Geochemistry and Geochronology of Upper Cretaceous, Magnetite Series Granitoids, Arghash-Ghasemabad, Ne Iran (original) (raw)
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Journal of Asian Earth Sciences, 2015
The Mahoor Cu-Zn-bearing porphyritic granitoid rocks belong to the Lut Block volcanic-plutonic belt (central Eastern Iran). These granitoid rocks occur mainly as dykes and stocks that intrude into Eocene volcanics and pyroclastic rocks. Petrographically, all the studied intrusives display porphyritic textures with mm-sized phenocrysts, most commonly of plagioclase and hornblende, embedded in a fine-grained groundmass with variable amounts of plagioclase, hornblende, clinopyroxene, quartz and opaque minerals. Hydrothermal alteration affected these granitoid rocks, as revealed by the common occurrence of sericite, chlorite, titanite, epidote and calcite. Chemical classification criteria show that the intrusives may be named as gabbrodiorites, diorites, monzodiorites and tonalites. Major elements geochemistry reveals that all the studied lithologies are typically metaluminous (A/CNK 6 0.9). Magnetic susceptibility (1485 Â 10 À5 SI) together with mineralogical and geochemical features shows that they belong to magnetite granitoid series (I-type). Trace element patterns normalized to chondrite and primitive mantle are very similar to each other and show enrichments in LREE relative to HREE and in LILE relative to HFSE, as well as negative anomalies of Ta, Nb and Ti. Eu/Eu ⁄ ratios vary from 0.88 (in the most mafic composition) to 0.65, showing that plagioclase played a role in magma differentiation. LA-MC-ICP-MS U-Pb zircon data from a diorite, yielded similar concordia ages of ca. 31.88 ± 0.2 Ma (Error: 2r), which corresponds to the Oligocene period. These granitoid rocks have (87 Sr/ 86 Sr)i values vary between 0.7055 and 0.7063. In terms of isotopic compositions, while eNdi is between À0.6 and À2.5, suggesting that magmas underwent contamination through being exposed to the continental crust. The whole set of geochemical data agree with the emplacement of the studied intrusions in a magmatic belt above a subduction zone. Primitive magmas should have formed by melting of mantle wedge peridotite, and during magma ascent to crustal levels, both magma differentiations took place by crystal fractionation and crustal contamination. Sulfide mineralizations (pyrite, chalcopyrite and sphalerite) related to these granitoid rocks is common and occurs as both disseminated and hydrothermal veins, indicating a high mineralization potential for this area.
Journal of Asian Earth Sciences, 2010
The Paleo-Tethys ocean opened in Silurian time, and its subduction under the Turan plate started in the Late Devonian. By Late Triassic time (225 Ma), no Paleo-Tethys crust remained on the surface of the Iranian plate. Subsequently, however, obduction of the Turan plate over the Iranian plate emplaced allochthonous sheets in what is now northeastern Iran. The sheets contain meta-ophiolites, which have been dated at 281.4 and 277.4 Ma by the 40 Ar-39 Ar method. These remnant Paleo-Tethys meta-ophiolites and associated metaflysch sequences were intruded by the Dehnow diorite and Kuhsangi granodiorite. Zircon U-Pb dating indicates that the age of the Kuhsangi granodiorite is 217 ± 4 Ma and that of the Dehnow diorite is 215 ± 4 Ma (Late Triassic, Norian). The granodiorite and diorite have magnetic susceptibilities of between 5  10 À5 and 20  10 À5 (SI units) and therefore are classified as belonging to the ilmenite series of reduced-type granitoids. Chemically, the Dehnow diorite and Kuhsangi granodiorite are moderately peraluminous S-type plutons with (La/Yb) N = 7-22 and no, or only small, negative Eu anomalies (Eu/ Euà = 0.55-1.1). Their initial 87 Sr/ 86 Sr ratios range from 0.707949 to 0.708589, and their initial e Nd values range from À6.63 to À5.90 when recalculated to an age of 216 Ma. These values could be considered to represent continental crust-derived magmas, and metagreywacke to metapelite with initial e Nd values of À15.01 may have been involved in their genesis, but these were not the sole parent material.
Revista Geoaraguaia, 2020
Dehaj-Sarduieh volcano-plutonic belt in Kerman province of Iran represents a part of Urumieh-Dokhtar Magmatic assemblage which is mainly composed of granodiorite, quartz diorite, tonalite granite and granophyre. These rocks emplaced in Eocene volcanic and pyroclastic deposits rocks and are considered to be Oligo-Miocene in age. Geochemical studies showed that the amphibole minerals in diorite and granodiorites are calcic in composition and range from actinolite to magnesio-hornblende. Geochemical and mineralogical results revealed that these bodies have been generated in the lower part of the lower crust at a temperature of 700 to 750 °C, with an oxygen fugacity of-13.57 to-15.76 and a low pressure of 1 to 3 kb through mixing of mantle-derived mafic magma with crustalderived felsic melts. These amphiboles are subduction-related and in accordance with the tectono-magmatic features suggested for these massifs, they show the characteristics of subduction and active continental margin environments. Field observations and mineralogical-geochemical evidence revealed that the original magma has been calc-alkaline in composition and metaluminous I-type. It is also showed that the process of fractional
Journal of Asian Earth Sciences, 2015
The Bornaward Granitoid Complex (BGC) in the Taknar Zone is located in the northeast of Central Iranian Block. The BGC consists of granite, alkaligranite, syenogranite, leucogranite, granophyre, monzogranite, granodiorite, tonalite and diorite that have intruded into the center of Taknar Zone. These intrusive rocks affected by low grade metamorphism. Because of there are no reliable isotope dating data, for the Bornaward Granitoid Complex rocks have been proposed discordant ages (Jurassic, Cretaceous or even younger ages) by many studies. In the present study, new isotopic information based on zircon U-Pb dating has revealed the origin and time of the formation of the BGC. These new results do not confirm previously proposed ages. The results obtained from zircon U-Pb dating of the BGC rocks suggest late-Neoproterozoic (Precambrian) age (540-550 Ma). The Bornaward Granitoid Complex is middle-high metaluminous to lower-middle peraluminous and belongs to tholeiite, calc-alkaline to high-K calc-alkaline rock series with enrichment in LIL (Cs, Rb and Ba, U, K, Zr, Y, Th) and depletion in HIL (Sr and Nb, Ta, Ti) elements. Chondrite-normalized Rare Earth Elements (REE) plots indicate minor enrichment of LREE compared to HREE, and strong negative anomaly of Eu compared to other Rare Earth Elements. Furthermore, initial 87 Sr/ 86 Sr and 143 Nd/ 144 Nd range from 0.70351 to 0.71689 and 0.511585 to 0.512061, respectively, and initial eNd isotope values for granite, granodiorite and diorite range from À6.73 to 2.52. These all indicate that the BGC has derived from partial melting of distinct basement source regions with very high initial 87 Sr/ 86 Sr and undergoing extensive crustal contamination (S-type granite).
The study area (Bornaward granite) is located in northeast of Iran (Khorasan Razavi province), about 280 km southwest of Mashhad city. Taknar zone is an exotic block, bordered by two major faults, Great Kavir fault (Drouneh) to the south and Rivash fault in the north. A complex of granite, granodiorite, monzonite and diorite crop out at the center of Taknar zone. They are named as "Bornaward granite". Published data using Rb-Sr whole-rock and biotite isotopic methods on granitoid rocks (Bornaward granite) gave ages of 154 to 111 Ma. The results of U-Pb zircon dating of granodiorite is 552.69 ± 10.89 Ma and granite is 538.22 -1.82, + 4.28 Ma (Late Neoproterozoic time). Both granite and granodiorite are classified as belonging to the ilmenite-series of reduced S-type granitoids. Chemically, they are per-aluminous, high-K calc-alkaline with relatively enriched in LILE, Rb, K and depleted in Sr, Ba, Nb, Ti, Ta, Y and Yb. Chondrite-normalized Rare Earth Element (REE) plots indicate minor enrichments of light REE in composition with heavy REE, with (La/Yb) N between 3.5-5.6 and high total with strong negative anomaly of Eu. They have a initial 87 Sr/ 86 Sr and 143 Nd/ 144 Nd ranging from 0.713566 to 0.716888 and 0.511791 to 0.511842, respectively, when recalculated to an age of 553 and 538 Ma, consistent with the new radiometric results. Initial εNd isotope values for granite and granodiorite range from -2.62 to -2.01. Granite and granodiorite of Bornaward yields a T DM age of 1.4-1.41 Ga. This indicates that the granites and granodiorite being derived from partial melting of distinct basement source regions with very high initial 87 Sr/ 86 Sr.
Lithos, 2013
Mashhad granitoids in northeast Iran are part of the so-called Silk Road arc that extended for 8300 km along the entire southern margin of Eurasia from North China to Europe and formed as the result of a north-dipping subduction of the Paleo-Tethys. The exact timing of the final coalescence of the Iran and Turan plates in the Silk Road arc is poorly constrained and thus the study of the Mashhad granitoids provides valuable information on the geodynamic history of the Paleo-Tethys. Three distinct granitoid suites are developed in space and time (ca. 217-200 Ma) during evolution of the Paleo-Tethys in the Mashhad area. They are: 1) the quartz diorite-tonalite-granodiorite, 2) the granodiorite, and 3) the monzogranite. Quartz diorite-tonalite-granodiorite stock from Dehnow-Vakilabad (217 ± 4-215 ± 4 Ma) intruded the preLate Triassic metamorphosed rocks. Large granodiorite and monzogranite intrusions, comprising the Mashhad batholith, were emplaced at 212 ± 5.2 Ma and 199.8 ± 3.7 Ma, respectively. The high initial 87 Sr/ 86 Sr ratios (0.708042-0.708368), low initial 143 Nd/ 144 Nd ratios (0.512044-0.51078) and low ε Nd(t) values (− 5.5 to − 6.1) of quartz diorite-tonalite-granodiorite stock along with its metaluminous to mildly peraluminous character (Al 2 O 3 /(CaO + Na 2 O + K 2 O) Mol. = 0.94-1.15) is consistent with geochemical features of I-type granitoid magma. This magma was derived from a mafic mantle source that was enriched by subducted slab materials. The granodiorite suite has low contents of Y (≤18 ppm) and heavy REE (HREE) (Yb b 1.53 ppm) and high contents of Sr (>594 ppm) and high ratio of Sr/Y (>35) that resemble geochemical characteristics of adakite intrusions. The metaluminous to mildly peraluminous nature of granodiorite from Mashhad batholiths as well as its initial 87 Sr/ 86 Sr ratios (0.705469-0.706356), initial 143 Nd/ 144 Nd ratios (0.512204-0.512225) and ε Nd(t) values (−2.7 to −3.2) are typical of adakitic magmas generated by partial melting of a subducted slab. These magmas were then hybridized in the mantle wedge with peridotite melt. The quartz diorite-tonalite-granodiorite stock and granodiorite batholith could be considered as arc-related granitoid intrusions, which were emplaced during the northward subduction of Paleo-Tethys Ocean crust beneath the Turan micro-continent. The monzogranite is strongly peraluminous (Al 2 O 3 /(CaO + Na 2 O + K 2 O) Mol. = 1.07-1.17), alkali-rich with normative corundum ranging between 1.19% and 2.37%, has high initial 87 Sr/ 86 Sr ratios (0.707457-0.709710) and low initial 143 Nd/ 144 Nd ratios (0.512042-0.512111) and ε Nd(t) values (−5.3 to − 6.6) that substantiate with geochemical attributes of S-type granites formed by dehydration-melting of heterogeneous metasedimentary assemblages in thickened lower continental crust. The monzogranite was emplaced as a consequence of high-temperature metamorphism during the final integration of Turan and Iran plates. The ages found in the Mashhad granites show that the subduction of Paleo-Tethys under the Turan plate that led to the generation of arc-related Mashhad granites in late-Triassic, finally ceased due to the collision of Iran and Turan micro-plates in early Jurassic.
Lithos, 2015
itoids (NE Iran): Petrogenetic constraints from U-Pb zircon geochronology and isotope geochemistry, LITHOS (2014), Abstract Kashmar granitoids outcrop for ~100km along the south flank of the Sabzevar ophiolite (NE Iran) and consist of granodiorite and monzogranite along with subordinate quartz monzonite, syenogranite and aplitic dikes. These granitoids intruded Early to Middle Eocene high-K volcanic rocks and can spatially be grouped into eastern and western granitoids. Five samples of granite have identical zircon U-Pb ages of ca. 40-41 Ma. The granitoids have quite high K 2 O (~1.3-5.3 wt.%) and Na 2 O (~1.1-4.6 wt.%) with SiO 2 A C C E P T E D M A N U S C R I P T
Major, Trace and REE geochemistry of Paleo – Tethys Collision – Related Granitoids from Mashhad, Ira
Journal of Sciences Islamic Republic of Iran, 2006
The study area is located in northeastern Iran (south of Mashhad). The Paleo-Tethys remnants (meta-ophiolite and meta-flysch) were intruded at three different episodes of magmatism (Triassic to Cretaceous time). 1) Dehnow-Kuhsangi hornblende biotite tonalite-granodiorite; 2) Sangbast Feldspar monzogranite; and 3) Khajehmourad biotitemuscovite leucogranite and pegmatite. They are moderately peraluminous to highly felsic peraluminous S-type granitoid. Paleo-Tethys opened in Silurian time and subduction under Turan plate was started in Late Devonian. By Late Carnian (225 m.y. ago) there was no Paleotethys left on an Iranian transect. Turan plate is abducted over Iran Plate. Only two stages of low grade regional metamorphism are exposed, Hercynian orogeny (Late Paleozoic) and Cimmerian orogeny (Jurassic time). Ophiolites constitute allochthonous sheets and they are dated by 40Ar-39Ar, 281.4 and 277.4 Ma. Dehnow to Kuhsangi tonalite-granodiorite (Early Triassic) are meta to moderately peraluminous S to I-type granitoids. They are sub-alkaline, calcic-type. They have low values of magnetic susceptibility [(1.5 to 2.5) × 10 −5 SI]. Sangbast feldspar monzogranite porphyry (Late Triassic) is moderately peraluminous, K-rich calc-alkaline type. Biotite-muscovite leucogranite and late pegmatite dikes (Jurassic age) are highly felsic peraluminous S-type granitoids. They are syn-collision granite. They have low values of magnetic susceptibility [(0.1 to 0.6) × 10 −5 SI]. Total REE content of tonalite-granodiorite is 101-136, in feldspar monzogranite is 221-238 and in leucogranite is 130-170 ppm. The leucogranite has the highest [(La/Yb)N = 37-124] tonalite-granodiorite has the lowest [(La/Yb)N = 7 to 22]. The Eu anomalies (Eu/Eu* = 0.55 to 1.1) is low in all of them. Tonalite-granodiorite magma has originated from a mafic source. Feldspar monzogranite has originated from a deeper source and contaminated in the crust. Biotite-muscovite leucogranite may have originated from the crustal materials.
Geosciences Journal, 2018
The Simorgh prospecting area is located in the central part of the Lut Block in eastern Iran. The Lut Block, the eastern part of the Central Iranian Microcontinent (CIM), has a complex tectonic evolution and is characterized by extensive magmatic activities with a range of geochemical signatures. The Simorgh intrusions have features typical of calc-alkaline to high-K calc-alkaline rocks, metaluminous to slightly peraluminous and formed in a volcanic arc setting. Mineralization in the area is believed to be related to these intrusions. To better understand the petrogenesis of these intrusions, we report zircon U-Pb dating and Hf isotopes and whole rock geochemistry of two granites and one diorite. Age dating using Zircon U-Pb method on pyroxene diorite porphyry stock and two granite porphyry dikes revealed 24.85 ± 0.51 Ma, 25.37 ± 0.56 Ma and 25.94 ± 0.76 Ma ages respectively (late Oligocene, Chattian). Field observations and U-Pb dating indicate that there are at least two stages of emplacement: pre-mineralization intrusions (diorite porphyry) and syn-mineralization intrusions (granite porphyry, granodiorite porphyry and pyroxene diorite porphyry). Mantle-normalized, trace-element spider diagrams display enrichment in large ion lithophile elements (LILE) and light rare earth elements ((La/Yb) N = 9.26-14.48), and depletion in high field strength elements (HFSE) and heavy rare earth elements, as well as negative Eu anomalies (Eu/Eu* = 0.49-0.91). Zircon Hf isotope data from the Simorgh intrusive rocks show largely positive εHf (t) (average = 3.6 ± 2.0). Hf model ages are ranging from 720 to 1320 Ma, indicating its derivation from a relatively juvenile source. The presence of zircon xenocrysts may prove its contamination by older continental crust (Siderian).
Iranian Journal of Crystallography and Mineralogy
Quchan-Esfarayen magmatic belt (north of Sabzevar) include Neogene adakitic domes with andesite to rhyolite in composition which is cut by Jurasic sedimentary rocks, Eocene volcano-sedimentary rocks, Miocene sedimentary rocks and even occasionally Peliocene conglomerate. The main minerals of these rocks are plagioclase and amphibole with various textures such as felsitic porphyry, microlitic porphyry, glomero porphyry, sieve and flow textures. The calc-alkaline and metaluminous to peraluminous nature, enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREE) and depletion in heavy rare earth elements (HREE) in primitive mantle and chondrite normalized spider diagrams, along with high contents of Na 2 O, Al 2 O 3 , Sr, high ratio of Sr/Y and low ratio of K 2 O/Na 2 O and depletion in HFSEs in these rocks are characteristics of the young arc volcanics. Furthermore, these rocks display initial 87 Sr/ 86 Sr ratios of 0.70390 to 0.70562 and <Nd(t) values of-0.86 to +4.98 respectively, which show that they are originated from partial melting of oceanic slab with crustal contamination. Emplacement age of these rocks into the quchan-Esfarayen magmatic belt obtained with U-Pb dating on separated zircons of 17.83±0.24 to 8.50±0.34 Ma. The results show that parental magma of the rocks generated by partial melting of a garnetamphibolitic to eclogitic subducted Sabzevar Neo-Thethyan oceanic slab underneath the Binaloud continental lithospher. Presence of continental metamorphic and sedimentary xenoliths, corrosion and chemical disequilibrium of the phenocrysts and their sieve textures in plagioclase along with Sr-Nd isotopic ratios in these rocks indicate the operation of differentiation crystallization, assimilation and crustal contamination (AFC) in the genesis and evolution of igneous rocks of this belt.