The Aligoodarz granitoid complex (AGC) is located in the Sanandaj-Sirjan Zone (SSZ), western Iran and consists of quartz-diorites, granodiorites and subordinate granites. Whole rock major and trace element data mostly define linear trends on Harker diagrams suggesting a cogenetic origin of the different rock types. (87Sr/86Sr)i and εNdt ratios are in the ranges 0.7074-0.7110 and −3.56 to −5.50, respectively. The trace elements and Sr-Nd isotopic composition suggest that the granitoids from the AGC are similar to crustal derived I-type granitoids of continental arcs. The whole rock suite was produced by assimilation and fractional crystallization starting from a melt with intermediate composition likely possessing a mantle component. In situ zircon U-Pb data on the granites with LA-ICP-MS yield a crystallization age of ∼165 Ma. Inherited grains spanning in age from ∼180 Ma up to 2027 Ma were also found and confirm that assimilation of country rock has occurred.Chemical and chronological data on the AGC were compared with those available for other granitoid complexes of the central SSZ (e.g., Dehno, Boroujerd and Alvand). The comparison reveals that in spite of the different origins that have been proposed, all these granitoid complexes are likely genetically related. They share many chemical features and are derived from crustal melts with minor differences. Alvand granites have the most peculiar compositions most likely related to the presence of abundant pelitic component. All these intrusions are coeval and reveal the presence of an extensive magmatic activity in the central sector of the SSZ during middle Jurassic. 相似文献
Biotite igneous ages and well‐defined isochron ages of plutons from the composite Blue Tier Batholith and the Coles Bay area in northeastern Tasmania range from 395 to 370 Ma. The older limit of this range, for the George River granodiorite, is considerably older than any age previously recorded for NE Tasmania. The ages of the youngest plutons (Mt Paris and Anchor granites), which host cassiterite ores, record pervasive hydrothermal alteration events. The initial 87Sr/80Sr ratios of the granitoids range from 0.7061 to 0.7136 and suggest different protolith compositions, consistent with mineralogical and geochemical characteristics of each pluton. The S‐type garnetbiotite granites (Ansons Bay and Booby alia granites) have initial ratios greater than 0.7119, indicative of enriched, high Rb/Sr ratio, crustal source‐rocks of Proterozoic age (1700–800 Ma). The S‐type biotite granites (Poimena and Pearson granites) have relatively high initial 87Sr/86Sr ratios (0.7070, 0.7105) but overlap with those of the I‐type granodiorites (George River, Scamander Tier, Pyengana and Coles Bay granodiorites) which are in the range of 0.7061 to 0.7073. The initial ratios of the enriched altered plutons are poorly constrained, and on both hand‐specimen and thin‐section scales, reveal open‐system Sr isotopic patterns. Isochron ages for the arenite‐lutite and lutite sedimentary associations of the Mathinna Beds, which are intruded by the granitoids, reflect an approach to Sr isotopic equilibrium during regional metamorphism. The metamorphic age (401 ± 7 Ma) of the early Pragian arenite‐lutite association indicates a relatively small time interval between deposition, regional metamorphism and granitoid intrusion. The isotopic age for the lutite sedimentary association (423 ± 22 Ma) is tentatively correlated with a Benambran‐age burial metamorphic event that has not previously been recorded in Tasmania. 相似文献
First U-Pb zircon isotopic dates were obtained for rocks from the Devonian volcanic belt in Kazakhstan. The granodiorites of the Zhabden Massif (Karamendinskii Complex) were dated at 391 ± 1 Ma. The Sm-Nd isotopic system of a whole-rock granodiorite sample (?Nd = 2.5) suggests a high percentage of mantle material in the initial granite melt, which is in good agreement with known data on granitoids in neighboring territories in Kazakhstan. With regard for the isotopic dates obtained for the granodiorites, the material of their source was separated from the mantle at 946 Ma. 相似文献
A variety of pre-Variscan granitoids and two Variscan monzogranites occurring in the central and western parts of the Lusatian Granodiorite Complex (LGC), Saxonia were dated by the single zircon evaporation method, complemented by whole rock Nd isotopic data and Rb-Sr whole rock and mineral ages. The virtually undeformed pre-Variscan granitoids constitute a genetically related, mostly peraluminous magmatic suite, ranging in composition from two-mica granodiorite, muscovitebearing biotite quartz diorite (tonalite) and granodiorite to biotite granodiorite and monozogranite.
207Pb/206Pb isotopic ratios derived from the evaporation of single zircons separated from 13 samples representing the above rock types display complex spectra which document significant involvement of late Archaean to late Proterozoic continental crust in the generation of the granitoid melts. Mean 207/Pb/206Pb ages for zircons considered to reflect the time of igneous emplacement range between 542 ± 9 and 587 ± 17 Ma, typical of the Cadomian event elsewhere in Europe, whereas zircon xenocrysts yielded ages between 706 ± 13 and 2932 ± Ma. Detrital zircons from greywackes intruded by the granitoids and found as xenoliths in them provided ages between 1136 ± 22 and 2 574 ± Ma. Rb-Sr whole rock data display good to reasonable linear arrays that, with one exception, correspond to the emplacement ages established for the zircons. Two post-tectonic Variscan monzogranites yielded identical 207/Pb/206Pb single zircon ages of 304 ± 14 Ma and record the end of Variscan granitoid activity in the LGC.The variations in Nd and Sr isotopic data of the Cadomian granitoids are consistent with an origin through the melting and mixing of Archean to early Proterozoic crust with variable proportions of mantle-derived, juvenile magmas. Such mixing may have occurred at the base of an active continental margin or in an intraplate setting through plume-related magmatic underplating. The LGC is interpreted here as a Cadomian (Pan-African) terrane distinct from adjacent Variscan and pre-Variscan domains, the origin of which remains obscure and which probably became involved in Palaeozoic terrane accretion late in the Variscan event. 相似文献
This paper reports an integrated petrological, geochronological, and isotopic geochemical study of the Pliocene Dzhimara granitoid massif (Greater Caucasus) located in the immediate vicinity of Quaternary Kazbek Volcano. Based on the obtained results, it was suggested that the massif has a multiphase origin, and temporal variations in the chemical composition of its granitoids and their possible sources were determined. Two petrographic types of granitoids, biotite-amphibole and amphibole, were distinguished among the studied rocks of the Dzhimara Massif belonging to the calc-alkaline and K-Na subalkaline petrochemical series. The latter are granodiorites, and the biotite-amphibole granitoids are represented by calc-alkaline granodiorites and quartz diorites and subalkaline quartz diorites. Geochemically, the granitoids of the Dzhimara Massif are of a “mixed” type, showing signatures of S-, I-, A-, and even M-type rocks. Their chemical characteristics suggest a mantle-crustal origin, which is explained by the formation of their parental magmas in a complex geodynamic environment of continental collision associated with a mantle “hot field” regime.
The granitoids of the Dzhimara Massif show wide variations in Sr and Nd isotopic compositions. In the Sr-Nd isotope diagram, their compositions are approximated by a line approaching the mixing curve between the “Common” depleted mantle, which is considered as a potential source of intra-plate basalts, and crustal reservoirs. It was suggested that the mantle source (referred here as “Caucasus”) that contributed to the petrogenesis of the granitoids of the Dzhimara Massif and most other youngest magmatic complexes of the region showed the following isotopic characteristics: 87Sr/86Sr ? 0.7041 ± 0.0001 and
The Middle-Late Pliocene K-Ar ages (3.3–1.9 Ma) obtained for the Dzhimara Massif are close to the ages of granitoids from other Pliocene “neointrusions” of the Greater Caucasus. Based on the geochronological and petrological data, the Dzhimara Massif is formed during four intrusive phases: (1) amphibole granodiorites (3.75–3.65 Ma), (2) Middle Pliocene amphibole-biotite granodiorites and quartz diorites (～3.35 Ma), (3) Late Pliocene amphibole-biotite granodiorites and quartz diorites (～2.5 Ma), and (4) K-Na subalkaline biotite-amphibole quartz diorites (～2.0 Ma).The close spatial association of the Pliocene multiphase Dzhimara Massif and the Quaternary Kazbek volcanic center suggests the existence of a long-lived magmatic system developing in two stages: intrusive and volcanic. Approximately 1.5 Ma after the formation of the Dzhimara Massif (at ca. 400–500 ka), the activity of a deep magma chamber in this area of the Greater Caucasus resumed (possibly with some shift to the east). 相似文献
Collisional granitoid magmatism caused by the Early Neoproterozoic orogeny in the west of the Siberian craton is considered. New data on the petrogeochemical composition, U-Pb (SHRIMP II), Ar-Ar, and Sm-Nd isotopic ages of the Middle Tyrada granitoid massif in the northwestern Yenisei Ridge are presented. Plagiogranites, granodiorites, and quartz diorites of the massif are of calcareous and calc-alkalic composition. The elevated alumina contents and presence of accessory garnet permit them to be assigned to S-type granitoids. Their spidergrams show Rb, Ba, and Th enrichment, minimum Nb, P, and Ti contents, and no Sr depletion. The granitoids formed through the melting of plagioclase-enriched graywacke source, obviously Paleoproterozoic metaterrigenous rocks of the Garevka Formation and Teya Group (TNd(DM) = 2.0-2.5 Ga), judging from the isotope composition of the granitoids (TNd(DM-2st) = 2200 Ma and 8Nd(T) = − 6.0) and the presence of ancient zircon cores (1.80-1.85 Ga). Formation of granitoids took place in the final epoch of the Grenville collision events in the late Early Neoproterozoic (U-Pb zircon age is 857.0 ± 9.5 Ma). In the Late Neoproterozoic, the granitoids underwent tectonothermal reworking caused by Vendian accretion and collision events on the southwestern margin of the Siberian craton, which explain the younger K-Ar biotite age, 615.5 ± 6.3 Ma. 相似文献
The Guandishan granitoids consist mainly of various granitoid intrusions with different scales, including the Huijiazhuang intrusion, Shizhuang intrusion and Hengjian intrusion, which were formed between 1906 Ma and 1848 Ma. On the basis of geological and petrological characteristics, these granitoids can be classified into two groups： the earlier gneissic granodiorites and monzogranites, and the later massive leuco-monzogranites. Their geochemical and Nd isotopic features indicate that they could be derived from complicated partial melting of supracrustal rocks with an affinity of continental arc materials, such as sandy shale and pelite, and with garnet, pyroxene, hornblende and plagioclase as residual phases. Biotite, feldspar and other minerals were most likely fractionated during the magma evolution. Their source may have an affinity with continental arcs, and the granitoids could be derived from the main syn-collisional to late-orogenic tectonic environment, which may be related to the final amalgamation between the Eastern and Western continental blocks in the North China Craton. 相似文献
Intrusions of the Irtysh Complex are spatially restricted to the regional Irtysh Shear Zone (ISZ) and are hosted in blocks
of high-grade metamorphic rocks (Kurchum, Predgornenskii, Sogra, and others) in the greenschist matrix of the ISZ. The massifs
consist of contrasting rock series from gabbro to plagiogranite and granite at strongly subordinate amounts of diorite and
the practical absence of rocks of intermediate composition (tonalite and granodiorite). The complex was produced in the Early
Carboniferous, simultaneously with the onset of the origin of the ISZ itself. The granitoids composing the complex affiliate
with diverse petrochemical series (from subaluminous plagiogranite of the andesite series to granite of the calc-alkaline
series) and contain similar REE and HFSE concentrations [total REE = 103–163 ppm (La/Yb)n = 3.59–5.44, Zr (200–273 ppm), Nb (7.6–10.6 ppm), Hf (6.1–7.6 ppm), and Ta (0.68–1.19 ppm)] but are different in concentrations
in LILE [Rb (3–9 and 121–221 ppm), Sr (213–375 and 77–148 ppm), and Ba (67–140 and 240–369 ppm)] and isotopic composition
of Nd (ɛNd(T) from +5.3 in the plagiogranite to −1.2 in the granite) and O (δ18O from +9.4 in the plagiogranite to +14.5 in the granite). Data on the geochemistry and isotopic composition of metamorphic
rocks of the Kurchum block and numerical geochemical simulations indicate that the granitoids were generated via the melting
of a heterogeneous crustal source, which consisted of upper crustal metapelites and metabasites of the oceanic basement of
the blocks of high-grade metamorphic rocks. The differences in the chemical and isotopic compositions of the granitoids were
predetermined by the mixing of variable proportions of granitoid magmas derived from metapelite and metabasite sources. 相似文献
The geological, geochemical, and geochronological data on the granitiods of the Shmakovka massif, which represents a petrotype of the synonymous complex (southern Russian Primorye), show that the granitoid intrusions of the Shmakovka Complex play a “coupling” role, occurring in different blocks of the Khanka composite terrane. The geochemical and isotopic features of the granitoids indicate that their formation resulted from melting of a “mixed,” substantially metapelite, source similar to the most intensely metamorphosed rocks of the Khanka massif. According to U–Pb measurements, the granitoids are 490 ± 1 Ma old. The analysis of the distribution of Early Paleozoic I-, S-, and A-type granitoids in southern Primorye reveals that Late Cambrian–Early Ordovician endogenic events marked the amalgamation of Precambrian–Early Paleozoic blocks and the eventual formation of the Bureya–Jiamusi superterrane (Bureya–Khanka orogenic belt). 相似文献
There are large volumes of the Phanerozoic granitoid rocks in China and neighboring areas. In recent years, numerous new and precise U-Pb zircon ages have been published for these granitoids, and define many important magmatic events, such as ca. 500 Ma granitoid events in the West Junggar, Altai orogens in the NW China, and Qinling orogen in the central China. These ages accurately constrain the time of important Early Paleozoic, Late Paleozoic, Early Mesozoic and Late Mesozoic magmatic events of the northern, central, western, southern and eastern orogenic Mountains in China. There occur various types of granitoids in China, such as calc-alkaline granite, alkali granite, highly-fractionated granite, leucogranite, adakite, and rapakivi granite. Rapakivi granites are not only typical Proterozoic as in the North China Craton, but were also emplaced during Paleozoic and Mesozoic in the Kunlun-Qinling orogen, a part of the China Central Orogenic Belt (CCOB). Nd-Hf isotopic tracing and mapping show that granitoids in the southern Central Asian Orogenic Belt (CAOB) in China (or the Northern China Orogenic Belt) are characterized predominantly by juvenile sources. The juvenile crust in this orogenic domain accounts for over 50% by area, distinguishing it from other orogenic belts in the world, and those in central (e.g., Qinling), southwestern and eastern China. Based on a large amount of new age data, a preliminary granitoid and granitoid-tectonic maps of China have been preliminarily compiled, and an evolutionary framework of Phanerozoic granitoids in China and neighboring areas has been established from the view of assembly and breakup of continental blocks. Research ideas on granitoid tectonics has also been proposed and discussed. 相似文献
The composition and mechanisms of formation of continental crust in Gorny Altai and the role of granitoid magmatism in its evolution are considered. Geochemical and isotope data for major types of rocks of primary crust and for Early–Middle Paleozoic granitoids of the region are presented. The role of granitoids as indicators of the different stages of the continental-crust evolution is discussed. A review of the main models of continental crust formation is maid, and their applicability to the Gorny Altai segment of the Central Asian Fold Belt is shown. Based on the complex of geological, geochemical, isotope, and geochronological data, it has been established that the formation of continental crust in the Early and Late Caledonian terranes of Gorny Altai proceeded nearly synchronously (in the Middle–Late Devonian).In the Early Caledonian terranes, this process was the consequence of the multistage fractionation of primary juvenile crust of basic composition, and in the Late Caledonian ones it was the result of one-cycle intracrustal melting of hybrid andesitic crust rich in recycled material. 相似文献
