Petrogeochemical Characteristics Research Articles

The Shalap Mélange of the Salairian Alambay Ophiolite Zone (Northwestern Central Asian Orogenic Belt), Geological Structure and Compositional Features of Amphibolites and Greenstone Basalts

The Alambay ophiolite zone (AOZ) is located in the axial part of the Early Paleozoic Salair orogen and includes the northern extension of the Alambay-Kaim zone, Salair and Altai Mountains. The Shalap area of the AOZ is predominantly composed of clastic mélange with occasional serpentine mélange. The geological and geochemical studies showed that in the Shalap mélange there are basalt blocks of the Alambay formation whose petrogeochemical features are similar to those of the oceanic island basalts (OIB). Metamorphic rocks of the Angurep complex, represented by garnet and non-garnet amphibolites, form a tectonic slab which is a part of the accretionary complex east of the Shalap mélange area. Metamorphic rocks also form blocks in the Shalap mélange. The amphibolites of the Angurep complex are similar in their petrogeochemical features to the basalts of intraoceanic island arcs. The Shalap mélange is a fragment of the Salairian Cambrian paleosubduction zone. The subduction and exhumation processes in this paleosubduction zone terminated by the 500 Ma time stage.

The formation of the granite complex in the Wuhe Mari area of Bayankala Mountain on the northeastern margin of the Tibetan Plateau: constraints from lithogeochemistry and U–Pb zircon dating

The granite complex in the Wuhe Mari area lies in the tectonic magma belt of the North Bayankala Mountains on the northeastern edge of the Qinghai-Tibet Plateau. It is located in the middle of the first member of the Changmahe Formation of the Early and Middle Triassic Bayankala Mountains Group. This article presents a systematic study of the petrological and geochemical characteristics and chronology of porphyrite granilite, monzogranite, porphyritic monzogranite and diorite in the granite complex in Wuhe Mari area. The genetic relationship between these four rock types as well as the type of source area and tectonic environment are clarified. Zircon LA-ICP-MS-U–Pb dating shows that the porphyritic granodiorite, monzogranite, porphyritic monzogranite and diorite have ages of 221.0 ± 2.7 Ma, 219.8 ± 3.0 Ma, 216.6 ± 4.3 Ma and 213.4 ± 1.6 Ma, respectively. The petrogeochemical characteristics show that the porphyritic granodiorite, monzogranite and porphyritic monzogranite in the granite complex have the characteristics of high Si, Al2O3, K, low Na, Ca, Mg, Fe, K, Rb and Th—Content in the strongly incompatible elements of the granite complex have three, the relative loss of Ba, Ta, Nb, Ce, slight enrichment or no anomaly, the loss of Sm, Hf and Zr, the strong loss of Y and Yb and the aluminum saturation index < 1.1. Combined with the geological data all three samples belong to Type I granite formed in the same collision environment. Based on the lithogeochemical characteristics and the results of U–Pb chronology, these three rock formations are believed to have been formed by a series of magmatic melting events and are the result of homologous magma crystallization and differentiation. The diorite forms in an intraplate tectonic setting as a result of the evolution of co-collision granite to intraplate granite.

Low-sulfide platinum–metal deposits in the Kola region: A comparative analysis of the Yuzhnosopchinskoye ore occurrence and the Fedorova Tundra deposit

Research subject. Platinum–metal objects of the Kola region (contact type mineralization), including the Yuzhnosopchinskoye ore occurrence within the same-name massif belonging to the Early Proterozoic Monchetundra intrusion and the Fedorova Tundra deposit located in the western part of the Early Proterozoic Fedorovo-Pansky layered complex. Aim. To establish the formation conditions of platinum-metal ores in the Yuzhnosopchinskoye ore occurrence and the Fedorova Tundra deposit. Methods. Comparison of the geological structure and petro-geochemical features of rocks and ores from the two objects using statistical analysis. Results. Both the Yuzhnosopchinskoye ore occurrence and the Fedorova Tundra deposit belong to the contact type of platinum group element deposits. The main characteristic feature is confinement of the ore zone to the contact of two magmatic phases. In the contact zone, igneous breccia, pegmatoid, and vein bodies are widespread, with the latter being especially common in the Yuzhnosopchinskoye ore occurrence. In Yuzhnosopchinskoye ore occurrence, breccia fragments are represented by orthopyroxenites and melanocratic norites of the early magmatic phase (layered series of rocks). They were cemented by barren gabbroids of the later magmatic phase. In the Fedorova Tundra deposit, breccia zone fragments are also composed of orthopyroxenites and melanocratic norites of the early magmatic phase (layered series of rocks). They were cemented by taxitic ore-bearing gabbronorites of the late magmatic phase. Rocks of the two objects with a similar nomenclature demonstrate slight systematic differences in the composition of petrogenic components, as well as in REE and rare elements. Taxitic gabbronorites (rocks of the marginal series) from the Fedorova Tundra deposit have no rock analogues in Yuzhnosopchinskoye ore occurrence. A comparison of similar amounts of two data sets (more than 2000 samples each) of Pt, Pd, Au, Ni, and Cu sampling showed that the content of all precious metals in the Fedorova Tundra deposit was consistently higher than that in the Yuzhnosopchinskoye ore occurrence. The Fedorova Tundra deposit is homogeneous, with an average Pd/Pt ratio of 4.5. The Yuzhnosopchinskoye ore occurrence is heterogeneous and, on average, slightly more ‘platinum’ and less ‘palladium’ than the Fedorova Tundra deposit. Conclusions. The two ore objects of the contact type are similar in many respects, mainly differing in the conditions of mineralization formation. The Yuzhnosopchinskoye ore occurrence entered the contact zone from the rocks of the layered series due to the activation of the ore matter during intrusion of the late gabbroid intrusive phase. The Fedorova Tundra deposit entered the contact zone together with the late ore-bearing gabbronorite magmatic phase.

Alkaline–Salicic Kurung Complex of the Ket-Kap–Yuna Igneous Province (Aldan Shield, Russia): Petrogenesis and Geodynamic Conditions of Formation

Abstract —Integrated geological data, petrogeochemical characteristics of magmatites of the Kurung complex (the Ket-Kap–Yuna igneous province of the Aldan Shield), and previously published isotopic data along with the results of geochronology and geochemistry research provide evidence for this complex evolving in the Late Cretaceous in a setting of riftogenesis (final phase) of continental margins. Similar to the Late Jurassic–Early Cretaceous polyformational volcano-plutonism of the Aldan Shield, the Late Cretaceous alkaline magmatism in the Ket-Kap–Yuna province is associated with the tectonomagmatic activation which manifested itself mainly as continental margin rifting associated with deep reorganization of the southwestern, southern and southeastern framing of the Siberian craton triggered by gravitational sliding of the lithospheric plates. Results of the petrogeochemical analysis of the studied magmatites revealed that the heterogeneous rock groups identified within this rock complex are not related to each other by fractional or other type of differentiation, thus suggesting their possible derivation as a result of fluid syntexis-type interaction between mantle-derived alkali–basite melt and felsic crustal melts. Alkali–basite parent melts are shown to have formed during partial melting of variably enriched mantle which is widely spread beneath the Aldan Shield and is varied in composition (from BSE enriched to nearly EM-I). Origination of such deep-seated melts (magma sources) was associated with the rifting processes (strike-slip tectonics) triggered by the setting of gravitational sliding of lithospheric plates. The formation of alkaline–salic magmas of the Kurung complex is associated with large-scale selective assimilation of crustal material by high-temperature fluidized mantle magmas during their ascent to the surface, possibly as a result of fluid syntexis of alkaline–basite mantle magmas and crustal smeltings formed under their influence.

Paleovolcanism of the eastern Magnitogorsk megazone, Southern Urals: Petrology, geochemistry, and gold-bearing perspectives

The geological-petrographic and petrogeochemical features of volcanic rocks are considered of the Gumbeika zone in the Southern Urals, that is the frontal easternmost portion of the East Magnitogorsk paleo-island arc. The volcanites are united into the Gumbeika volcanic association. The association is shown to be represented by the basalt– andesite–dacite–rhyodacite “uninterrupted” homodrom igneous series. The compositional features of the volcanics allow confident assigning them to the island-arc calc-alkaline series, or more precisely, to formations of “developed” island arcs. It is concluded that the main process that determines the general appearance and composition of the unified petrogenetic series of rocks of the Gumbeika association was the fractional crystallization of the parental basaltic melts in deep-seated chambers and, then, in near-surface peripheral ones. The emplacement of some of the magmatic bodies was also accompanied by in situ gravitational differentiation. The general similarity of the volcanics-associated gold-silver deposits with the analogs within recent island arcs allows us to suggest a great perspectives for gold-silver mineralization throughout the Gumbeika zone. Two forecasted ore fields have been identified.

Mineralogy and geochemistry of the Aushkul, Kamatal and Shartym granite massifs (Balbuk comlex, Southern Urals)

The article discusses the petrographic, mineralogical and petrogeochemical features of alkaline granites of the Balbuk complex in three massifs - Aushkul, Kamatal and Shartym. The rocks of the massifs are similar in structural and textural features and mineral composition: they are composed of acidic plagioclase, potassium feldspar, quartz and muscovite. In the Aushkul massif, phenocrysts of potassium feldspar, plagioclase, quartz and primary oligoclase are found in the groundmass, while in the Kamatal and Shartym massifs only phenocrysts of altered plagioclase and quartz are developed, and secondary albite is present in the groundmass. The existing differences in the geochemistry of the rocks of the Aushkul massif in comparison with Kamatal and Shartym (depleted in barium and enriched in niobium) may be associated with minor differences in the composition of magmas and with the peculiarities of their fractionation in intermediate chambers (fractionation of alkali feldspar and Nb-containing phases).

Traps of the Morkoka River Basin and their morphology as response to the possible presence of kimberlites

The traps in outcrops of the middle course of the Morkoka River were formed in three stages and implementation phases. Each subsequent introduction phase of the basite melt was distinguished by its petrogeochemical features, degree of crystallization of the magmatic melt, and density. An unusual form of intrusion introduction in the second phase (crushing of the sill and the introduction of an early intrusion into the rocks) was revealed. During the formation of kimberlite diatremes, the carbonate rocks containing them became denser and thermoelastic stress fields associated with the magnetoelastic Villari effect arose. As a result, the so-called “protective shield” was formed around the kimberlites. A comparison of the trap sill behavior of the Morkoka River with the similar behavior of traps near kimberlites (Komsomolskaya and Morkoka tubes) suggests the presence of an unknown kimberlite body under traps in this area.

Geodynamics and Early Cretaceous Magmatism of the Northern Volcanic-Plutonic Belt of Verkhoyan-Kolyma Fold Area (Northeastern Russia)

New data on the geological position, U‒Pb SIMS zircon ages, petro-geochemical features, Sr‒Nd isotopic composition and geodynamic setting of the granitoids and volcanites of the Northern volcanic-plutonic belt, Verkhoyan-Kolyma fold area, are presented. Magmatites of the belt include granitoids of Elikchan, Kuranakh, Bakyn plutons, composed of elikchansky granite-granodiorite complex, and volcanites of predominantly intermediate-felsic Tumusskaya sequence with subvolcanic bodies of the same composition. They form single Early Cretaceous (127–121 Ma) volcanic-plutonic assemblage. Granitoid plutons are elongated in sub-latitudinal-northwestern direction and are discordant to main fold and thrust structures. Granitoids intrude and metamorphose Jurassic terrigenous and Early Cretaceous volcanites of Tumusskaya sequence and are cut by younger Late Cretaceous subvolcanic bodies. Granitoids of Bakyn, Elikchan and Kuranakh plutons combine petro-geochemical features of I-, S- and A-type granites. Such diversity of petro-geochemical granitoid types as well as interrelations of major (\({\text{F}}{{{\text{e}}}_{{\text{2}}}}{\text{O}}_{3}^{{{\text{tot}}}}\)–TiO2–MgO) and rare (Ba/La–Nb × 5–Yb × 10) elements in granitoids and the same age volcanites of Tumusskaya sequence allow to refer them to magmatites of transform margin or plates translation boundaries. Collision between Chukotka microcontinent and Siberian continent with earlier accreted Kolyma-Omolon microcontinent in Barremian-Aptian time changed to post-collisional extension and formation of volcanic-plutonic assemblage of the Northern volcanic-plutonic belt. Post-collisional extension took place in the regime of plates translation boundaries. Sr–Nd isotopic characteristics of granitoids of all plutons indicate the interrelation of mantle and crustal sources of granitoid melts in this process.

Petrogeochemical Characteristics of Late Devonian Metagabbro-Dolerites of the Kara Astrobleme, Nenets Autonomous District, Russia

Petrogeochemical Characteristics of Late Devonian Metagabbro-Dolerites of the Kara Astrobleme, Nenets Autonomous District, Russia

Petrogeochemical Characteristics of Late Devonian Metagabbro-Dolerites of the Kara Astrobleme (Nenets Autonomous District, Russia)

The article presents new results of detailed petrographic and petrogeochemical studies of metagabbro-dole-rites from the center of the Kara Astrobleme. The data obtained made it possible to narrow the petrographic diversity of the rocks to two varieties: metagabbro-dolerites and quartz metagabbro-dolerites, formed during the differentiation of the original magmatic melt. The geochemical features of the rocks indicate the heterogeneity of the magma-generating source. Metagabbro-dolerites and quartz metagabbro-dolerites are characterized by the presence of planar elements of low and middle stages of impact metamorphism.

Vodorazdelny Granite Massif (Subpolar Urals) and Correlation Problems of the Pre-Ordovician Granitoids and Volcanic Rocks from the Northern Part of the Lyapinsky Anticlinorium

Petrogeochemical features of the Vodorazdelny massif granites (Subpolar Urals, Lyapinsky anticlinorium) indicate these rocks are close to I-granites and were formed in suprasubduction environment. The ratios of the key elements (Rb, Ba, Th, Sr, Y, Nb) suggest that the basites of the melting slab and the fluid separated during their dehydration could participate in the granite generation. The U–Pb age of the main population of magmatogenic zircons is 593 ± 4 Ma and corresponds to the Vendian (Ediacarian). It coincides with the age of the granites from the nearby Vangyr massif (598 ± 5 Ма), as well as with the age of zircon cores from the granites of the Kozhim massif located to the north. Values of εHf(t) from –2 to 0 in magmatogenic zircons with an age corresponding to the age of Vodorazdelny granites indicate a heterogeneous source of melts. The zircons of these granites also contain ancient cores with U–Pb ages from 2200 to 700 Ma, where the values of εHf(t) from +0.8 to +13 indicate the presence of a crust component in the substrate (the substance of the ancient platform basement). Petrogeochemical and isotope-geochronological parameters of granites (and their zircons) do not confirm the validity of attributing of Vodorazdelny granite massif (and its analogues – the Vangyr and Kozhim massifs) to the Cambrian Salner-Mankhambo complex. We consider there are the possibility of separating of independent complex (about 598 Ma, Vendian?) during geological mapping. The presence in the Lyapinsky anticlinorium of several stages of granite generation (Middle Riphean–Vendian–Cambrian), accompanied by metamorphism, and complicate composition of ancient metamorphic strata from this structure basement led to varying isotopic parameters characterizing the heterogeneity of the source of melts, on the one hand, and the convergence of a number of geochemical features, on the other.

Петрогеохимия гранитов Бадьяюского массива (Приполярный Урал)

Magmatic formations of various ages are developed within the northern part of the Circumpolar Urals, the oldest peripheral part of the Ural belt. Including the Late-Riphean-Vendian granitoids of the salner-mankhambov intrusive complex, which includes the Badiayu granite massif. The conducted research allowed us to identify a number of petrographic and petrogeochemical features of the granites under consideration. The analysis of rock-forming minerals, which are a typical set for granites, with the help of a polarization microscope allowed us to determine the characteristic structures of the rock, to identify the presence of plagioclases and biotites of two generations, to detect partial substitution of quartz with a granular variety. The data of the silicate method allowed us to establish that the studied rock is characterized by an increased content of silica, the main alkali metals, and a very high alumina content. ICP-MS method data and their normalization with respect to S. S. San chondrite and the hypothetical plagiogranite COX showed that the rocks were formed from crustal-type melts saturated with rare-earth, as well as individual lithophilic elements (rubidium, barium). According to the diagnostic diagrams of J. A. Pierce, D. Papu, N. B. Harris, the formation of the studied massif occurred in the conditions of an intraplate geodynamic situation.

AN ACTIVE NEOPROTEROZOIC CONTINENTAL MARGIN OF THE ZAVKHAN MICROCONTINENT (MONGOLIA): ISOTOPIC-GEOCHRONOLOGICAL EVIDENCE

There have been presented the results of the study of a thick (no less than 2–3 km), extended (for more than 200 km) volcanogenic formation (Tsetsen-Uul or Yargait) in the south of the Zavkhan terrane of the Central Asian fold belt. The formation is an assemblage of frequently intercalating effusive rocks of the subalkaline basalt-andesite-dacite-rhyolite series, their tuffs, tuffites, ignimbrites, and terrigenous rocks. Felsic rocks dominate over basites, and tuffogenic rocks dominate over effusives. There is some evidence that the formation emerged in a subaerial setting, with explosive eruptions, and the petrogeochemical features of the effusive rocks are typical for subduction environment. The felsic effusive rocks have high negative ε Nd from –11.5 to –12.8 and Early Precambrian model age T Nd (DM)=2.4–2.5 Ga, which indicates the presence of an ancient crust at the depth and its involvement in magma. The evidence supports the formation of volcanic rocks within an active continental margin. The continental-margin formation stage ranges from ~860 Ma to ~780 Ma based on the LA-ICP-MS U-Pb dating of zircons. The Tsetsen-Uul (Yargait) formation is similar in structure and composition to the Zavkhan formation of the Zavkhan terrane and the Sarkhoi group of the Tuva-Mongolian massif, and partially overlaps them in formation time. It is concluded that all three volcanogenic formations emerged in the same geodynamic setting and in the same time interval, and are the fragments of a continental volcanic arc belonging to both Zavkhan and Tuva-Mongolian paleomicrocontinents.

INFLUENCE OF THE ANCIENT SUBDUCTION PROCESS ON THE ORICINE OF LATE COLLISION VOLCANISM IN THE LESSER CAUCASUS

The article considers the petrogeochemical features of the Late Cenozoic collisional volcanism of the Lesser Caucasus. Based on new geochemical data, it is shown that Nb, Ta, Hf, and Zr minima are observed for basic and intermediate rocks. The salic rocks are strongly enriched in Rb, Ba, Th, La and depleted in Ti, Yb, Y relative to the primitive mantle. The enrichment in incompatible elements suggests that the source of the melt from which the magma was derived was a metasomatized lithospheric mantle enriched in potassium and incompatible elements. Late Miocene-Quaternary volcanics were formed at different degrees of melting of subduction-enriched subcontinental lithospheric mantle. The role of the suprasubduction material decreases during the evolution of volcanism over time due to an increase in the share of the asthenospheric component in the interval from the Upper Miocene to the Quaternary.

Petro-geochemical features of the Bajocian island-arc volcanism in the Lesser Caucasus (Azerbaijan)

&#x0D; &#x0D; &#x0D; This article discusses the petro-geochemical features of the Bajocian volcanism in the Azerbaijan Lesser Caucasus. Jurassic volcanism, manifested with varying intensity in the Lok-Karabakh zone, took place in various geodynamic settings, depending on the alternation of extension and compression processes in the island arc. Under these conditions, in the Lesser Caucasus during Middle Jurassic Epoch, two volcanic associations were formed: the Bajocian basalt-rhyolite and the basalt-andesite-dacite-rhyolite of the Bathonian age. It was found that the volcanic rocks of the Lower Bajocian complex belong to the tholeiitic series, and the Upper Bajocian rocks belong to the calc-alkaline series. In the rocks of the association, light REE slightly prevail over heavy ones and form almost flat spectra, the normalized plots are characterized by the chondritic nature of the distribution of rare earth elements, and the lines are parallel to the spectrum of the distribution of rare earth elements in MORB. In such rocks particularly the europium ratio (Eu / Eu * = 0.81–1.21) approaches 1 and low La / Yb ratios are observed. In some samples of more basic rocks, the content of heavy REE increases. Such a distribution of REE in the studied volcanic rocks is common for basic rocks of the tholeiitic series in typical island arcs. In the analyzed single rhyolite sample, a negative Eu anomaly is observed (Eu / Eu * = 0.56). The volcanic rocks on the primitive mantle normalized multi-element plots are characterized by depletion in Ta, Nb and enrichment in LILE (Rb, Ba, Pb, U, Th), which is characteristic of island arc-related volcanic rocks of supra-subduction zones (SSZ). The rocks are also depleted in titanium, potassium, and phosphorus. It was concluded that, in terms of geochemical features, the Middle Jurassic igneous rocks were formed at the ensimatic island arc, which was the initial stage of the development of the island arc tectonic setting, replaced in the Upper Jurassic by ensialic subduction.&#x0D; &#x0D; &#x0D;

GENETIC TYPE AND CONDITIONS OF FORMATION OF GRANITOIDS OF THE&#x0D; KISEGACH, CHASHKOV, AND ELANCHIK MASSIFS (ILMENOGORSK&#x0D; ANTICLINORIUM)

The article provides a description of the geological structure of the Kisegach, Chashkov and Elanchik migmatite-gneiss granite massifs located in the southern and southeastern parts of the IlmenogorskSysert block. The petrographic, petrogeochemical characteristics of all varieties of their constituent rocks are given. It is shown that the Kisegach massif is composed mainly of gneissic biotite granites of phase I, much less granosyenites and porphyritic granites of phase II, which are intruded by dikes of phase III leucogranites. The Chashkov and Elanchik massifs are represented by granitoids, the formation of which occurred in two stages: migmatites and gneissic granites formed in the first stage, and biotite, muscovite, and two-mica granites formed in the second stage. Phase I granitoids belong to the potassium-sodium and potassium series and belong to the migmatite-granite formation. According to biotite-garnet and biotite-amphibole thermobarometers, it was found that the formation of gneissic granites and gneissic biotite granites of the Kisegach massif occurred at a temperature of 510–540°C as a result of metasomatic processes, and porphyritic granites crystallized from the melt at a temperature of 680–700°C in the abyssal zone on depth of about 23–24 km (Р=7.1–7.4 kbar). Subsequently, all its rocks, including monzogabbro and monzodiorite, experienced regional metamorphism under the conditions of the epidote-amphibolite facies (T=550–575°C, P=5.4–6.0 kbar). Based on the study of the garnet-biotite paragenesis, which is widely represented in the granitoids of the Elanchik and Chashkov massifs, the formation temperatures of gneissic granites (530–550°C and 510–530°C, respectively) and gneissic biotite granites (540–560°C and 520–540°C) were obtained, as well as an approximate estimate of the depth of rock formation was achieved, corresponding to the near-surface or hypabyssal zones (a few kilometers). The obtained data on the physicochemical conditions of formation of the rocks of the massifs made it possible to draw a conclusion about their metasomatic nature and exclude magmatic genesis. The obtained physicochemical characteristics repeat the parameters of metamorphism for the Precambrian stratigraphic units of the Ilmenogorsk-Sysert block, as well as the Kochkar anticlinorium (East Ural uplift). This indicates a single stage in the formation of migmatite-gneiss-granite domes within the entire Southern Urals, which apparently occurred of at the Upper Precambrian — Lower Paleozoic boundary.

Geodynamic Setting, Age, and Petrogeochemical Features of Granitoids in the Chimalga Pluton, Main Batholith Belt (Verkhoyan–Kolyma Fold Area)

Geodynamic Setting, Age, and Petrogeochemical Features of Granitoids in the Chimalga Pluton, Main Batholith Belt (Verkhoyan–Kolyma Fold Area)

Physicochemical and geodynamic conditions for the formation of the Sarsanginsky complex of the border zone of the Southern and Middle Urals

The article describes the geological structure of the Sarsanginsky gabbro-diorite-plagiogranite complex located in the border zone of the Middle and South Urals. The formation of its massifs took place in the late Silurian time in the abyssal zone at depths of about 6,5–7,0 km. The temperature range of crystallization of granodiorites was 900–990 С, and for gabbro 1180–1280 С. The system pressure at this moment corresponded to 190–200 MPa. The gabbro that make up the massifs under consideration were formed under stretching conditions on the oceanic crust. In terms of petrogeochemical features, they correspond to rocks at the base of island arcs and belong to the ophiolite formation.

Late Carboniferous gabbro-granite suite from West Ujimqin of central Inner Mongolia: Petrogenesis and geodynamic implication

辉长岩和花岗岩组成的双峰式火成岩系列通常产出于威尔逊板块构造旋回的诸多伸展周期。基于其岩石地球化学特征示踪伸展地球动力学过程与相关壳幔相互作用的独特视角，本文报道了中亚造山带东段内蒙古中部西乌旗地区新近识别的晚石炭世猴头庙辉长岩-花岗岩系列。SIMS锆石U-Pb定年揭示辉长岩和花岗岩的侵位年龄分别为~307Ma和~305Ma。辉长岩主要由斜长石、辉石和角闪石组成；SiO₂含量介于50.4%~53.4%之间，呈现镁质、准铝质和钙碱性特征；富集大离子亲石元素，亏损高场强元素；并具有OIB型全岩Sr-Nd （I_Sr（t）=0.704249~0.704330，ε_Nd（t）=+1.73~+3.81）和锆石Hf （ε_Hf（t）=+4.58~+15.16）同位素组成，其锆石δ¹⁸O介于5.75‰~6.61‰之间。这些特征指示辉长岩可能源于俯冲板片流体交代的亏损地幔楔部分熔融。同期花岗岩主要由斜长石、钾长石、石英和黑云母组成；其SiO₂含量变化于76.3%~77.6%，高硅碱、贫铁镁、弱过铝、富钍铀、亏锶钡、Eu负异常，契合典型高分异I型花岗岩的元素地球化学特征；花岗岩具有中等放射性成因的全岩I_Sr（t）（0.704923~0.704981）、ε_Nd（t）值（-0.15~+0.57）和锆石ε_Hf（t）值（-2.63~+7.40），以及高的锆石δ¹⁸O （6.44‰~8.06‰）。鉴于元素和同位素特征指示的高分异特征和高演化源区，猴头庙高硅花岗岩可能衍生自中元古代和古生代多期增生物质所组成的复合中基性地壳的部分熔融及其后的结晶分异作用。综合区域石炭纪-早二叠世蛇绿混杂岩和岛弧岩浆岩时空展布格局，晚石炭世猴头庙辉长岩-花岗岩系列记录了内蒙古中部其时因洋脊俯冲引发的弥散性区域伸展事件。一方面，该事件既有别于建造西乌旗早-中石炭世弧-盆体系的板片回退阶段，又迥异于早二叠世大规模后碰撞伸展过程；另一方面，这些周期性伸展事件共同见证了中亚造山带东段晚古生代威尔逊造山旋回的完整历程。;Coeval bimodal igneous suites of gabbro and granite commonly typify frequent extensional episodes in the Wilson cycle of plate tectonics. With a unique view to tracing extensional geodynamic processes and related crust-mantle interactions through the petro-geochemical characteristics of such suites, this paper reports the newly identified Late Carboniferous Houtoumiao gabbro-granite suite from West Ujimqin of central Inner Mongolia, eastern Central Asian Orogenic Belt (CAOB). SIMS zircon U-Pb dating unravels the emplacement age of gabbro at ca. 307Ma and that of granite at ca. 305Ma. The gabbros mainly consist of plagioclase, pyroxene and amphibole. They range in SiO₂ from 50.4% to 53.4%, exhibiting magnesian, metaluminous and calc-alkalic affinities, with enrichment in large ion lithophile elements (LILEs) and depletion in high field strength elements (HFSEs). They possess OIB-type whole-rock Sr-Nd (I_Sr(t)=0.704249~0.704330, ε_Nd(t)=+1.73~+3.81) and zircon Hf (ε_Hf(t)=+4.58~+15.16) isotope compositions, and zircon δ¹⁸O values from 5.75‰ to 6.61‰. These features suggest that the gabbros might be derived from the partial melting of a depleted metasomatised mantle wedge from subduction-derived fluids. The coeval granites mainly comprise plagioclase, K- feldspar, quartz and biotite. They span in SiO₂ from 76.3% to 77.6%, with high alkalis, thorium and uranium but low iron, magnesium, strontium and barium. They are weakly peraluminous with negative Eu anomalies. These features are typical of highly fractionated I-type felsic magmas. With respect to isotopic compositions, the granites are characterized with medium radiogenic whole-rock I_Sr(t) (0.704923~0.704981), ε_Nd(t) (-0.15~+0.57) and zircon ε_Hf(t) (-2.63~+7.40), and high zircon δ¹⁸O (6.44‰~8.06‰). Given their highly fractionated character and highly evolved sources, the Houtoumiao granites tend to have been derived from the partial melts of the composite mafic to intermediate lower crust composed of multi-stage accretionary materials in the Mesoproterozoic and Paleozoic times, with subsequent fractional crystallization yielding the high-silica granites. Combined with the spatial and temporal distribution patterns of regional Carboniferous-Early Permian ophiolitic mélange and island arc magmatic complexes, the Late Carboniferous Houtoumiao gabbro-granite suite seems to record diffuse regional extension event due to ridge subduction in central Inner Mongolia. On one hand, this event is not only distinct from slab rollback episode of the Early-Middle Carboniferous arc-basin system in West Ujimqin, but also in contrast with large-scale post-collisional extension during Early Permian time. On the other hand, when taken together, these episodic extensional events tend to witness the complete course of the Late Paleozoic Wilson cycle in the eastern CAOB.

Mineralogy and geochemistry of native iron

Basite magmatism has been manifested repeatedly for a long time in various geodynamic structures within the eastern part of the Siberian platform. In the Middle Paleozoic, it was related to rifting processes, and in the Late Paleozoic-Early Mesozoic – to the initiation and development of trap syneclises. Differences of the geodynamic regime of magma formation are displayed in the material composition of rocks. This report presents a generalizing study of the petro-geochemical features of the tholeiitic basaltic melts formed in different geodynamic settings. The initial magmas composition changes significantly at different stages of the magmatic system development. Using multicomponent analysis, we reviewed the impact of the fractionation processes of the basal melt, which occurred under various PT conditions, on its material composition. Among the trapp bodies there are powerful differentiated intrusions. A significant change of the composition occurs during the intra-chamber differentiation of the melt in a sequence of rock strata varied from the basic magnesian to felsic alkaline rocks. In the resulting series of rocks, the content of rare elements included in the lattice of the early femic phases decreases, as well as the accumulation of almost all incompatible elements. The evolution of melts of normal alkalinity occurs with an increase of REE content and their insignificant separation. Intrusions that have undergone the stage of high-pressure fractionation in the deep transitional chamber are of particular importance. As a result of such differentiation, a peculiar group of rocks is formed in the cross section of the Middle Paleozoic bodies, such as monzonite-porphyries in one case and anorthosite gabbro-dolerites - in the other. It is established that the monzoitoid type of differentiation is characterized by accumulation of LREE, LILE and elements of the zirconium group Nb, Ta, Hf and Y. Isolation of anorthosite gabbro-dolerites in the cross-section of bodies, as well as an increase in the content of aluminum, calcium, and strontium in them, is an indication of the anorthositic tendency of magmatic melt differentiation/When the basite-tholeiite melt interacts with the mantle reducing fluid in the deep core, its metallization occurs with the release of drop-liquid separations of native iron up to the formation of its large segregations. Intrusions with a large-scale content of native iron are found among the trap formations of Siberia. All this leads to a decrease in the total concentration and activity of iron in the partially metallized silicate matrix, there is a significant increase in the content of MgO and trace elements-Ni, Co, Cr. The Fe-phase-containing intrusives are characterized by minimal LILE, HFSE, and REE contents. Start your abstract here… 250 to 500 words concise and factual abstract is required. The abstract should include the purpose of research, principal results and major conclusions. References should be avoided, if it is essential, only cite the author(s) and year(s) without giving reference list. Prepare your abstract in this file and upload it into the registration web field.