Sr–Nd isotope geochemistry and tectonomagmatic setting of the Dehsalm Cu–Mo porphyry mineralizing intrusives from Lut Block, eastern Iran

The Dehsalm Cu-Mo bearing porphyritic granitoids belong to the Lut Block volcanic-plutonic belt (central eastern Iran). These rocks range in composition from gabbro-diorite to granite, with dominance of monzonites and quartz monzonites, and have geochemical features of high-K calc alkaline to shoshonitic volcanic arc suites. Primitive mantle-normalized trace element spider diagrams display strong enrichment in LILE such as Rb, Ba and Cs and depletions in some high field strength elements (HFSE), e.g. Nb, Ti, Y and HREE. Chondrite-normalized plots display significant LREE enrichments, high LaN/YbN and a lack of Eu anomaly. High Sr/Y and La/Yb ratios of Dehsalm intrusives reveal that, despite their K-rich composition, these granitoids show some resemblances with adakitic rocks. A Rb-Sr whole rock-feldspar-biotite age of 33 ± 1 Ma was obtained in a quartz monzonite sample and coincides, within error, with a previous geochronological result in Chah-Shaljami granitoids, further north-west within the Lut Block. (87Sr/86Sr)i and εNdi isotope ratios range from 0.70481 to 0.70508 and from +1.5 to +2.5, respectively, which fits into a supra-subduction mantle wedge source for the parental melts and indicates that crustal contribution for magma diversification was of limited importance. Sr and Nd isotope compositions together with major and trace element geochemistry point to an origin of the parental magmas by melting of a metasomatized mantle source, with phlogopite breakdown playing a significant role in the geochemical fingerprints of the parental magmas; small amounts of residual garnet in the mantle source also help to explain some trace element patterns. Geochemical features of Dehsalm porphyries and its association with Cu-Mo mineralization agree with a mature continental arc setting related to the convergence of Afghan and Lut plates during Oligocene

Dados geocronológicos e geoquímicos sobre o cortejo hipabissal de Dehsalm (leste do Irão): contributo para o conhecimento do arco vulcânico terciário no limite oriental do Bloco de Lut

A associação de rochas intrusivas hipabissais, de textura geralmente porfirítica, da zona de Dehsalm faz parte da cintura vulcano-plutónica do Bloco de Lut, na parte central da região oriental do Irão. Estudos anteriores incidindo sobre a alteração, as mineralizações e o papel dos fluidos hidrotermais revelaram que, em consequência da instalação das referidas rochas intrusivas, teve lugar a actividade de um sistema mineralizante do tipo pórfiro de Cu-Mo (Arjmandzadeh et al., 2013). As rochas estudadas neste trabalho variam desde as composições gabro-dioríticas até às graníticas, com predomínio das monzoníticas e quartzo-monzoníticas, e apresentam características geoquímicas de sequência calco-alcalina rica de potássio a shoshonítica, de zona de arco vulcânico. A conjugação da informação petrográfica com a projecção dos dados de elementos maiores em diagramas de Harker sugere que a cristalização fraccionada de clinopiroxena, plagioclase, horneblenda, apatite e óxidos teve um papel fundamental na diferenciação magmática. Nos perfis multi-elementares normalizados em relação ao manto primordial nota-se um nítido enriquecimento de elementos litófilos de grande raio iónico, como o Rb, o Ba e o Cs, e empobrecimento de alguns elementos com grande força de campo, como o Nb, o Ti, o Y e as terras-raras pesadas. Quanto aos perfis de lantanídeos com normalização condrítica, eles mostram, por um lado, um nítido fraccionamento entre as terras-raras leves e as pesadas, com valores elevados de LaN/YbN (21.5 to 31.0), enquanto, por outro lado, são desprovidos de anomalias de Eu. Na associação intrusiva de Dehsalm, registam-se ainda valores entre 31.6 e 72.2 para a razão Sr/Y e entre 21.5 e 33.5 para La/Yb, o que revela que, apesar de serem ricas de potássio, estas rochas possuem alguma afinidade adaquítica. As análises isotópicas efectuadas para o sistema Rb-Sr permitiram obter uma idade de 33 ± 1 Ma (87Sr/86Sr inicial = 0.70481 ± 0.00001; MSWD = 0.112), definida pelas composições de rocha total, feldspato e biotite de uma amostra de quartzo-monzonito. O resultado referido pode ser interpretado como sendo muito próximo da idade de intrusão, tendo em conta que a amostra escolhida tem uma textura que indica um rápido arrefecimento do magma e que, além disso, a composição mineralógica não inclui testemunhos significativos de alteração. A idade agora obtida coincide, considerando a margem de erro, com um dado geocronológico reportado num estudo anterior (Arjmandzadeh et al., 2011) efectuado em materiais semelhantes na área de Chah-Shaljami, a qual se situa a NW da presente zona de estudo, ao longo do bordo oriental do Bloco de Lut. Os valores de 87Sr/86Sr(33Ma) e εNd(33Ma) variam de 0.70481 a 0.70508 e de +1.5 a +2.5, respectivamente, o que é compatível com uma fonte, para os magmas parentais, em ambiente de cunha mantélica supra-subducção. Adicionalmente, as gamas estreitas das composições isotópicas indicam que a contribuição crustal para a diversificação magmática não foi significativa. Conciliando os diferentes tipos de dados geoquímicos - isotópicos, oligoelementares e macroelementares - parece poder sugerir-se que os líquidos parentais se terão originado por fusão de uma fonte mantélica metassomatizada, em que a granada se comportou como fase residual, enquanto a flogopite terá contribuído para os fundidos gerados. Quer as características geoquímicas dos pórfiros de Dehsalm, quer a sua associação com mineralizações de Cu-Mo estão de acordo com a sua instalação em ambiente de arco continental maduro, o qual deverá estar relacionado com a convergência das placas do Afeganistão e de Lut durante o Oligocénico. As características dos granitóides de Dehsalm revelam uma forte afinidade com as rochas contemporâneas de Chah-Shaljami, estudadas por Arjmandzadeh et al. (2011). O facto de em Dehsalm estar presente um leque mais amplo de litologias, incluindo composições mais máficas (nalguns casos, praticamente gabróicas) do que as encontradas em Chah-Shaljami, reforça a ideia, já apresentada no trabalho anterior, de os magmas parentais terem origem mantélica

Two-sided asymmetric subduction; implications for tectonomagmatic and metallogenic evolution of the Lut Block, Eastern Iran

West directed subduction zones show common characteristics, such as low structural elevation, deep trench, steep slab and a conjugate back-arc basin that are opposite to those of the east directed subduction zones. The tectonomagmatic and metallogenic setting of the Lut Block is still a matter of debate and several hypotheses have been put forward. Despite some authors denying the influence of the operation of Benioff planes, the majority propose that it occurred beneath the Afghan Block, while others consider that oceanic lithosphere was dragged under the Lut Block. Cu-Au porphyry deposits seem to occur in an island arc geotectonic setting during the middle Eocene while Mo-bearing deposits are coincident with the crustal thickening during Oligocene. We introduce new trace element and isotope geochemical data for granitoids and structural evidences testifying the two-sided asymmetric subduction beneath both Afghan and Lut Blocks, with different rates of consumption of oceanic lithosphere

Zircon U-Pb geochronology, geochemistry, Sr-Nd isotopic compositions, and tectonomagmatic implications of Nay (NE Iran) postcollisional intrusives in the Sabzevar zone

The mafic to felsic intrusive rocks of Nay (IRN) are located in the northeast of the central Iranian block. In this study, we present new major and trace element geochemistry, U-Pb zircon ages, and Sr-Nd isotopic data to discuss the origin of the IRN postcollisional units. The oldest units in the Nay area belong to Paleocene–early Eocene volcanic and pyroclastic series including basalt-andesite, latite, dacite, and tuff. These series are crosscut by subvolcanic and granitoid rocks with lithological composition varying from quartz gabbro to K-feldspar granite. The youngest igneous activity is represented by quartz monzodiorite dikes. Hornblende-biotite quartz monzonite from Nay granitoids was dated at 40 Ma (zircon U-Pb). The IRN rocks are metaluminous to peraluminous with high-K calc-alkaline and shoshonitic affinities. They display enrichment in light REEs [(La/Yb)N = 3.79–8.71] and LILEs (such as Ba, Th, Rb, U, and K), with depletion in HFSEs (such as Nb, Zr, Y, and Ti). All rocks have negative Eu anomalies [(Eu/Eu*)N = 0.17–0.88] and relatively flat heavy REE patterns [(Gd/Yb)N = 1.12–1.69]. Granitoids have initial 87Sr/86Sr values from 0.7053 to 0.7061 and εNd values from –1.65 to –0.02 calculated at 40 Ma. The geochemical composition of IRN rocks along with the low ISr and positive εNd values and mantle model ages of 0.6–0.8 Ga indicate that two end-members, enriched mantle and a continental crust, were involved in the magma generation. We argue that the Eocene IRN magmatism occurred as a postcollisional product by asthenospheric upwelling owing to the convective removal of the lithosphere during an extensional collapse of the central Iranian block.publishe

Sr-Nd isotope geology and tectonomagmatic setting of the Dehsalm intrusives (Lut Block, Eastern Iran)

The Dehsalm porphyritic shallow intrusives belong to the Lut Block volcanic-plutonic belt (central eastern Iran). Previous research on alteration, mineralization and hydrothermal fluids indicates that a Cu-Mo porphyry type mineralization system is related with these intrusives (Arjmandzadeh et al., 2012). The rocks studied in this work range in composition from gabbro-diorite to granite, with dominance of monzonites and quartz monzonites, and have geochemical features of high-K calc alkaline to shoshonitic volcanic arc suites. The trends of major element oxides on Harker diagrams, together with textural evidence, point to the crystal fractionation of clinopyroxene, Ca – plagioclase, hornblende, apatite and oxide minerals. Primitive mantle - normalized trace element spider diagrams display strong enrichment in LILE, such as Rb, Ba and Cs, and depletions in some high field strength elements (HFSE), such as Nb, Ti, Y and HREE. Chondrite-normalized plots show significant LREE enrichments, high LaN/YbN (21.5 to 31.0) and the lack of Eu anomaly. Sr/Y and La/Yb ratios of Dehsalm intrusives are respectively 31.6-72.2 and 21.5-33.5, which reveals that, despite their K-rich composition, these rocks also have some adakitic affinity. A Rb-Sr whole rock-feldspar-biotite age of 33.4±1 Ma was obtained in a quartz monzonite sample; this date may be interpreted as close to the intrusion age, considering that the chosen sample is almost unaltered and should have suffered fast cooling. The obtained age coincides, within error, with a previous geochronological result in a similar rock from the Chah-Shaljami area (Arjmandzadeh et al., 2011), further northwest along the eastern border of the Lut Block. 87Sr/86Sr(33Ma) and εNd(33Ma) values range from 0.70481 to 0.70508 and from +1.5 to +2.5, respectively, which fits into a supra-subduction mantle wedge source for the parental melts and indicates that crustal contribution for magma diversification was not relevant. Sr and Nd isotope compositions together with major and trace element geochemistry point 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. Both geochemical features of Dehsalm porphyries and its association with Cu-Mo mineralization agree with a mature continental arc setting related to the convergence of Afghan and Lut plates during Oligocene. The data on the Dehsalm granitoids reveal a strong affinity with the contemporary rocks from Chah-Shaljami, studied in a previous work (Arjmandzadeh et al., 2011). Moreover, the wider range of compositions (including more mafic compositions) at Dehsalm provides additional support for the suggestion that parental magmas have a mantle origin

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

Hydrothermal fluids evolution from various alteration – mineralization zones of Dehsalm porphyry type system, Lut block, Eastern Iran

منطقه اکتشافي دهسلم در خراسان جنوبي و در کمربند آتشفشاني – نفوذي بلوک لوت قرار گرفته است. تودههاي نيمه عميق حدواسط تا اسيدي مربوط به اليگوسن، درون تواليهاي آتشفشاني، ماسهسنگ و سيلتستون ائوسن نفوذ کردهاند. زونهاي دگرساني شامل انواع پتاسيک، پروپليتيک، سريسيت- رسي، اپيدوتي، سريسيت - کلسيت - سيليس و سيليسي ميباشند. کانيسازي بصورت رگه – رگچهاي و پراکنده شامل مگنتيت، پيريت، موليبدنيت، کالکوپيريت، بورنيت، طلا، آرسنوپيريت، اسفالريت، گالن، کوليت، ديژنيت و کانيهاي سولفوسالت ميباشد. مطالعه سيالات درگير تاثير فرايندهاي جوشش، ناآميختگي، سرد شدن و رقيق شدگي توسط آيهاي جوي را طي تحول سيالات کانهساز نشان داده است. ميزان دما و شوري سيالات درگير از زون دگرساني پتاسيک به سمت زون دگرساني سريسيتي - رسي در حال کاهش است که احتمالا نشان دهنده افزايش دخالت آبهاي جوي ميباشد. شواهد زمينشناسي، دگرساني، کاني- سازي و تحول سيالات هيدروترمال نشان دهنده کانيسازي سيستم پورفيري در منطقه ميباشد. کليد واژهها: بلوک لوت، سيالات درگير، جوشش، سيستم پورفيريDehsalm exploration area is located in the Southern Khorasan and belongs to the Lut Block volcanic-plutonic belt of the Lut block. Oligocene intermediate to acidic subvolcanic rocks intruded into Eocene volcanic, sandstone and siltstone sequences. Alteration zones include potassic, propylitic, sericite – calcite – silica, sericite – argillic, epidote and silicification. Vein – veinlet and disseminated mineralization comprise magnetite, pyrite, molybdenite, chalcopyrite, bornite, arsenopyrite, sphalerite, galena, covellite, digenite and sulfosalts. Fluid inclusion studies have shown the affect of boiling, fluid immiscibility, cooling and dilution processes by meteoric fluids during the evolution of mineralizing fluids. Temperature – salinity of fluid inclusions decrease from potassic through sericite – argillic alteration which indicate the increase of the role of meteoric fluids. The gathered data on alteration, mineralization and hydrothermal fluids together with field evidence indicate that a porphyry type mineralization system occurs in the area

Fluid inclusion geothermometry of various alteration – mineralization zones of Chah-shaljami prospect, Eastern Iran

منطقه اکتشافي چاهشلغمي در خراسان جنوبي و در کمربند آتشفشاني – نفوذي بلوک لوت قرار گرفته است. تودههاي نيمه عميق گرانيتوئيدي مربوط به اليگوسن، درون تواليهاي آتشفشاني - پيروکلاستيک ائوسن نفوذ کردهاند. انواع کانيهاي دگرساني شامل آلونيت، ژاروسيت، کلريت، ديکيت، سريسيت، مونتموريلونيت، کوارتز و اکسيدهاي آهن شناسايي شدهاند. کانيسازي شامل پيريت، آرسنوپيريت، موليبدنيت، کالکوپيريت، اسفالريت، گالن و انارژيت است. ميزان دما و شوري بالاي سيالات درگير در زون دگرساني سيليس - کلريت ميتواند در تعيين مرکز سيستم کانيسازي در اکتشافات بعدي مورد استفاده قرار گيرد. دما و شوري سيالات به سمت زون دگرساني کوارتز حفرهاي در حال کاهش است که احتمالا نشان دهنده افزايش دخالت آبهاي جوي ميباشد. شواهد زمينشناسي، دگرساني، کانيسازي و تحول سيالات هيدروترمال نشان دهنده کانيسازي اپيترمال سولفيداسيون بالا مرتبط با سيستم پورفيري عمقي در منطقه ميباشد. کليد واژهها: بلوک لوت، آلونيت، سيالات درگير، اپيترمال.Chah-shaljami exploration area is located in the Southern Khorasan and belongs to the Lut Block volcanic-plutonic belt. Oligocene subvolcanic granitoids intruded into Eocene volcanic - volcaniclastic sequences. Alteration minerals include alunite, jarusite, chlorite, dickite, sericite, montmorillonite, quartz and iron oxide. Mineralization includes pyrite, arsenopyrite, molybdenite, chalcopyrite, sphalerite, galena and enargite. High temperature – salinity of fluid inclusions from sericite alteration is an indicator that can direct the next exploration toward the mineralization center. Temperature – salinity of fluid inclusions decrease toward the vuggy quartz alteration which indicate the increase of the role of meteoric fluids. The gathered data on alteration, mineralization and hydrothermal fluids together with field evidence evidence indicate that the high-sulfidation epithermal mineralization is related to the deep porphyry system in the area

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