Tectono-magmatic Activity Research Articles

Triassic granites in the West Qinling Orogen, China: implications for the Early Mesozoic tectonic evolution of the Paleo-Tethys ocean

ABSTRACT The Western Qinling Orogen is marked by secular Triassic magmatism, a thorough understanding of the mechanism of which could provide critical insights into the reconstruction of the Palaeo-Tethys tectono-magmatic activity. Here, we present new geochemical, geochronological and Lu-Hf isotopic data for three batholiths and review regional data. These batholiths have similar rock assemblages (mainly granodiorite and monzogranite), which are characterized by dominantly plagioclase, quartz, and K-feldspar, subsequently amphibole and biotite. Zircon U-Pb data reveal that they represent the long-duration magmatism during the Triassic (ca. 251–223 Ma). Mineralogical characteristics and geochemical affinities manifest that these rocks in the Zeku district can be explicitly delineated as high-K, calc-alkaline, weakly fractionated I-type granites. They yield significantly negative εHf(t) values ranging from −12.81 to −1.26 with old two-stage mantle depleted model ages between 2054 and 1319 Ma. In tandem with Th/Nb (0.98), Th/La (0.39) and La/Nb (2.40) ratios and moderate pressure conditions (ca. 7–10 kbar), the studied granites were derived from partial melting of the Middle Paleoproterozoic to Middle Mesoproterozoic lower crust source region with minor mafic hydrous magma addition. Our new understandings, in conjunction with the temporal-spatial distribution characteristics of magmatism in the West Qinling Orogen, as well as the regional tectonic evolution, suggest that the superimposed orogeny evolved from the northward subduction of the Palaeo-Tethys Ocean (264–225 Ma) through syn-collision (225–215 Ma) to post-collision (beginning at ca.215 Ma) between the North China Craton and South China Block. In this scenario, at the convergent continental margin, the oceanic plate may have undergone melting producing the melts parental to the Zeku granites.

Titanite as a tracer for Nb mineralization during magmatic and hydrothermal processes: The case of Fangcheng alkaline complex, Central China

Titanite is presented here as a tracer for reconstructing the mineralization history of Nb during magmatic and hydrothermal processes in the Fangcheng Nb deposit, central China. Three types of titanites with magmatic and hydrothermal origins are distinguished. The magmatic titanite (Ttn I), is generally wedge-shaped with larger grain size (up to 1.5 mm). The hydrothermal titanite, either overgrows the magmatic titanite as a thin rim (Ttn IIA), or occurs as bead-like clusters coexisting with hydrothermal albite, fluorite and/or Nb-rich oxides (Ttn IIB; anhedral and lesser than 200 μm). The Nb contents in the magmatic titanite (mean of 1.2 wt%), tend to be lower than in the hydrothermal types (mean of 1.7 wt%). The hydrothermal titanites show enrichment in Al2O3, F, Ta, Y, HREEs and Sn and depletion in TiO2, Zr, Hf, Th and LREEs relative to the magmatic titanite. Using Zr-in-titanite as a geothermometer, the magmatic titanite yields higher crystallization temperatures (mean of 760 °C) than the hydrothermal titanites (mean of 610 °C). Titanite U-Pb dating results reveal that the Fangcheng magmatic and hydrothermal titanites were formed at 870 Ma and 406 Ma, respectively. These results are consistent with the zircon U-Pb ages of this study and previous publication as well as the regional tectono-magmatic activities, indicating two discrete episodes of Nb mineralization events at Fangcheng. Isotopic data show distinctly lower εNd (t) values (−4.8 to −10.3) in the hydrothermal titanites as compared to the magmatic titanite (−0.6 to −4.1), confirming that these two generations of titanite involve distinct sources.Based on all results, we propose that the early magmatic titanite nucleated and crystallized in a high-T and Nb-rich alkaline magma during the Neoproterozoic. Early Paleozoic hydrothermal fluids partly replaced the magmatic titanite (Ttn I), forming the hydrothermal titanite rims (Ttn IIA). During this process, Nb and other HFSEs and REEs were re-activated and subsequently re-precipitated into secondary titanite (Ttn IIB), rutile, pyrochlore and euxenite.

Age and Chemostratigraphy of the Finlayson Lake District, Yukon: Implications for Volcanogenic Massive Sulfide (VMS) Mineralization and Tectonics along the Western Laurentian Continental Margin

Abstract The Yukon-Tanana terrane in the Finlayson Lake district, Yukon, represents one of the first arc–back-arc systems that formed adjacent to the Laurentian continental margin in the mid-Paleozoic. Back-arc rocks contain many large and high-grade volcanogenic massive sulfide (VMS) deposits. This study integrates U-Pb zircon geochronology, lithogeochemistry, and Hf-Nd isotopes to establish precise controls on tectonomagmatic activity adjacent to the western Laurentian margin in the Late Devonian to Early Mississippian. High-precision chemical abrasion- (CA-) ID-TIMS U-Pb zircon geochronology defines coeval arc (ca. 363.1 to 348 Ma) and back-arc (ca. 363.3 to 355.0 Ma) magmatism in the Finlayson Lake district that intruded continental crust of Laurentian affinity (e.g., Snowcap assemblage). Mafic and felsic rocks display geochemical and isotopic characteristics that are consistent with being formed from mixtures of depleted asthenosphere and enriched lithospheric mantle sources. These melts variably entrained Laurentian continental crust via high-temperature crustal melting due to basaltic underplating. The high-temperature back-arc felsic magmatism occurs at specific time periods coinciding with VMS deposits and supports previous genetic models for VMS mineralization that suggest elevated heat flow and hydrothermal circulation were due to regional-scale rift-related magmatism rather than from local subvolcanic intrusions. The short timescales and transient nature of tectonomagmatic events in the Finlayson Lake district suggest that rapid and complex subduction initiation of oceanic and continental crust fragments facilitated coeval compression, extension, and magmatism in the arc and back-arc regions. We thus reevaluate the presently accepted tectonostratigraphic framework of the Finlayson Lake district and suggest revised interpretations that shed light on VMS depositional environments and a possible broader association with the ca. 358 Ma Antler Orogeny. Results of this study have implications for incipient tectonics, magmatism, and mineralization along the western Laurentian continental margin and other orogenic belts globally.

Lithospheric thinning of the North China craton: Insights from Early Cretaceous intermediate–mafic dyke swarms in Jiaodong peninsula

The coupling/decoupling relationships between shallow crustal deformation and deep mantle tectono-magmatic activities, during lithospheric thinning and destruction of cratons, remain hotly debated in the last decades. Multidisciplinary studies were done on intermediate–mafic dyke swarms diffusively located in southern Jiaodong peninsula, southeastern North China craton (NCC) to explore the crustal and lithospheric mantle responses to regional tectonic extension. Uniform ages (122–121 Ma) of the dykes indicate intensive magma generation at the mantle depth around 122 Ma related to large-scale tectonic extension of regional lithospheric mantle. Systemic anisotropy of magnetic susceptibility (AMS), geochemical, and Sr-Nd isotope analyses suggest that the dykes were originated from enriched lithospheric mantle sources and emplaced along crustal fractures formed in a WNW-ESE oriented extensional stress field. We show that the Jiaodong lithosphere experienced two stages of Early Cretaceous tectonic evolution, i.e., an early stage (135–122 Ma) lithospheric thinning characterized by large-scale tectonic extension of the crust and limited magmatic activities of crustal sources, and a late stage (122–108 Ma) lithospheric root collapse dominated by intensive tectonic extension and magmatism in the lithospheric mantle level. The decoupling crust-mantle evolution during lithospheric thinning and destruction of the NCC is ascribed to continuous tectonic extension in WNW-ESE direction.

Chronology and Geochemistry of Early Cretaceous Magmatism in the Northwestern Erguna Block, Northeast China

This study was conducted to define the background structure and petrogenetic significance of the Early Cretaceous magmatic rocks in the Badaguan area of northern Daxing’anling and to explore the Late Paleozoic tectonic evolution of the Mongol-Okhotsk suture zone. The Early Cretaceous magmatic rock was systematically investigated using zircon U-Pb dating and geochemical and petrological analyses. The results show that the rock: mainly consists of granites and rhyolites; has an age of 125–140 Ma; has a strong MgO, Al2O3, and total alkali content; has a SiO2 content of 61.68 wt% to 77.41 wt%; and contains Rb, Th, U, and light REEs with depleted levels of of Sr, P, Ti, and heavy REEs. When combined with the Hf isotopic characteristics of the Early Cretaceous magmatic rock from the Erguna Massif, these results suggest that the magma originated from the partial melting of basal crustal materials during the Neoproterozoic–Phanerozoic period and that various mineral forms (including hornblende, plagioclase, and apatite) underwent fractional crystallization processes during the evolution of the magma. The Early Cretaceous magmatic rock from the Badaguan area recorded the extensional environment of the lithosphere after the closure of the Mongol-Okhotsk Ocean, and this hypothesis is consistent with the results of previous studies on the tectono-magmatic activities in Northeast China during the same period.

AGE AND DURATION OF CRYSTALS GROWTH IN CHAMBERS OF VOLYN PEGMATITES (UKRAINIAN SHIELD)

Formation of chamber pegmatites is associated with tectonomagmatic activation of the region of their distribution. It should be expected that the granitic chamber pegmatites of Volyn were formed by products of degassing of acidic magma. However, in the growth of quartz of the late generation, the beginning of crystallization of which was about 200ºC, CO2-fluids were involved. They are products of degassing of basic magma, which also took part in the growth of crystals at higher temperatures (˃573ºC). Crystallization of minerals in chambers was long: from 1.75±0.10 billion years (age of protogenetic inclusions of zircon and uraninite in topaz crystals) to 1.39 billion years (age of galena inclusions in late-generation quartz). So, for the first time, it was substantiated that the duration of crystal growth in the chambers of Volyn pegmatites was at least 360±100 million years. Therefore, it is assumed that the growth of crystals in chambers Volyn pegmatites lasted for quite a long time.

Criteries and prospects of diamonds of the Vitebsk granulite massif

The article describes the history of studying the diamond content of tectonic structures of the territory of Belarus. Based on the results of magnetometric, mineralogical, tectonic studies carried out by industrial geologists and scientists over the past 50 years, new scientifically substantiated criteria for the search for explosion pipes have been developed using Clifford’s rule, according to which kimberlite explosion pipes are developed within the Archean cratons, where the thickness of the lithosphere is 175–270 km, and are absent in the zones of Early Proterozoic stabilisation and tectonomagmatic activation. Explosion tubes on the African-Arabian, East Siberian, Sino-Korean and East European platforms demonstrate their confinement to the Archean cratons and may be associated with zones of paleosubduction of the Proterozoic oceanic crust beneath the Archean cratons. Based on this, the authors scientifically substantiated the hypothesis that during the closure of the Early Proterozoic paleoocean separating the Fenno-Scandinavian craton from the Volga-Ural and Sarmatian cratons, subduction of the younger crust took place under these cratons, the southwestern corner of which on the territory of Belarus is the Vitebsk granulite massif. The article concludes that the Vitebsk granulite massif is the most promising in terms of diamond-bearing on the territory of Belarus, and within its limits – the Smolensk regional deep fault at the intersection of this fault of northeastern striking with the Odessa-Gomel regional deep fault of submeridional striking south of the city of Orsha. Recommendations are given for further study of promising areas in order to determine their diamond content.

Quantifying the growth of continental crust through crustal thickness and zircon Hf-O isotopic signatures: A case study from the southern Central Asian Orogenic Belt

Abstract Accretionary orogens function as major sites for the generation of continental crust, but the growth model of continental crust remains poorly constrained. The Central Asian Orogenic Belt, as one of the most important Phanerozoic accretionary orogens on Earth, has been the focus of debates regarding the proportion of juvenile crust present. Using published geochemical and zircon Hf-O isotopic data sets for three belts in the Eastern Tianshan terrane of the southern Central Asian Orogenic Belt, we first explore the variations in crustal thickness and isotopic composition in response to tectono-magmatic activity over time. Steady progression to radiogenic zircon Hf isotopic signatures associated with syn-collisional crustal thickening indicates enhanced input of mantle-derived material, which greatly contributes to the growth of the continental crust. Using the surface areas and relative increases in crustal thickness as the proxies for magma volumes, in conjunction with the calculated mantle fraction of the mixing flux, we then are able to determine that a volume of ~14–22% of juvenile crust formed in the southern Central Asian Orogenic Belt during the Phanerozoic. This study highlights the validity of using crustal thickness and zircon isotopic signatures of magmatic rocks to quantify the volume of juvenile crust in complex accretionary orogens. With reference to the crustal growth pattern in other accretionary orogens and the Nd-Hf isotopic record at the global scale, our work reconciles the rapid crustal growth in the accretionary orogens with its episodic generation pattern in the formation of global continental crust.

GEOCHRONOLOGY OF THE CHADOBETS ALKALINE ULTRAMAFIC CARBONATITE COMPLEX (SIBERIAN CRATON): NEW U-Pb AND Ar-Ar DATA

The Chadobets alkaline ultramafic carbonatite complex is located on the Siberian craton within the southern boundary of the Permian-Triassic plume activity. The dating of xenogenic zircons from the weathering crust of carbonatites of the Chuktukon complex yielded four clusters with ages of 1870–1820, 495–385, 290–210 and 215–162 Ma. The first two clusters correspond to the dates of activity of Paleoproterozoic granitoid magmatism and Paleozoic alkaline-mafic tectono-magmatic activity, widely occurred in the Siberian craton and its southern framing. The age of crystallization of alkaline rocks of the Chadobets complex falls within the interval of 255–240 Ma. Ar-Ar dating of damtjernite and carbonatite minerals of the Chuktukon complex falls within the intervals of 250.5±3.7 and 247.1±5.7 Ma, respectively. The crystallization ages of the mela-aillikites and damtjernites of the Terina complex, according to the Ar-Ar dating, correspond to the intervals of 257.4±3.9, 241.1±3.7, and 240±3.6 Ma. The age interval of 215–162 Ma based on zircons from the carbonatite weathering crust of the Chuktukon complex reflects the geochronology of superimposed processes and indicates the different stages of alteration of igneous rocks of the Chadobets complex. The data obtained on the age of crystallization of alkaline rocks of the Chadobets complex are consistent with the age interval of Siberian plume activity within a large igneous province (LIP).

Vilyui-Markha interfluve of Yakutia: a region prospective for Cu-Ni-PGM mineralization

Materials are discussed on geologically similar structure of Norilsk ore district (NOD) and Vilyui-Markha interstream area (VMIA), which implies the latter prospects for Cu-Ni-PGM mineralization. Data is provided on Cu-Ni-Co-Zn mineral occurrences within Ygyattinsky diamondiferous region centered on VMIA. Geological similarities of NOD and VMIA are summarized below. Both regions are located in Mesozoic tectonomagmatic activation domain at the edge of large troughs: NOD is localized in the Siberian platform foredeep, and VMIA lies at Vilyui syneclise margin. NOD deposits are hosted by centroclines of large brachysynclines at slopes of Pyasinskoye dome. Within VMIA, prospects are located at Syuldyukarskoye dome slopes in margibal parts of large troughs. NOD and VMIA comprise Paleozoic marl-carbonate strata overlain by carbonaceous Carboniferous-Permian overburden, which could be assimilated by basaltic magma in Mesozoic contributing to its ore differentiation. Norilsk-Kharaelakh ore-bearing intrusion in VMIA appears to be similar to Kholomolokh sulfide-rich intrusion with its inferred extensive ore-bearing sills. They have similar composition and structure including presence of pegmatites. Ore-controlling Norilsk-Kharaelakh fault is believed to be simi- lar to Khatyryk-Kholomolokh fault, which was traced for 24 km by drilling and is one of sutures within deep-seated kimberlite-controlling Vilyui-Markha zone. This fault’s impact zone host concentrated geochemical anomalies and Cu-Ni-Co-Zn-Pt-Au-Ag Khomustakh occurrence. Based on this, Norilsk-type Cu-Ni prospects ranked as a potential ore cluster and three ore fields were identified

The Diversity of Exoplanets: From Interior Dynamics to Surface Expressions

The coupled interior–atmosphere system of terrestrial exoplanets remains poorly understood. Exoplanets show a wide variety of sizes, densities, surface temperatures, and interior structures, with important knock-on effects for this coupled system. Many exoplanets are predicted to have a “stagnant lid” at the surface, with a rigid stationary crust, sluggish mantle convection, and only minor volcanism. However, if exoplanets have Earth-like plate tectonics, which involves several discrete, slowly moving plates and vigorous tectono-magmatic activity, then this may be critical for planetary habitability and have implications for the development (and evolution) of life in the galaxy. Here, we summarize our current knowledge of coupled planetary dynamics in the context of exoplanet diversity.

A new tectonic framework for the composite orogenic metallogenic systems in the east of North China: The role of the Heilongjiang Ocean in the Late Paleozoic to Mesozoic

Since the Paleozoic, the composite orogenic belt in the east of North China (the eastern Central Asian Orogenic Belt) has undergone multiple stages of subduction-accretion, tectonic superposition and destruction driven by multiple tectonic domains, e.g., the Paleo-Asian Ocean, the Panthalassa, and the Paleo-Pacific Ocean. Multiple episodes of tectono-magmatic activities and associated composite orogenic metallogenic systems have also been occurred. However, the tectonic affinities of these composite orogenic metallogenic systems are still not well understood, due to the poor knowledge of the temporal and spatial transitions among the three tectonic domains. Recently, a regional ocean, namely the Heilongjiang Ocean, has been proposed to be a critical link among the three tectonic domains that drove the Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt. To constrain the tectonic history of the Heilongjiang Ocean, here we reported new petrological, whole-rock major and trace elemental, and zircon U-Pb geochronological data of sedimentary and magmatic rocks from the western edge of the Jiamusi-Khanka Massif in the east of Heilongjiang Province. Integrating our new results with previous studies in the region, we established a novel tectonic framework for the eastern Central Asian Orogenic Belt: (1) During 380–310 Ma, a tectonic switch occurred in the region from weakened influence of the Paleo-Asian Ocean domain in the south to enhanced influence of the westward subduction of the Panthalassa into the eastern Jiamusi-Khanka Massif; the latter induced back-arc extension and eventually the opening of the Heilongjiang Ocean, which drove the Jiamusi-Khanka Massif to drift eastward away from the Central Asian Orogenic Belt; (2) during 300–270 Ma, subduction of the Heilongjiang Ocean was triggered in its eastern margin, producing arc-type magmatism in the west edge of the Jiamusi-Khanka Massif; by 270–210 Ma, subduction of the Heilongjiang Ocean expanded to its west margin (beneath the Songliao Massif); (3) following the eventual closure of the Heilongjiang Ocean in ~ 180 Ma and subduction of the Paleo-Pacific Ocean in the east, the Jiamusi-Khanka Massif rejoined the conterminous Central Asian Orogenic Belt, marking the final amalgamation of the Central Asian Orogenic Belt; since then, the tectonic history of the composite orogenic metallogenic systems in the east of North China was taken over by the Paleo-Pacific domain. This new tectonic model not only links the evolution of the three tectonic domains, but also provides a vital basis for the geodynamic framework of the contemporary endogenetic metallogenesis in this region.

Stages of Tectono-Magmatic Activity in the Border Zone of the Siberian Platform and the Tannuola–Khamsara Segment of the CAFB (According to the Results of U–Pb Isotope Studies)

Stages of Tectono-Magmatic Activity in the Border Zone of the Siberian Platform and the Tannuola–Khamsara Segment of the CAFB (According to the Results of U–Pb Isotope Studies)

Multistage Evolution of Proterozoic Crust of East Antarctica by the Example of the Filla Terrane (Rauer Islands): New Geological and Isotope Data

Abstract —The paper presents new data on the Rauer Islands, one of the unique objects of the East Antarctic Shield. The interest in this area is triggered by its complex geologic structure, including both Archean and Proterozoic fragments of the Earth’s crust, and by its multiphase formation. A detailed scheme of the geologic structure of the area is proposed, new petrologic complexes are revealed, and the stages of tectonomagmatic activity at ~1400–1320 Ma and 1150 Ma are reliably dated. This serves as a factual basis for comparison the study area with other regions of East Antarctica. Based on the geological and isotope data obtained, the Meso–Neoproterozoic Filla Terrane in the area of the Rauer Islands is recognized. It is composed of metamorphic and primarily intrusive rocks, whose protoliths formed in the time interval 1400–950 Ma. Three periods of tectonothermal activity have been established in the Filla Terrane: Mid-Mesoproterozoic (1400–1320 Ma), Meso–Neoproterozoic (1150–886 Ma), and early Cambrian (536–504 Ma). The first period is the formation time of Mesoproterozoic crust, and it is time-correlated with the tectonogenesis phase in the adjacent Rayner province. The second period corresponds to the later phase of tectonothermal activity in the Rayner province. In the Filla Terrane, this period can be divided into two intervals, 1150–1100 Ma and 1010–886 Ma. The former interval is treated as intense crustal growth in the course of granitoid and mantle magmatism. The latter interval is a period of tectonothermal processes accompanied by intense deformations, high-temperature metamorphism, and intrusion of porphyritic granitoids. Apparently, the gap between the first and the second intervals is the time of deposition of the sedimentary protolith of paragneisses, which, together with the surrounding rocks, underwent high-temperature metamorphism and deformations at 950–914 Ma. The synchronous evolution of the Archean block and the Filla Terrane began at least within 1100–1000 Ma. The youngest, early Cambrian period of tectonic activity coincides with the development of local low-temperature mylonite zones and the intrusion of synkinematic pegmatite veins. Thus, the tectonothermal evolution of the Filla Terrane includes almost the same main phases of crustal growth and transformation as the Rayner province. This indicates that the Filla Terrane is a fragment of the Rayner province, which accreted to the Archean terrane at least in the late Mesoproterozoic.

The metallogenic epoch and geological implications of the tungsten-tin polymetallic deposits in southern Jiangxi Province, China: Constraints from cassiterite U-Pb and molybdenite Re-Os isotopic dating

The Nanling Range is one of the rare large granite provinces in China, and many of the exposed Mesozoic granites are closely related to tungsten-tin polymetallic mineralization in time, space and genesis. Southern Jiangxi Province, characterized by densely distributed tungsten deposits and multiple associated resources (Sn, Mo, Bi, Cu, Ag, Sb, Hg, and rare earth elements), is an important part of the Nanling region. Keshuling, Baxiannao and Bikeng in southern Jiangxi are exocontact-zone quartz vein subtype tungsten deposits, while Jinzhuping is a endocontact-zone quartz vein subtype tungsten-tin deposit. In this study, we present four cassiterite U-Pb ages and five molybdenite Re-Os ages from samples of the above four deposits to define the metallogenic era. The cassiterite U-Pb ages for Keshuling, Baxiannao and Bikeng are 157.5 ± 4.1 Ma, 158.8 ± 2.9 Ma and 159.0 ± 2.0 Ma within the 2σ error, while the cassiterite U-Pb and molybdenite Re-Os ages of the endocontact-zone quartz vein subtype ores in Jinzhuping are 156.6 ± 3.8 Ma and 157.9 ± 4.2 Ma, respectively. Comparison of these ages of ore minerals with the genetically related granitic rocks shows that there was no resolvable time difference between the granite emplacement and hydrothermal mineralisation, both of which were products of early tectono-magmatic activity in the Yanshanian period in Nanling. The ore-forming ages of the different types of ore bodies generally become younger from the granitic bodies outward. We present a genetic model in which ore forming fluids migrated outward from the granitic source and formed ore bodies in tungsten-tin deposits of southern Jiangxi Province.

Mineralogical features of gold of the Permian conglomerates of the Sololiy uplift of the Olenek high (Northeastern Siberian platform)

Typomorphic features of placer gold of conglomerates of the Ortokinskaya formation of the Early Permian age (P1or) of the Sololiy Uplift of the Olenek High and modern channel alluvium of the Ortoku Eekit river, which drains these deposits, are studied. It is found that extremely heterogeneous composition and complex inner structure are typical features of the vast majority of gold of the Permian conglomerates. There are several stages of different fineness (from 251‰ to 999‰) within a single gold particle, as a result, gold has a mosaic-block inner structure. It is proposed that such heterogeneity is formed due to epigenetic transformations of primary medium-grade gold in an intermediate reservoir of the Permian age, and also under influence of superposed hydrothermal mineralization with low-grade gold, related to the processes of the Mesozoic tectonomagmatic activation. The latter is indicated by the discovery of impregnated gold-sulfide mineralization in the Permian conglomerates. Ore mineralization is represented by gold, silver, pyrite, sphalerite, chalcopyrite, galena, argentite, native tin, and barite. Association mineralization to thin tectonic zones of conglomerate fragmentation, suggests that superposed gold-sulfide hydrothermal mineralization of impregnated type was formed as a result of manifestations of the Mesozoic tectonomagmatic activation, when gold-bearing hydrothermal solutions migrated in faults. It is determined that auriferous conglomerates of the Ortokinskaya formation of the Permian age were major sources of placer gold of modern alluvium in the studied part of the Ortoku Eekit.

Mapping Surface Deformation Over Tatun Volcano Group, Northern Taiwan Using Multitemporal InSAR

The Tatun Volcano Group (TVG) is located at the northern coast of Taiwan Island with only 15 km to the Taipei metropolis. Recent geothermal and geochemical studies suggest that the TVG is dormant-active rather than extinct, implying the eruption potential to devastate the nearby area of 7 million inhabitants. Although some geodetic tools (e.g., global positioning system and precise leveling) have been utilized to analyze the activity associated with volcanism, it is still challenging for conventional interferometric synthetic aperture radar (InSAR) technique to obtain clear ground surface movement at the TVG due to decorrelation and complex atmospheric delay. In this study, we present an improved multi-temporal InSAR (MTInSAR) approach to explore the temporal evolution and spatial extent of displacement at the TVG from 19 L-band ALOS/PALSAR images acquired between 2007 and 2011. Stratified atmospheric delays and orbit error are corrected with a patch-based joint model as different phase components can be separated according to their distinct spatiotemporal characteristics. The spatial deformation patterns indicate an uplift of 10 mm/year at the SW-NE ridge and subsidence with a rate of 10 mm/year at the E-W ridge. The temporal deformation variations at Mt. Chihshin and Huangzuei have high similarity with correlation coefficients of 0.9 above. This indicates that the subsidence at Mts. Chihshin and Huangzuei might be caused by released hydrothermal fluids related to tectono-magmatic activity within the hydrothermal system beneath the TVG.

Petrogenesis and tectonic implication of the Permian-Triassic syenogranites from the eastern segment of the East Kunlun Orogen, China

Permian-Triassic granitoids are widespread in the East Kunlun Orogen (EKO) and are influential in the re-construction of Paleo-Tethyan tectono-magmatic activities. In this contribution, zircon U–Pb dating and Lu–Hf isotopic as well as whole rock major and trace elements analysis have been conducted on a series of syenogranite plutons from the eastern segment of the EKO to constrain their petrogenesis and tectonic implication. The syenogranites are characterized by dominant mineral assemblages of K-feldspars and minor plagioclase and biotite, in contrast to the coexisting granodiorites that are rich in amphibole and plagioclase. Zircon U–Pb dating reveals that the studied syenogranites represent a two-stage magmatism from Middle Permian to Late Triassic (ca. 265 Ma and 235–232 Ma). Geochemical and mineralogical evidences show that the syenogranites are classified as high-K calc-alkaline, weakly peraluminous, highly fractionated (DI = 93–95) and moderately fractionated (DI = 82–91) I-type granites. They yield negative ɛHf (t) values (−13.25 to −0.11), which, together with their high Th/Nb (0.73–4.88), Th/La (0.29–2.65) and La/Nb (1.07–4.48) ratios and moderate pressure conditions (7–10 kbar) imply magma generation through partial melting of the normal-thickened lower crust. The magma underwent extensive plagioclase and subordinate K-feldspar fractionation during evolution. Given the old two-stage Hf model ages (TDM2 = 1270–2100 Ma), we interpret the ancient lower crust as their dominant source rocks with limited contribution from the juvenile lower crust. Our new data, in tandem with published data show that the Middle-Permian (ca. 265 Ma) Jialuhe syenogranites were formed during a period of local extension concomitant with the northward subduction of the Paleo-Tethyan ocean. In contrast, the Late-Triassic Qingshuihe (235 Ma), Keri (234 Ma), Wutuo (232 Ma) and Balong syenogranite plutons were generated in response to asthenospheric upwelling, lower crust delamination and subsequent continental rifting in a post-collisional extension stage along the convergent plate margins.

Natural Amalgam of Gold in Placers of the Ebelyakh Area -Indicator of Tectono-Fluid Activation (North-Eastern Siberian Platform)

The results of studying the typomorphic features of placer gold in the unique diamond-bearing placers of the Ebelakh river basin (Anabar diamond-bearing region) are given. Detailed study of the morphology, micro-relief of the surface and internal structure of the gold and photographing was performed using a scanning electron microscope JEOLJSM-6480LV. The gold fineness was determined using the Camebax-Micro microanalyzer and the JEOL OXFORD INCA-sight energy spectrometer. The internal structure of native gold was studied by etching gold in mounted thin sections using a proven method, using a reagent: HCl + HNO3 + FeCl3 × 6H2O + CrO3 + thiourea + water. It is determined that, modern placer occurrences were formed mainly due to the redeposition of fine high-grade gold from ancient gold-bearing intermediate sources. At the same time, in the placer of the Kamenisty creek a natural amalgam of gold is discovered, which is an aggregate consisting of several cemented rounded gold particles of small size (-0.25 mm) of various morphology. The cement is superimposed medium-grade gold with Hg content of up to 13.3%. Its internal structure is porous, and zoning is noted due to the uneven distribution of Hg. The surface of mercury gold is characterized by a brain-like microsculpture. Along with this, in some placers of the studied area, it was possible to find small (>0.2 mm) gold particles with a specific surface with the thinnest (first microns) fringe of mercury (ртутистого) gold. Obviously, these are single grains of the disintegrated aggregates of auro amalgam. We also found gold particles in an aluminosilicate film of variable Al, Si, K, Fe composition, and the smallest (1-2 microns) mineral phases of gold, sphalerite, galena, zincite and zinc-containing iron are identified on this film. It is assumed that natural amalgamation of placer gold occurred as a result of migration of mercury-containing gold-bearing hydrothermas on fault zones during tectonomagmatic activation. Based on the above-mentioned, it is assumed that there are adjacent sources of supply - low-temperature hydrothermal ore occurrences confined to the faults and formed as a result of tectonomagmatic activation processes. This proposition is confirmed by the identification of hydrothermal-metasomatic formations of K-spar-quartz-pyrite composition with disseminated gold-sulfide mineralization on the studied territory. The similarity of geological conditions of localization and the material composition of apocarbonate hydrothermal-metasomatic formations of the Ebelyakh area with the gold-bearing rocks of the Central Aldan ore district allow to estimate positively the prospects for their further study.

Features of the Formation of Geochemical Types of Natural Waters in Certain Regions of Central Eurasia

The report presents extensive factual data on the chemical composition of natural waters in different regions of Central Eurasia. The features of the chemical composition of natural waters are revealed for several regions with a humid and arid climate, as well as for tectonomagmatic activation conditions. The abundance of over 50 chemical elements in natural waters is characterized. The geochemical types of waters corresponding to rigorously defined evolution stages of the water–rock system are established for natural waters of all considered regions based on saturation of waters in secondary minerals. The influence of the geochemical conditions on the dissolution of primary minerals and the formation of secondary mineral phases is revealed. The composition of groundwaters is systematized by the features of the origin of their chemical compositions. The role of climatic, geological, and structural factors in the formation of geochemical types of waters in several Central Eurasian regions is shown.