Eocene Kashmar granitoids (NE Iran): Petrogenetic constraints from U–Pb zircon geochronology and isotope geochemistry (original) (raw)
Related papers
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.
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.
journal of sciences islamic republic of iran, 2020
Oligo-Miocene Bagh-e-Khoshk granitoid stock is intruded into the Eocene volcanic rocks in the southeastern part of the Urumieh-Dukhtar Magmatic assemblage in Iran. The granitoids are mainly consisting of diorite, quartz diorite and granodioritic rock types. They are metaluminous to slightly peraluminous, medium to high K calc-alkaline, with SiO2 ranging from 50.2 to 66 wt.%. The major elements mostly define linear trends and negative slopes with increasing of SiO2, while K2O is positively correlated with silica. There is a higher content of Ba, Rb, Nb and Zr elements with increasing SiO2, whereas Sr shows an opposite behavior. Primordial mantle-normalized multi-element patterns show enrichment in LILE relative to HFSE with distinctive Nb, Ta, Ti negative anomalies. These signatures are typical of subduction related magmas that formed in an active continental margin. The high Ba/La Ba/TiO2, Ba/Nb and Th/Nb ratios emphasizes the significant involvement of fluids during subduction proc...
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.
International Geology Review, 2016
The aim of this article is to examine the geochemistry and geochronology of the Cadomian Mishu granites from northwest Iran, in order to elucidate petrogenesis and their role in the evolution of the Cadomian crust of Iran. The Mishu granites mainly consist of two-mica granites associated with scarce outcrops of tonalite, amphibole granodiorite, and diorite. Leucogranitic dikes locally crosscut the Mishu granites. Two-mica granites show S-type characteristics whereas amphibole granodiorite, tonalities, and diorites have I-type signatures. The I-type granites show enrichment in large-ion lithophile elements (e.g. Rb, Ba and K) and depletion in high field strength elements (e.g. Nb, Ti and Ta). These characteristics show that these granites have been formed along an ancient, fossilized subduction zone. The S-type granites have high K, Rb, Cs (and other large ion lithophile elements) contents, resembling collision-related granites. U-Pb zircon dating of the Mishu rocks yielded 238 U/ 206 Pb crystallization ages of ca. 550 Ma. Moreover, Rb-Sr errorchron shows an early Ediacaran age (547 ± 84 Ma) for the Mishu igneous rocks. The two-mica granites (S-type granites) show high 87 Sr/ 86 Sr (i) ratios, ranging from 0.7068 to 0.7095. Their ɛNd values change between −4.2 and −4.6. Amphibole granitoids and diorites (I-type granites) are characterized by relatively low 87 Sr/ 86 Sr (i) ratios (0.7048-0.7079) and higher values of ɛNd (−0.8 to −4.2). Leucogranitic dikes have quite juvenile signature, with ɛNd values ranging from +1.1 to +1.4 and Nd model ages (T DM) from 1.1 to 1.2 Ga. The isotopic data suggests interaction of juvenile, mantle-derived melts with old continental crust to be the main factor for the generation of the Mishu granites. Interaction with older continental crust is also confirmed by the presence of abundant inherited zircon cores. The liquid-line of descend in the Harker diagrams suggests fractional crystallization was also a predominant mechanism during evolution of the Mishu I-type granites. The zircon U-Pb ages, whole rock trace elements, and Sr-Nd isotope data strongly indicate the similarities between the Mishu Cadomian granites with other late Neoproterozoic-early Cambrian (600-520 Ma) granites across Iran and the surrounding areas such as Turkey and Iberia. The generation of the Mishu I-type granites could be related to the subduction of the Proto-Tethyan Ocean during Cadomian orogeny, through interaction between juvenile melts and old (Mesoproterozoic or Archaean) continental crust. The S-type granites are related to the pooling of the basaltic melts within the middle-upper parts of the thick continental crust and then partial melting of that crust.
elsiver, 2018
Tuyeh-Darvar granitoid, which outcrop ca 45 km Sw of Damghan city, in the Eastern Alborz zone, comprise mainly the pluton emplaced into the Barut Formation of Lower Cambrian ages. Zircon U-Pb ages show Carboniferous ages (325 ± 3 Ma) for the formation of this granitoid. The granitoid is mostly metaluminous, ferroan and alkalic mon-zonite to monzodiorite. "These rocks have high values of FeOT/MgO and Ga/Al, high concentrations of K2O+Na2O, low abundances of MgO and transitional elements. Plots normalized to chondrite and primitive mantle compositions show strong enrichments of LREE relative to HREE and of LILE relative to HFSE, accompannied by negative anomalies of Nb and Sr."They contain Fe-rich hydrous mafic minerals and magnetite. These features are typical of A-type granites. Sr-Nd isotopic geochemistry, with initial ɛNd values from −1.1 to −1.5 and initial 87 Sr/ 86 Sr ratios between 0.70562 and 0.70678, are consistent with magmatic differentiation from mafic melts produced from an enriched mantle source. However, other models such as melting of mafic crust or mixing of components from depleted mantle and continental crust cannot be discarded. On the basis of the U-Pb zircon age (325 ± 3 Ma) and the known magmatic tectonic regime in Iran during the Paleozoic, it is suggested that the pluton, formed in a rift environment related to extensional structures of the Alborz block in Early Carboniferous time.
Gondwana Research, 2018
The Sanandaj-Sirjan zone (SSZ) of Iran comprises sedimentary and metamorphic basement rocks, which are generally regarded as having been derived from the southern active margin of the Eurasian plate. Within the SSZ, a number of Mesozoic to Cenozoic granitoid intrusions of various size, elongated in a NW-SE direction are exposed. With the benefit of precise age dating, geochemical and isotopic data over the past decade, the magmatic history of these intrusions has become clearer. This study presents further geochronological and geochemical data for previously dated and undated granitoids together with considerable zircon Lu-Hf isotopic data, which were limited in the past. Combined with previous work, these new data, including the finding of ca. 170 Ma adakite, lead to improved constraints on the Meso-Cenozoic tectonic evolution of Neo-Tethyan lithospheric subduction. The dominant early-middle Jurassic magmatism is proposed to have occurred with a major contribution of crustal components during the initiation of Neo-Tethyan subduction. Subsequent, late Jurassic magmatism suggests the involvement of lower crust partial melting in an extensional tectonic setting. Cretaceous magmatism almost ceased after formation of a flat slab, caused by a trench retreat rate exceeding that of slab roll-back. Eocene magma sources in the SSZ are dominated by mantle-derived input through an asthenospheric window with subordinate crustal contamination during the subduction of the Neo-Tethyan ridge-spreading center. This interpretation differs from Paleocene-Eocene magmatic flare-up proposed for the northern Iranian interior, which may have been driven by an episode of slab retreat or slab roll-back following Cretaceous flat slab subduction.
2020
Intrusive rocks are well-exposed in the south Birjand around the Koudakan is herein compared to previously studied outcrops along the middle Eocene to late Oligocene Eastern Iran Magmatic Belt. This pluton is composed mainly of monzonite, quartz-monzonite, and granite with high-K calc-alkaline to shoshonitic affinities. The U-Pb zircon geochronology from monzonite and quartz-monzonite reveals the crystallization ages of 40.96 ± 0.48 to 38.78 ± 0.78 Ma (Bartonian). The monzonite, quartz-monzonite, and granite rocks show similar REEs and trace element patterns, as well as limited variations in εNd (i) and 87 Sr/ 86 Sr (i) ratio, suggesting that they are a comagmatic intrusive suite. The chondrite and primitive mantle normalized rare earth and trace element patterns show enrichment in the light rare earth elements, K, Rb, Cs, Pb, Th, and U and depletion in heavy rare earth elements, Nb, Zr, and Ti. The εNd (i) and 87 Sr/ 86 Sr (i) values range from +1.32 to +1.68 and 0.7044 to 0.7047, respectively, identical to island-arc basalt composition. The whole-rock Nd model age (T DM) for the intrusive rocks range between 0.69 and 0.73 Ga. These geochemical and isotopic signatures indicate a subduction-related sub-continental lithospheric mantle source for these rocks. Our new geochemical, isotopic, and geochronological studies integrated with previously published data indicate that the middle Eocene to late Oligocene magmatism in eastern Iran was formed in a post-collisional tectonic environment. We suggest the northeastward subduction of the Neo-Tethys ocean beneath the Lut block and the eastward subduction of the Sistan ocean beneath the Afghan block caused mantle wedge to be metasomatized by slab components. At a later stage, a collision between the Lut and Afghan blocks was accompanied by the lithospheric delamination, and the subsequent asthenospheric upwelling led to the melting of the metasomatized sub-continental lithospheric mantle and the generation of middle Eocene to late Oligocene magmatism in the Eastern Iran Magmatic Belt. ARTICLE HISTORY
Lithos, 2010
Three plutons (Deh-Siahan, Bande-Bagh and Baghe-Khoshk Sharghi, collectively referred to as the DBB hereafter) in southwestern Kerman, in the southeastern part of the Urumieh-Dokhtar magmatic assemblage (UDMA) of the Zagros orogenic belt differ from the typical calc-alkaline metaluminous, I-type intrusions of the region. The DBB intrusions have a distinct lithological assemblage varying from diorite through monzogranite and monzonite to alkali feldspar syenite and alkali granite. The DBB granitoids are metaluminous to slightly peraluminous, alkaline to shoshonitic in composition and have high total alkali contents with K 2 O > Na 2 O, high FeO T /MgO values, and low CaO and MgO contents. They are enriched in some LILEs (such as Rb and Th) and HFSEs (such as Zr, Y and REEs except Eu) and depleted in Sr and Ba relative to primordial mantle, and have low concentrations of transitional metals. These features along with various geochemical discriminant diagrams suggest that the DBB granitoids are post-collisional A-type granitoids, which had not been recognized previously in the UDMA. The chondrite-normalized REE patterns of the DBB granitoids show slightly enriched light REEs [(La/Sm) N = 2.26-4.13], negative Eu anomalies [(Eu/Eu*) N = 0.19-0.74] and flat heavy REE patterns [(Gd/Yb) N = 0.80-1.87]. The negative Eu anomaly indicates an important role for plagioclase and/or K-feldspar during fractional crystallization. Whole-rock Rb-Sr isotope analysis yields an isochron age of 33 ± 1 Ma with an initial 87 Sr/ 86 Sr value of 0.7049 ± 0.0001. Whole-rock Sm-Nd isotope analysis gives ε Nd t values from + 2.56 to + 3.62 at 33 Ma. The positive ε Nd t
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).