Origin and geodynamic evolution of Late Paleogene magmatic associations along the Periadriatic-Sava-Vardar magmatic belt

Abstract

Along the Periadriatic Lineament in the Alps and the Sava-Vardar Zone of the Dinarides and Hellenides, Paleogene magmatic associations form a continuous belt, about 1700 km long. The following magmatic associations occur: (1) Eocene granitoids; (2) Oligocene granitoids including tonalites; (3) Oligocene shoshonite and calc-alkaline volcanics with lamprophyres; (4) Egerian-Eggenburgian (Chattian) calc-alkaline volcanics and granitoids. All of these magmatic associations are constrained by radiometric ages, which indicate that the magmatic activity was mainly restricted to the time span between 55 and 29 Ma. These igneous rocks form, both at surface and in the subsurface, the distinct linear Periadriatic-Sava-Vardar magmatic belt, with three strikes that are controlled by the indentation of Apulia and Moesia and accompanying strike-slip faulting. The geology, seismicity, seismic tomography and magnetic anomalies within this belt suggest that it has been generated in the African-Eurasian suture zone. Based on published analytical data, the petrology, major and trace element contents and Sr, Nd and O isotopie composition of each magmatic association are briefly defined. These data show that Eocene and Oligocene magmatic associations of the Late Paleogene Periadriatic-Sava-Vardar magmatic belt originated along a consuming plate margin. Based on isotopie systems, two main rock groups can be distinguished: (1) ⁸⁷Sr/⁸⁶Sr = 0.7036–0.7080 and δ¹⁸O = 5.9–7.2‰, indicating basaltic partial melts derived from a continental mantle-lithosphere, and (2) ⁸⁷Sr/⁸⁶Sr = 0.7090–72131 and δ¹⁸O = 7.3–11.5‰, indicating crustal assimilation and melting. The mantle sources for the primary basalt melts are metasomatized garnet peridotites and/or spinel lherzolites and phlogopite lherzolites of upper mantle wedge origin. The geodynamic evolution of the plutonic and volcanic associations of the Periadriatic-Sava-Vardar magmatic belt was related to the Africa-Eurasia suture zone that was dominated by break-off of the subducted lithospheric slab of Mesozoic oceanic crust, at depths of 90–100 km. This is indicated by their contemporaneity along the 1700 km long belt. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.     

Laser-ICP-MS U–Pb zircon ages and geochemical and Sr–Nd–Pb isotopic compositions of the Niyasar plutonic complex,Iran: constraints on petrogenesis and tectonic evolution

We conducted geochemical and isotopic studies on the Oligocene–Miocene Niyasar plutonic suite in the central Urumieh–Dokhtar magmatic belt, in order better to understand the magma sources and tectonic implications. The Niyasar plutonic suite comprises early Eocene microdiorite, early Oligocene dioritic sills, and middle Miocene tonalite + quartzdiorite and minor diorite assemblages. All samples show a medium-K calc-alkaline, metaluminous affinity and have similar geochemical features, including strong enrichment of large-ion lithophile elements (LILEs, e.g. Rb, Ba, Sr), enrichment of light rare earth elements (LREEs), and depletion in high field strength elements (HFSEs, e.g. Nb, Ta, Ti, P). The chondrite-normalized rare earth element (REE) patterns of microdiorite and dioritic sills are slightly fractionated [(La/Yb)_n = 1.1–4] and display weak Eu anomalies (Eu/Eu* = 0.72–1.1). Isotopic data for these mafic mantle-derived rocks display I_Sr = 0.70604–0.70813, ?_Nd (microdiorite: 50 Ma and dioritic sills: 35 Ma, respectively) = +1.6 and ?0.4, TDM = 1.3 Ga, and lead isotopic ratios are (²⁰⁶Pb/²⁰⁴Pb) = 18.62–18.57, (²⁰⁷Pb/²⁰⁴Pb) = 15.61–15.66, and (²⁰⁸Pb/²⁰⁴Pb) = 38.65–38.69. The middle Miocene granitoids (18 Ma) are also characterized by relatively high REE and minor Eu anomalies (Eu/Eu* = 0.77–0.98) and have uniform initial ⁸⁷Sr/⁸⁶Sr (0.7065–0.7082), a range of initial Nd isotopic ratios [?Nd(T)] varying from ?2.3 to ?3.7, and Pb isotopic composition (²⁰⁶Pb/²⁰⁴Pb) = 18.67–18.94, (²⁰⁷Pb/²⁰⁴Pb) = 15.63–15.71, and (²⁰⁸Pb/²⁰⁴Pb) = 38.73–39.01. Geochemical and isotopic evidence for these Eocene–Ologocene mafic rocks suggests that the magmas originated from lithospheric mantle with a large involvement of EMII component during subduction of the Neotethyan ocean slab beneath the Central Iranian plate, and were significantly affected by crustal contamination. Geochemical and isotopic data of the middle Miocene granitoids rule out a purely crustal-derived magma genesis, and suggest a mixed mantle–crustal [MASH (melting, assimilation, storage, and homogenization)] origin in a post-collision extensional setting. Sr–Nd isotope modelling shows that the generation of these magmas involved ～60% to 70% of a lower crustal-derived melt and ～30% to 40% of subcontinental lithospheric mantle. All Niyasar plutons exhibit transitional geochemical features, indicating that involvement of an EMII component in the subcontinental mantle and also continental crust beneath the Urumieh–Dokhtar magmatic belt increased from early Eocene to middle Miocene time.     

Adakite-like signature of porphyry granitoid stocks in the Meiduk and Parkam porphyry copper deposits,NE of Shahr-e-Babak,Kerman, Iran: Constrains on geochemistry

The Middle Miocene porphyry granitoid stocks of Meiduk and Parkam porphyry copper deposits are intruded in the north-western part of the Dehaj-Sarduiyeh volcano-sedimentary belt in the south-eastern extension of the Urumieh-Dukhtar Magmatic Arc (UDMA) in Iran. The porphyritic to microgranular granitoids are mainly consist of quartz diorite, granodiorite and diorite. The whole rock geochemical analyses of these rocks reveals sub-alkaline, calc-alkaline, meta-peraluminous and I-type characteristics. Their geochemical characteristics such as Al₂O₃ content of 13.51–17.05 wt%, high Sr concentration (mostly >400 ppm), low Yb (an average of 0.74 ppm) and Y (an average of 9.02 ppm) contents, strongly differentiated REE patterns (La/Yb ≥ 20), lack of Eu anomaly (Eu/Eu¹ ≥ 1) are indicative of adakitic signature. Their enrichment in low field strength elements (LFSE) and conspicuous negative anomalies for Nb, Ta and Ti are typical of subduction related magmas. Detailed petrological studies and geochemical data indicated that Meiduk and Parkam porphyry granitoids were derived from amphibole fractionation of hydrous melts at a depth of >40 km in a post-collisional tectonic setting.     

Recycling of orogenic arc crust triggers porphyry Cu mineralization in Kerman Cenozoic arc rocks,southeastern Iran

Pre-collisional Eocene–Oligocene arc diorites, quartzdiorites, granodiorites, and volcanic equivalents in the Kerman arc segment in central Iran lack porphyry Cu mineralization and ore deposits, whereas collisional middle-late Miocene adakite-like porphyritic granodiorites without volcanic equivalents host some of the world’s largest Cu ore deposits. Petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment. Ore-hosting Kuh Panj porphyry intrusions exhibit high Sr (>400 ppm), low Y (<12 ppm) contents, significant REE fractionation (La/Yb > 20), no negative Eu anomalies (Eu/Eu^* ≥ 1), and relatively non-radiogenic Sr isotope signatures (⁸⁷Sr/⁸⁶Sr = 0.7042–0.7047), relative to Eocene–Oligocene granitoids (mainly Sr < 400 ppm; Y > 12; La/Yb < 15; Eu/Eu^* < 1; ⁸⁷Sr/⁸⁶Sr = 0.7053–0.7068). Trace element modeling indicates peridotite melting for the barren Eocene–Oligocene intrusions and a hydrous garnet-bearing amphibolite source for middle-late Miocene ore-hosting intrusions. The presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30–35 to 40–45 km or 12 kbar. The changes in residual mineralogy in the source of Eocene to Miocene rocks in the Kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel. Underplating of Cu and sulfur-rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust–mantle boundary, and dehydration melting under oxidizing conditions produced syn- and post-collisional ore-hosting intrusions, while the lack of post-collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur-rich and oxidized adakitic magmas. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

西藏浦桑果铜多金属矿床中酸性岩石成因及动力学背景:年代学、地球化学及Sr-Nd-Pb-Hf同位素约束

浦桑果矿床位于拉萨地块冈底斯成矿带中段,为侵入岩体与钙质围岩接触带内形成的矽卡岩型高品位铜多金属矿床(Cu@1. 42%,Pb+Zn@2. 83%),是冈底斯成矿带目前唯一一个大型富铜铅锌(钴镍)矿床。本文以浦桑果矿床相关中酸性侵入岩体(黑云母花岗闪长岩和闪长玢岩)为主要研究对象,开展LA-ICP-MS锆石U-Pb年代学、全岩主微量元素、全岩SrNd-Pb及锆石Lu-Hf同位素研究,旨在厘定侵入岩体的形成时代、岩石成因及成岩成矿的动力学背景。LA-ICP-MS锆石U-Pb定年结果表明,黑云母花岗闪长岩和闪长玢岩侵位年龄分别为13. 6～14. 4Ma和13. 6～14. 6Ma,岩体形成时代均属中新世。岩石地球化学特征表明,闪长玢岩和黑云母花岗闪长岩均属高钾钙碱性I型花岗质岩石;岩石普遍具高Sr含量(599×10~(-6)～1616×10~(-6))、高Sr/Y(48. 2～132. 3)和高(La/Yb)N(19. 6～25. 4)比值特征,具低Y(10. 38×10~(-6)～12. 70×10~(-6))和Yb含量(0. 79×10~(-6)～1. 17×10~(-6))特征,表现出埃达克质岩的地球化学属性。全岩稀土元素表现为明显富集轻稀土元素(LREEs)和大离子亲石元素(LILEs),而相对亏损重稀土元素(HREEs)和高场强元素Nb、Ta、P、Ti等(HFSE)。全岩Sr-Nd-Pb及锆石Hf同位素分析结果表明,浦桑果矿床相关中酸性岩石与冈底斯成矿带中新世大多斑岩-矽卡岩矿床紧密相关的埃达克质侵入岩体具相似的同位素组成特征,指示岩石具同源岩浆特征且埃达克质岩浆主要起源于拉萨地块加厚新生下地壳。浦桑果矿床中酸性岩体主要形成于后碰撞伸展的构造背景,因碰撞挤压向后碰撞伸展背景的构造转换,引起印度大陆岩石圈发生拆沉(42～25Ma)及拉萨地块中富集岩石圈地幔发生部分熔融,从而形成富含Cu、Co等基性岩浆熔体底侵加厚新生下地壳(25～18Ma),导致拉萨地块加厚新生下地壳中部分石榴子石角闪岩相发生部分熔融,最终形成闪长质熔体于浦桑果矿区有利构造部位形成具埃达克质属性的中酸性侵入岩体(13～14Ma)和矽卡岩型铜多金属矿体。     

藏南拉萨地块东段米拉山地区中新世中酸性火山岩地球化学特征及成因研究

藏南拉萨地块内广泛发育中新世中酸性岩浆岩,为探讨其岩浆源区和岩石成因,进一步了解藏南后碰撞深部过程,本文对拉萨地块东部米拉山地区的中新世火山岩进行了岩石学、年代学和地球化学研究。结果表明,岩石类型主要为英安岩,形成于中新世(16~18 Ma);地球化学组成上表现出高硅、高钾、富铝;高Sr、低Y、高Sr/Y值,富集轻稀土,亏损重稀土,Eu正异常;具有高的⁸⁷Sri/⁸⁶Sri值(0.706038~0.707154)和低的ε_Nd(t)值(-1.37~-2.75),表现出一定埃达克质岩特征。结合前人研究成果认为,米拉山地区中新世中酸性火山岩不属于林子宗群,可能是岩石圈拆沉引起幔源物质上涌,导致后碰撞环境下增厚的拉萨地块新生下地壳部分熔融而形成。     

Petrogenesis of post-collisional A-type granitoids from the Urumieh–Dokhtar magmatic assemblage,Southwestern Kerman,Iran: Constraints on the Arabian–Eurasian continental collision

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 K₂O > Na₂O, 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 ⁸⁷Sr/⁸⁶Sr 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 and low I_Sr values of the DBB granitoids together with their T_DM of 0.6–0.7 Ga suggest their formation from partial melting of a lithospheric mantle source, modified by fluids or melts from earlier subduction processes. Melting of lithospheric mantle occurred via a dehydration melting process at pressures below the garnet stability field, as a consequence of lithospheric mantle delamination or break-off of a subducted slab and melting of the lithospheric mantle by upwelling of hot asthenosphere. On the basis of Rb/Sr age dating and the post-collisional geochemical signatures of the DBB granitoids, along with extensive pre-collisional volcanic eruptions in Middle Eocene, we suggest Late Eocene for the time of collision between the Arabian and Central Iranian plates. This also implies that the calc-alkaline I-type intrusions in the southwestern Kerman and in other parts of the UDMA may have formed in a post-collisional context.     

Late Paleozoic volcanic rocks of the Intra-Sudetic Basin, Bohemian Massif: petrological and geochemical characteristics

Late Paleozoic volcanic rocks in the Intra-Sudetic Basin of the Bohemian Massif in the Czech Republic can be subdivided into two series: (I) a minor bimodal trachyandesite-rhyolite series of Upper Carboniferous age with initial ⁸⁷Sr/⁸⁶Sr of ca. 0.710 and ε_Nd values of −6.1 also characteristic of volcanics of the near Krkonoše Piedmont Basin (0.707 and −6.0, Ulrych et al., 2003) and (II) a major differentiated basaltic trachyandesite-trachyandesite-trachyte-rhyolite series of Lower Permian age with lower initial ⁸⁷Sr/⁸⁶Sr of ca. 0.705-0.708 and ε_Nd values ranging from −2.7 to −3.4/−4.1/. The newly recognized volcanic rocks of trachytic composition indicate that the rocks were formed by magmatic differentiation of similar parental melts rather than constituting a bimodal mafic-felsic sequence from different sources. Both series are generally of subalkaline affinity and calc-alkaline character with some tholeiitic tint (FeO/MgO vs. SiO₂, presence of orthopyroxene). The magmatic activity occurred in cycles in a layered chamber, each starting primarily with felsic volcanics and ending with mafic ones. The mafic rocks represent mantle-melt(s) overprinted by crust during assimilation-fractional crystallization. The Sr-Nd isotopic data confirm a significant crustal component in the volcanic rocks that may have been inherited from the upper mantle source and/or from assimilation of older crust during magmatic underplating and shallow-level melt fractionation.     

Adakite-like volcanism of Ecuador: lower crust magmatic evolution and recycling

In the Northern Andes of Ecuador, a broad Quaternary volcanic arc with significant across-arc geochemical changes sits upon continental crust consisting of accreted oceanic and continental terranes. Quaternary volcanic centers occur, from west to east, along the Western Cordillera (frontal arc), in the Inter-Andean Depression and along the Eastern Cordillera (main arc), and in the Sub-Andean Zone (back-arc). The adakite-like signatures of the frontal and main arc volcanoes have been interpreted either as the result of slab melting plus subsequent slab melt–mantle interactions or of lower crustal melting, fractional crystallization, and assimilation processes. In this paper, we present petrographic, geochemical, and isotopic (Sr, Nd, Pb) data on dominantly andesitic to dacitic volcanic rocks as well as crustal xenolith and cumulate samples from five volcanic centers (Pululagua, Pichincha, Ilalo, Chacana, Sumaco) forming a NW–SE transect at about 0° latitude and encompassing the frontal (Pululagua, Pichincha), main (Ilalo, Chacana), and back-arc (Sumaco) chains. All rocks display typical subduction-related geochemical signatures, such as Nb and Ta negative anomalies and LILE enrichment. They show a relative depletion of fluid-mobile elements and a general increase in incompatible elements from the front to the back-arc suggesting derivation from progressively lower degrees of partial melting of the mantle wedge induced by decreasing amounts of fluids released from the slab. We observe widespread petrographic evidence of interaction of primary melts with mafic xenoliths as well as with clinopyroxene- and/or amphibole-bearing cumulates and of magma mixing at all frontal and main arc volcanic centers. Within each volcanic center, rocks display correlations between evolution indices and radiogenic isotopes, although absolute variations of radiogenic isotopes are small and their values are overall rather primitive (e.g., ε_Nd = +1.5 to +6, ⁸⁷Sr/⁸⁶Sr = 0.7040–0.70435). Rare earth element patterns are characterized by variably fractionated light to heavy REE (La/Yb_N = 5.7–34) and by the absence of Eu negative anomalies suggesting evolution of these rocks with limited plagioclase fractionation. We interpret the petrographic, geochemical, and isotopic data as indicating open-system evolution at all volcanic centers characterized by fractional crystallization and magma mixing processes at different lower- to mid-crustal levels as well as by assimilation of mafic lower crust and/or its partial melts. Thus, we propose that the adakite-like signatures of Ecuadorian rocks (e.g., high Sr/Y and La/Yb values) are primarily the result of lower- to mid-crustal processing of mantle-derived melts, rather than of slab melts and slab melt–mantle interactions. The isotopic signatures of the least evolved adakite-like rocks of the active and recent volcanoes are the same as those of Tertiary ”normal” calc-alkaline magmatic rocks of Ecuador suggesting that the source of the magma did not change through time. What changed was the depth of magmatic evolution, probably as a consequence of increased compression induced by the stronger coupling between the subducting and overriding plates associated with subduction of the aseismic Carnegie Ridge.     

Cretaceous lower crust of the continental margins of the northern pacific: Petrological and geochronological data on lower to middle crustal xenoliths

Despite the exposures of Precambrian and Paleozoic rocks and the accretionary tectonic history of the northern Pacific (northeastern Asia, Alaska, and Kamchatka), it is likely that a considerable portion of the lower crust of the continental margins is much younger and was generated by Cretaceous postaccretion magmatic events. Data on xenoliths suggest that Late Cretaceous and Paleocene mafic intrusions and cumulates of calc-alkaline magmas may become more important with increasing depth. This conclusion is based on the petrological and geochronological investigation of lower-middle crustal xenoliths borne by mantlederived alkali basalt lavas and U-Pb dating of zircon cores from the igneous rocks of the region. We studied deep mafic xenoliths of granulites and gabbroids (accounting for <2% of the general xenolith population) from the Late Neogene alkali basalt lavas of the Enmelen and Viliga volcanic fields (Russia) and the Imuruk volcanic field in the Seward Peninsula, St. Lawrence Island, and Nunivak Island (Alaska). Depleted MORB-like varieties and relatively enriched in radiogenic isotopes and LREE rocks were distinguished among plagioclase-bearing xenoliths. The most representative collection of Enmelen xenoliths was subdivided into three groups: LREE enriched charnockitoids and mafic melts, pyroxene-plagioclase cumulates with a positive Eu anomaly, and LREE depleted garnet gabbroids. Mineral thermobarometry and calculated seismic velocities (P = 5–12 kbar, T = 740–1100°C, and V _p = 7.1 ± 0.3 km/s) suggest that the xenoliths were transported from the lower and middle crust, and the rocks show evidence for their formation through the magmatic fractionation of calc-alkaline magmas and subsequent granulite-facies metamorphism. The U-Pb age of zircon from the xenoliths ranges from the Cretaceous to Paleocene, clustering mainly within 107–56 Ma (147 crystals from 17 samples were dated). The zircon dates were interpreted as reflecting the magmatic and metamorphic stages of the growth and modification of the regional crust. The distribution of the obtained age estimates corresponds to the main magmatic pulses in two largest magmatic belts of the region, Okhotsk-Chukchi and Anadyr-Bristol. The absence of older inherited domains in zircons from both the xenoliths and igneous rocks of the regions is a strong argument in favor of the idea on the injection of juvenile material and underplating of calc-alkaline magmas in the lower crust during that time interval. This conclusion is supported by isotope geochemical data: the Sr, Nd, and Pb isotope ratios of the rocks and xenolith minerals show mantle signatures (⁸⁷Sr/⁸⁶Sr = 0.7040–0.70463, ¹⁴³Nd/¹⁴⁴Nd = 0.51252–0.51289, ²⁰⁶Pb/²⁰⁴Pb = 18.32–18.69) corresponding to an OIB source and are in general similar to those of the Cretaceous calc-alkaline basalts and andesites from continental-margin suprasubduction volcanoplutonic belts. Xenoliths from Nunivak Island and Cape Navarin show more depleted (MORB-like) geochemical and isotopic characteristics, which indicates variations in the composition of the lower crust near the southern boundary of the Bering Sea shelf.     

Geochemical and Sr–Nd isotopic constraints on the genesis of the Soheyle-PaKuh granitoid rocks (central Urumieh-Dokhtar magmatic belt,Iran)

ABSTRACT

Soheyle-Pakuh granitoid rocks, with a variety of quartz diorite, quartz monzodiorite, granodiorite, tonalite, and granite, have been emplaced into the Tertiary volcanic rocks in the Urumieh-Dokhtar magmatic arc in central Iran. Zircon U–Pb dating yields an age of 39.63 ± 0.93 Ma for the crystallization of this body. Whole-rock compositions show that SiO₂ changes from 52.31 to 65.78 wt.% and Al₂O₃ varies from 15.54 to 18.24 wt.%, as well as high concentrations of large-ion lithophile elements (LILE, e.g. Cs, Rb, Ba, and K) and quite low contents of high field strength elements (HFSE, e.g. Nb, Ti, P), as expected in I-type arc granitoids formed in an active continental margin setting. Initial ratios of ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd exhibit ranges 0.7043–0.7047 and 0.51284 to 0.51287, respectively, with positive εNd_(t) from +4.9 to +5.5 with a young TDM1 age (483–674 Ma); this tracer isotopic data suggesting that the SPG originated from juvenile basaltic crust derived from depleted mantle (~90%) with variable contributions from undepleted mantle and approximately 10% old lower crust, despite diverse processes (e.g. magma mixing and fractional crystallization) during their evolution and emplacement into a local extensional setting within the continental margin arc. The isotopic data are similar to those of other Phanerozoic granitoids of the Central Asian Orogenic Belt and corroborate melting of predominantly mantle-derived juvenile crustal protoliths and indicating extensive addition of new continental crust, during Cambrian-Neoproterozoic time, in the suprasubduction zone beneath the central Urumieh-Dokhtar magmatic arc. Generation of these types of granitoids favours a model whereby rollback and (or) break-off of a subducted slab with subsequent lithospheric extension triggered by mantle upwelling, heat advection, and underplating resulting in melting of the central UDMA mantle-derived juvenile lower continental crust in the Late Eocene.     

Petrogenesis and geodynamic evolution of the Kajan Neogene subvolcanic rocks,Nain, Central Iran

Kajan subvolcanic rocks in the Urumieh–Dokhtar magmatic arc (UDMA), Central Iran, form a Late Miocene-Pliocene shallow-level intrusion. These subvolcanics correspond to a variety of intermediate and felsic rocks, comprising quartz diorite, quartz monzodiorite, tonalite and granite. These lithologies are medium-K calc-alkaline, with SiO₂ (wt.%) varying from 52% (wt.%) to 75 (wt.%). The major element chemical data also show that MgO, CaO, TiO₂, P₂O₅, MnO, Al₂O₃ and Fe₂O₃ define linear trends with negative slopes against SiO₂, whilst Na₂O and K₂O are positively correlated with silica. Contents of incompatible trace elements (e.g. Ba, Rb, Nb, La and Zr) become higher with increasing SiO₂, whereas Sr shows an opposite behaviour. Chondrite-normalized multi-element patterns show enrichment in LILE relative to HFSE and troughs in Nb, P and Ti. These observations are typical of subduction related magmas that formed in an active continental margin. The Kajan rocks show a strong affinity with calc-alkaline arc magmas, confirmed by REE fractionation (La_N/Yb_N = 4.5–6.4) with moderate HREE fractionation (Sm_N/Yb_N = 1.08–1.57). The negative Eu anomaly (Eu/Eu* <1), the low to moderate Sr content (< 400 ppm) and the Dy/Yb values reflect plagioclase and hornblende (+- clinopyroxene) fractionation from a calc-alkaline melt Whole–rock Sr and Nd isotope analyses show that the ⁸⁷Sr/⁸⁶Sr initial ratios vary from 0.704432 to 0.705989, and the ¹⁴³Nd/¹⁴⁴Nd initial ratios go from 0.512722 to 0.512813. All the studied samples have similar Sr-Nd isotopes, indicating an origin from a similar source, with granite samples that has more radiogenic Sr and low radiogenic Nd isotopes, suggesting a minor interaction with upper crust during magma ascent. The Kajan subvolcanic rocks plot within the depleted mantle quadrant of the conventional Sr-Nd isotope diagram, a compositional region corresponding to mantle-derived igneous rocks.     

Geochemical constraints on the genesis of the volcanic rocks in the southeast of Isfahan area, Iran

Late Miocene–Pliocene to Quaternary calc-alkaline lava flows and domes are exposed in southeast of Isfahan in the Urumieh Dokhtar magmatic belt in the Central Iran structural zone. These volcanic rocks have compositions ranging from basaltic andesites, andesites to dacites. Geochemical studies show these rocks are a medium to high K calc-alkaline suite and meta-aluminous. Major element variations are typical for calc-alkaline rocks. The volcanic rocks have SiO₂ contents ranging between 53.8% and 65.3%. Harker diagrams clearly show that the dacitic rocks did not form from the basaltic andesites by normal differentiation processes. They show large ion lithophile elements- and light rare earth elements (LREE)-enriched normalized multielement patterns and negative Nb, Ti, Ta, and P. Condrite-normalized REE patterns display a steep decrease from LREE to light rare earth elements without any Eu anomaly. These characteristics are consistent with ratios obtained from subduction-related volcanic rocks and in collision setting. The melting of a heterogeneous source is possible mechanism for their magma genesis, which was enriched in incompatible elements situated at the upper continental lithospheric mantle or lower crust. The geochemical characteristics of these volcanic rocks suggested that these volcanic rocks evolved by contamination of a parental magma derived from metasomatized upper lithospheric mantle and crustal melts.     

Geochronology and geochemistry of Cretaceous–Eocene granites,Tengchong Block (SW China): Petrogenesis and implications for Mesozoic-Cenozoic tectonic evolution of Eastern Tethys

The Early Cretaceous–Early Eocene granitoids in the Tengchong Block record the evolutionary history of the Mesozoic-Cenozoic tectono-magmatic evolution of Eastern Tethys. (a) The Early Cretaceous granitoids with relatively low (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7090–0.7169 and ε_Nd(t) values of ?9.8 to ?7.8 display metaluminous, calc-alkaline dominated by I-type granite affinity and hybrid mantle–crust geochemical signatures. They may have been derived from melting of the subducted Meso-Tethyan Bangong-Nujiang oceanic crust with terrigenous sediments in an arc-continent collisional setting. (b) The Late Cretaceous–Paleocene granitoids with relatively high (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7109–0.7627, and ε_Nd(t) values of ?12.1 to ?7.9 exhibit metaluminous to peraluminous, calc-alkaline dominated by S-type granite affinity and hybrid Lower–Upper crust geochemical signatures, which may be originated from partial melting of the Meso-Proterozoic continental crust in the collision setting between the Tengchong Block and Baoshan Block. (c) The Early Eocene granitoids have metaluminous, calc-alkaline I-type and S-type granites dual affinity, with relatively high (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.711–0.736, ε_Nd(t) values of ?9.4 to ?4.7, showing crust-mantle mixing geochemical signatures. They may have been originated from partial melting of the late Meso-Proterozoic upper crustal components mixed with some upper mantle material during the ascent process of mantle magma caused by the subduction of the Neo-Tethyan Putao–Myitkyian oceanic crust, and collision between the Western Burma Block and the Tengchong Block. It is these multi-stage subductions and collisions that caused the spatial and temporal distribution of the granitic rocks in the Tengchong Block.     

Petrochemistry of the south Marmara granitoids, northwest Anatolia, Turkey

Post-collision magmatic rocks are common in the southern portion of the Marmara region (Kap?da?, Karabiga, Gönen, Yenice, Çan areas) and also on the small islands (Marmara, Av?a, Pa?aliman?) in the Sea of Marmara. They are represented mainly by granitic plutons, stocks and sills within Triassic basement rocks. The granitoids have ages between Late Cretaceous and Miocene, but mainly belong to two groups: Eocene in the north and Miocene in the south. The Miocene granitoids have associated volcanic rocks; the Eocene granitoids do not display such associations. They are both granodioritic and granitic in composition, and are metaluminous, calc-alkaline, medium to high-K rocks. Their trace elements patterns are similar to both volcanic-arc and calc-alkaline post-collision intrusions, and the granitoids plot into the volcanic arc granite (VAG) and collision related granite areas (COLG) of discrimination diagrams. The have high ⁸⁷Sr/⁸⁶Sr (0.704–0.707) and low ¹⁴³Nd/¹⁴⁴Nd (0.5124–0.5128). During their evolution, the magma was affected by crustal assimilation and fractional crystallization (AFC). Nd and Sr isotopic compositions support an origin of derivation by combined continental crustal AFC from a basaltic parent magma. A slab breakoff model is consistent with the evolution of South Marmara Sea granitoids.     

Geochemical and Sr-Nd isotopic evidence for origin and evolution of the Miocene Pangeon granitoids,Southern Rhodope,Greece

The Sr-Nd isotopic ratios of selected post-collisional, calc-alkaline, I-type granitoids from the Pangeon pluton, intruding the lower tectonic unit (LTU) in the Southern Rhodope in the Miocene, support the existence of two types of granitoids (PTG porphyritic tonalite granodiorite and MGG biotite granodiorite to two-mica granite) unrelated by crystal fractionation and likely derived by partial melting of the same source under different P-T conditions. The Sr-Nd isotopic ratios of mafic enclaves in the granitoids as well as metamorphic rocks from the LTU have also been determined. At 22 Ma, the IR_Sr range between 0.706850 and 0.708381, whereas the ε_Nd(22) range from –3.86 to –1.05, with no relationship to granitoid types. The relationships between Sr and Nd isotopes as well as these isotopes and SiO₂ provide evidence of contamination of mafic melts by interaction with crust during magma differentiation. Both partial melting and AFC processes (r = 0.2) may account for compositional variations in the Pangeon magmas. The mafic enclaves display IR_Sr from 0.706189 to 0.707139, and ε_Nd(22) from –2.29 to –1.94, similar to the granitoids, supporting the hypothesis of a common origin. Amphibolites inferred to be subduction-enriched metabasalts under-plated crust during old subduction can represent the source of the Pangeon melts. The T_DM of the Pangeon granitoids is in the range 0.7–1.1 Ga for the inferred extraction age of the LILE-enriched subcontinental lithospheric mantle source. The upper crustal geochemical signatures and the relatively small isotopic composition of the Pangeon granitoids make these rocks similar to the coeval eastern-Mediterranean lamproites emplaced within the same geodynamic setting; this prompts similar melt sources. Lastly, the Pangeon granitoids display geochemical characteristics, isotopic ratios, and T_DM also similar to other Tertiary magmatic rocks from the Southern Rhodope and Biga peninsula, western Anatolia, suggesting a similar tectonic environment and co-magmatic evolution throughout the area.     

Petrogenesis of ore-forming and pre/post-ore granitoids from the Kounrad,Borly and Sayak porphyry/skarn Cu deposits,Central Kazakhstan

Ore-forming porphyries and barren granitoids from porphyry Cu deposits differ in many ways, particularly with respect to their adakitic affinity and calc-alkaline characteristics. In this study, zircon U–Pb and molybdenite Re–Os dating, whole rock geochemistry, whole rock Sr–Nd–Pb and zircon O–Hf isotopic analyses were carried out on the ore-forming granitoids from the Kounrad, Borly and Sayak deposits, and also on pre-ore and post-ore granitoids in adjacent regions of Central Kazakhstan. Geochronology results indicate that pre-ore magmatism occurred in the Late Devonian to Early Carboniferous (361.3–339.4 Ma), followed by large scale Cu mineralization (325.0–327.3 Ma at Kounrad, 311.4–315.2 Ma at Borly and 309.5–311.4 Ma at Sayak), and finally, emplacement of the Late Carboniferous post-ore barren granitoids (305.0 Ma). The geochemistry of these rocks is consistent with calc-alkaline arc magmatism characterized by strong depletions in Nb, Ta and Ti and enrichments in light rare earth elements and large ion lithophile elements, suggesting a supra-subduction zone setting. However, the ore-forming rocks at Kounrad and Sayak show adakitic characteristics with high Sr (517.5–785.3 ppm), Sr/Y (50.60–79.26), (La/Yb)_N (9.37–19.62) but low Y (6.94–11.54 ppm) and Yb (0.57–1.07 ppm), whereas ore-forming rocks at Borly and barren rocks from northwest of Borly and Sayak have normal arc magma geochemical features. The Sr–Nd–Hf–O isotopic compositions show three different signatures: (1) Sayak granitoids have very young juvenile lower crust-derived compositions ((⁸⁷Sr/⁸⁶Sr)_i = 0.70384 to 0.70451, ɛ_Nd (t) = + 4.9 to + 6.0; T_DM2 (Nd) = 580 to 670 Ma, ɛ_Hf (t) = + 11.3 to + 15.5; T_DM^C (Hf) = 330 to 600 Ma, δ¹⁸O = 6.0 to 8.1‰), and were probably generated from depleted mantle-derived magma with 5–15% sediment melt addition in the magma source; (2) the Kt-1 granite from northwest of Sayak shows extremely enriched Sr–Nd isotopic compositions ((⁸⁷Sr/⁸⁶Sr)_i = 0.71050, ɛ_Nd (t) = − 7.8, T_DM2 (Nd) = 1700 Ma), likely derived from partial melting of ancient continental crust; (3) other granitoids have transitional Sr–Nd compositions between the Sayak and Kt-1 samples, indicating a juvenile lower crust source with the addition of 10–30% of ancient crustal material. The pre-ore magmatism was probably related to partial melting of juvenile lower crust due to northward subduction of the Junggar–Balkhash Ocean, whereas the ore-forming adakitic rocks at Aktogai, Kounrad and Sayak formed by partial melting of thickened lower crust which subsequently delaminated. The ore-forming rocks at Borly, and the later post-ore barren granites, formed by partial melting of juvenile lower crust with normal thickness. This tectonic setting supports the existence of an Andean-type magmatic arc in the Devonian to the Late Carboniferous, resulting from the subduction of the Junggar–Balkhash oceanic plate. The link between whole rock geochemistry and scale of mineralization suggests a higher metallogenic potential for adakitic rocks than for normal arc magmatism.     

Mineral chemistry and Ti in zircon thermometry: Insights into magmatic evolution of the Sangan igneous rocks,NE Iran

The Sangan Magmatic complex (SMC) is, a large I-type magmatic complex, located in the northeastern Iran. Zircons extracted from the intrusive and volcanic rocks within the SMC record a similar Hf compositions and REE patterns, indicating that these chemical signatures have likely been inherited from the same source and simple history of magmatic crystallization during the evolution of the orogeny. The zircon from volcanic rocks yield Ti-in-zircon crystallization temperatures of 667–1145?°C with average temperatures of 934?°C while those from granitoids indicate crystallization temperatures of 614–898?°C with an average of 812?°C. Ti-in-zircon, Ti in biotite thermometries also indicates that the crystallization temperatures of volcanic rocks are relatively higher than those of granitoids. The biotite chemistry studies reveal that this mineral crystallized at approximately 725°–800?°C and 758° to 816?°C for granitoid and volcanic rocks, respectively, which is similar to obtained temperatures by Zir-saturation of Eq. (1). T_zicsat and T_magma trend lines on the T-SiO₂ diagram cross at high silica contents of ～68?wt.%, at which temperature the magma becomes zircon-saturated and new zircons are crystallized. The zircon REE data including Ce/Ce*, Eu/Eu*, and Th/U ratios suggest that SMC igneous rocks are formed from oxidized magma. However, the zircon Th/U and Hf data suggest that the SMC became progressively more oxidized and also indicate lower temperatures from volcanic and plutonic rock with decreasing time.     

Adakites and adakitic melts: Compositions of rocks,quenched glasses,and inclusions in minerals

Data set of rocks and glasses whose compositions correspond to the term “adakite” (SiO₂ > 56 wt %, Sr > 400 ppm, Sr/Y > 18) was compiled from two large geochemical data bases. It was revealed that the adakitic melts are characterized by extremely low abundance as compared to adakitic rocks. Only 50 adakitic compositions (~0.5%) were identified in the data base that includes the major and trace element compositions of over 9700 quenched and melt inclusion glasses. It was established that only 22 of selected analyses characterize melt inclusion glasses, while other analyses represent residual glass or “pocket melts” in ultramafic mantle xenoliths. The question of a genetic relationship between adakitic rocks, adakitic melts, and melting of subsiding plate remains open. Original data on the Shiveluch volcanic center (Kamchatka) were used to demonstrate the formation of adakitic signatures through mineral accumulation.     

Origin and geodynamic evolution of Late Paleogene magmatic associations along the Periadriatic–Sava–Vardar magmatic belt

Along the Periadriatic Lineament in the Alps and the Sava–Vardar Zone of the Dinarides and Hellenides, Paleogene magmatic associations form a continuous belt, about 1700 km long. The following magmatic associations occur: (1) Eocene granitoids; (2) Oligocene granitoids including tonalites; (3) Oligocene shoshonite and calc-alkaline volcanics with lamprophyres; (4) Egerian–Eggenburgian (Chattian) calc-alkaline volcanics and granitoids. All of these magmatic associations are constrained by radiometric ages, which indicate that the magmatic activity was mainly restricted to the time span between 55 and 29 Ma. These igneous rocks form, both at surface and in the subsurface, the distinct linear Periadriatic–Sava–Vardar magmatic belt, with three strikes that are controlled by the indentation of Apulia and Moesia and accompanying strike-slip faulting. The geology, seismicity, seismic tomography and magnetic anomalies within this belt suggest that it has been generated in the African–Eurasian suture zone. Based on published analytical data, the petrology, major and trace element contents and Sr, Nd and O isotopic composition of each magmatic association are briefly defined. These data show that Eocene and Oligocene magmatic associations of the Late Paleogene Periadriatic–Sava–Vardar magmatic belt originated along a consuming plate margin. Based on isotopic systems, two main rock groups can be distinguished: (1) ⁸⁷Sr/⁸⁶Sr = 0.7036–0.7080 and δ¹⁸O = 5.9–7.2‰, indicating basaltic partial melts derived from a continental mantle–lithosphere, and (2) ⁸⁷Sr/⁸⁶Sr = 0.7090–72131 and δ¹⁸O = 7.3–11.5‰, indicating crustal assimilation and melting. The mantle sources for the primary basalt melts are metasomatized garnet peridotites and/or spinel lherzolites and phlogopite lherzolites of upper mantle wedge origin. The geodynamic evolution of the plutonic and volcanic associations of the Periadriatic–Sava–Vardar magmatic belt was related to the Africa–Eurasia suture zone that was dominated by break-off of the subducted lithospheric slab of Mesozoic oceanic crust, at depths of 90–100 km. This is indicated by their contemporaneity along the 1700 km long belt.