U–Pb geochronology of the Southern Black Forest Batholith (Central Variscan Belt): timing of exhumation and granite emplacement

Some granites, granitoid dykes and volcanic rocks of the Southern Black Forest were dated by U–Pb techniques using zircon and monazite. An effusive rhyolite, which is interbedded in upper Visean sedimentary sequences of the Badenweiler-Lenzkirch zone, was dated at 340 ±2?Ma. This weakly metamorphic zone of supracrustal rocks borders high-grade gneiss terrains in the north and the south, which are intruded by a series of granitoid intrusions: the strongly sheared Schlächtenhaus granite is dated by monazite at 334±2?Ma and the hypothesis of a Devonian emplacement is therefore discarded. The emplacement of all other granites, crosscutting dykes and of an ignimbrite were all within analytical uncertainty: St. Blasien granite 333±2?Ma; Bärhalde granite 332±3?Ma; Albtal granite 334±3?Ma; and a porphyry dyke at Präg 332+2/-4?Ma. Deformation and thrusting of the basement units near the Badenweiler-Lenzkirch zone occurred after the emplacement of the Schlächtenhaus granite, but before the intrusion of the other granitoids, and may therefore be constrained to the time period unresolved between 334±2 and 333±2?Ma. The ignimbritic rhyolite of Scharfenstein was deposited in a caldera 333±3?Ma ago. This age coincides within error limits with published U–Pb monazite and Rb–Sr small slab ages of mimatitic gneisses, Ar–Ar hornblende ages of metabasites and Sm–Nd mineral isochron ages of eclogitic rocks in the underlying basement. This suggests that exhumation and cooling of this basement unit must have been active at rates of approximately 20?km and a few 100°C per million years. The silicic melts are interpreted to be of hybrid crust/mantle origin and their formation was most likely linked to these exhumation tectonics. A phase of mantle upwelling and heat advection into the crust is proposed to be the reason for this short-episodic magmatic pulse.     

Paleozoic accretionary orogenesis in the eastern Beishan orogen: Constraints from zircon U–Pb and 40Ar/39Ar geochronology

The continental growth mechanism of the Altaids in Central Asia is still in controversy between models of continuous subduction–accretion versus punctuated accretion by closure of multiple oceanic basins. The Beishan orogenic belt, located in the southern Altaids, is a natural laboratory to address this controversy. Key questions that are heavily debated are: the closure time and subduction polarity of former oceans, the emplacement time of ophiolites, and the styles of accretion and collision. This paper reports new structural data, U- Pb and Ar–Ar ages from the eastern Beishan orogen that provide information on the accretion process and tectonic affiliation of various terranes. Our geochronological and structural results show that the younging direction of accretion was northwards and the subduction zone dipped southwards under the northern margin of the Shuangyingshan micro-continent. This long-lived and continuous accretion process formed the Hanshan accretionary prism. Our field investigations show that the emplacement of the Xiaohuangshan ophiolite was controlled by oceanic crust subduction beneath the forearc accretionary prism of the Shuangyingshan–Mazongshan composite arc to the south. Moreover, we address the age and terrane affiliation of lithologies in the eastern Beishan orogen through detrital zircon geochronology of meta-sedimentary rocks. We provide new information on the ages, subduction polarities, and affiliation of constituent structural units, as well as a new model of tectonic evolution of the eastern Beishan orogen. The accretionary processes and crustal growth of Central Asia were the result of multiple sequences of accretion and collision of manifold terranes.     

The 40Ar/39Ar and Rb–Sr chronology of the Precambrian Aksu blueschists in western China

Three metapelite samples from the Aksu blueschist terrane, Xinjiang, China, were dated by the ⁴⁰Ar/³⁹Ar method on separated phengite grains, obtaining plateau ages in the range of 741−757 Ma. In contrast, the measured Rb and Sr isotope data for the three samples yielded isochron ages ranging from 630 Ma to 900 Ma, suggesting large heterogeneity in the blueschist protolith and suppression of diffusional exchange owing to the low-temperature metamorphic conditions. Because the protolith of Aksu blueschist is composed of oceanic materials that formed ⁴⁰Ar-free phengite during HP and UHP metamorphism and the apparent ⁴⁰Ar/³⁹Ar plateaus ages in this study are similar to previous K–Ar and Rb–Sr ages, the existence of excess argon in these rocks is considered to be insignificant. As a result, the ⁴⁰Ar/³⁹Ar plateau ages in this study (ca. 750 Ma) likely represent the approximate time for peak metamorphism, given the low peak metamorphic temperatures for the Aksu blueschist terrane (300−400 °C). This strongly implies that modern style, cold subduction tectonics operated along the margin of the Aksu terrane no later than 750 Ma, in Neoproterozoic time.     

Zircon U–Pb and biotite 40Ar/39Ar geochronology from the Anzan emerald deposit in Zambia

The Kafubu Emerald Area in Zambia is an important producer of gemstone-quality emeralds. The country rocks include carbonatization altered rock and emerald-hosting biotite chlorite schist from the Anzan emerald deposit in the Kafubu area, Zambia. The technique of LA-MC-ICP-MS is used to perform chronology measurements of the country rock and emerald-hosting rock which belong to Muva Supergroup, yielding zircon U-Pb concordia ages of 1966 ± 12 Ma in carbonatization altered rock and 1853 ± 58 Ma and 1344 ± 30 Ma in biotite chlorite schist. Meanwhile, dating of biotite chlorite schist using the biotite ⁴⁰Ar–³⁹Ar method has obtained the plateau age of t = 578.3 ± 2.6 Ma, isochron age of 577.5 ± 3.0 Ma and reverse isochron age of 577.4 ± 3.0 Ma. Thus, we have redefined the age of Muva Supergroup in the Copperbelt Province in Zambia to be older than or equal to 1966 ± 12 Ma, and found that the ore bodies in the Anzan emerald deposit underwent three phases of metamorphism at 1853 ± 58 Ma, 1344 Ma ± 30 and 578.3 ± 2.6 Ma and finally accomplished the emerald mineralization. The age of the Anzan emerald deposit is earlier than the Kagem (452.1 ± 16 Ma) and the Kamakanga emerald deposits (447 ± 8.6 Ma).     

Pre-metamorphic 40Ar/39Ar and U–Pb ages in HP metagranitoids from the Hercynian belt (France)

In most orogenic belts, the age of HP metamorphism and subsequent exhumation events still remain open to debate since geochronology can yield results which appear to conflict with the closure temperature concept [Dodson, M.H., 1973. Contrib. Mineral. Petrol. 40, 259–274], and because the behaviour of daughter radiogenic isotopes under HP to UHP conditions is poorly constrained. To obtain new data on isotope migration under high-pressure conditions, two undeformed HP metagranites with partially preserved magmatic assemblages from the French Variscan belt were investigated using the ⁴⁰Ar/³⁹Ar laser probe and U–Pb ion probe methods. In both cases, ⁴⁰Ar/³⁹Ar biotite and U–Pb zircon ages are consistent and could be related to the emplacement of pre-orogenic granites, despite petrological evidence of a strong metamorphic overprint during the Variscan orogeny. Temperatures experienced by the granites during subduction and exhumation events were more than 400 °C above that normally estimated for argon retention in biotite, but failed to cause significant resetting of the mica ⁴⁰Ar/³⁹Ar chronometer. Only a weak intragrain redistribution of argon is evidenced with the laser probe up to the contact with metamorphic garnet fringing biotite. By contrast, a complete resetting of biotite ages occurs in gneisses enclosing the metagranites. These results suggest that, in these dry undeformed HP metagranites, the thermally activated diffusion was relatively ineffective and that recrystallisation is the main process which controlled isotopic exchanges of Ar and Pb. It is likely that the absence of pervasive deformation and fluid circulation has also exercised some control on the preservation of pre-metamorphic isotopic signature in the studied rocks. The possible influence of several other parameters is also discussed. This example reveals that recovering thermochronological information in high-pressure metamorphic rocks is not straightforward and that great caution must be paid in the use of ages for the reconstruction of P–T–t paths.     

40Ar/39Ar and U–Pb SHRIMP dating of Aptian tuff cones in the Aisén Basin,Central Patagonian Cordillera

Surtseyan tuff cones of the Baño Nuevo Volcanic Complex erupted in shallow marine water during the waning stage of the Aisén Basin, the northern part of the Austral Basin of the Central Patagonian Cordillera. This volcanic complex was emplaced within the Hauterivian to early Aptian Apeleg Formation, the youngest sedimentary unit of this basin, whilst the sediments were still wet. Three new Ar/Ar dates (amphibole) and one U–Pb SHRIMP date (zircon) from this complex yielded concordant early Aptian ages of 122–121 Ma. These data agree with the contact relationships between the Apeleg Formation and the tuff cones. These dates also agree with those of early Aptian ammonites collected from the Apeleg Formation 100 km south of the study area, which represent the youngest fossils identified in this unit. Aptian to Albian subaerial volcanic rocks of the Divisadero Group, paraconformably overlie the Apeleg Formation. The emplacement of the Baño Nuevo Volcanic Complex pre-dates the disappearance of the Aisén Basin.     

Zircon U–Pb geochronology,whole-rock geochemical,and Sr–Nd–Pb isotopic constraints on the timing and origin of Permian and Triassic mafic dykes from eastern North China Craton

Acta Geochimica - This work reports an important episode of extensional, mafic magmatism that impacted the North China Craton (NCC) during the Permo-Triassic and influenced the evolution of this...     

Genesis of the Dadonggou Pb–Zn deposit in Kelan basin,Altay, NW China: Constraints from zircon U–Pb and biotite 40Ar/39Ar geochronological data

The genesis of polymetallic deposits in southern Altay, NW China has been disputed between a syngenetic seafloor hydrothermal process and an epigenetic orogenic-type mineralization. The Dadonggou Pb–Zn deposit occurs as NW-trending veins in the Devonian Kangbutiebao Formation volcanic-sedimentary sequence in the Kelan basin, southern Altay. A set of integrated zircon U–Pb and biotite ⁴⁰Ar/³⁹Ar geochronological data were applied to constrain the forming ages of the ores and their country rocks. Three samples of host volcanic rocks yielded weighted mean ²⁰⁶Pb/²³⁸U ages of 397.1 ± 4.5 Ma, 391.7 ± 3.6 Ma and 391.1 ± 4.2 Ma, respectively, indicating that the Kangbutiebao Formation was deposited in a Devonian back-arc basin. Two biotite samples separated from the Pb–Zn-containing quartz veins yielded ⁴⁰Ar/³⁹Ar plateau ages of 205.9 ± 2.1 Ma and 204.3 ± 2.2 Ma, respectively, which represent the age of the Pb–Zn mineralization that is attributed to the closure of the Kelan back-arc basin and the Late Triassic orogeny. Combining the available geological and geochronological data, this contribution outlines the successive evolution from the development of a Devonian back-arc basin to the Late Triassic post-subduction orogeny, and proposes that the Dadonggou Pb–Zn deposit is an epigenetic orogenic-type deposit placed in the Late Triassic orogeny.     

The alteration, mineralogy and geochronology (SHRIMP U–Pb and 40Ar/39Ar) of copper-bearing Anjerd skarn, north of the Shayvar Mountain, NW Iran

A Cu-bearing skarn zone occurs north of the Shayvar Mountain in northwestern Iran. Skarn-type metasomatic alteration and mineralization occur along the contact between Upper Cretaceous impure carbonates and a Miocene Cu-bearing granitic stock. Both endoskarn and exoskarn developed in the rocks. Exoskarn is the principal skarn zone and is enclosed by a skarnoid–hornfelsic zone. Skarn formation occured during stages: (1) prograde, (2) middle stage and (3) late stage. In the prograde stage, there were two main processes: (a) metamorphic–bimetasomatic and (b) prograde metasomatic. The metamorphic process began immediately after intrusion of the pluton into the enclosing impure carbonates. The prograde metasomatic stage commenced with segregation and evolution of a fluid phase in the pluton and movement into fractures and micro-fractures in the skarnoid–hornfelsic rocks developed in a metamorphic zone. The introduction of considerable amounts of Fe, Si and Mg led to the development of voluminous medium- to coarse-grained anhydrous calc-silicates. During the middle stage, the previously formed skarn zones were affected by intense multiple hydrofracturing in the Cu-bearing stock. In addition to Fe, Si and Mg, substantial amounts of Cu, Pb and Zn, along with volatile components such as H₂S and CO₂ were added to the skarn system. Consequently, substantial amounts of hydrous calc-silicates (epidote, tremolite–actinolite), sulfides (pyrite, chalcopyrite and molybdenite), oxides (magnetite, hematite) and carbonates (calcite) replaced the anhydrous calc-silicates. The retrograde stage was synchronous with the incursion of relatively low-temperature, more oxidized fluids into skarn system, resulting in partial alteration of the early-formed calc-silicates and development of a series of very fine-grained aggregates of chlorite, clay, hematite and calcite. Zircon grains from the endoskarn zone provide constraints on the timing of solidification of the granite stock (9.91 ± 0.31 Ma) that caused mineralization in the Anjerd area. One sample of primary hornblende from the monzogranitic Shayvar batholith has an ⁴⁰Ar/³⁹Ar age of 26.54 ± 0.65 Ma and indicates that intrusion of the Miocene stock and associated Cu skarn formation occurred a considerable time after intrusion of the batholith.     

Stratigraphy of the Okhotsk–Chukotka Belt in the Headwaters of the Malyi Anyui River (the Vicinity of Kupol Deposit): U–Pb and 40Ar/39Ar Age Data

Doklady Earth Sciences - U–Pb and 40Ar/39Ar age data obtained for volcanic rocks of the Okhotsk–Chukotka Belt in the headwaters of the Malyi Anyui River (the vicinity of Kupol deposit)...     

40Ar–39Ar dating, whole-rock and Sr–Nd–Pb isotope geochemistry of post-collisional Eocene volcanic rocks in the southern part of the Eastern Pontides (NE Turkey): implications for magma evolution in extension-induced origin

The Eocene volcano-sedimentary units in the southern part of the Eastern Pontides (NE Turkey) are confined within a narrow zone of east–west trending, semi-isolated basins in Bayburt, Gümü?hane, ?iran and Alucra areas. The volcanic rocks in these areas are mainly basalt and andesite through dacite, with a dominant calc-alkaline to rare tholeiitic tendency. ⁴⁰Ar–³⁹Ar dating of these volcanic rocks places them between 37.7 ± 0.2 and 44.5 ± 0.2 Ma (Middle Eocene). Differences in the major and trace element variations can be explained by the fractionation of clinopyroxene ± magnetite in basaltic rocks and that of hornblende + plagioclase ± magnetite ± apatite in andesitic rocks. Primitive mantle-normalized multi-element variations exhibit enrichment of large-ion lithophile elements and to a lesser extent, of light rare earth elements, as well as depletion of high field strength elements, thus revealing that volcanic rocks evolved from a parental magma derived from an enriched mantle source. Chondrite-normalized rare earth element patterns of the aforementioned volcanic rocks resemble each other and are spoon-shaped with low-to-medium enrichment (La_N/Lu_N = 2–14), indicating similar spinel lherzolitic mantle source(s). Sr, Nd and Pb isotopic systematics imply that the volcanic rocks are derived from a subduction-modified subcontinental lithospheric mantle. Furthermore, post-collisional thickened continental crust, lithospheric delamination and a subduction-imposed thermal structure are very important in generating Tertiary magma(s). The predominantly calc-alkaline nature of Eocene volcanic rocks is associated with increasing geodynamic regime-extension, whereas tholeiitic volcanism results from local variations in the stress regime of the ongoing extension and the thermal structure, as well as the thickness of the crust and the mantle-crust source regions. Based on volcanic variety and distribution, as well as on petrological data, Tertiary magmatic activity in Eastern Pontides is closely related to post-collisional thinning of the young lithosphere, which, in turn, is caused by extension and lithospheric delamination after collisional events between the Tauride–Anatolide Platform and the Eurasian Plate.     

Refinement of the time-space evolution of the giant Mio-Pliocene Río Blanco-Los Bronces porphyry Cu–Mo cluster, Central Chile: new U–Pb (SHRIMP II) and Re–Os geochronology and 40Ar/39Ar thermochronology data

Representing one of the largest known (estimated >5 Gt at 1 % Cu and 0.02 % Mo) porphyry system, the Río Blanco-Los Bronces deposit incorporates at least five hypabyssal intrusive and hydrothermal centres, extending for about 5 km from the Río Blanco and Los Bronces mines in the north, through the Don Luis mine, to the Sur Sur mine, La Americana and Los Sulfatos in the south. The new geochronology data, which now include data on different molybdenite vein types, confirm the U–Pb ages of the pre-mineralisation intrusions but slightly increase their age range from 8.8 to 8.2 Ma. The distinct magmatic pulses of the mineralisation-associated porphyritic intrusives (Late Porphyries) indicate an age interval instead of the previously suggested individual ages: the quartz monzonite porphyry ranges from 7.7 to 6.1 Ma (Sur Sur 5.74?±?0.13 Ma), the feldspar porphyry shows an interval from 5.8 to 5.2 Ma and the Don Luis porphyry from 5.2 to 5.0 Ma. The new Re–Os data on distinct molybdenite vein types confirm the protracted history of Cu(–Mo) mineralisation, inferred previously. The vein development occurred at least from 5.94 to 4.50 Ma, indicating a time-span of 1.5 Ma for the hydrothermal activity. Hydrothermal minerals dated by the ⁴⁰Ar/³⁹Ar method are generally too young to record the age of early, high-temperature mineralisation. The majority of the ⁴⁰Ar/³⁹Ar data in the Río Blanco porphyry cluster record reheating by either the youngest member of the Late Porphyry suite or the post-mineralisation dacite or rhyolite plug formations at around 4.9–4.7 Ma.     

Exact timing of granulite metamorphism in the Namche-Barwa,eastern Himalayan syntaxis: new constrains from SIMS U–Pb zircon age

Zircon grains separated from 2 granulites from the eastern Himalaya were investigated by Raman spectroscopy, cathodoluminescence imaging, and secondary ion mass spectrometry. These grains have a thin homogeneous rim and an oscillatory inner zone domain with or without a relict inherited core. Garnet, kyanite, and rutile inclusions were identified within only the rim domain of zircon grains, indicating that the rim had formed during peak granulite-facies metamorphism. U–Pb zircon data record three distinct age populations: 1,805 Ma (for the inherited core), ca. 500 Ma (oscillatory inner zone), as well as 24–25 Ma and ca. 18 Ma (for the metamorphic rim). These new precision ages suggest that the peak metamorphic age for the HP granulite is at ca. 24–25 Ma, and subsequent amphibolite-facies retrograde metamorphism occurred at ca. 18 Ma.     

REE and isotope (Sr,S, and Pb) geochemistry to constrain the genesis and timing of the F–(Ba–Pb–Zn) ores of the Zaghouan District (NE Tunisia)

The F–(Ba–Pb–Zn) ore deposits of the Zaghouan District, located in NE Tunisia, occur as open space fillings or stratabound orebodies, hosted in Jurassic, Cretaceous and Tertiary layers. The chondrite-normalized rare earth element (REE) patterns may be split into three groups: (i) “Normal marine” patterns characterizing the wallrock carbonates; (ii) light REE (LREE) enriched (slide-shaped) patterns with respect to heavy REE (HREE), with small negative Ce and Eu anomalies, characteristic of the early ore stages; (iii) Bell-shaped REE patterns displaying LREE depletion, as well as weak negative Ce and Eu anomalies, characterizing residual fluids of subsequent stages. The ⁸⁷Sr/⁸⁶Sr ratios (0.707654–0.708127 ± 8), show that the Sr of the epigenetic carbonates (dolomite, calcite) and ore minerals (fluorite, celestite) are more radiogenic than those of the country (Triassic, Jurassic, Cretaceous, lower Miocene) sedimentary rocks. The uniformity of this ratio, throughout the District, provides evidence for the isotopic homogeneity and, consequently, the identity of the source of the mineralizing fluids. This signature strongly suggests that the radiogenic Sr is carried by Upper Paleozoic basinal fluids.The δ³⁴S values of barite, associated to mineralizations, are close to those of the Triassic sea water (17‰). The δ³⁴S values of sulfide minerals range from − 13.6‰ to + 11.4‰, suggesting two sulfur-reduced end members (BSR/TSR) with a dominant BSR process.Taking account of the homogeneity in the Pb-isotope composition of galenas (18.833–18.954 ± 0.001, 15.679–15.700 ± 0.001 and 38.690–38.880 ± 0.004, for the ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios respectively), a single upper crustal source for base-metals is accepted. The Late Paleozoic basement seems to be the more plausible source for F–Pb–Zn concentrated in the deposits. The genesis of the Zaghouan District ore deposits is considered as the result of the Zaghouan Fault reactivation during the Late Miocene period.     

Petrogenesis of adamellites from eastern Shandong Province: geochronological,geochemical, and Sr–Nd–Pb isotopic evidence

Geochronology, geochemistry, and whole-rock Sr–Nd–Pb isotopes were studied on a suite of Mesozoic adamellites from eastern China to characterize their ages and petrogenesis. Sensitive high-resolution ion microprobe U–Pb zircon analyses were done, yielding consistent ages of 123.2 ± 1.8 to 122.1 ± 2.1 Ma for the samples. These rocks belong to the alkaline magma series in terms of K₂O + Na₂O contents (8.45–9.58 wt.%) and to the shoshonitic series based on their high K₂O contents (5.23–5.79 wt.%). The adamellites are further characterized by high light rare earth element contents [(La/Yb)_N = 14.96–45.99]; negative Eu anomalies (δEu = 0.46–0.75); positive anomalies in Rb, Th, Pb, and U; and negative anomalies in Sr, Ba, and high field-strength elements (i.e. Nb, Ta, P, and Ti). In addition, all of the adamellites in this study display relatively low radiogenic Sr [(⁸⁷Sr/⁸⁶Sr)_i = 0.7081–0.7089] and negative ?_Nd(t) values from –16.70 to –17.80. These results suggest that the adamellites were derived from low-degree partial melting of an enriched lithospheric mantle below the North China Craton (NCC). The parent magmas likely experienced fractional crystallization of potassium feldspar, plagioclase and Fe–Ti oxides (e.g. rutile, ilmenite, and titanite), apatite, and zircon during the ascent of alkaline rocks without crustal contamination.     

U–Pb dating, Hf-isotope characteristics and trace-REE-patterns of zircons from Medet porphyry copper deposit, Bulgaria: implications for timing, duration and sources of ore-bearing magmatism

Precise U–Pb geochronology, Hf isotope compositions and trace element distributions in zircons are combined in the present study to define the timing and sources of the magmatism forming the Medet porphyry copper deposit, Bulgaria. ID-TIMS U–Pb-zircon dating demonstrates that ore-bearing magmatism extended for less than 1.12 Ma. As inferred from the field relationships, it started with the intrusion of a quartz-monzodiorite at 90.59?±?0.29 Ma followed by granodiorite porphyries at 90.47?±?0.30 and 90.27?±?0.60 Ma and by crosscutting aplite dykes at 90.12?±?0.36 Ma. These units were overprinted by potassic alteration and host economic copper-(Mo–Au) mineralization. The main magmatic–hydrothermal activity ceased after that, and a later quartz-granodiorite porphyry dyke, dated at 89.26?±?0.32 Ma, only contains an uneconomic quartz–pyrite mineralization. Assimilation of Lower Paleozoic rocks with a mantle to mantle–crust signature is characteristic of the fertile magma in the Medet deposit, as defined by positive ?-Hf values of the inherited zircons. The positive Ce-anomalies and the higher Eu/Eu* ratios of the zircons in the mineralized Cretaceous rocks of Medet deposit argue for crystallization from a generally more oxidized magma compared to the later quartz-granodiorite porphyry dyke. A change in paleostress conditions occurred during the intrusion of the Medet pluton and its dykes. The initial stage reveals E–W extension associated with N–S compression, whereas the younger granodiorite dyke was emplaced during subsequent N–S extension. The large-scale switch of the extensional stress regime during the mineralization was favourable for ore deposition by channelling the fluids and increasing the effective permeability.     

Isotope (U–Pb,Sm–Nd,Rb–Sr) geochronology of alkaline basic plutons of the Kuznetsk Alatau

On the northeastern slope of the Kuznetsk Alatau, small differentiated alkaline basic intrusive massifs form an isometric area ~ 100 km across. They are composed of subalkalic and alkali gabbroids, basic and ultrabasic foidolites, nepheline and alkali syenites, and carbonatites. Results of complex (U–Pb, Sm–Nd, and Rb–Sr) isotope dating suggest that alkaline basic magmatism developed at two stages, in the Middle Cambrian–Early Ordovician (~ 510–480 Ma) and in the Early–Middle Devonian (~ 410–385 Ma). Finding of accessory zircons (age 1.3–2.0 Ga) in alkaline rocks suggests that the ascent of mantle plume was accompanied by the melting of fragments of Proterozoic mature continental crust composing the basement of the Caledonian orogen of the Kuznetsk Alatau. Probably, parental Cambrian–Ordovician alkaline mafic melts initiated metasomatism and lithosphere erosion. During the next melting of lithosphere substrate in ~ 100 Myr, this caused the generation of magmas of similar composition with inherited isotope parameters (ε_Nd(T) ≈ + 4.8 to + 5.7, T_Nd(DM) ≈ 0.8–0.9 Ga) pointing to the similar nature of their matter sources in the moderately depleted mantle.     

The Tumannoe Gold–Antimony Occurrence (East Sayan,Russia): Mineralogy,Fluid Inclusions,S and O Isotopes,and U–Pb and 40Ar/39Ar Age

Geology of Ore Deposits - The article discusses the features of the composition, age, and genesis of gold–antimony mineralization of the East Sayan based on the example of the largest...     

SHRIMP U–Pb and Ar–Ar geochronology of major porphyry and skarn Cu deposits in the Balkhash Metallogenic Belt,Central Asia,and geological implications

The Balkhash Metallogenic Belt (BMB) in Kazakhstan, Central Asia, with the occurrence of the super-large Kounrad and Aktogai, the large Borly porphyry Cu–Mo deposits, and the large Sayak skarn polymetallic ore-field, is one of the central regions of the Paleozoic Central Asian metallogenic domain and orogenic belt. In this study, newly obtained SHRIMP zircon U–Pb ages of nine samples and ⁴⁰Ar/³⁹Ar ages of six mineral samples (inclding hornblende, biotite and K-feldspar) give more detailed constraints on the timing of the granitic intrusions and their metallogeny. Porphyritic monzonite granite and tonalite porphyry from the Kounrad deposit yield U–Pb zircon SHRIMP ages of 327.3 ± 2.1 Ma and 308.7 ± 2.2 Ma, respectively. Quartz diorite and porphyritic granodiorite from the Aktogai deposit yield U–Pb SHRIMP ages of 335.7 ± 1.3 Ma and 327.5 ± 1.9 Ma, respectively. Porphyritic granodiorite and granodiorite from the Borly deposit yield U–Pb SHRIMP ages of 316.3 ± 0.8 Ma and 305 ± 3 Ma, respectively. Diorite, granodiorite, and monzonite from the Sayak ore-field yield U–Pb SHRIMP ages of 335 ± 2 Ma, 308 ± 10 Ma, and 297 ± 3 Ma, respectively. Hornblende, biotite, and K-feldspar from the Aktogai deposit yield ⁴⁰Ar/³⁹Ar cooling ages of 310.6 Ma, 271.5 Ma, and 274.9 Ma, respectively. Hornblende, biotite, and K-feldspar from the Sayak ore-field yield ⁴⁰Ar/³⁹Ar cooling ages of 287.3 ± 2.8 Ma, 307.9 ± 1.8 Ma, and 249.8 ± 1.6 Ma, respectively. The new ages constrain the timing of Late Paleozoic felsic magmatism to ∼336 to ∼297 Ma. Skarn mineralization in the Sayak ore-field formed at ∼335 and ∼308 Ma. Porphyry Cu–Mo mineralization in the Kounrad deposit and the Aktogai deposit formed at ∼327 Ma, and in the Borly deposit at ∼316 Ma. The Late Paleozoic regional cooling in the temperature range of ∼600 °C to ∼150 °C occurred from ∼307 to ∼257 Ma.