Subduction and Collision of the Jinsha River Paleo-Tethys: Constraints from Zircon U-Pb Dating and Geochemistry of the Ludian Batholith in the Jiangda–Deqen–Weixi Continental Margin Arc

The Jiangda–Deqen–Weixi continental margin arc(DWCA) developed along the base of the Changdu–Simao Block and was formed as a result of the subduction of the Jinsha River Ocean Slab and the subsequent collision. The Ludian batholith is located in the southern part of the DWCA and is the largest batholith in northwest Yunnan. Granite samples from the Ludian batholith yield an early Middle Permian age of 271.0 ± 2.8 Ma. The geochemical data of the early Middle Permian granitoids show high Si2 O, low P2 O5 and MgO contents that belong to calc-alkaline series and peraluminous I-type rocks. Their εHf(t) values range from-5.01 to +0.58, indicating that they were formed by hybrid magmas related to the subduction of the Jinsha River Tethys Ocean. The monzonite and monzogranite samples yield Late Permian ages of 250.6 ± 1.8 Ma and 252.1 ± 1.3 Ma, respectively. The Late Permian granitoids are high-K calc alkaline and shoshonite series metaluminous I-type rocks. Their εHf(t) values range from-4.12 to-1.68 and from-7.88 to-6.64, respectively. The mixing of crustal and mantle melts formed the parental magma of the Late Permian granitoids. This study, combined with previous work, demonstrates the process from subduction to collision of the Jinsha River Paleo-Tethys Ocean.     

New Discovery of the Devonian Orthoclase Granite of Nenjiang–Heihe Structural belt, China and its Zircon U-Pb Data

正Objective The Nenjiang–Heihe structural belt is located in the eastern Xing’anling Mongolian Orogenic Belt between the Songnen block and Xiang’an block.This structural belt has long been the focus of geological scholars(Miao Laicheng et al.,2003;Liang Chenyue et al.,2011;Li Chao et al.,2017),which has complex geological condition,     

Timing of Back–Arc Spreading of the Paleozoic Island Arc of the Urals: Implication of Sm–Nd and U–Pb Dating of Dolerites and the Composition of Inclusions in Zircon

Doklady Earth Sciences - Dolerites of the parallel dikes formed in a back-arc spreading setting have been dated by Sm–Nd to the Silurian (426 ± 34 Ma) for Mount Azov in the Central...     

Secondary alterations of globular and platy phyllosilicates of the glauconite–illite series in the Precambrian and Vendian–Cambrian rocks

Previously published and new data on secondary transformations of the globular and platy phyllosilicates of the glauconite–illite series from the Upper Proterozoic terrigenous rocks of the Olenek and Anabar uplifts (East Siberia), Srednii Peninsula (Murmansk coast), and Vendian–Cambrian boundary rocks of the Podolian Dniester area (Ukraine) are generalized for the first time. Plastic deformation, aluminization, chloritization, berthierinization, as well as replacement of phyllosilicates of different morphology by corrensite- chlorite and pyrite at different lithogenesis stages, are considered and lithological-mineralogical characteristics of the glauconite-bearing rocks are reported. The structural, crystal-chemical, genetic, and isotopegeochronological features of di- and trioctahedral phyllosilicates are discussed.     

Minerals of the Fe–Ni–Co–Cu–S System in Picrite Intrusions of the Southern Urals: Signatures of Liquation and Differentiation of the Sulfide Melt

Doklady Earth Sciences - New data on the minerals of the Fe–Ni–Co–Cu–S system in the differentiated intrusions of the Southern Urals are presented. Based on a detailed study...     

The tectonics and stages of the geological history of the Yenisei–Khatanga Basin and the conjugate Taimyr Orogen

A new interpretation of the seismic profile series for the Taimyr Orogen and the Yenisei–Khatanga Basin is given in terms of their tectonics and geological history. The tectonics and tectonostratigraphy of the Yenisei–Khatanga and the Khatanga–Lena basins are considered. In the Late Vendian and Early Paleozoic, a passive continental margin and postrift shelf basin existed in Taimyr and the Yenisei–Khatanga Basin. From the Early Carboniferous to the Mid-Permian, the North and Central Taimyr zones were involved in orogeny. The Late Paleozoic foredeep was formed in the contemporary South Taimyr Zone. In the Middle to Late Triassic, a new orogeny took place in the large territory of Taimyr and the Noril’sk district of the Siberian Platform. A synorogenic foredeep has been recognized for the first time close to the Yenisei–Khatanga Basin. In the Jurassic and Early Cretaceous, this basin was subsided under transpressional conditions. Thereby, anticlinal swells were formed from the Callovian to the Aptian. Their growth continued in the Cenozoic. The Taimyr Orogen underwent tectonic reactivation and apparently right-lateral transpression from Carboniferous to Cenozoic.     

Isotopic constraints on the age of the Earth’s core: Mutual consistency of the Hf-W and U-Pb systems

The estimation of the time of Earth??s core formation on the basis of isotopic systems with short-lived and long-lived parent nuclides gives significantly different results. Isotopic data for the ¹⁸²Hf-¹⁸²W system with a ¹⁸²Hf half-life of approximately 9 Myr can be interpreted in such a way that the core was formed 34 Myr after the origin of the solar system assuming complete core-mantle equilibrium. Similar estimates on the basis of the U-Pb isotopic system suggest a significantly longer mean time of core formation of approximately 120 Myr. If the Earth??s core were formed instantaneously, both isotopic systems would have shown identical values corresponding to the true age. The discrepancy between the U-Pb and Hf-W systems can be resolved assuming prolonged differentiation of prototerrestrial material into silicate and metallic phases, which occurred not simultaneously and uniformly in different parts of the mantle. This resulted in the isotopic heterogeneity of the mantle, and its subsequent isotopic homogenization occurred slowly. Under such conditions, the mean isotopic compositions of W and Pb in the mantle do not correspond to the mean time of the separation of silicate and metallic phases. This is related to the fact that the exponential function of radioactive decay is strongly nonlinear at high values of the argument, and its mean value does not correspond to the mean value of the function. There are compelling reasons to believe that the early mantle was heterogeneous with respect to W isotopic composition and was subsequently homogenized by convective mixing. This follows from the fact that the lifetime of isotopic heterogeneities in the mantle is close to 1.8 Gyr for various long-lived isotopic systems. There is also no equilibrium between the mantle and the core with respect to the contents of siderophile elements. Because of this, the mean isotopic ratios of W and Pb cannot be used for the direct computation of the time of metal-silicate differentiation in the Earth. Such estimation requires more sophisticated models accounting for the duration of the differentiation process using several isotope pairs. Given the prolonged core formation, which has probably continued up to now, the question about its age becomes ambiguous, and only the most probable growth rate of the core can be estimated. The combined use of the U-Pb and Hf-W systems constrains the time of formation of 90% of the core mass between 0.12 and 2.7 billion years. These model estimates could have been realistic under the condition of complete disequilibrium between the silicate and metallic phases, which is as improbable as the suggestion of complete equilibrium between them on the whole Earth scale.     

Age and Sources of Metasedimentary Rocks of the Tokur Terrane of the Mongol–Okhotsk Fold Belt: Results of U–Pb and Lu–Hf Isotope Studies

Doklady Earth Sciences - This paper presents the results of U–Pb (LA-ICP-MS) and Lu–Hf isotope studies of detrital zircons from the presumably Permian meta sedimentary rocks of the...     

Nature of the Skarn–Borosilicate Deposit Giants of the Sikhote-Alin and Pamir Mountains

Doklady Earth Sciences - It is shown that the giant Sikhote-Alin and Pamir deposits of boron are associated with fragments of the boron-bearing evaporite strata of paleoceanic atolls in the...     

Zircon U-Pb Geochronology and Hf Isotopic Geochemistry of the Liwan Cu–Mo Deposit, Guichi Ore Cluster Field

Please refer to the attachment(s) for more details.     

Sources of the Jurassic terrigenous rocks of the Upper Amur and Zeya–Dep troughs of the eastern part of the Central Asian fold belt: Results of Sm–Nd isotopic–geochemical and U–Pb (LA-ICP-MS) geochronological studies

The results of U–Pb geochronological studies of detrital zircons and Sm–Nd isotopic–geochemical studies of terrigenous rocks of the Upper Amur and Zeya–Dep troughs indicate that the beginning of orogenic processes, which led to the formation of the Mongol–Okhotsk fold belt, occurred in the Early Jurassic.     

Geochemical and Sr–Nd–Pb-Isotope Characteristics of Ice-Rafted Sediments of the Arctic Ocean

The paper discusses the geochemical and Sr–Nd–Pb-isotope data on ice-rafted sediments (IRS) from different areas of the Arctic Ocean. Samples were collected during the Cruise of R/V Polarstern between Spitsbergen and North Pole, Yermak Plateau, as well as in Fram Strait. It is shown that the studied IRS samples in terms of La_N/Yb_N and εNd values are close to the composition of suspended particulate matter (SPM) from the mouth parts of large rivers and rivers transporting the sedimentary erosion products. This also follows from their Th/Sc, Th/Co, La/Sc, La/Sm, Sc/Th ratios and Sc content and from the position of their data points in the Sc–Th/Sc, La/Sc–Th/Co, and La/Sm–Sc/Th diagrams between the average SPM compositions of the Ob and Lena rivers. The values of ²⁰⁷Pb/²⁰⁶Pb and εNd in IRS samples give grounds to suggest that the rock complexes of the European, North American, and Asian continental margins could be potential sources for this sedimentary material. In the ²⁰⁷Pb/²⁰⁶Pb–εNd diagram, the IRS samples from all three studied areas define a compact cluster and are mainly confined to the triangle with corners represented by the Mackenzie River, Okhotsk–Chukotka volcanic area, and Lena River, being closer to the latter. In the Sm/Nd–εNd diagram, IRS points also form a compact field, being located almost in the middle between the average SPM compositions of the Yenisei and Ob rivers, on the one hand, and Lena River, on the other. In all diagrams, IRS samples from the different West Arctic areas show no significant scatter. With allowance for the fact that sediments are not subjected to significant homogenization during ice rafting, sediments from all three areas were obtained from a common source. As seen from the position of IRS data points in the ⁸⁷Sr/⁸⁶Sr–εNd diagram, this source was the Asian continental margin.     

Rb–Sr and Sm–Nd study of granite–charnockite association in the Pudukkottai region and the link between metamorphism and magmatism in the Madurai Block

Pudukkottai region in the northeastern part of the Madurai Block exposes the garnetiferous pink granite that intruded the biotite gneiss. Charnockite patches are associated with both the rock types. Rb–Sr biotite and Sm–Nd whole-rock isochron ages indicate a regional uplift and cooling at ～550 Ma. The initial Nd isotope ratios (\(\varepsilon _{\text {Nd}}^{\mathrm {t}}=-20\) to ?22) and Nd depleted-mantle model ages (T_DM = 2.25 to 2.79 Ga) indicate a common crustal source for the pink-granite and associated charnockite, while the biotite gneiss and the charnockite within it represent an older crustal source (\(\varepsilon _{\text {Nd}}^{\mathrm {t}}= -29\) and T_DM = > 3.2 Ga). The Rb–Sr whole-rock data and initial Sr–Nd isotope ratios also help demonstrate the partial but systematic equilibration of Sr isotope and Rb/Sr ratios during metamorphic mineral-reactions resulting in an ‘apparent whole-rock isochron’. The available geochronological results from the Madurai Block indicate four major periods of magmatism and metamorphism: Neoarchaean–Paleoproterozoic, Mesoproterozoic, mid-Neoproterozoic and late-Neoproterozoic. We suggest that the high-grade and ultrahigh-temperature metamorphism was preceded by magmatism which ‘prepared’ the residual crust to sustain the high P–T conditions. There also appears to be cyclicity in the tectono-magmatic events and an evolutionary model for the Madurai Block should account for the cyclicity in the preserved records.     

Age of Carbonates and Phosphorites in the Sedimentary Cover of the Tuva–Mongolian Microcontinent

The ages of the two main stages of carbonate cover formation within the Tuva–Mongolian microcontinent have been determined. The Pb–Pb age and Sr–chemostratigraphic characteristics of the carbonate rocks of the Irkutnaya, Agaringol, and Zabita formations, as well as of the Zabita Formation phosphorite, demonstrate that the first stage began in the Middle Riphean (Late Ectasian) at about 1290 Ma and the second stage started in the Early Vendian (Early Ediacaran) at 630–600 Ma. The accumulation of phosphorite deposits started in the Ediacaran at about 580 Ma.     

Kinematic analysis of Jurassic grabens of soulthern Turgai and the role of the Mesozoic stage in the evolution of the Karatau–Talas–Ferghana strike-slip fault,Southern Kazakhstan and Tian Shan

The Karatau–Talas–Ferghana Fault (KTF) extending for 1500 km from Turgai to western Tarim is one of the world’s largest intracontinental strike-slip faults. This paper overviews the evolution of the KTF, providing insight into its relatively poorly studied northern segment in the Karatau Range and Turgai, known as the Main Karatau Fault (MKF). The right-lateral strike-slip along the KTF developed during three stages in the late Permian–Triassic, Early–Middle Jurassic, and late Cenozoic. The total strike-slip decreases northward from 200 km in the Ferghana Range to 100 km in the Karatau Range and decreases to zero in southern Turgai. Kinematic analysis of Jurassic grabens compensating the strike-slip in southern Turgai shows that strike slip along the KTF in the Jurassic, previously regarded as insignificant, actually measures tens of kilometers and 50% of the total strike slip in the northern segment of this fault.     

Peculiarities of Subduction in the Junction of the Kuril–Kamchatka and Aleutian Island Arcs

Doklady Earth Sciences - The peculiarities of the junction between the Kuril–Kamchatka and Aleutian island arcs are studied using different techniques and experimental data. The models of...     

Late Paleozoic subduction–accretion along the southern margin of the North Qinling terrane,central China: Evidence from zircon U-Pb dating and geochemistry of the Wuguan Complex

The Qinling Orogen separating the North China plate from the Yangtze plate is a key area for understanding the timing and process of aggregation between the two plates. Two competing and highly contrasting tectonic models currently exist to explain the timing and nature of collision; one advocates a Devonian continental collision while the other favors a Triassic collision. The Wuguan Complex, between the early Paleozoic North Qinling and the Mesozoic South Qinling terranes, can provide important constraints on the late Paleozoic evolutionary processes of the Qinling Orogen. Metamorphosed sedimentary rock of the Wuguan Complex have a detrital zircon age spectrum with two major peaks at 453 Ma and 800 Ma, several minor age populations of 350–430 Ma and 1000–2868 Ma, and a youngest weighted mean age of 358 ± 3 Ma, indicating a mixed source from the North Qinling terrane. The recrystallized zircons yield a weighted mean age of 333 ± 2 Ma, representing the metamorphic age. Geochemical analyses imply that the sedimentary rocks were originally deposited in an active continental margin dominated by an acidic-arc source with a subordinate mafic-ultramafic source. The youngest population of detrital zircons (358 Ma) suggests that the Wuguan Complex developed as forearc basin along the southern accreted margin of the North Qinling terrane during the early Carboniferous, whereas the ca. 520–460 Ma mafic rocks with E-MORB, N-MORB, OIB or island arc basalt signatures probably derived from the Danfeng Group. In combination with regional data, we suggest that the depositional age of the Wuguan Complex is ca. 389–330 Ma, but it was subsequently incorporated into tectonic mélange by the northward subduction of the Paleo-Qinling Ocean. A long-lived southward-facing subduction-accretionary system in front of the North Qinling terrane probably lasted until at least the early Carboniferous.     

Native Alloys of the Pd–Pt and Ni–Cu–Al Systems from the AS Luna-24

The close intergrowth of two native alloys of the compositions Ni_0.59Cu_0.24Al_0.15Fe_0.01Mn_0.01 and Pd_0.55Pt_0.36Rh_0.09 with a size of 10 μm has been discovered in the regolith from the Mare Crisium. A conclusion on its exhalative origin is made.