The first data on U–Pb (SHRIMP) dating of zircon from metamorphic rocks of the crystalline base of the Taigonos-Paren Uplift (southern margins of the Omolon Massif)

U–Pb SHRIMP dating of zircons from metamorphic rocks of the crystalline basement of the Omolon-Taigonos area (northeastern margins of Asia) has been used to determine the periods of early endogenic activity of the crust. These periods correlate to the time of formation of the magmatic rock protolith (3.2–3.3 Ga), the stage of regional metamorphism (2.6–2.8 Ga), and the superimposed granitization. The resulting data can be used to reconstruct the history of development of the crust in the Precambrian.     

Paleoproterozoic gabbro–diorite–granite magmatism of the Batomga Rise (NE Aldan Shield): Sm–Nd isotope geochemical evidence

The geochemical similarity and almost simultaneous (2055–2060 Ma) formation of Utakachan gabbro-amphibolite, Jagdakin granodiorite-diorite, Khoyunda granitoid, and Tygymyt leucogranite complexes, which inruded metamorphic formations of the Batomga Group are evidence of their formaton from unified magmatic source. All this makes it possibble to combine aforementioned complexes into the unified Early Proterozoic diferentiated gabbro-diorite-granite complex.     

The first data on breithauptite in chromitite from the northern part of the Voykar–Synya ultramafic massif (Polar Urals)

Doklady Earth Sciences - This work presents the results of studying the mineral composition of chromite ores of the Khoila area. For the first time, nickel antimonide (breithauptite), including an...     

The Itmurundy Pacific-type orogenic belt in northern Balkhash,central Kazakhstan: Revisited plus first U–Pb age,geochemical and Nd isotope data from igneous rocks

The Itmurundy zone/belt is located in the northern Balkhash area of central Kazakhstan. Geologically it belongs to the Kazakh orocline located in the western Central Asian Orogenic Belt (CAOB), north of the Tarim craton and west of the Junggar block. The Itmurundy belt, which surprisingly has remained unstudied in terms of up-to-date geochronological, geochemical and isotope methods compared to other regions of the CAOB, was revisited and reinvestigated. The belt possesses a very complicated geological structure and hosts rocks of mantle, orogenic and post-orogenic associations. This paper focuses on the orogenic association and presents original geological data, first U–Pb age and first up-to-date geochemical and Nd isotope data from igneous rocks. The orogenic association of the Itmurundy belt includes volcanic and sedimentary rocks of three formations, Itmurundy (O_1-2), Kazyk (O_2-3) and Tyuretai (O₃–S₁), and represents an accretionary complex. The most lithologically diverse Itmurundy Fm. (O_1-2) consists of oceanic basalt, pelagic chert, hemipelagic siliceous mudstone and siltstone, and greywacke sandstones. Both sedimentary and igneous rocks were strongly deformed by syn- and post-accretion processes, which, in places, formed duplex structures. The igneous rocks are basalt/dolerite/gabbro, andesibasalt, trachybasalt and diorite. The diorite yielded a U–Pb age of ca. 500 Ma. The subalkaline volcanic and subvolcanic rocks belong to the tholeiitic series. Based on major oxides three groups of rocks can be distinguished: high-Ti, mid-Ti and low-Ti. The rocks of these three groups are variably enriched in LREE (La_N = 122, 23 and 2 in average, respectively) showing LREE enriched (high-Ti), LREE depleted (mid-Ti) and flat (low-Ti) REE patterns. The high-Ti group shows enrichment in Nb, Th, and Zr compared to the mid-Ti and low-Ti groups. The low-Ti group is special for the Nb troughs in primitive mantle normalized multi-element diagrams, which are typical of supra-subduction settings. The values of εNd are mostly positive for the mid-Ti and low-Ti groups, but negative for the high-Ti group. The geochemical features of the igneous rocks suggest their formation in oceanic (oceanic floor and oceanic island/seamount) and supra-subduction (intra-oceanic arc) settings. In general, the structural position, lithology and deformation styles of Itmurundy sedimentary and igneous rocks and the geochemical features of the igneous rocks all accord well with the models of Ocean Plate Stratigraphy (OPS) and Pacific-type orogeny. Thus, the Itmurundy belt at northern Balkhash represents an Ordovician-Silurian Pacific-type orogenic belt formed at a convergent active margin of the Paleo-Asian Ocean.     

Geochronological and geochemical constraints on the Erguna massif basement,NE China – subduction history of the Mongol–Okhotsk oceanic crust

We present new geochronological and geochemical data for granites and volcanic rocks of the Erguna massif, NE China. These data are integrated with previous findings to better constrain the nature of the massif basement and to provide new insights into the subduction history of Mongol–Okhotsk oceanic crust and its closure. U–Pb dating of zircons from 12 granites previously mapped as Palaeoproterozoic and from three granites reported as Neoproterozoic yield exclusively Phanerozoic ages. These new ages, together with recently reported isotopic dates for the metamorphic and igneous basement rocks, as well as Nd–Hf crustal-residence ages, suggest that it is unlikely that pre-Mesoproterozoic basement exists in the Erguna massif. The geochronological and geochemical results are consistent with a three-stage subduction history of Mongol–Okhotsk oceanic crust beneath the Erguna massif, as follows. (1) The Erguna massif records a transition from Late Devonian A-type magmatism to Carboniferous adakitic magmatism. This indicates that southward subduction of the Mongol–Okhotsk oceanic crust along the northern margin of the Erguna massif began in the Carboniferous. (2) Late Permian–Middle Triassic granitoids in the Erguna massif are distributed along the Mongol–Okhotsk suture zone and coeval magmatic rocks in the Xing’an terrane are scarce, suggesting that they are unlikely to have formed in association with the collision between the North China Craton and the Jiamusi–Mongolia block along the Solonker–Xra Moron–Changchun–Yanji suture zone. Instead, the apparent subduction-related signature of the granites and their proximity to the Mongol–Okhotsk suture zone suggest that they are related to southward subduction of Mongol–Okhotsk oceanic crust. (3) A conspicuous lack of magmatic activity during the Middle Jurassic marks an abrupt shift in magmatic style from Late Triassic–Early Jurassic normal and adakite-like calc-alkaline magmatism (pre-quiescent episode) to Late Jurassic–Early Cretaceous A-type felsic magmatism (post-quiescent episode). Evidently a significant change in geodynamic processes took place during the Middle Jurassic. Late Triassic–Early Jurassic subduction-related signatures and adakitic affinities confirm the existence of subduction during this time. Late Jurassic–Early Cretaceous post-collision magmatism constrains the timing of the final closure of the Mongol–Okhotsk Ocean involving collision between the Jiamusi–Mongolia block and the Siberian Craton to the Middle Jurassic.     

Areas and sources of metasedimentary rocks in the Tukuringra terrane of the Mongolian–Okhotsk mobile belt: Results of Sm–Nd isotope study

The results of Sm–Nd studies of metasedimentary rocks from the Tukuringra terrane, one of the largest units in the structure of the eastern part of the Mongolian–Okhotsk mobile belt, are reported. Metasedimentary rocks of the Algainskaya, Garmakanskaya, and Teploklyuchevskaya formations are characterized by similar model ages t_Nd(DM) = 1.5–1.1 Ga. This shows that the major protoliths of metasedimentary rocks of the terrane are characterized by Mesoproterozoic estimates of the Nd model ages. The results obtained allow us to assume that introduction of terrigenous material into the sedimentary basin mostly occurred from the continental massifs united into the Amur superterrane, since their magmatic and sedimentary complexes are characterized by identical values of the Nd model ages.     

Sr–Nd isotope data of basement rocks from the northernmost argentine Precordillera and its implications for the early Paleozoic evolution of SW Gondwana margin

The Precordillera terrane (Cuyania) in western Argentina is commonly accepted as an exotic fragment derived from Laurentia in the Early Paleozoic. Evidence supporting such an interpretation is manly based on similarities in the sedimentary cover successions and their paleontological content. Little is known about the basement of the Precordillera terrane. Its isotopic characterization is essential to better constrain the present areal distribution of the terrane and it may provide more insight into the pre-rifting evolution of the Precordillera terrane along the Iapetan margin of Laurentia. We present new Sr and Nd isotope data of pre-Late Ordovician meta-igneous rocks from the Río Bonete region in NW Argentina, interpreted as the northernmost extent of the Precordillera. The Nd systematics of the Río Bonete basement rocks including greenschists and metagabbros (εNd₍₄₇₀₎ = +2.14–−0.19; T_DM = 0.99–1.2 Ga), a garnet-amphibolite (εNd₍₄₇₀₎ = −0.53; T_DM = 1.32 Ga) and a quartz-phyllite (εNd₍₄₇₀₎ = −3.83; T_DM = 1.55 Ga), are similar to other pre-Ordovician meta-igneous rocks from Sierra de Umango, Pie de Palo and the Ullum xenoliths, usually interpreted as the basement of the Precordillera terrane. Nd model ages around 1.2 Ga are also typical from the Mesoproterozoic Grenvillian basement of southern North America, currently exposed in the Llano region. In addition, the greenschists and metagabbros show a robust correlation with the Late Neoproterozoic Catoctin volcanics in the central Appalachians. The Sr isotope data (when not disturbed) also supports this novel interpretation and suggests the presence of the Blue Ridge rifting event in Precordillera. According to our interpretation, some lithotypes included within the basement complex of the Río Bonete area belonged to the basement of the Precordillera terrane supporting previous correlation between both regions.     

Geochemical and Sm–Nd isotope–geochemical patterns of metavolcanic rocks,diabase, and metagabbroids on the northeastern flank of the South Mongolian–Khingan orogenic belt

The first results of geochemical and Sm–Nd isotope–geochemical studies of metavolcanic rocks, metagabbroids, and diabase of the Nora-Sukhotino terrane, the least studied part of the South Mongolian–Khingan orogenic belt in the system of the Central Asian orogenic belt are reported. It is established that the basic rocks composing this terrane include varieties comparable with E-MORB, tholeiitic, and calc-alkaline basalt of island arc, calc-alkaline gabbro-diabase, and gabbroids of island arcs. Most likely, these formations should be correlated with metabasalt and associated Late Ordovician gabbro-amphibolite of the Sukdulkin “block” of the South Mongolian–Khingan orogenic belt, which are similar to tholeiite of intraplate island arcs by their geochemical characteristics.     

Sm–Nd systematics of metaultramafic-mafic rocks from the Arroio Grande Ophiolite (Brazil): Insights on the evolution of the South Adamastor paleo-ocean

In this contribution we present new insights on the evolution of the Dom Feliciano Belt, southernmost Mantiqueira Province, integrating new whole-rock Sm–Nd isotopic data for the Arroio Grande Ophiolite (Punta del Este Terrane, Brazil/Uruguay border) with previously published bulk-rock and isotope geochemistry of the South Adamastor paleo-ocean metamafic rocks located in Uruguay (Paso del Dragón Complex, Punta del Este Terrane) and Namibia (Chameis Subterrane, Marmora Terrane, Gariep Belt). For the regional geology, the new data corroborate previous hypothesis and demonstrate the depleted mantle features of the amphibolites and metagabbros of the studied ophiolite. The Arroio Grande Ophiolite rocks are compared with its Uruguayan and Namibian counterparts, demonstrating their isotopic and geochemical similarities and differences, and the back-arc affinity of the South Adamastor paleo-ocean. The MORB-affinity amphibolites from the Arroio Grande Ophiolite-Paso del Dragón Complex are, so far, the most juvenile rocks in the eastern sector of the Dom Feliciano Belt, yielding ε_{Nd(640 ​Ma)} between +7.3 and ​+​9, and high ¹⁴⁷Sm/¹⁴⁴Nd (>0.169) and ¹⁴³Nd/¹⁴⁴Nd_(640 ​Ma) ratios (0.51219–0.51229). The South Adamastor is interpreted in this paper as an internal back-arc ocean, with limited lateral extension, opened at around 750–650 ​Ma as the result of the closure of the older Charrua-Goianide paleo-ocean during the Brasiliano/Pan-African orogenic cycle and final configuration of the West Gondwana paleocontinent.     

Geodynamic evolution of the Eastern Sierras Pampeanas (Central Argentina) based on geochemical, Sm–Nd, Pb–Pb and SHRIMP data

Whole-rock geochemical analyses using major and trace elements in combination with the Sm–Nd and Pb–Pb isotope systems, together with SHRIMP age dating on metasedimentary rocks from the Sierras de Chepes, the Sierras de Córdoba, the Sierra Norte and the San Luis Formation in the Sierra de San Luis, have been carried out to unravel the provenance and the geodynamic history of the Eastern Sierras Pampeanas, Central Argentina. The geochemical and the Sm–Nd data point to a slightly stronger mafic and less-fractionated material in the provenance area of the Sierras de Córdoba when compared to the other units. The T_DM model ages from the Sierras de Chepes (~1.82 Ga) and the Sierra Norte (~1.79 Ga) are significantly older than the data from the Sierras de Córdoba (1.67 Ga). The Pb data are homogeneous for the different units. Only the ²⁰⁸Pb/²⁰⁴Pb ratios of some samples from the Sierras de Córdoba are higher. A late Pampean detrital zircon peak around 520 Ma from the Sierras de Chepes is in accordance with the new data from the San Luis Formation. This is similar to the literature data from the Famatina Belt located to the northwest of the Sierras de Chepes and also fits the detrital zircon peaks in the Mesón group. These maximum depositional ages were also reported from some locations in the Puncoviscana Formation but are absent in the Sierras de Córdoba. An improved model for the development of the Eastern Sierras Pampeanas in the area between the Sierras de Córdoba and the Puncoviscana Formation is provided. This gives new insights into the late Pampean development of the Sierra de San Luis and the complex development of the Eastern Sierras Pampeanas. This new model explains the younger detrital ages in the Puncoviscana Formation compared with the older ages of the Sierras de Córdoba. Another model of the Sierra de San Luis explains the younger depositional ages of the Pringles Metamorphic Complex and the San Luis Formation when compared to the Nogolí Metamorphic Complex and the Conlara Metamorphic Complex. Additionally, the rather fast change of the high-grade metamorphic conditions in the Pringles Metamorphic Complex and the low-grade metamorphic conditions in the San Luis Formation is explained by extension, the ascent of (ultra) mafic material and later folding and erosion.     

The first U–Pb geochronological and geochemical data on Late Vendian and Early Paleozoic acid volcanic rocks of the Mamyn Terrane (Central Asian Fold Belt)

The first results of U–Pb geochronological studies of acid volcanic rocks from the Oktyabrsk Complex of the Mamyn Terrane, which had previously been conventionally attributed to the Late Proterozoic, are reported. It is established that rhyodacite of the Gar’–Dzheltulak volcanic field has Late Vendian age (546 ± 14 Ma) and trachyrhyodacite of the Kosmatinsk field has Late Cambrian age (490 ± 2 Ma). As a whole, the data obtained indicate two stages of acid volcanism on the Mamyn Terrane of the eastern part of the Central Asian Fold Belt covering the boundary between the Paleozoic and Neoproterozoic, as well as the Late Cambrian. Based on the geochemical peculiarities of rocks, it may be assumed that the early stage of volcanism was controlled by subduction, whereas the late stage was governed by riftogenic processes.     

U–Pb zircon,zircon Hf and whole-rock Sm–Nd isotopic constraints on the evolution of Paleoproterozoic rocks in the northern Gawler Craton

U–Pb zircon analyses from a series of orthogneisses sampled in drill core in the northern Gawler Craton provide crystallisation ages at ca 1775–1750 Ma, which is an uncommon age in the Gawler Craton. Metamorphic zircon and monazite give ages of ca 1730–1710 Ma indicating that the igneous protoliths underwent metamorphism during the craton-wide Kimban Orogeny. Isotopic Hf zircon data show that 1780–1750 Ma zircons are somewhat evolved with initial ε_Hf values –4 to +0.9, and model ages of ca 2.3 to 2.2 Ga. Isotopic whole rock Sm–Nd values from most samples have relatively evolved initial ε_Nd values of –3.7 to –1.4. In contrast, a mafic unit from drill hole Middle Bore 1 has a juvenile isotopic signature with initial ε_Hf zircon values of ca +5.2 to +8.2, and initial ε_Nd values of ～+3.5 to +3.8. The presence of 1775–1750 Ma zircon forming magmatic rocks in the northern Gawler Craton provides a possible source for similarly aged detrital zircons in Paleoproterozoic basin systems of the Gawler Craton and adjacent Curnamona Province. Previous provenance studies on these Paleoproterozoic basins have appealed to the Arunta Region of the North Australian Craton to provide 1780–1750 Ma detrital zircons, and isotopically and geochemically similar basin fill. The orthogneisses in the northern Gawler Craton also match the source criteria and display geochemical similarities between coeval magmatism in the Arunta Region of the North Australian Craton, providing further support for paleogeographic reconstructions that link the Gawler Craton and North Australian Craton during the Paleoproterozoic.     

Geochemistry and the Sm–Nd model age of sedimentary rocks from the lower horizon of the cover in the northeastern part of the West Siberian Platform

The pre-Jurassic basement and lower (Jurassic) horizons of the sedimentary cover in Hole Borovaya 6 were studied. Analysis of rare and rare-earth elements shows that Jurassic sedimentary rocks were most likely formed at the expense of erosion and mixing of heterogeneous materials, namely acid sources of the Siberian Platform and Triassic riftogenic basaltoids. The variations of ¹⁴⁷Sm/¹⁴⁴Nd (0.1076–0.1250) and ¹⁴³Nd/¹⁴⁴Nd (0.512202–0.512437), as well as the Sm–Nd model ages of Jurassic sediments (1146–1362 Ma), provide certain evidence for participation of the Mesoproterozoic substrate in the formation of the rocks studied. The Sm–Nd model age of pre-Jurassic rocks (1281 Ma) is Mesoproterozoic as well. The Precambrian crystalline basement of the Siberian Platform is a likely source of these sedimentary rocks.     

The Paleoproterozoic Fedorov–Pana Layered PGE complex of the northeastern Baltic Shield,Arctic Region: New U–Pb (baddeleyite) and Sm–Nd (sulfide) data

For the first time zircons have been extracted from gabbro–norite of a lower layered horizon of the West Pana Massif in the Pt–Pd Kievei deposit of the Fedorov–Pana Layered Complex. Those zircons have been used for U–Pb dating along with Sm–Nd age determination on sulfide minerals. The obtained new isotopic data are a U–Pb zircon age of 2500 ± 4 Ma, while the Sm–Nd (mineral and whole-rock) isochron yielded 2483 ± 86 Ma. These results correspond to the first phase of the Pt–Pd reef complex formation in the Layered Complex. The Pt–Pd reef formation has been dated by U–Pb baddeleyite and zircon analyses in the East Pana Massif to 2464 ± 12 Ma. The 2485–2464 Ma time span corresponds to the second phase of the Pt–Pd reef formation in the Fedorov–Pana ore cluster.     

The first Lu–Hf zircon isotope data for gabbro–diorite–tonalite associations of the Urals

Doklady Earth Sciences - The Lu–Hf isotope systematics of zircon from the gabbro–plagiogranite association (gabbro, diorite, tonalite, and plagiogranite), which is one of the most...     

The Vendian age of granodiorites and plagiogranites of the Tallainskii complex (Baikal–Muya Belt): U–Pb isotope data

This work presents the results of U–Pb isotope dating of zircons from granodiorites and plagiogranites of the Tallainskii gabbro–granodiorite–plagiogranite complex of the Karalon–Mamakan zone of the Baikal–Muya belt, ascribed to the Tallainskii pluton. The age datings obtained for granodiorite of the Eleninskii massif (605 ± 6 Ma) and plagiogranite of the Ust-Berezovo massif (609 ± 6 Ma) are in close agreement within the limits of error. Taking into account previously published data, the emplacement of the Tallainskii complex occurred within the age interval of 615–603 Ma in connection with postcollision extension. The “island arc” geochemical characteristics of granodiorites and plagiogranites can be explained by magmatic differentiation and (or) participation in the formation of a melt source enriched in the suprasubduction component involved in petrogenesis during the preceding Neoproterozoic period.     

U–Pb isotopic age of apatite-bearing carbonatites in the Kursk block,Voronezh crystalline massif (central Russia)

In the central part of the European part of Russia in the southeastern part of the Kursk tectonic block, some deposits and occurrences of apatite genetically related to the alkaline–carbonatite complex have been revealed. The results of U–Pb analysis of titanite provided the first confident age estimate of silicate–carbonate (phoscorite) rocks in the Dubravin alkaline–ultramafic–carbonatite massif: they formed no later than 2080 ±13 Ma, which indicates their crystallization in the pre-Oskol time during the final stage of the Early Paleoproterozoic (post-Kursk time) stabilization phase of the Kursk block of Sarmatia (about 2.3–2.1 Ga).     

The age and geochemistry of volcanic rocks on the eastern flank of the Umlekan–Ogodzha volcanoplutonic belt (Amur region)

⁴⁰Ar/³⁹Ar dating yielded the reliable ages of andesite from the Unerikan complex (102.1 ± 1.4 Ma) and basaltic andesite from the Burunda complex (107.3 ± 2.4 Ma). The established age of volcanism is close to one of the stages of formation of the Khingan–Okhotsk volcanoplutonic belt. The petrography and geochemistry of basic, normal-basic, and normal rocks point to their dual character: They combine features specific for tholeiitic and calc-alkalic rocks. Most likely, these rocks formed in the setting of transform continental margin.     

Contrasting provenance of Late Archean metasedimentary rocks from the Wutai Complex, North China Craton: detrital zircon U–Pb, whole-rock Sm–Nd isotopic, and geochemical data

Detrital zircon U–Pb ages, whole-rock Nd isotopic, and geochemical data of metasedimentary rocks from the Wutai Complex in the Central Zone, North China Craton, have been determined. Compositionally, these rocks are characterized by a narrow variation in SiO₂/Al₂O₃ (2.78–3.96, except sample 2007-1), variable Eu anomalies, spanning a range from significantly negative Eu anomalies to slightly positive anomalies (Eu/Eu* = 0.58–1.12), and positive ε _Nd (t) values (0.1–1.97). The 18 detrital zircons of one sample yielded age populations of 2.53 Ga, 2.60 Ga, and 2.70–2.85 Ga. Geochemical data reveal intermediate source weathering, varying degrees of K-metasomatism in the majority of these metasedimentary rocks, whereas other secondary disturbances seem to be negligible. Detailed analysis in detrital zircon U–Pb geochronology, whole-rock Nd isotope, and geochemistry shows that these metasedimentary rocks are derived from a mixed provenance. The predominant derivation is from the late Archean granitoids and metamorphic volcanics in the Wutai Complex, and there is also input of older continental remnants, except TTG gneisses, from the Hengshan and Fuping Complexes. The sediments were probably deposited in fore-arc or/and intra-arc basins within an arc system.