Geochronology, Isotope Geochemistry and Petrogenesis of Tertiary Granitoids from Eastern Iran

Os granitóides sub-vulcânicos da zona de Chah-Shaljami fazem parte da faixa vulcânico-plutónica cenozóica do Bloco de Lut (Irão central-oriental). Tratam-se de quartzo-monzonitos, granodioritos e monzodioritos que, de acordo com a geoquímica de elementos maiores e vestigiais, são co-genéticos e têm características de rochas calco-alcalinas ricas de potássio a shoshoníticas, de ambiente de arco vulcânico. Numa amostra de quartzo-monzonito foi obtida uma idade Rb-Sr (rocha total - minerais) de 33.6±1 Ma; visto que esta amostra está praticamente livre de efeitos de alteração e que o arrefecimento foi provavelmente rápido, a idade de ~34 Ma deve corresponder à instalação magmática. Excepto em duas amostras, os valores iniciais de 87Sr/86Sr e εNd nos granitóides estudados estão concentrados nos intervalos de 0.7047 a 0.7051 e de +1.9 a +2.7, respectivamente, o que é consistente com uma fonte em cunha mantélica supra-subducção e indica que não houve contribuição crustal significativa na diversificação magmática; contudo, uma amostra tem (87Sr/86Sr)i superior e εNdt inferior, revelando que, ocasionalmente, a assimilação de rochas crustais também contribuiu para a variação geoquímica; uma outra amostra, fortemente afectada por alteração hidrotermal, afasta-se do grupo principal somente pelo relativamente elevado valor de (87Sr/86Sr)i, sugerindo que o processo hidrotermal envolveu fluidos crustais.Chah-Shaljami sub-volcanic granitoids belong to the Cenozoic volcanic-plutonic belt within the Lut Block (central eastern Iran). These intrusive rocks are mostly quartz monzonites, granodiorites and monzodiorites. Major and trace element geochemical evidence reveals that they are co-genetic and that they have features typical of high-K calc-alkaline to shoshonitic rocks from a volcanic arc setting. A Rb-Sr whole rock-mineral age of 33.6±1 Ma was obtained in a quartz monzonite sample; taking into account that this sample was almost unaffected by alteration and that cooling was probably fast, the ~34 Ma date is interpreted as the intrusion age. With the exception of two samples, initial 87Sr/86Sr ratios and εNd values of the studied granitoids are clustered in the restricted ranges from 0.7047 to 0.7051 and from +1.9 to +2.7, respectively, which fits into a supra-subduction mantle wedge source for the parental melts and indicates that, in general, crustal contribution for magma diversification was not relevant; however, one sample shows higher (87Sr/86Sr)i and lower εNdt, revealing that, occasionally, crustal rock assimilation also contributed to the geochemical variation; one other sample, strongly affected by hydrothermal alteration, departs from the main group only by higher (87Sr/86Sr)i, suggesting that its alteration involved crustal fluids

Geochemistry, petrogenesis, zircon U-Pb geochronology and Sr-Nd isotopic composition of Kuh-e-Shah volcanic rocks: Implications for an active continental margin along with eastern Iran during the Paleogene

The Kuh-e-Shah complex includes the Paleogene volcano-plutonic belt of the Lut Block, eastern Iran. The volcanic rocks which outcropped in this complex mainly consist of trachy-andesites, andesites, and basaltic-andesites that mineralogically contain plagioclase, pyroxene, hornblende, and minor biotite and olivine. Geochemically, they have features typical of high-K calc-alkaline to shoshsonitic magmas with enrichment in large ion lithophile elements (LILE), and depletion in high field strength elements (HFSE) and heavy rare earth elements (HREE). Chondrite-normalized REE plots show enrichment in light REE (4.9 < LaN/YbN < 11.6), Nb depletion and the slight negative Eu anomalies (Eu/Eu* = 0.80–0.99). Tectonic discrimination diagrams are used to infer a volcanic arc setting related to a continental subduction zone. It is concluded that the studied volcanic rocks have resulted from FC of a parental magma which formed by partial melting of the subducted oceanic crust and the overlying mantle wedge with spinel-lherzolite composition. Zircon Usingle bondPb dating indicates an age of 38.6 to 38.9 Ma for volcanic rocks (Middle Eocene, Bartonian). Initial 87Sr/86Sr and 143Nd/144Nd ratios (0.704350–0.704820 and 0.512619–0.512779, resp.), are compatible with parental melts formation in a subduction mantle wedge. The ɛNdi values (+0.60 to +3.73) are in the range of mantle-derived melts. We suggest that volcanic rocks of the Lut Block are part of the Paleogene volcanism resulted from the Sistan oceanic crust subduction under the Lut Block during the Cretaceous.publishe

Geochronology, Petrology and Geochemistry of Intermediate and Mafic Rocks of Bornaward Plutonic Complex (Northwest Bardaskan, Iran)

The study area is located in the northeast of Iran (the Khorasan Razavi province) and 28 km northwest of Bardaskan city and in position of 57˚ 46΄ to 57˚ 52΄ latitude and 35˚ 21΄ to 35˚ 24΄ longitude. The study area is a part of Taknar zone. The Taknar geological-structural zone is situated in the north Central Iranian microcontinental and it is a part of Lut block (Fig.1). Taknar plutonic complex that is situated in the Taknar structural zone is located in the northern part of Iranian microcontinent. Chemical analysis of REE and minor elements of samples of the Bornaward diorites and gabbro’s took place in the ACME Lab. in Vancouver, Canada, by the ICP-MS method (Table. 1). For the Bornaward diorite dating by the U-Pb method, zircon grains of material remaining in the sieve, Bromoform were isolated from light minerals by cleaning and were isolated with a minimum size of 25 microns, and then studies took place in the Crohn's Laser Lab Arizona (Gehrels et al., 2008). Measurement of Rb, Sr, Sm and Nd isotopes and (143Nd/144Nd)i , (87Sr/86Sr)i ratios and ƐNd (T=552), ƐNd (T=0), ƐSr (T=552) and ƐSr (T=0) took place in radioisotope Laboratory, University of Aveiro in Portugal. Geology of study area The study area forms the central part of the Bornaward plutonic complex. This complex is a granitoid assemblage including granite, granodiorite, tonalite and granophyre. The central part has been formed by intermediate and basic intrusive rocks such as diorite, quartz diorite and gabbro units (Fig. 2). From the genetic point of view, the intermediate and mafic rocks of the Taknar plutonic complex does not have any relationship with granitoid rocks of this assemblage, and they are related to a similar magmatic phase but are separated from this granitoid assemblage. However, these mafic and intermediate units are older than granitic units at the rim of the complex that are called Bornaward granite. The main minerals in the diorite and quartz diorite rocks are plagioclase and hornblende and we can see biotite in the quartz dioritic rocks. Quartz exists as tiny grains and anhedral and in the matrix rock. The amount of Quartz in the quartz diorites is 5 to 20%. Plagioclases usually have normal zoning and are highly altered to sericite. Most of the plagioclases were saussuritized. Altered minerals resulted from plagioclase and hornblende are sericite, epidote, chlorite, zoisite and clinozoisite.The main minerals in the gabbro are pyroxene, hornblende, and fine grains plagioclase. Minor minerals in the rocks are apatite, magnetite and other opaque. The main texture of intermediate and mafic rocks in this assemblage is medium granular to coarse grain and especially in the intermediate rocks and gabbro rocks, we can see scattered poikilitic, intersertal, sub-ophitic and porphyroid texture. The area diorite and gabbro is located locate in Tholeiitic and Calc-alkaline series (Fig. 9). Shand index (Al2O3/(CaO+Na2O+K2O)) is obtained under 1.1, in Metaluminous field (Fig. 7) and I-type granite field (Chappell and White, 2001). Based on the TAS diagram (Middlemost, 1985), all the diorite and gabbro samples are located in diorite, gabbro-diorite and gabbro-norite groups (Fig. 6). The diorite and gabbro show enrichment LREE and low ascending pattern ((La/Yb)N =1.40-6.12 and LaN =12.26-75.81). Measurement of U-Th-Pb isotopes of the Bornaward diorite zircons of BKCh-03 sample (Table 2) show that its age is related to 551.96±4.32 Ma ago (Upper Precambrian (Neoproterozoic) (Ediacaran). The (87Sr/86Sr)i and (143Nd/144Nd)i content of Bornaward diorite and gabbro rocks is located in the range of 0.7038 to 0.7135 and 0.51203 to 0.51214, respectively (Tables 3 and 4). It shows that the diorite and gabbro rocks can be affected by hydrothermal alteration because their (87Sr/86Sr)i is above (Fig. 16). The numeral amounts of ƐNd(T=552) of Bornaward diorite and gabbro are 2.0 to 4.0. The Bornaward diorite and gabbro rocks show a widespread enriched pattern of Rb, U, K, Pb, La and Th elements than chondrite, while Ba, Ti, Ta, Sr and Nb elements show reduction as a result of fractional crystallization (Fig. 11). The rocks of this complex are formed at the continental margin and VAG environment (Fig. 18) which is related to the subduction of the oceanic crust that exists between the Iranian microcontinent and the Afghan Block. This assemblage with age of Late Neoproterozoic is the result of extensive magmatism in the northern part of the Iranian microcontinent due to Katangahi orogeny event. The similar magmatism in the northern part of the Iranian microcontinent is existing as Khaf-Kashmar-Bardeskan volcanoplutonic belt. Based on the geochemical investigations, the magmatism of these rocks has been tholeiitic and calk-alkaline and have formed the coexistent rocks with I-type granites. Alumina saturation index for intermediate and mafic rocks of Bornaward complex is metalumina. These are medium-K rocks and enriched in the LILE such as Rb, Pb, U and Th while depleted of the Nb, Ti, Ta, Sr and Ba. Therefore, it shows that these rocks have resulted from the mixing by the lower crust. The low (87Sr/86Sr)i Bornaward diorite and gabbro rocks and the numeral amounts of Ɛ0Nd(present) of these rocks from -0.2 to 4.0 show that production of such intrusive masses can be attributed to the source of upper mantle or contaminated lower continental crust. Environment of formation of the intermediate and basic rocks of the Bornaward plutonic complex is active continental margin and volcanic arc environment.کمپلکس پلوتونیک برنورد واقع در زون ساختاري تکنار، در شمال خرد قاره ایران مرکزي و د ر 20 کیلومتري شما لغر ب شهرستان بردسکن قرار دارد. این مجموعه با سنی معادل اواخر پرکامبرین (نئوپروتروزوئیک)، نتیجه فعالیت ماگمایی وس یع شمال خرد قاره ایران مرکزي در اثر پدیده کوهزایی کاتانگاهی است. مشابه این ماگماتیسم در شمال خرد قاره ایران مرکزي بهصورت کمربند ولکانو- پلوتونیک خواف- کاشمر- بردسکن همچون گرانیتوئیدهاي کاشمر وجود دارد. این کمپلکس بزرگمقیاس در واقع مجموع هاي گرانیتوئید ي شامل سنگهاي گرانیت ی، گرانودیوری تی، تونالی تی و گرانوفی ري است که بخ ش مرکزي آن از ی ک گرو ه واحدهاي گابرویی، دیوریت ی و کوارتزدیوریتی تشکیلشده است. بافت اصلی این سن گهاي حدواسط و مافی ک، گرانولار متوسط تا درش تبلور اس ت و باف تهاي پورفیروئید بهویژه در سنگهاي حدواسط و بافتهاي پوئیکلیتیک و سابافیتیک در سن گهاي گابرویی ب هصورت پراکنده به چشم میخورد. کانی اصلی فرومنیزیندار سنگهاي مافیک و حدواسط، کانی هورنبلند است و در نمونههاي کوارتزدیوریتی، بیوتیت نیز دیده میشود. سنگهاي حدواسط و مافیک کمپلکس پلوتونیک برنورد از لحاظ ژنتیکی با سنگهاي گرانیتوئیدي این مجموعه ارتباطی مستقیم دارند. از لحاظ ارتباط صحرایی و بررسیهاي سنی چنین مشخص میشود که این واحدهاي مافیک و حدواسط نسبت به واحد گرانیتی و دیگر واحدهاي نفوذي اسیدي این کمپلکس قدیمیتر بوده و توسط این واحدها قطع شدهاند. 551 میلی ون /96 ±4/ سن این توده هاي نفوذي 32 ،U-Pb بر اساس سنسنجی دیوریتهاي منطقه برنورد با استفاده از کانی زیرکن بهروش سال قبل (اواخر پرکامبرین) بهدست آمده اس ت. بر پایه بررس یها ي ژئوشیمیایی، تحولات ماگمایی این سن گها از نوع تولئیتی و کالکآلکالن بوده و شاخص اشباع از آلومین این سنگها متاآلومین است. دیوریتها و گابروهاي برنورد از نوع پتاسیم متوسط بوده و از غنیشدگی نشان میدهند؛ در حالیکه عناصري Th بههمراه La, Rb, K, U, Pb لحاظ ویژگیهاي ژئوشیمیایی نسبت به عناصر ناسازگار تهیشدگی شاخصی را در مقایسه با کندریت ارائه میدهند. Nb, Ti, Ta, Sr, Ba مانند 0 بهدست آمده است. مقدار عددي نسبت / 0 تا 51214 / 143 ) دیوریتها و گابروهاي برنورد در گستره 51203 Nd/144Nd)i Sr)i 86 Sr/ 87 دیوریتها و گابروهاي ƐNd(T= 0 اندازهگیري شده است. مقدار عددي ( 552 / 0 تا 7135 / ) این تودههاي نفوذي در گستره 7038 Ɛ0Nd(present) 87 ) نمونههاي دیوریت و گابروهاي منطقه برنورد و مقادیر Sr/86Sr)i 4 بهدست آمده است. مقادیر پایین / 2 تا 0 / برنورد از 0 4 محاسبهشده است، نشاندهنده آن است که تولید چنین تودههاي نفوذي م یتواند به منبعی از گوشته / 0- تا 0 / این تودههاي نفوذي که 2 بالایی یا پوسته قارهاي زیرین تحت آلایش قرارگرفته شده، نسبتداده شود. محیط تشکیل این دسته از سن گهاي کمپلک س پلوتونیک برنورد، حاشیه فعال قاره و محیط کمان آتشفشانی 1 است که میتواند به فرورانش پوسته اقیانوسی موجود ب ین خرد قاره ایران مرکزي و بلوك افغان مرتبط باشد. واژههاي کلیدي: کمپلکس، سنسنجی، خرد قاره، ماگماتیسم، پرکامبرین، بردسکن، تکناpublishe

Petrogenesis of Granitoids, U-Pb zircon geochronology, Sr-Nd Petrogenesis of granitoids, U-Pb zircon geochronology, Sr-Nd isotopic characteristics, and important occurrence of Tertiary mineralization within the Lut block, eastern Iran

Tertiary intrusive granitoids within the Lut block in the Khorasan Razavi and South Khorasan provinces are mainly sub-volcanic with porphyry texture and their composition varies from granite to diorite but monzonite is dominant. With the exception of Hired, these are classified as belonging to the magnetite-series of I-type granitoids. Chemically, these rocks are meta-aluminous. Those with mineralization are K-rich and those without mineralization such as Najmabad are Na-rich. All intrusive rocks plot in the field of calc-alkaline to adakite except Najmabad that plot in the adakite field. Based on low content of Nb (30), low initial 87Sr/86Sr (17 ppm), low ratio of Zr/Nb (0.707) and low initial εNd value (-3), magmas in the Kaybar-Kuh were more contaminated in the continental crust. Based on depletion in HREE and high ratio of (La/Yb)N (17-23), magma in Najmabad originated in the deep region in which garnet was present. Based on REE pattern and ration of Eu/Eu* (0.8-1), intrusive rocks within Maherabad, Khoopik, Chah-Shaljami, Kuh Shah and Dehsalm are calc-alkaline and their magma formed in an oxidant condition whereas Kaybar Kuh magma with low ratio of Eu/Eu* (<0.8) was contaminated in the continental crust under reduced conditions. The age of these granitoids is between Middle Eocene and Lower Oligocene. Kaybar-Kuh (43.3 Ma) is situated in the north and Chah-Shaljami (33.3 Ma) in the south. The initial 87Sr/86Sr ratios decrease from north (0.7077) to south (0.7047) as the age decreases. εNd of Maherabad, Khoopik, Dehsalm, and Chah-Shaljami granitoids is between +0.5 and +2.49 and the initial 87Sr/86Sr ratio is less than 0.7055. The age of the source rock (TDM, which was calculated based on Sm-Nd isotopes) indicates that these magma originated from oceanic crust with different ages. Kaybar-Kuh originated from the oldest oceanic crust (840 Ma) and was contaminated more in continental crust, but Najmabad originated from a younger oceanic crust (360 Ma) with minor contamination. Dehsalm and Chah-Shaljami magma which had some differences with Maherabad and Khoopik, originated from oceanic crust of 200 Ma. The period between 42 and 33 Ma (Middle Eocene to Lower Oligocene) is the most important stage of mineralization in eastern Iran especially in South Khorasan. Some of the major systems, which are identified so far are: porphyry Cu-Au, reduced intrusive related Au, high sulfidation Au, Fe- skarn, Pb-Zn-Sb vein and IOCG deposits. Granitoid rocks formed between 42 and 33 Ma within the Lut block and northern area has great potential for exploring porphyry Cu-Au, IOCG, Fe, Pb-Zn, Au etc

Investigation of alteration zones, geochemistry and petrogenesis of the Chahshaljami prospect, Easthern Iran

Texto principal em Persa, com resumo em Inglês. O trabalho é datado de 2010, mas o número da revista só foi efectivamente publicado em 2012.Chahshalghami mineral index is located 190 km to the south of Birjand in the Lut Block volcanic-plutonic belt. Intrusive rocks of Chahshalghami include quartz monzonite, monzonite, granodiorite and diorite and classified as volcanic arc granites, high-K calc alkaline to shoshonite rocks. Processing Aster Satellite image has detected alteration minerals such as alunite, jarusite, chlorite, dickite, sericite, montmorillonite, quartz and iron oxide. Silicic, sulfide and stockwork zones show anomalies of Au, Cu, As, Bi, Mo, Sb, Pb and Zn. Microcrystalline and disseminated pyrite is associated with silicic alteration and many veins include molibdenite, chalcopyrite, sphalerite, galena and enargite. Intrusive rocks have similar trend on Harker diagrams for several major oxides, suggesting a common source and evolution of their magmas. Primitive mantle normalized trace element spider diagram display strong enrichment in LILE such as Rb, Sr, Ba, Zr, Cs and depletion in some high field strength elements (HFSE) e.g. Nb, P and Y. On chondrite normalized plots, display significant LREE enrichments and high degrees of La/Yb > 21.4-33.7 for intrusive rocks and the lack of Eu anomaly is evident. Sr/Y and La/Yb are respectively 31.6-72.2, 21.5-33.5 and cover characteristics of adakites and Sr-Nd isotope studies show that the source is related to the mantle melts contaminated by the lower crust

Geochronology and petrogenesis of the Late Neoproterozoic granitic gneisses of Golpayegan metamorphic complex: a new respect for Cadomian crust in the Sanandaj-Sirjan Zone, Iran

The studied granitic gneiss bodies of the Golpayegan metamorphic complex, located in the central part of the Sanandaj Sirjan Zone (SaSZ), in western Iran. Zircon U-Pb dating of two samples shows that the crystallization of the protolith occurred at 557 ± 12 Ma in the Late Neoproterozoic (Ediacaran), broadly coeval to the Neoproterozoic-Early Palaeozoic basement in other parts of Iran. Geochemically, the protolith of the gneisses probably corresponds to differentiated I-type granites with subalkaline affinities in composition. The ratios of Y/Nb >1.2 reveal an affinity to Cordilleran I-type granites for the granitic gneisses. The high Th/U ratios (2.8 to 9), low Eu/Eu* (0.13 to 0.73), with, low contents of FeO (0.55 to 1.72 wt.%), MgO (0.07 to 0.53 wt.%) and MnO (0.01 to 0.04 wt.%) and the high 87Sr/86Sr(i) ratios (0.70693 to 0.73557), negative ƐNd(t) values (−4.4 to −1.7) and Nd model ages (TDM2 = 1.35 to 1.56 Ga) suggest that the protolith may have been derived from partial melting of a pre-existing felsic crustal source (most likely differentiated granitoids). The new results reveal that the granitic source magma has been evolved in an active continental margin tectonic regime during the southward subduction of the Proto-Tethys ocean beneath the northern margin of Gondwana, like other coeval fragments dispersed in the entire Cadomian active continental margins. Also, the Cadomian crust widely extended in western Iran and it confirms these rocks have some clear affinity with Cadomian crust in the world.publishe

Sr-Nd isotope geochemistry and petrogenesis of the Chah-Shaljami granitoids (Lut Block, Eastern Iran)

Chah-Shaljami porphyritic granitoids belong to the Lut Block volcanic–plutonic belt of central eastern Iran. These intrusive rocks are mostly quartz monzonites, granodiorites and diorites. Geochemical evidence reveals that they are co-genetic and that they have features typical of high-K calc-alkaline to shoshonitic rocks from volcanic arc setting. Primitive mantle-normalized trace element spider diagrams display strong enrichment in LILE, such as Rb, Ba, and Cs, and depletion in some HFSE, e.g. Nb, Ti, Y and HREE. Chondrite-normalized plots show a very marked REE fractionation, with significant LREE enrichment (23 ⩾ LaN/YbN ⩾ 14) and the lack of Eu anomaly. Sr/Y and La/Yb ratios of Chah-shaljami intrusives are respectively 20–67 and 21–34, which reveals that, despite their K-rich composition, these rocks also, have some adakitic affinity. Plots on the Sr/Y–Y and La/Yb–Yb diagrams show that the Chah-Shaljami intrusives may be subdivided into two distinct classes. A Rb–Sr age of 33.5 ± 1 Ma, mainly dependent on the Sr isotopic composition of biotite, was obtained in a quartz monzonite sample. Taking into account that this sample was almost unaffected by hydrothermal and meteoric alteration and that cooling was probably fast, the 33–34 Ma date is interpreted as the intrusion age. With the exception of two samples, initial 87Sr/86Sr ratios and Nd values are clustered in the restricted ranges of 0.70470–0.70506 and +1.9–+2.7, which fits into a supra-subduction mantle wedge source for the parental melts and indicates that, in general, crustal contribution for magma diversification was not relevant; however, one sample shows higher 87Sr/86Sr and lower Nd, revealing that, occasionally, crustal rock assimilation also contributed to geochemical variation; one other sample, strongly affected by hydrothermal alteration, departs from the main group only by higher 87Sr/86Sr, suggesting that its alteration involved crustal fluids. Sr and Nd isotope compositions together with major and trace element geochemistry points to the origin of the parental magmas by melting of a metasomatized mantle source, with garnet behaving as a residual phase, whilst phlogopite was an important contributor to the generated melts