca tonalite, without inherited zircons) formed by partial melting of mafic rocks at >1000 ℃ in mantle or subduction zones of continental margins, and (2) S-type (low-temperature or Caledonian granitoids with inherited zircons) granites formed by partial melting of felsic crust at ~700-800 ℃. Northeast of Iran is a key location for studying the Cimmerian Orogeny, which is related to the Late Triassic collision between it and Eurasia, and the closure of the Paleo-Tethys (Samadi et al., 2014). Mesozoic Mashhad granitoids have cropped out along with the Paleo-Tethys suture zone. Distinct granitoid suites, i.e., monzogranite, granodiorite, tonalite, and diorite occur in Mount Khalaj located in the south of Mashhad. It comprises of monzogranite and granodiorite. However, monzogranite is the most abundant. To study the plutonic events during the Turan and Central Iran collision, the origin and tectonic setting of monzogranite of Mount Khalaj are investigated in this study based on whole rock geochemical data. Materials and methods This research study is based on field studies and petrography. Fresh thin sections samples were selected for geochemical analysis. Whole rock composition was measured on pressed powder tablets by X-ray fluorescence (XRF) using a Philips PW 1480 wavelength dispersive spectrometer with a Rh-anode X-ray tube and a 3 MeV electron beam Van de Graaff Accelerator, at the center for Geological Survey of Iran. The trace element data of a sample was measured at the Activation Laboratories, Ontario, Canada (ActLabs). Samples were digested by lithium metaborate/tetraborate fusion and analyzed with a Perkin Elmer Sciex ELAN 6000, 6100 or 9000 ICP/MS. GCDkit 4.1 and CorelDraw software packages were used for plotting diagrams and calculation of saturation temperatures. Results The Khalaj granitoid is mineralogically composed of quartz, potassic feldspar, plagioclase, mica, and accessory minerals of zircon and apatite. Geochemically, it is an unaltered acidic intrusion with ~72-73 wt.% SiO2. It is a granitoid (monzogranite) based on various classification diagrams (e.g., Cox et al., 1979; etc.). It shows the peraluminous nature (A/CNK~ 1.08-1.24) with negative Eu anomaly of ~0.62-0.73 (Eu/Eu*
Article
The Triassic Dehnow pluton of NE Iran is a garnet-bearing I-type calc-alkaline metaluminous diorite-tonalite-granodiorite intrusion. The parental magma formed as the result of partial melting of intermediate to felsic rocks in the lower crust. Petrological and geochemical evidence which favors of a magmatic origin for the garnet includes: large size (~10 to 20 mm) of crystals, absence of reaction rims, a distinct composition from garnet in adjacent metapelitic rocks, and similarity in the composition of mineral inclusions (biotite, hornblende) in the garnet and the same minerals in the matrix. Absence of garnet-bearing enclaves in the pluton and lack of sillimanite (fibrolite) and cordierite inclusions in magmatic garnet suggests that the garnet was not produced by assimilation of meta-sedimentary country rocks. Also, the δ18O values of garnet in the pluton (8.3 to 8.7‰) are significantly lower than δ18O values of garnet in the metapelitic rocks (12.5 to 13.1‰). Amphibole-plagioclase and garnet-biotite thermometers indicate crystallization temperatures of 708 and 790 °C, respectively. A temperature of 692 °C obtained by quartz-garnet oxygen isotope thermometry points to a closure temperature for oxygen diffusion in garnet. The composition of epidote (Xep) and garnet (Xadr) indicate ~800 °C for the crystallization temperature of these minerals. Elevated andradite-content in the rims of garnet suggest that oxygen fugacity increased during crystallization.
Article
Full-text available
Fibrolite garnet staurolite mica schist and staurolite garnet mica schist cropped out around the northwest of Khalaj (in the south of Mashhad) in a southeast to northwest direction along the metamorphic complex of Kuh-e-Majuni. They have similar mineralogy and consist of quartz, annite, staurolite, almandine, muscovite, zircon, and ilmenite; however, fibrolite in fibrolite garnet staurolite mica schist, and chlorite and tourmaline in the staurolite garnet mica schist are additionally found. Application of garnet - biotite thermometry and GBMAQ barometry indicates temperatures and pressures of 560 and 605 °C / 3.5 and 5 kilobar for fibrolite garnet staurolite mica schist and temperatures of 489 and 547 °C (in 3.5 to 5 kilobar) for the staurolite garnet mica schist. Pressure and temperature increase during the garnet growth indicates the effect of regional and contact thermal metamorphism on these rocks. Based on mineral paragenesis in KFMASH system, the metamorphic degree of regional metamorphism was about lower amphibolite (in staurolite garnet mica schist) to middle amphibolite facies (in fibrolite garnet staurolite mica schist). Meanwhile, intrusion of Khalaj granitoid and its thermal diffusion raised the metamorphic temperature up to lower amphibolite facies (in staurolite garnet mica schist) and middle amphibolite facies (in fibrolite garnet staurolite mica schist), and consequently this caused the fibrolite formation in the sample close to the pluton (i.e. fibrolite garnet staurolite mica schist).
Article
Full-text available
The granitoids of Dehnow in NE Iran are part of a calc-alkaline plutonic series (diorite-tonalite-granodiorite) that intruded the remnants of the Paleo-Tethys oceanic crust during the Triassic. New major and trace element data together with isotopic compositions elucidate their I-type nature and a deep magma origin. P-T calculations based on amphibole and plagioclase suggest crystallization stages in the upper lithosphere at an approximate pressure of 6.4 kbar and temperature of 708°C. The Dehnow granitoids are characterized by high concentrations of LILE, LREE, HFSE and low concentrations of HREE, similar to some worldwide I-type granites, including examples from Harsit (along the Alpine-Himalayan suture zone), Iberia and the Martins Pereira plutons. The new geochemical data in combination with mineral parageneses and field observations suggest that the origin of the low temperature, Caledonian-type, arc-related granitoids of Dehnow resulted from the subduction of the Paleo-Tethys oceanic slab beneath the Turan block (along the Alpine-Himalayan suture zone) and involved the contribution of lower crust and mantle melts in this collisional setting.
Article
Full-text available
The Dehnow area is located in the northwest of Mashhad city and in the structural zone of Binalood, along the east Alborz range. The major rock units in the study area include tonalite (to diorite and granodiorite), hornfels and surrounding schist. The regional metamorphism that produced the schists occurred in Triassic, while the granitoids intruded in them during Upper Triassic, a thin layer of hornfels (~ 200m) has occurred in the intrusion, and schists contact. The Dehnow plutonic rocks, hornfels and schist contain garnet as an accessory mineral. In this work, diffusion effect of Fe, Mn, Mg and Ca in the garnet was studied. According to the geochemical data, low content of Ca in the garnet rim, falling trend of Fe core to rim, low diffusion rates of these elements and the large size of garnets indicate that the garnets within tonalite are not distinctly affected by diffusion of these elements, but their elemental variation is resulted mostly by the chemical evolution of the melt which they crystallized. In addition, erratic trends of Fe and Mn and the constant Ca and Mg trends core to rim of garnets within the schist and hornfels, and also the low temperature of crystallization and the short time of garnets growth in these rocks show that diffusion effects on these garnets growth is negligible.
Article
Full-text available
Metamorphic rocks of Dehnow area mainly consist of gray to black fine-grained schists. Garnet schists are closer to the tonalitic body than the garnet chloritoid schists. There is a thin layer of staurolite and andalusite bearing hornfels between these schists and the Dehnow tonalitic body. Garnet schists and garnet chloritoid schists of Dehnow area are mineralogically comprised of quartz, biotite, muscovite, garnet, chlorite, chloritoid, tourmaline and ilmenite. Geothermobarometry results indicate that hornfels (550oC, 4.3 kbar) and garnet chloritoid schist (486-497oC) have formed in lower equilibrium condition in comparison with garnet schist (569oC, 5.3 kbar).
Conference Paper
Full-text available
The granitoids of Dehnow in NE Iran are part of a calc-alkaline stock (tonalite to granodiorite and diorite) that intruded the remnants of the Paleo-Tethys Ocean in the Triassic [1]. Epidote is commonly known as primary igneous mineral in intermediate plutonic rock [2]. In Dehnow granitoid it occurred as inclusions in the phenocrystic garnet grains or as subhedral grains associated with biotite.
ResearchGate has not been able to resolve any references for this publication.