Radioactive elements in collisional and within-plate Sodic-Potassic Granitoids: Accumulation levels and metallogenic significance

New data are reported on the content of radioactive elements in the Precambrian Na-K granitoids from the southwestern margin of the Siberian Craton, Aldan and Ukrainian shields, and Kursk-Voronezh Massif. Analytical data on other regions were generalized for comparison. Two global epochs of Na-K granitoid magmatism bearing elevated contents of radioactive elements (U, Th, K) were distinguished in the Early Precambrian (in Ga): Neoarchean (2.8-2.6) and Late Paleoproterozoic (1.9-1.75). Mesoarchean (3.1-2.8 Ga) epoch of Na-K granite formation has been additionally distinguished at the Australian, South African, and Canadian shields. These epochs of granitization provided high maturity of the crust: geochemical differentiation of the oldest continental blocks and their geochemical and metallogenic specialization for trace elements and RAE. In the southern margin of the Siberian Craton, the most intense granite formation occurred in the Late Paleoproterozoic. The extended South Siberian belt of collisional and within-plate Na-K granitoids is characterized by intense influx of RAE and other trace elements in the upper crustal shell. The southwestern margin of the craton (Yenisei Range) was spanned by repeated Late Neoproterozoic Na-K granite formation, with wide development of collisional and within-plate Na-K granites having elevated Th content and [Th]/[U] ratio. The higher RAE concentrations are typical of within-plate Paleo and Neoproterozoic granitoids. The highest uranium content was found in the postcollisional and within-plate Na-K granites and subalkaline leucogranites. Uranium ore concentrations were formed at the riftogenic stages of evolution of these crustal blocks, when within-plate subalkaline acid magmatism and accompanying hydrothermal metamorphism overprinted granitized crystalline massifs, including high-U sedimentary and volcanic complexes. Areas with the most favorable geological-geochemical environments for the formation of uranium mineralization were distinguished in the southern margin of the Siberian Craton and its nearest folded framing.     

Synkinematic granitoid magmatism of Western Sangilen,South-East Tuva

The problems of tectonic control of composition, size, and morphology of synkinematic crustal granitoids are discussed by the example of the Western Sangilen granites (South-East Tuva). Comparative analysis was performed for felsic bodies and massifs spatially confined to tectonic zone (Erzin shear zone): Erzin migmatite–granite complex (510–490 Ma), Matut granitoid massif (510–490 Ma), Bayankol polyphase gabbro-monzodiorite–granodiorite–granite massif (490–480 Ma), and the Nizhneulor Massif (480–470 Ma). It is shown that synkinematic felsic melts during the transition from collisional compression to transpression were formed at different crustal levels. An increase of shear component provided favorable conditions for the migration of felsic melts, increase of size and morphology of intrusive bodies from vein type to harploith (likely, loppoliths and laccoliths) and further to stocks. All kinematic granitoids of the Erzin tectonic zone are ascribed to the crustal S-type granites. Dispersion and average chemical composition of the synkinematic granites strongly depend on the degree of their “isolation” from protolith. From auto- and paraautochthonous granitoids to allochthonous granites, the compositional dispersion decreases and the chemical composition is displaced toward I-type magmatic rocks.     

华东地区花岗岩类成因类型及其与铀成矿的关系

本文对华东地区的花岗岩类按改造型 变质混合交代型、重熔型和同熔型———同熔型 (Ⅰ型 )、深源分异型 (A型 )进行了成因分类 ,并对各类花岗岩的岩石化学成分、岩石学特征、副矿物、稀土元素、锶、氧同位素等特征进行了较为详细的论述 ,列举了各类花岗岩的分布地区和代表性岩体 ;论述了各类花岗岩的空间分布与铀矿床产出的关系 ,指出重熔型花岗岩是铀矿床产出的主要岩体类型 ,其次是深源分异型 (A型 )花岗岩。变质混合交代型和同熔型 (Ⅰ型 )花岗岩只有铀矿点或矿化点产出。文章最后系统地总结了改造型与同熔型花岗岩的铀矿化特征。     

南岭稀土花岗岩、钨锡花岗岩及其成矿作用的对比

南岭地区的钨锡和稀土矿床都与花岗岩类有直接成因联系,但二者的成矿作用有许多不同之处.钨锡是典型的热液成矿,而稀土则主要形成于风化作用.随着花岗岩类的分异演化,岩石中的W、Sn等元素含量逐渐增加,因此钨锡等矿床主要与高度分异演化的晚阶段小岩体有关;但是稀土的表现与钨锡不同,由于花岗岩类的分异演化导致稀土栽体黑云母及许多副矿物的减少,因此稀土元素含量在晚阶段岩体中反而降低.赣南的五里亭-大吉山岩体、桂东北的花山-姑婆山岩体等提供了很好的范例.因此,南岭地区与风化壳型稀土矿床有关的岩石主要有:印支期准铝质花岗岩,燕山期A型花岗岩,燕山中-晚期黑云母二长花岗岩等.     

Paleozoic Granitoids of the Southern Part of the Voznesenka Terrane (Southern Primorye): Age,Composition, Melt Sources,and Tectonic Settings

This paper presents data on the geological position, geochemistry, age, and isotopic characteristics of the granitoids of the southern part of the Voznesenka terrane, Southern Primorye (Muraviev–Amursky Peninsula and its vicinities). All of the studied granitoids were formed in three stages: the Ordovician, Silurian, and Permian. The Silurian and Permian ages of the granitoid intrusions have been previously determined (Ostrovorussky Massif, 432–422 Ma, and 250 ± 4 Ma, early and late associations, respectively; Sedanka massif, 261 ± 3 Ma). The granites of the Artem and Nadezhdinsky massifs define an U–Pb zircon age of 481 ± 6 and 452 ± 4 Ma, respectively. The geochemical and isotope data show mainly the crustal nature of the granitoids. Their formation was related to melting of relatively immature rocks of the continental crust (mafic–intermediate volcanic rocks). The Nd isotope composition of the granitods (TNd(DM–2) = 1.3 Ga) indicates the absence of the mature ancient crust at the basement of the southern Voznesenka terrane. The maximum contribution of mantle sources to the granite formation is recorded in the Permian associations. A comparison of the peaks of intrusive magmatism in the southern part of the Voznesenka terrane and adjacent territories suggests that the formation of the granitoids of the Muraviev–Amursky Peninsula and its vicinities was caused by the interaction of continental blocks with two oceanic basins: the Paleoasian (and its fragments) and Paleopacific ones.     

New data on the age and nature of the Khan–Bogd alkaline granites,Mongolia

New age dating (291 Ma) was obtained for one of the largest alkaline granite massifs in the world, the Khan–Bogd Massif (Mongolia). For the first time, apart from zircon, other zirconium silicates, elpidite and armstrongite, have been analyzed. Our determinations showed the highly depleted nature of the mantle sources of granites with ε_Nd = 12. All the studied Zr-silicates demonstrate positive Eu anomalies in the REE patterns, which indicate a low oxidation potential during alkaline granite formation.     

Paleoproterozoic anorogenic granitoids of the Zheltav sialic massif (Southern Kazakhstan): Structural position and geochronology

The basement of the Zheltav sialic massif (Southern Kazakhstan) is composed of different metamorphic rocks united into the Anrakhai Complex. In the southeastern part of the massif, these rocks form a large antiform with the core represented by amphibole and clinopyroxene gneissic granite varieties. By their chemical composition, dominant amphibole (hastingsite) gneissic granites correspond to subalkaline granites, while their petroand geochemical properties make them close to A-type granites. The U–Pb geochronological study of accessory zircons yielded an age of 1841 ± 6 Ma, which corresponds to the crystallization age of melts parental for protoliths of amphibole gneissic granites of the Zheltav Massif. Thus, the structural–geological and geochronological data make it possible to define the Paleoproterozoic (Staterian) stage of anorogenic magmatism in the Precambrian history of the Zheltav Massif. The combined Sm–Nd isotopic—geochronological data and age estimates obtained for detrital zircons indicate the significant role of the Paleoproterozoic tectono-magmatic stage in the formation of the Precambrian continental crust of sialic massifs in Kazakhstan and northern Tien Shan.     

Geology and geochronology of neoarchean anorogenic magmatism of the Keivy structure, Kola Peninsula

Anorogenic magmatic complexes were formed during protoplatformal evolution of the Keivy structure. This evolution ended with development of aluminous schists, which were derived by deep disintegration and redeposition of the rocks from the lower parts of the sequence and surrounding of the structure. The anorogenic rocks of the region are represented by the following magmatic complexes: gabbro-labradorite-latite-monzonite-granites; ophitic gabbro and gabbrodiabases; quartz syenite-alkaline granites; alkaline and nepheline syenites. The magmatic activity of this period, starting from the emplacement of gabbrolabradorite massifs and ending with alkaline and nepheline syenite bodies, was caused by ascent of mantle asthenolith, which destructed the Earth’s crust basement in this area. The anorogenic magmatism of the Keivy structure lasted for no more than few or few tens of million years. The granitoid subcomplex of the gabbro-labradorite-latite-monzonite-granite complex is dated at 2674 ± 6 Ma, which is comparable with an age of alkaline granites of the Ponoy and Beliye Tundry massifs (2673 ± 6 Ma). The considered complexes are separated in time by intrusion of amphibole-biotite plagiomicrocline granites with an age of 2667 ± 8 Ma. Gabbrolabradorites of the Shchuch’e Ozero and Tsaga massifs have close ages (2663 ± 7 and 2668 ± 10 Ma, respectively, Bayanova, 2004), but were formed earlier than granitoids (Bayanova, 2004). Formation of alkaline syenites of the Sakharijok I Massif, which finalized the Neoarchean anorogenic magmatism of the region, falls in the same interval. During Paleoproterozoic transformations, the rocks of the Keivy structure were sheared and uranium was introduced in the contact zones of the alkaline granite massifs, which caused formation of palingenetic melts and subsequent formation of pegmatites in the outer contact zones of the granite bodies.     

额尔古纳地块新元古代岩浆作用与微陆块构造属性:来自侵入岩锆石U-Pb年代学、地球化学和Hf同位素的制约

对额尔古纳地块新元古代花岗岩进行了锆石LA-ICP-MS U-Pb年代学、岩石地球化学和锆石Hf同位素研究,以便对其新元古代岩浆作用历史与微陆块构造属性给予制约.所测花岗质岩石中锆石的CL图像特征和Th/U比值(0.17~1.46) 显示其为岩浆成因.测年结果并结合前人定年结果,可以判定额尔古纳地块上至少存在~929 Ma、~887 Ma、~850 Ma、~819 Ma、~792 Ma、~764 Ma和~738 Ma岩浆事件.岩石地球化学特征显示,~887 Ma花岗岩为一套后碰撞花岗岩类;而850~737 Ma花岗质岩石整体上属于A-型花岗岩,也有部分岩体(漠河、阿木尔、碧水和室韦岩体)显示I-型花岗岩特征.锆石Hf同位素特征反映这些花岗岩的源区既有中-新元古代(T_DM2=884~1 563 Ma)新增生地壳物质的部分熔融,同时伴有少量古老地壳物质的混染,也有残留的古老中基性下地壳物质的部分熔融.综合研究区新元古代侵入岩的地球化学特征,同时对比新元古代全球构造热事件,认为额尔古纳地块上新元古代岩浆活动记录了Rodinia超大陆形成和演化过程中的地壳响应:927~880 Ma的岩浆作用应是Rodinia超大陆汇聚造山的产物;而850~737 Ma的岩浆作用应是对Rodinia超大陆快速裂解的记录.通过岩浆事件对比发现,额尔古纳地块与邻近的西伯利亚南缘微陆块(如中蒙古地块和图瓦地块)具有亲缘性,而与塔里木板块和华南板块至少在新元古代岩浆活动上具有一定的相似性,而明显区别于华北板块和西伯利亚板块.      

Early paleozoic granitoids in the Lesser Khingan terrane, Central Asian Foldbelt: Age, geochemistry, and geodynamic interpretations

The U-Pb zircon dates obtained for the Sutara (480 ± 4 Ma), Kabalinskii (471 ± 10 Ma), and Durilovskii (461 ± 5 Ma) massifs reliably confirm an Early Proterozoic orogenic event, which took place after granulite metamorphism at approximately 500 Ma (Wilde et al., 2003) in the Lesser Khingan (Jiamusi) terrane. The rocks emplaced most shortly after the main metamorphic event are the granites of the Sutara Massif and leucogranites of the Kabalinskii Massif, whose geochemistry is close to that of collision granites. The quartz diorites and subalkaline granites of the Durilovskii Massif, whose geochemistry suggests their origin in a postcollision environment with the participation of an enriched mantle source, were emplaced longer after metamorphic event and after the aforementioned massifs.     

The Genetic Types of Some Granite Intrusions Associated with Tin Polymetallic Deposits in the Nanling Region

Tin polymetallic deposits are the most important type of tin deposit in the Nanling region. Manyresearchers both at home and abroad consider this type of tin deposit to be the product of differentiation andevolution of granite magmas resulting from anatexis of continental crust and to be genetically related to thetransformation-type (S-type) granitoids. In this paper, on the basis of the geological settings, petrology, REEgeochemistry and strontium and oxygen isotopic compositions of 6 granite intrusions associaied with tinpolymetallic deposits in the Nanling region, the authors suggest that the ore-bearing granites of this type areprobably the products of differentiation and evolution of acid magmas resulting from 40-50‰ fractionalcrystallization of magmas formed by partial melting of the pre-existing intermediate-basic volcanic rocks ofmantle origin in the lower crust and a small amount of sialic material and belong to crust-mantle-derivedgranitoids (approaching I-type of B. W. Chappell and A.J.R. White, but being evidently different from theS-type granitoid related to W, Sn, Nb, Ta and REE deposits).     

A study of igneous rocks related to Zn–Pb mineralization in the Shinyemi and Gagok deposits of the Taebaeksan Basin,South Korea

The Shinyemi and Gagok deposits, located in the Taebaeksan Basin, South Korea, display Zn–Pb mineralization along a contact between Cretaceous granitoids and Cambrian–Ordovician carbonates of the Joseon Supergroup. The Shinyemi mine is one of the largest polymetallic skarn‐type magnetite deposits in South Korea and comprises Fe and Fe–Mo–Zn skarns, and Zn–Cu–Pb replacement deposits. Both deposits yield similar Cretaceous mineralization ages, and granitoids associated with the two deposits displaying similar mineral textures and compositions, are highly evolved, and were emplaced at a shallow depth. They are classified as calc‐alkaline, I‐type granites (magnetite series) and were formed in a volcanic arc. Compositional variation is less in the Shinyemi granites and aplites (e.g., SiO₂ = 74.4–76.6 wt% and 74.4–75.1 wt%, respectively) than in the Gagok granites and aplites (e.g., SiO₂ = 65.6–68.0 wt% and 74.9–76.5 wt%, respectively). Furthermore, SiO₂ vs K/Rb and SiO₂ vs Rb/Sr diagrams indicate that the Shinyemi granitoids are more evolved than the Gagok granitoids. Shinyemi granitoids had been already differentiated highly in deep depth and then intruded into shallow depth, so both granite and aplite show the highly evolved similar chemical compositions. Whereas, less differentiated Gagok granitoids were separated into two phases in the last stage at shallow depth, so granite and aplite show different compositions. The amounts of granites and aplite are similar in the Shinyemi deposit, whereas the aplite appears in an amount less than the granite in the Gagok deposit. For this reason, the Shinyemi granitoids caused not only Fe enrichment during formation of the dolomite‐hosted magnesian skarn but also was associated with Mo mineralization in the Shinyemi deposit. Zn mineralization of the Gagok deposit was mainly caused by granite rather than aplite. Our data suggest that the variation in mineralization displayed by the two deposits resulted from differences in the compositions of their associated igneous intrusions.     

New Data on Crystallization Conditions of Monzodiorite—Granite Massifs on the Eastern Slope of the Urals

The geological structure of monzodiorite—granite massifs (Stepninskii, Biryukovskii, Vandyshevskii, and Uiskii) of the Stepninskii complex extending as a chain of intrusive bodies crossing the submeridional structures of the Ural Fold Belt is described. These granite massifs are ascribed to the Permian and, as suggested, are related to a mantle plume. Based on the results of studying melt and gas—liquid inclusions in quartz from granitoids, it was established that the rock crystallization depth in the given series of massifs decreases gradually in the northwesterly direction from hypabyssal to hypabyssal—subsurface facies. It is shown that leucocratic and aplitic varieties of granites with a higher level of fluid content have rare-metal metallogenic specificity and are promising in the search for W—Mo ore mineralization.     

Early to Middle Jurassic (ca. 182–164 Ma) fractionated granitoids in the Korean Peninsula: Implication for the tectonomagmatic history of East Asia

The Jurassic granitoids (200–164 Ma) are distributed in the Korean Peninsula due to the Paleo-Pacific plate subduction. Early Jurassic (200–182 Ma) granitoids are mainly distributed in the southern Korean Peninsula. By contrast, Early to Middle Jurassic (182–164 Ma) granitoids are distributed in the central Korean Peninsula. In this study, we report detailed petrology, zircon U–Pb ages, and whole-rock geochemistry from the Seoul–Uijeongbu and Pocheon–Gimhwa pluton units in the central Korean Peninsula. The Seoul–Uijeongbu unit is dominated by biotite granite, with minor porphyritic biotite and garnet-biotite granite while the Pocheon–Gimhwa unit consists of biotite granite and porphyritic biotite granite, garnet-biotite granite, and two-mica granite. Zircon U–Pb age from those granites gives 180–167 Ma. The granitoids in the Pocheon-Gimhwa unit formed through fractional crystallization from biotite granite and porphyritic biotite granite to garnet-biotite granite, and two-mica granite based on gradually decreasing their Nb/Ta, Zr/Hf, and Eu/Eu* ratios. The strongly fractionated granitoids are garnet-biotite granite and two-mica granite. The LILE enrichment, Ta–Nb, Sr–P, and Eu–Ti troughs, and Ba depletion in most granitoids are similar to those of granitoids due to the subduction in the arc environment. Thus, these Jurassic granitoids (180–167 Ma) are mainly peraluminous granites with moderate crystal fractionation corresponding to I-type granite. Alkali feldspar granite associated with ore mineralization occurs in the Gwanaksan pluton from the southwestern Seoul–Uijeongbu unit. The alkali feldspar granite displays distinct negative Eu anomaly with high contents of Rb, Hf, Cs, and Nb compared with other granites. These characteristics imply that alkali feldspar granite experienced strong hydrothermal activity leading to feldspar ore mineralization compared to the other granites. The formation of a wide range of moderately evolved peraluminous granitoids is presumed to be related to rapid flat-subduction during 182–164 Ma, and the mineralization-related alkali feldspar granite indicates the termination of Jurassic granitoid magmatism in the central Korean Peninsula.     

Zr/Hf ratio as an indicator of fractionation of rare-metal granites by the example of the Kukulbei complex,eastern Transbaikalia

The concept of granitic melt fractionation as the main process in the concentration of rare elements in granites calls for the development of a reliable method to determine the evolutionary sequences of granite series. We propose to use for this purpose a zirconium-hafnium indicator, the Zr/Hf weight ratio in granitic rocks (Zaraisky et al., 1999, 2000). By the example of three classic regions of rare-metal deposits, eastern Transbaikalia, central Kazakhstan, and Erzgebirge (Czech Republic and Germany), it was empirically shown that the Zr/Hf ratio of granites decreases during the fractional crystallization of granite magmas in the sequence granodiorite → biotite granite → leucogranite → lithium-fluorine granite. The reason is the higher affinity of Hf compared with Zr to a granite melt. This implies that the crystallization and settling of accessory zircon will cause the progressive enrichment of Hf relative to Zr in the residual melt. As a result, the Zr/Hf ratio decreases regularly in the series of sequential phases of granite intrusion related to a single magma chamber from granodiorite to biotite granite, leucogranite, and Li-F granite (from 45-30 to 10-2). Our experimental investigations supported the preferential enrichment of haplogranite melt in Hf and zircon crystals in equilibrium with melt in Zr (T= 800°C and P = 1 kbar). The Zr/Hf indicator was tested by the example of the wellknown Kukulbei rare-metal granite complex of eastern Transbaikalia (J3), which is unique in the degree of fractionation of initial granite melt with the formation of three phases of granite emplacement and vein derivatives. An important feature of the complex is its “short” differentiation trend. It was supposed that the granite magma of the first phase is parental, and the later phases forming small intrusive bodies in large massifs of biotite granites of the first phase are sequential products of its crystallization differentiation in a magma chamber. The biotite granites of the first phase are barren. The leucocratic granites of the second phase are accompanied by tin-tungsten greisen deposits (e.g., Spokoininskoe), and the upper part of cupola-like stocks of Li-F amazonite granites of the third phase host apogranite-type tantalum deposits (Orlovka, Etyka, and Achikan). In addition to three granite phases, the Kukulbei complex includes dikes of ongonites, elvans, amazonite granites, and chamber miarolitic pegmatites. All of the granitic rocks of the complex have similar isotopic ages of 142± 0.6 Ma. The Zr/Hf ratio decreases systematically from phase 1 (40–25), to phase 2 (20–10), and phase 3 (10–2). The ongonites, elvans, and pegmatites have similar Zr/Hf ratios (15-5), falling between the ranges of leucocratic muscovite granites and Li-F granites. Compared with other granite series, the granitic rocks of the Kukulbei complex show specific petrographic and geochemical features: they are strongly enriched in Rb, Li, Cs, Be, Sn, W, Mo, Ta, Nb, Bi, and F but depleted in Mg, Ca, Fe, Ti, P, Sr, Ba, V, Co, Ni, Cr, Zr, REE, and Y. From the early to late intrusion phases, the degree of enrichment and depletion in these element groups increases regularly. This is accompanied by a significant decrease (from 40 to 2) in Zr/Hf, which can be used as a reliable indicator of genetic relations, degree of fractionation, and rare-metal potential of granites. Granites with Zr/Hf values lower than 25 are promising for prospecting for Sn, W, Mo, and Be greisen deposits, whereas the formation of Ta deposits requires Zr/Hf values lower than 10.     

柴达木盆地北缘西端冷湖花岗岩

冷湖花岗岩体由花岗闪长岩和二长花岗岩组成，岩体中发育较多的辉绿岩墙和花岗闪长斑岩岩墙。岩石的常量、稀土、微量元素地球化学研究表明花岗岩类和脉岩类为同源岩浆分异演化而成，Rb-Sr、Sm-Nd同位素特征反映其源岩来自地幔。地球化学判别图解得出，冷湖花岗岩类属I型花岗岩，早期的花岗闪长岩形成于岛弧环境，与柴达木板块、南祁连板块的碰撞有关；晚期的二长花岗岩形成于板块碰撞隆起环境，与阿尔金大型走滑断裂的活动有关。     

Late Paleozoic rare-metal granitoid magmatism of the Southern Baikal region

The Late Paleozoic intraplate magmatism of the Selenga-Vitim structural zone of the Baikal region (Khamar-Daban Range) produced granitoids of different geochemical types: palingenic calc-alkaline granitoids, subalkaline monzogranites, and rare-metal Li-F granitoids and their subvolcanic analogues. Subalkaline and rare-metal granitoids occur in the periphery of the Late Paleozoic magmatic zone. Rare metal granite magmatism is manifested in this region as nearly N-S trending intrusive-dike belts comprising multiphase intrusions (Kharagul, Urugudei, and Bitu-Dzhida massifs) with an exposed area of ∼10 km² and an age of formation from 311 to 321 Ma and series of accompanying dikes. The early phases of the intrusions are made up of biotite granites usually with fluorite, which are changed during the late stage by typical topazbearing rare-metal amazonite-albite granites. In the subvolcanic facies, thicker subalkaline dikes of monzonite porphyry, granite porphyry, and elvan are changed by ongonites, topaz rhyolites, and topazites, which occasionally serve as cement in eruptive and fluid-explosive breccias. The development of multiphase intrusions from early biotite granites to late amazonite-albite granites with Li-F mica was accompanied by an increase in SiO₂ and, especially, Na₂O contents, whereas the level of (FeO + Fe₂O₃), CaO, and K₂O declined. Geochemical evolution includes an increase in the same direction in the contents of F, Li, Rb, Cs, Sn, Be, Ta, and Pb and a decrease in Ba, Sr, Zn, Zr, Th, and U. Similar evolution is also characteristic of the subvolcanic rocks, which emphasizes the genetic relation of the whole intrusive-dike complex of the Khamar-Daban province. Significant differences were detected in the distribution of K, Ba, Sr, and Zr between the calc-alkaline granitoids and rare-metal Li-F granites. The continental crust-normalized patterns of the raremetal granites show positive anomalies for Li, Rb, Nb, and Pb. The rare-metal Li-F granites could not be produced by palingenesis only, and their formation required specific conditions causing extensive accumulation of characteristic trace elements. During the evolution of granite melts, Li, Rb, Ta, Nb, Sn, W, and F are extensively accumulated in late intrusive phases, which indicates an important role of the processes of magmatic and fluid-magmatic differentiation during their formation. The composition and isotope geochemical characteristics of the supposed magma source material correspond to the ancient Precambrian continental crust with a mean model age of more than 1200 Ma.     

赣南不同类型花岗岩体的锆石形态群特征及其意义

根据赣南不同时期的各类型花岗岩体的锆石形态群的研究,确定了赣南在前燕山期形成的隘地体、安西－龙州岩体都是造山花岗岩,寨背岩体,陂头岩体,柯树北岩体和安西－龙州岩体均可能是地幔物质混染地壳物质后形成的。     

Age,Mineralogical and Geochemical Features,and Tectonic Position of Gabbroids of the Dzhigdinskii Massif,Southeastern Environ of the North Asian Craton

Complex mineralogical, geochemical, and geochronological studies of the gabbroids from the Dzhigdinskii Massif located in the western part of the Dzhugdzhur–Stanovoy Superterrane are performed. It is established that the age of the rocks from the Dzhigdinskii Massif is Middle Triassic (244 ± 5 Ma), rather than Early Archean, as was previously assumed. The age of the Dzhigdinskii Massif is close to the age of the formation of the other Triassic gabbroid massifs, such as the Amnunaktinskii (~240 Ma), Lukindinskii (~250 Ma), and Luchinskii (~248 Ma) in the southeastern environ of the North Asian Craton. One of the stages in the formation of the Selenga–Vitim volcanoplutonic belt falls in this period as well. This indicates that the Selenga–Vitim volcanoplutonic belt, along with the granitoids and volcanic rocks, is composed of ultrabasic–basic and basic massifs and that this belt is superposed on the structures of the Selenga–Stanovoy Superterrane, as well as on the western part of the Dzhugdzhur–Stanovoy Superterrane. The gabbro, gabbro–diorite, and series of gabbro and gabbro–diorite with high sodic alkalinity from the Dzhigdinskii Massif show obvious geochemical features of duality, including combination of intraplate and super-subduction origin. In this relation, we can assume that the origin of the gabbroids of the Dzhigdinskii Massif is related to the detachment of the oceanic lithosphere and its subduction into the mantle with the formation of an “asthenospheric window.”     

Aptian bimodal volcanic associations and granitoids in the northern margin of the Amur microcontinent: Age, sources of material, and geodynamic environments

Data on the composition, age, and source of material of Aptian rocks composing a bimodal volcanic complex and related granitoids in the northern margin of the Amur microcontinent indicate that the granodiorites of the Talalinskii Massif and subalkaline granites of the Dzhiktandiunskii Massif crystallized at 117 ± 2 and 119 ± 2 Ma, respectively (⁴⁰Ar/³⁹Ar method), and their crystallization ages coincide with the age of volcanic rocks of the Gal’kinskii bimodal complex. These data make it possible to combine the rocks within a single volcano-plutonic association. Geochemical and isotopic-geochemical features of trachybasaltic andesites of the Gal’kinskii bimodal complex suggest that the parental melts were derived from such sources as PREMA (or DM) and an enriched source of the EMII type at a subordinate contribution of a crustal source. The parental melts of rhyolites of the Gal’kinskii Complex and granitoids of the Talalinskii and Dzhiktandinskii massifs were derived from crustal material with minor amounts of juvenile material. The bimodal volcanic association and related granitoids dated at 119–115 Ma were most likely formed in geodynamic environments implying the ascent of the asthenospheric mantle.