Acid Magmas Research Articles

Geochemical characteristics of fluorine- and chlorine-bearing biotite from Tusham Ring Complex, NW India: Constraints on halogen distribution and geodynamic evolution

The present study is carried out to understand the factors controlling halogens present in biotites, role of halogens in metallogeny in context to the magmatic evolution of Tusham Ring Complex (TRC), NW Indian Shield. The investigated rocks are identified with hypersolvus, high-K calc-alkaline, peraluminous, ferroan-enriched and typical A-type granitoids affinity. They are enriched in SiO2, Na2O + K2O, REEs (except Eu), LILE + HFSE, elevated in Fe/Mg, Ga/Al, Th/U, A/CNK ratio and depleted in CaO, MgO, Sr, Cr, Ni, P, Ti, V and Eu abundances. The sequential accumulation of incompatible trace elements (LILE, HFSE, REEs and others) in studied rocks overlaps almost entirely the range of rare metal granitoids and high heat-producing granitoids. The elemental geochemistry in conjunction with high abundances of F (0.80–7.11 wt%) and Cl (0.44–1.56 wt%) in biotite mineral collectively attribute to hydrothermal fluid activity and the subsequent mineralization around TRC region. Our new results suggest that the acidic magmatism that occurred in the TRC is considered as a part of the plume-related Neoproterozoic Malani Igneous Suite (MIS) anorogenic magmatism.

Age Benchmark of Granulite Metamorphism in the Angara–Kan Block, South Yenisei Range: Evidence from Zircon Dating of Postcollisional Granite–Aplite Dikes

The paper presents isotope–geochronological data on zircons from a granite–aplite dike that cuts garnet–hypersthene gneisses of the Kuzeyev unit of the Neoarchean–Paleoproterozoic Kan Group in the southern extension of the Ishimba–Tatarka regional shear zone, Kan River. The morphology and internal structure of most of the zircon grains indicate that the zircons are metamorphic and xenogenic and were captured by the acidic magma from the host rocks when the magma intruded the granulites. Based on these data, the obtained Paleoproterozoic U–Pb age of 1784 ± 6 Ma can be interpreted as the age of granulite metamorphism. The interpretation of available geological and isotopic data confirms a postcollisional age of the aplite, which was emplaced nearly synchronously with the formation of anorogenic leucogranites of the late phase of the Tarak complex, during the final stage of the formation of the Nuna supercontinent.

Au‐Ag‐S‐Se‐Cl‐Br Mineralization at the Corrida Deposit (Russia) and Physicochemical Conditions of Ore Formation

The mineral and chemical compositions of ores from the Corrida epithermal Au-Ag deposit (Chukchi Peninsula, Russia) were studied using the optical and scanning electron microscopy with X-ray energy-dispersion microanalysis. The deposit was formed at the time close to the period when the basic volume of acid magmas had been emplaced within the Okhotsk–Chukotka belt (84 to 80 Ma). The Au–Ag mineralization is distinguished with Au-Ag sulphides and selenides (uytenbogaardtite-fischesserite solid solution, Se-acanthite, S-naumannite) and Ag halides of the chlorargyrite-embolite-bromargyrite series. The ores were formed in two stages. Using microthermometric methods, it has been established that the ore-bearing quartz was formed in the medium-temperature environment (340–160 °C) with the participation of low-salt (3.55 to 0.18 wt.% NaCl eq.) hydrotherms, mostly of the NaCl composition with magnesium, iron and low-density СО2. According to our results of thermodynamic modeling at temperatures from 300 to 25 °C and data on mineral metasomatic alterations of the host rocks, the Au-Ag-S-Se-Cl-Br mineralization was formed at decreasing temperature and fugacity of sulphur (logƒS2 from −6 to −27), selenium (logƒSe2 from −14 to −35), and oxygen (logƒО2 from −36 to −62), with near-neutral solutions replaced by acid solutions. Analysis of the obtained data shows that the Corrida refers to the group of the LS-type epithermal deposits. This deposit is a new example of epithermal deposits with significant quantities of Au–Ag chalcogenides (acanthite, uytenbogaardtite, fischesserite, naumannite and others).

New data on absolute age, petrology and potential of ore mineralization within Murzinsky intrusive massif (northwestern Altai)

The geological, petrogeochemical data, absolute age dating and information about endogenetic ore mineralization of Murzinsky intrusive massif of Altai are presented. Comparison of rock compositions and melanocratic inclusions suggests that gold potential of deep spot melting is related to hybrid melts forming as basalt and crust acidic magma mixed. Along with skarn, the ore field could host copper-gold-porphyry mineralization. Gold was supplied from acidic melting as a result of amphibolites and lower crust greywacke melting.

Petrogenesis and geodynamic setting of the Late Carboniferous granodiorite porphyry in Miaoergou pluton, southern West Junggar

位于西准噶尔南部的庙尔沟岩体主体由碱长花岗岩和少量紫苏花岗岩组成。本文在前人工作基础上，以岩体东南边缘新发现的花岗闪长斑岩为研究对象，开展岩石学、年代学和Hf同位素以及全岩地球化学研究，确定花岗闪长斑岩形成时代、揭示岩石成因类型及源区属性、探讨其与碱长花岗岩和紫苏花岗岩岩浆演化成因联系及其形成的深部动力学过程。锆石U-Pb定年结果显示，花岗闪长斑岩形成于317.4±1.9Ma，为晚石炭世早期岩浆活动的产物，明显早于紫苏花岗岩（~307Ma）和碱长花岗岩（~303Ma）。岩石地球化学数据表明，花岗闪长斑岩具有较高硅、中等铝，贫钙、铁、镁，富集Rb、K、Th、U，强烈亏损Nb、Ta、Ti的特征，为钙碱性弱过铝质I型花岗岩；紫苏花岗岩更多的表现出钙碱性-高钾钙碱性镁质I型紫苏花岗岩特征；碱长花岗岩为碱性准铝质-弱过铝质A型花岗岩。锆石Hf同位素分析结果表明，花岗闪长斑岩、紫苏花岗岩和碱长花岗岩均具有高正的ε_Hf（t）值（+11.6~+15.8）和年轻的二阶段模式年龄（325~600Ma），表明其原始岩浆主要起源于亏损地幔新衍生的年轻地壳物质。综合分析认为，庙尔沟岩体花岗闪长斑岩形成于晚石炭世早期洋壳俯冲背景，由底侵的、受流体交代的幔源基性岩浆与其诱发的年轻下地壳酸性岩浆在深部混合而成。紫苏花岗岩和碱长花岗岩形成于弧后伸展背景，前者是伸展初期继续底侵于下地壳的幔源玄武质岩浆降温释放大量的水和热诱使早期侵位于下地壳的镁铁质岩石再次发生部分熔融的产物，后者是伸展后期大规模软流圈地幔上涌底垫加热年轻中下地壳使其部分熔融而成。;The Miaoergou pluton, located in southern West Junggar, is mainly composed of alkali-feldspar granites with small amount of charnockites. On the basis of previous researches, this paper mainly focuses on the newly discovered granodiorite porphyry in southwestern margin of the Miaoergou pluton. A comprehensive study of petrographical, zircon U-Pb geochronological and in-situ Hf isotopic, whole-rock geochemical analyses were carried out to determine its diagenetic age and reveal the petrogenesis, the nature and composition of the magma source of this porphyry, and furthermore, to discuss the genetic relationships among the granodiorite porphyries, alkali-feldspar granites and charnockites and their geodynamic processes. LA-ICP-MS zircon U-Pb dating for the granodiorite porphyry yielded crystallization age of 317.4±1.9Ma, defining an early Late Carboniferous magmatic event in southern West Junggar, which is significantly earlier than the ages of charnockites (~307Ma) and alkali-feldspar granites (~303Ma). The geochemical characteristics indicate that the studied granodiorite porphyries belong to cal-alkaline weakly peraluminous I-type granite, and are characterized by slightly high silicon, medium aluminum, but low ferrum, calcium and magnesium, and also enrichment in Rb, K, Th, U with pronounced negative Nb, Ta and Ti anomalies. The charnockites possess calc-alkaline to high-K calc-alkaline magnesian I-type charnockite affinities, which were previously considered A-type granites by some geologists, while alkali-feldspar granites belong to alkaline metaluminous to weakly peraluminous A-type granites. In-situ zircon Hf isotope analyses show that these granites have high positive ε_Hf(t) values (+11.6~+15.8) and very young two-stage Hf model ages of 325~600Ma, indicating that the magma was sourced from juvenile crust originated from depleted mantle during the Late Neoproterozoic to Early Carboniferous period. In association with previous analysis, it is proposed that the Miaoergou granodiorite porphyries were formed in an oceanic crust subduction setting during early Late Carboniferous. They are probably the products of the acidic magma formed by partial melting of the juvenile lower crust and mixed with the underplated basaltic magma derived from the fluid metasomatic mantle wedge in the deep crust to some extent. Both the charnockites and alkali-feldspar granites were formed in a back-arc extensional setting related to the northwestward subduction of the Junggar oceanic crust. The charnockites may be generated by re-melting of juvenile lower crust mafic rocks, probably triggered by addition of water and heat released from cooling of underplated depleted mantle-derived basaltic magma during the incipient rifting stage of the back-arc basin, and the alkali-feldspar granites may be generated by partial melting of the juvenile middle-lower crust induced by the large-scale upwelling of asthenosphere during the later stage of the back-arc extension.

Structural Elements of the Sea of Japan’s Basin and Adjacent Continental and Island Dry Land, According to Data from Space-Based Geological Investigations

A representative system of fault and block dislocations in the Sea of Japan segment of the continent–ocean transition zone, identified using space-based geological data and a set of available geomorphological, geological, and geophysical materials, allow the eponymous Late Paleozoic mega-arch to be constructed. The ring form, duration, and scales of basite, acidic magmatism, and the presence of geological and geophysical signs of mantle diapirism associate the main features of its structure and development with plume activity. The geological prehistory, plume tectonics, and periodic inversions of the geodynamic regime determined the direction and character of destructive transformations of the continental margin in the Early Mesozoic and Middle and Late Cenozoic, and the specific character of the region evolution in general. Features of the inherited development of the structural plan include the preservation of the granite core of the mega-arch, associated with the underwater Yamato rise having a continental type of crust, in the geometric center of the Sea of Japan basin; the presence of radial-concentric hypsometric and structural-magmatic zonation; and the relict nature of many other underwater rises. The absence of compensatory collision–accretion dislocations in the east of Honshu Island and on the island arc slope of the adjacent deep-sea trench, the weak variability of strikes of dry land–sea tectonic marks through faults in satellite images, the preservation of the paleoarch structural elements, and other data contradict ideas about large horizontal movements of lithospheric blocks within the Sea of Japan segment of the Eurasia–Pacific Ocean transition zone.

Mineralogical characterization and diagenetic history of Permian marine tuffaceous deposits in Guangyuan area, northern Sichuan basin, China

Based on thin section identification, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis of samples from cuttings and cores in drillings, tuffaceous deposits were identified to intercalate in marine carbonate rocks and mudstones in the upper part of Maokou Formation and the middle to lower part of the Wujiaping Formation in Guangyuan area, northern Sichuan basin, China. These tuffaceous deposits are of significance to understand the influence range of magmatic activity of the Emeishan Large Igneous Provinces (ELIP), and explore and exploit oil and gas reservoirs in Permian strata in the Sichuan basin. The research results indicated that tuffs formed 0.1–10 mm-thick laminae, and they formed lamellar interbedding with organic mudstones and carbonaceous mudstones, which were sandwiched among bioclast limestones and marls. Tuffaceous deposits in the study area include tuff, sedimentary tuff and tuffaceous sedimentary rock. Under the influence of sulfate reduction, acidic hydrotherm and alkaline fluid, tuffaceous deposits were altered by diagenesis such as dolomitization, argillization, pyritization and dissolution, and formed a variety of secondary rocks and pores which characterized by the micron-scale solution pores in tuff components and the nanometer-scale intercrystal pores among authigenic clay minerals. In addition, the primary directional sedimentary structure of tuffs and sedimentary tuffs and developed laminae in the rocks are conducive to the formation of fissures parallel to laminae, and effectively improve the reservoir property of rocks. The tuffaceous deposits in the study area are mainly the products of subaqueous pyroclastic flow that were dominated by acidic magmatism and indicated that they may not be directly related to the ELIP, which is located in the southwest Sichuan-Yunnan provinces and dominated by continental eruption of basalt.

Magmatic systems beneath Ashikule volcanic cluster (Western Kunlun, China): insights from compositional and textural features of lavas

This study considered the petrology, chemical composition, texture, and magma temperature and pressure of the volcanic rocks in the Ashikule volcanic cluster (AVC), Western Kunlun, China, to investigate the magmatic systems prior to eruption. The whole rock geochemistry of AVC lavas revealed a wide compositional range that included phonotephrite, basaltic trachyandesite, trachyandesite, trachyte, and acid rhyolite but mainly trachyandesite. The K2O/Na2O ratios were greater than 1, falling into the shoshonite series in a K2O vs. SiO2 diagram. Oxide diagrams showed that intermediate and acidic volcanic rocks have similar magmatic evolutions, mainly related to the fractional crystallization of pyroxene, plagioclase, apatite, and ilmenite. Acidic magma was found as the product of magmatic crystallization in the final stage. Trace element contents indicated that the magma underwent mixing with crustal components in the process of crystallization before eruption. Xishan phonotephrite revealed a different evolutionary series compared with the intermediate and acidic volcanic rocks, highlighting the differences of their magmatic sources. The equilibrium temperature and pressure of phonotephrite were 1146–1316 °C and 0.38–1.70 GPa, respectively, which correspond to a depth of 14–62 km. The equivalent values for intermediate rocks were 1062–1215 °C and 0.22–1.18 GPa, respectively, corresponding to a depth of 8–43 km. Acidic rocks had lower magmatic temperatures (778–889 °C). Active tectonics led to multiple events of magma upwelling, and the magma in each event underwent its own evolution. There were many different components of magma beneath the study area contemporaneously, i.e., multiple magma capsules with different compositions.

Late Early-Cretaceous Magma Mixing in the Langqi Island, Fujian Province, China: Evidences from Petrology, Geochemistry and Zircon Geochronology

The mafic enclaves from Mesozoic intermediate-acid magmatic rocks, widely developed along Fujian coast, are considered to be the results of large-scale crust-mantle interaction and magma mixing. In this paper, petrography, mineralogy, and geochemistry of granites and mafic microgranular enclaves (MMEs) in Langqi Island are studied to provide new information for tracing crust-mantle interaction. The zircon U-Pb dating results show that the Langqi rocks were formed at ~101 Ma, which are metaluminous, enriched in silica and high-K calc-alkaline I-type granites. The enclaves have a typical magmatic structure, which is characterized by magma mixing between high-temperature basic magma and low-temperature acidic magma through injecting. The enclaves and host granites show a tendency to mixed major and trace elements, displaying a clear-cut contact relationship, which is indicative of coeval magmatism. The genesis of Langqi rocks is related to the extensional setting caused by the subduction of Paleo-Pacific Plate, and they are the results of mixing of subduction-related metasomatized mantle-derived mafic and induced crustal-melted granitic magma originating from partial melting of the crustal material.

Geochronological and geochemical features of the Xiaowulangou complex plutons, Xilinhot, Inner Mongolia, and their geological significance

The southern margin of the Central Asian Orogenic Belt (CAOB) is pivotal to understanding the ultimate closure process of the Palaeo‐Asian Ocean; however, controversial issues regarding the petrogenesis and tectonic setting of its Late Palaeozoic igneous rocks have caused uncertainty regarding the Late Palaeozoic oceanic and continental evolution of the area. Herein, the Xiaowulangou complex plutons near Xilinhot, Inner Mongolia, were considered as a case study for the southern margin of the CAOB, and they were analysed via multiple geological methods, including field geology, petrology, zircon U–Pb isotopic geochronology, and geochemistry to achieve greater clarity on these issues. Lithologically, the plutons consist of diorite, quartz diorite, granodiorite, and monzonitic granite. Zircon U–Pb dating gives weighted mean ages of the diorite, quartz diorite, and granodiorite plutons as 329 ± 1 (mean squared weighted deviation [MSWD] = 0.22) and 306 ± 1 (MSWD = 0.83), 310 ± 1 (MSWD = 0.23), and 328 ± 1 (MSWD = 0.40) and 300 ± 1 Ma (MSWD = 1.4), respectively, corresponding to the late Early Carboniferous to the Late Carboniferous. The diorites and the quartz diorites constitute a suite of low‐K tholeiitic calc‐alkaline I‐type granitoids. They have low rare earth element (REE) content with a flat distribution pattern lacking pronounced negative Eu anomalies (δEu = 0.74–1.06). Geochemically, they are more enriched in large‐ion lithophile elements (LILEs) such as Rb, Th, K, and Sr than in high‐field‐strength elements (HFSEs) such as Nb, Ta, Ti, and P, indicating that these rocks were formed in a subduction setting as a result of partial melting of a mantle wedge that had been metasomatized by subduction fluids. The granodiorites and monzonitic granites belong to the peraluminous and calc‐alkaline to high‐K calc‐alkaline series and feature high silicon and alkali content; low P2O5 and CaO content; enrichment in Rb, Th, K, Zr, and Hf; depletion in Nb, Ta, Sr, P, and Ti; and significant negative Eu anomalies (δEu = 0.66–0.95 and 0.06–0.46, respectively). The granodiorites and monzonitic granites show the characteristics of I‐type granite that were mainly derived from partial melting of the crust. The petrological and geochemical characteristics of the rocks indicate that the plutonic complex is a result of superposed injection of a mixture of mantle‐ and crust‐derived magmas with different degrees of evolution. This was probably triggered by underplating of mantle magmas that originated from the partial melting of a wedge mantle metasomatized by hydrous fluids from the subducted slab. The diorites and quartz diorites were produced by fractional crystallization of mantle‐derived magma. The granodiorites and monzonitic granites crystallized from magma formed by mixing of the intermediate to basic magma and crust‐derived acidic magma. Considering their petrological and geological features, the Xiaowulangou complex plutons were formed in an active continental margin setting related to the northward subduction of the Palaeo‐Asian Ocean from the Early Carboniferous to the Late Carboniferous. Furthermore, consequently, a tectonic evolution model was established from the Late Palaeozoic to the Early Mesozoic in the Xilinhot–Xi Ujimqin Banner regions based on these new data and the regional geology.

Evidence of mingling between contrasting magmas in the Ribeirão do Óleo Pluton, Coastal Terrane and the tectonic implications on the Ribeira Belt, Brazil

Gneiss–migmatitic rocks and granites between the Cubatao and Itariri shear zones characterize the Mongagua Complex-Coastal Terrane. Three major units are defined: (1) the Itariri Suite (IS) composed of monzogranites, granodiorites, tonalites, and locally gneiss–migmatitic rocks; (2) the Areado pluton composed of monzogranite and locally tonalite; and (3) the Ribeirao do Oleo Pluton mainly composed of monzogranites, which is the subject of this article. Combined field observations, petrography, Sr–Nd–Hf isotopes, U–Pb zircon data, and preliminary geochemical studies are presented for the Ribeirao do Oleo Pluton (ROP), intrusive in granite-gneisses of the IS. It is a plutonic association of weakly peraluminous, medium-to-high-K biotite monzogranites that surround microgranular intermediate enclaves, which are products of magma mingling. Different from the most examples of magma mingling described in the literature, the ROP mingling did not result from the intrusion of hot mafic magma into colder host felsic magma. Conversely, the emplacement of the monzogranite started most likely during the medium-to-final stage of crystallization of the quartz microdiorite. A detailed study of LA-ICP-MS U–Pb zircon ages, including zircon morphology and internal structure, was useful to determine more precisely the emplacement sequence and the relation between the units of the ROP. Intermediate and acid facies have Paleoproterozoic and Neoproterozoic inheritances, moreover a mixture of xenocrysts, antecrysts, and autocrysts, indicative of a complex evolution of the ROP. Several magma crystallization pulses are recorded at 655–624 Ma, 627–601 Ma, and 613–586 Ma. The negative eHf(t) ranging from − 17.26 to − 12.51 in monzogranites, eNd(t) values of − 10.66 to − 7.83 at t = 600 Ma in both facies, 87Sr/86Sr of ca. 0.708 for the monzogranite and 0.706 for the quartz microdiorite indicate a strong crustal contribution in the genesis of intermediate and acid magmas of this pluton.

Mesozoic Acid Magmatites of Southeastern Transbaikalia: Petrogeochemistry and Relationship with Metasomatism and Ore Formation

The characteristic features of the manifestations of acid magmatism and metasomatic hydrothermal alteration processes in Southeastern Transbaikalia, an important mining region in Russia, are discussed. The zoned or beltlike distribution of the ores of various metals, uranium in particular, and other mineral deposits is due to the general evolutionary trends of the geodynamic regimes of the respective blocks of the territory and the subsequent magmatic differentiation trends. The highly differentiated and fluorine-rich granitoids of Southeastern Transbaikalia are located only in the zones of the consolidated crust, which are characterized by low gravity and negative quiet magnetic field values. In other zones, i.e., volcanic belts, volcanogenic troughs, and the regions dominated by the intrusive massifs of the Shakhtama complex, rare metal manifestations are absent. It was demonstrated that there is no correlation between the localization of large uranium deposits and leucocratic rare metal granite domains and that these deposits are concentrated in large volcanic calderas or volcanic troughs, controlled by long-lived fault systems. In addition to uranium, these volcanogenic structures control base metal, molybdenum, gold, fluorite, and some other mineral deposits. The results of a comparative analysis of the geochemical features of the acid volcanics that host the uranium mineralization and are classified as the last differentiation products of the contrasting latite volcanism, on the one hand, and the subvolcanic and hypabyssal derivatives of the rare metal granites, on the other, are presented. The analysis revealed the signatures of their fundamental difference from each other and that they belong to different branches of magmatic differentiation. A comparative analysis of the metasomatic aureoles of the altered wallrocks in the Late Mesozoic volcanics and the Shakhtama granitoid domains, on the one hand, and the leucocratic rare metal granite domain, on the other, is given. The data presented attest to the existence of a mixed geodynamic regime within the study area of the Central Asian mobile belt during the Jurassic and the earliest Cretaceous time: residual collisions with strong deformations in a compressional setting, accompanied by the development of late acid differentiation products of the magmatic latite series, and the incipient rifting associated with the intrusion of the leucogranites of the Kukul’bei complex in a more quiet extensional setting.

Silurian anorogenic basic and acidic magmatism in Northwest Turkey: Implications for the opening of the Paleo-Tethys

The Sakarya Zone (northern Turkey) is a Gondwana-derived continental block accreted to northern Laurussia during the Carboniferous, and is regarded as the eastward extension of Armorica. Timing of its detachment from the northern margin of Gondwana, thus opening of the Paleo-Tethys, is poorly known. Here, we report on metagranite and amphibolite with Silurian igneous crystallization ages from the Early Carboniferous high-temperature/middle to low-pressure amphibolite-facies metamorphic rocks of the Sarıcakaya Massif within the Sakarya Zone (NW Turkey). The metagranite-amphibolite complex is exposed mainly along the southern margin of the Sarıcakaya Massif over an area of ca. 12 km by 1.5 km. The metagranite contains preserved domains of porphyric texture, indicative of derivation from a former granite porphyry. The amphibolite is devoid of any relict igneous texture. Both the metagranite and amphibolite are crosscut by late up to 50 cm thick felsic veins. Uranium-Pb dating on igneous zircons from both metagranite and amphibolite yielded Silurian ages of ca. 419 ± 6 to 434 ± 7 Ma (2σ), and on those from a felsic vein an age of 319 ± 5 Ma (2σ) (Late Carboniferous). Geochemically, amphibolite displays anorogenic transitional tholeiitic to alkaline signatures. Initial εHf values of the igneous zircons from both metagranite and amphibolite show a large variation with medial values of −16 to −9 and + 3 to +6, respectively. Thus, the protoliths of amphibolite were derived from melts of depleted mantle, and those of the metagranite, on the other hand, from melts of reworked crustal material. We suggest that the Silurian anorogenic magmatism is related to a rifting event at the northern margin of Gondwana leading to the detachment of the Sakarya Zone and hence placing an age on the initial opening of the Paleo-Tethys. This interpretation is based on (i) the presence of Late Silurian to Devonian deep-sea sedimentary blocks in the Paleo-Tethyan accretionary complexes, and (ii) the resemblance of the UPb age spectra of detrital zircons in the metaclastic sequence of the Sarıcakaya Massif to those of Cambro-Ordovician sandstones in Jordan (Gondwana), and (iii) the local occurrence of anorogenic A-type granites of Late Ordovician-Silurian age in the Anatolide-Tauride Block, a continental block which rifted from Gondwana during the Early Triassic. Wholly anorogenic nature of the Late Ordovician to Silurian igneous rocks in the Sarıcakaya Massif and reported in literature does not support the opening of the Paleo-Tethys as back-arc ocean, as suggested in most paleogeographic reconstructions.

Structure System and It Controls to Mineralization of Primary Tin Deposit, Airdibi Area, Jebus Subdistrict, West Bangka, Bangka and Belitung

Bangka Island is one of the most potential areas with abundant mineral resource in indonesia. The main commodities in the exploration of metal mineral deposits on Bangka Island are tin. Tin deposits located on Bangka Island are formed from acid magma produced of collision. The research location is in Airdibi area, Jebus subdistrict, West Bangka regency, Bangka and Belitung province. The objective of this research is to know the characteristics of primary tin deposit by observing the geological aspect, and the distribution of alteration and mineralization. Research method are used is surface geological mapping. Analyzes performed to process surface geological data are petrographic analysis, mineral graphic analysis, ASD analysis (Analitycal Spectral Devices), and XRF (X-Ray Fluorescence) analysis. Stratigraphy of this research areas from the old to the young, namely the Complex Pemali Uni, the Tanjunggenting Sandstone Unit, the Fine Grain Granite Klabat Unit and Alluvial Deposit. Assemblages Minerals alteration at the study sites results from an ASD analysis showing the minerals resulting from a hydrothermal process consisting of six zone there are Tourmaline + Muscovite + Chlorite + Illite + Smectite, Silica + Tourmaline, Illite + Smectite + Chlorite + Tourmaline, Illite + Smectite + Tourmaline, Muskovite + Quartz + Illite + Smectite + Halloysite, Kaolinite + Illite + Smectite. From the XRF analysis showing the various grade of tin on the vein. The geologic structure that developed in the research area is highly controlling the primary tin mineralization process. Veins with a relatively NW-SE direction which is an extension faults product has a higher level than a sheeted veins with a Relatively NE - SW direction which is a compression faults product. Based on field data and the results of laboratory analysis, deposit type greisen deposits in the vein phase.

Origins and occurrences of Ti-nanominerals in a superhigh-organic-sulfur coal

Two Ti-nanomineral types seldom seen in a superhigh-organic-sulfur coal (Ganhe coal) are identified through the integrated techniques of high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectrometer (EDS), and fast Fourier transformation (FFT). The first Ti-nanomineral type is that of irregular-shaped Ti-nanominerals (Rutile, Ti4O7, and Ti6O11) associated with minor proportions of Cr and V. This is unusual, because Ti4O7 and Ti6O11, which are referred to as Ti magnéli phases (very high temperature products), are rarely found in coal. In addition, other integrated evidence of acid volcanic-ash components in Ganhe coal are also confirmed, including sanidine associated with Tl, flocculated texture illite, La-monazite associated with minor proportions of V, and rare-earth elements (REEs) distribution patterns (Eu negative anomalies). It is thus implied that the origin of the irregular-shaped Ti-nanominerals is the transformation of rutile to Ti4O7 and Ti6O11 under the influence of acid magma followed by transportation and deposition in the Ganhe peat swamp. The second type is that of spherical Ti-nanominerals that exist individually within the organic matrix; they have minimum areas of 3.79–56.10 nm2 and contain large proportions of Cr and V. It is considered that owing to the euxinic, anoxic, and reducing marine deposition environment, Ti, Cr, and V could easily have been originally precipitated or adsorbed by the organic macromolecular structure within the peat and low-rank coal. With elevation of the coal rank, they could then have been expelled by dehydration, decarboxylation, and demetallation via closed nano-size pores (nano pores) prior to finally entering mineralization under natural hydrothermal conditions. Although this result is promising, the hydrothermal formation of nano TiO2 particles requires further demonstration using an artificial coalification experiment.

The Relationship of the Relative Abundance of Masses of Granites and Rhyolites in the Earth’s Crust with the Patterns of the Rheology of the Granitic Magmas

Many years ago, V.S. Sobolev suggested that the reason for the relative prevalence of intrusive and effusive rock masses in the earth’s crust lies in the regularities of viscosity of water-bearing magmas in a variable field of temperatures and pressures. Alas, in those years it was not possible to solve this problem on a quantitative physical-chemical basis, since experimental and theoretical studies of the viscosity of such melts at high pressures were just beginning. In the present work, new regularities of the viscosity of near-liquid water-bearing acidic magmas in a wide range of thermodynamic parameters and depths of the Earth’s crust (1–30 km) is established using the structural-chemical model of reliable and correct predictions and calculations of the viscosity of magmas of virtually any composition. It determined that these regularities really are a quantitative physical-chemical basis explaining the reason for the relative distribution of masses of intrusive and effusive rocks of acidic composition in the earth’s crust.

Geochronology, geochemistry, and Pb–Hf isotopes of mineralization-related magmatism in the Dongyang gold deposit, Fujian Province, southeastern China

The recently discovered Dongyang low-sulphidation epithermal Au deposit is located in Fujian Province. The Au mineralization hosted in rhyolite porphyry and the Lower Jurassic Nayuan Formation continental volcanic rocks is considered to be related to intermediate–acidic intrusions (rhyolite porphyry, quartz diorite porphyry, and dacite porphyry). The zircon U–Pb ages of these samples are 160.3 ± 0.8, 156.6 ± 0.8, and 154.1 ± 0.6 Ma, respectively, and the sulphide Rb–Sr isotope isochron age is 152.4 ± 1.7 Ma, indicating a temporal link between porphyry emplacement and Au mineralization. Porphyries are enriched in large-ion lithophile elements and light rare earth elements and slightly depleted in heavy rare earth elements and high field strength elements, belong to the high-potassium calc-alkaline or shoshonitic series, and show characteristics of volcanic arcs or active continental margins. Moreover, the εHf(t) values of the porphyries range from −11.6 to −7.6, −11.2 to −5.4, and −9.8 to −4.6, respectively. The 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb values of the ore minerals are from 38.417 to 38.406, 15.603, and from 18.179 to 18.175, respectively. Pb and Hf isotopes indicate that the intermediate–acidic magma related to mineralization originated from Mesoproterozoic lower crust. Consequently, these data favour an intermediate–acidic magma origin for Au mineralization in the Dongyang deposit. Integrating new and published data on the tectonic evolution, we suggest that the rhyolite porphyry, quartz diorite porphyry, dacite porphyry, and associated Au mineralization in the Dongyang deposit formed at 160–152 Ma in an extensional environment related to subduction of the Palaeo-Pacific Plate beneath the South China block.

Geologia, petrografia e geoquímica das rochas metavulcânicas ácidas da Estrada Real, Rio de Contas (BA)

Ao longo da Estrada Real, no município de Rio de Contas (BA), afloram rochas metavulcânicas ácidas representativas da Formação Novo Horizonte, Supergrupo Espinhaço, que se formaram na fase sin-rifte do Espinhaço. Estas rochas foram submetidas a intensos processos de deformação e metamorfismo, que modificaram as suas feições originais. Este trabalho visa compreender a gênese do magmatismo ácido sin-rifte do Espinhaço e os processos metamórficos e hidrotermais que afetaram a região, com base em dados de campo, petrográficos e geoquímicos de rocha total. As metavulcânicas ácidas possuem mineralogia constituída por blasto-pórfiros de quartzo, porfiroblastos de andaluzita e cianita, pseudomorfos de granada, feldspatos, biotita, muscovita, sericita, clorita, epidoto, monazita, zircão e minerais opacos imersos em uma matriz quartzo-feldspática. Os processos de sericitização e muscovitização estão presentes nas rochas e indicam a ocorrência de alterações hidrotermais. De acordo com as características petrográficas e geoquímicas, os protólitos das rochas metavulcânicas ácidas foram classificadas como riolitos. Os diagramas de Harker mostram valores dispersos dos elementos maiores Ca, Na e K e dos LILEs, indicando uma provável mobilidade desses elementos. No diagrama multielementar de elementos-traço e ETRs são visualizadas anomalias negativas de Nb-Ta, Sr, P e Eu, além de enriquecimento de ETRL em relação aos ETRP. A formação dessas rochas em um ambiente de rifte continental é sugerida, a partir de um processo de fusão crustal com a interação de um manto previamente modificado por zona de subducção (manto metassomatizado).

The relationship of the relative abundance of masses of granites and rhyolites in the earth’s crust with the regularities of the rheology of the granitic magmas

Many years ago, V.S. Sobolev suggested that the reason for the relative prevalence of intrusive and effusive rock masses in the earth’s crust lies in the regularities of viscosity of water-bearing magmas in a variable field of temperatures and pressures. Alas, in those years it was not possible to solve this problem on a quantitative physical-chemical basis, since experimental and theoretical studies of the viscosity of such melts at high pressures were just beginning. In the present work, new regularities of the viscosity of near-liquid water-bearing acidic magmas in a wide range of thermodynamic parameters and depths of the Earth’s crust (1–30 km) is established using the structural-chemical model of reliable and correct predictions and calculations of the viscosity of magmas of virtually any composition. It determined that these regularities really are a quantitative physical-chemical basis explaining the reason for the relative distribution of masses of intrusive and effusive rocks of acidic composition in the earth’s crust.

The great escape: Petrogenesis of low-silica volcanism of Pliocene to Quaternary age associated with the Altiplano-Puna Volcanic Complex of northern Chile (21°10′-22°50′S)

The Pliocene to Quaternary volcanic arc of the Central Andes formed on 70–74 km thick continental crust. Physical interaction between mafic and acid magmas for this arc are therefore difficult to recognize due to the differentiation of mantle-derived magma during ascent through the thickened crust and a corresponding lack of erupted primitive lavas. However, a rare concentration of less evolved rocks is located marginal to the partially molten Altiplano-Puna Magma Body (APMB) in the Altiplano-Puna Volcanic Complex of northern Chile, between 21°10′S and 22°50′S. To unravel the relationship between this less evolved magmatism and the APMB, we present major and trace element data, and Sr and Nd isotope ratios of fourteen volcanoes. Whole-rock compositional and Sr and Nd isotope data reveal a large degree for compositional heterogeneity, e.g., SiO2 = 53.2 to 63.2 wt%, MgO = 1.74 to 6.08 wt%, Cr = 2 to 382 ppm, Sr = 304 to 885 ppm, 87Sr/86Sr = 0.7055 to 0.7088, and 143Nd/144Nd = 0.5122 to 0.5125. The combined dataset points to magma spatial compositional changes resulting from magma mixing, fractional crystallization and crustal assimilation. The least evolved products erupted along the periphery of the APMB and are likely equivalent to the replenishing magmas that thermally sustain the large APMB system. We suggest that the mafic to intermediate eruptives we have investigated reflect mafic melt injections that underplate the APMB and escape along the side of the large felsic body to avoid significant compositional modifications during ascent, which helps to assess the evolution of the APMB through space and time.