Episodic crustal growth in the Bundelkhand craton of central India shield: Constraints from petrogenesis of the tonalite–trondhjemite–granodiorite gneisses and K-rich granites of Bundelkhand tectonic zone

Tonalite–trondhjemite–granodiorite gneisses (TTG) and K-rich granites are extensively exposed in the Mesoarchean to Paleoproterozoic Bundelkhand craton of central India. The TTGs rocks are coarse- grained with biotite, plagioclase feldspar, K-feldspar and amphibole as major constituent phases. The major minerals constituting the K-rich granites are K-feldspar, plagioclase feldspar and biotite. They are also medium to coarse grained. Mineral chemical studies show that the amphiboles of TTG are calcic amphibole hastingsite, plagioclase feldspars are mostly of oligoclase composition, K-feldspars are near pure end members and biotites are solid solutions between annite and siderophyllite components. The K-rich granites have biotites of siderophyllite–annite composition similar to those of TTGs, plagioclase feldspars are oligoclase in composition, potassic feldspars have \(\hbox {X}_{\mathrm{K}}\) ranging from 0.97 to 0.99 and are devoid of any amphibole. The tonalite–trondhjemite–granodiorite gneiss samples have high \(\hbox {SiO}_{2}\) (64.17–74.52 wt%), \(\hbox {Na}_{2}\hbox {O}\) (3.11–5.90 wt%), low Mg# (30–47) and HREE contents, with moderate \((\hbox {La/Yb})_{\mathrm{CN}}\) values (14.7–33.50) and Sr/Y ratios (4.85–98.7). These geochemical characteristics suggest formation of the TTG by partial melting of the hydrous basaltic crust at pressures and depths where garnet and amphibole were stable phases in the Paleo-Mesoarchean. The K-rich granite samples show high \(\hbox {SiO}_{2}\) (64.72–76.73 wt%), \(\hbox {K}_{2}\hbox {O}\) (4.31–5.42), low \(\hbox {Na}_{2}\hbox {O}\) (2.75–3.31 wt%), Mg# (24–40) and HREE contents, with moderate to high \((\hbox {La/Yb})_{\mathrm{CN}}\) values (9.26–29.75) and Sr/Y ratios (1.52–24). They differ from their TTG in having elevated concentrations of incompatible elements like K, Zr, Th, and REE. These geochemical features indicate formation of the K-granites by anhydrous partial melting of the Paleo-Mesoarchean TTG or mafic crustal materials in an extensional regime. Combined with previous studies it is interpreted that two stages of continental accretion (at 3.59–3.33 and 3.2–3.0 Ga) and reworking (at 2.5–1.9 Ga) occurred in the Bundelkhand craton from Archaean to Paleoproterozoic.     

Origin of Archean tonalite–trondhjemite–granodiorite (TTG) suites and granites in the Fiskenæsset region,southern West Greenland: Implications for continental growth

Mesoarchean to Neoarchean orthogneisses (2.95–2.79 Ga) in the Fiskenæsset region, southern West Greenland, are composed of an older suite of metamorphosed tonalites, trondhjemites, and granodiorites (TTGs), and a younger suite of high-K granites. The TTGs are characterized by high Al₂O₃ (14.2–18.6 wt.%), Na₂O (3.4–5.13 wt.%), and Sr (205–777 ppm), and low Y (0.7–17.4 ppm) contents. On chondrite- and N-MORB-normalized trace element diagrams, the TTGs have the following geochemical characteristics: (1) highly fractionated REE patterns (La/Yb_cn = 14–664; La/Sm_cn = 4.3–11.0; Gd/Yb_cn = 1.5–19.7); (2) strong positive anomalies of Sr (Sr/Sr* = 1.0–15.9) and Pb (Pb/Pb* = 1.4–34.9); and (3) large negative anomalies of Nb (Nb/Nb* = 0.01–0.34) and Ti (Ti/Ti* = 0.1–0.6). The geochemical characteristics of the TTGs and trace element modeling suggest that they were generated by partial melting of hydrous basalts (amphibolites) at the base of a thickened magmatic arc, leaving a rutile-bearing eclogite residue. Field observations suggest that spatially and temporarily associated tholeiitic basalts (now amphibolites) in the Fiskenæsset region might have been the sources of TTG melts. The high-K granites have steep REE patterns (La/Yb_cn = 3.8–506; La/Sm_cn = 2.7–18.9; Gd/Yb_cn = 0.92–12.1) and display variably negative Eu anomalies (Eu/Eu* = 0.37–0.96) and moderate Sr (84–539 ppm) contents. Four outlier granite samples have variably positive Eu (Eu/Eu* = 1.0–12) anomalies. Given that the granodiorites have higher K₂O/Na₂O than the tonalites and trondhjemites, it is suggested that the granites were derived from partial melting of the granodiorites. It is speculated that the dense eclogitic residues, left after TTG melt extraction, were foundered into the sub-arc mantle, leading to basaltic underplating beneath the lower rust. Melting of the granodiorites in response to the basaltic underplating resulted in the production of high-K granitic melts. Formation of the Fiskenæsset TTGs, the foundering of the eclogitic residues into the mantle, and the emplacement of the high-K granites led to the growth of Archean continental crust in the Fiskenæsset region.     

Early Paleozoic monzodiorite–granodiorite association in the northeastern flank of the South Mongolia–Khingan orogenic belt (Nora–Sukhotinsky Terrane): Age and tectonic setting

The paper presents the results of U–Pb geochronological and geochemical studies of the rocks of the monzodiorite–granodiorite association in the northeastern flank of the South Mongolia–Khingan orogenic belt, which composes a tectonic block among the provisionally Lower Paleozoic volcanosedimentary complexes of the Nora–Sukhotinsky Terrane. It is shown that the studied rocks have similar petrographic features (with the presence of transitional varieties) and form common trends in the petrographic diagrams. This suggests that they are members of a single magmatic association. The geochemical features of the monzodiorites, quartz monzodiorites, and granodiorites, in particular their enrichment in large ion lithophile elements (LILE) and depletion in some HFSE, indicate their similarity with island-arc magmatic rocks. The presence of monzonites and quartz monzonites in the studied monzodiorite–granodiorite association along with high K, Rb, Th, and Pb concentrations gives reasons to believe that it formed in active continental margin or ensialic island-arc environments. The granodiorites of the monzodiorite–granodiorite associations of the Nora–Sukhotinsky Terrane are dated at 440 ± 10 Ma and may be considered as a fragment of the early Silurian active continental margin or ensialic mature island arc in the structure of the South Mongolia–Khingan orogenic belt.     

The Cambrian–Ordovician diorite–granodiorite–granite association of the Mamyn Terrane (Central Asian Fold Belt): U–Pb geochronological and geochemical data

Doklady Earth Sciences - New results of U–Pb geochronological and geochemical studies of rocks that form two structurally different massifs in the Mamyn Terrane are presented here. It has...     

The Sr,Nd, and Hf isotopic geochemistry of rocks of the gabbro–diorite–tonalite association from the Eastern Segment of the Middle Urals as an indicator of the age of the continental crust in this area

According to isotopic analysis of rocks of the Reft gabbro–diorite–tonalite complex (Middle Urals), gabbro and related diorite and dikes and vein-shaped bodies of plagiogranitoids, crosscutting gabbro, are similar to the depleted mantle substance in ε_Nd(T) = 8.6–9.7 and ε_Hf(T) = 15.9–17.9. Their model Hf ages are correlated with the time of crystallization. Here, the tonalites and quartz diorites constituting most of the Reft massif are characterized by lower values: ε_Nd(T) = 3.7–6.0, ε_Hf(T) = 11.1–12.7, and T _DM values significantly exceeding the age datings. This is evidence that Neoproterozoic crustal rocks were a source of parental magma for these rocks. The primary ⁸⁷Sr/⁸⁶Sr ratio in rocks of both groups is highly variable (0.70348–0.70495). The data obtained allow us to reach the conclusion that the Reft gabbro–diorite–tonalite complex was formed as a result of nearly synchronous processes occurring in the crust and the mantle within a limited area.     

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...     

On the problem of variability in the chemical composition of mud–volcanic waters: Evidence from the Yuzhno-Sakhalinsk mud volcano

The results of hydrogeochemical observations on the Yuzhno-Sakhalinsk mud volcano in 2010–2014 are considered. The chemical analysis of samples of mud–volcanic waters was carried out at various analytical centers, which is similar to the common situation where hydrochemical data for a volcano are obtained by different researchers. It is shown that the chemical composition of the mud–volcanic waters is relatively stable in time and space (for different gryphons of the volcano). This allows us to determine the characteristic range of hydrogeochemical indicators. For each year of observations, the coefficients of variation for the concentrations of Na, Mg, Ca, K, and HCO₃ mostly range from 10 to 30%. However, the concentrations analyzed in individual samples may differ significantly from each other. These natural variations are a likely source of errors in the interpretation of hydrochemical data. In addition, it is necessary to account for the specifics of mud–volcanic waters as an object of analytical chemical investigations.     

Rhyolite–granite association in the Central Taimyr zone: evidence of accretionary-collisional events in the Neoproterozoic

The Central Taimyr accretionary belt includes two granite-metamorphic terranes: Faddey and Mamont-Shrenk, which include the oldest igneous formations of the Taimyr folded area in the Arctic framing of the Siberian craton—granitoids and granite-gneisses with U–Pb zircon ages of 900–830 Ma. The [FeO*/(FeO* + MgO)]-enriched granitoids of these terranes are products of highly fractionated I-type magmas. This paper presents results of new petrographic, geochemical, geochronological, and paleomagnetic investigations of acid rocks from a volcanic-plutonic association (in the region of the Leningradskaya River) in the Faddey terrane in the northeastern Taimyr area. These rocks formed during the final stage of continent–island arc accretion and collision that occurred at approximately 870–820 Ma. We established that the studied rocks belong to a long granitoid belt extending from Mamont-Shrenk to Faddey terrane, where all the igneous bodies are deformed and oriented uniformly. The paleomagnetic pole we calculated differs significantly from the apparent polar-wander path interval of corresponding age for Siberia. The 33.8°±5.4° angular distance between the poles indicates that the formation of this volcanic-plutonic association took place at a significant distance from the Taimyr margin of the Siberian paleocontinent.     

The Late Neoproterozoic rift-related metarhyolite–basalt association of the Glushikha trough (Yenisei Ridge): petrogeochemical composition,age, and formation conditions

New data are presented on the petrogeochemical composition, age, and formation conditions of the Late Neoproterozoic metarhyolite–basalt association of the Glushikha trough (Yenisei Ridge). The association is localized within the subaerial and shallow-water terrigenous-carbonate sediments of the Orlovka Group, which overlies Proterozoic rocks with unconformity. The felsic volcanics are essentially potassic and enriched in Rb, U, Th, and Fe. They show a weakly fractionated REE pattern with a prominent negative Eu anomaly. The basalts and picrite basalts have higher contents of Ti, Fe, P, HFSE, REE, U, Th, Ba, and Sr, and their spidergrams show no Nb or Ta depletion with respect to Th and LREE. These rocks have the petrochemical parameters of intraplate magmatic associations in continental rift zones. New geochronological data (SHRIMP II) on single zircon grains from the felsite porphyry of the metarhyolite–basalt association (717 ± 15 Ma) indicate Late Neoproterozoic volcanism in the Yenisei part of the Central block of the Trans-Angara region. According to Sm–Nd isotopic data, the rhyolites originate from Paleoproterozoic crust (T_Nd(DM) = 1757 Ma; T_Nd(DM-2st) = 1651 Ma; ∑ _Nd(T) = ? 2.7). The Orlovka volcanosedimentary rocks are rift-related, as evidenced by the following facts: (1) localization of the volcanosedimentary rocks in a narrow fault-line trough; (2) bimodal rhyolite-basaltic composition of the volcanics; and (3) petrology and geochemistry of the picrite basalts and basalts, typical of intraplate environments. The studies show that Late Neoproterozoic rifting and intraplate plume magmatism took place not only in the Tatarka–Ishimba fault zone but also in the Yenisei fault zone of the Yenisei Ridge.     

Isotope Lu–Hf composition of detrital zircon from paragneisses of the Sharyzhalgai uplift: evidence for the Paleoproterozoic crustal growth

We present results of study of the trace-element and Lu–Hf isotope compositions of zircons from Paleoproterozoic high-grade metasedimentary rocks (paragneisses) of the southwestern margin of the Siberian craton (Irkut terrane of the Sharyzhalgai uplift). Metamorphic zircons are represented by rims and multifaceted crystals dated at ~ 1.85 Ga. They are depleted in either LREE or HREE as a result of subsolidus recrystallization and/or synchronous formation with REE-concentrating garnet or monazite. In contrast to the metamorphic zircons, the detrital cores are enriched in HREE and have high (Lu/Gd)_n ratios, which is typical of igneous zircon. The weak positive correlation between ¹⁷⁶Lu/¹⁷⁷Hf and ¹⁷⁶Hf/¹⁷⁷Hf in the zircon cores evidences that their Hf isotope composition evolved through radioactive decay in Hf = the closed system. Therefore, the isotope parameters of these zircons can give an insight into the provenance of metasedimentary rocks. The Paleoproterozoic detrital zircon cores from paragneisses, dated at ~ 2.3–2.4 and 2.0–1.95 Ga, are characterized by a wide range of ε_Hf values (from + 9.8 to –3.3) and model age T ^C 2.8–2.0 Ga. The provenance of these detrital zircons included both rocks with juvenile isotope Hf parameters and rocks resulted from the recycling of the Archean crust with a varying contribution of juvenile material. Zircons with high positive ε_Hf values were derived from the juvenile Paleoproterozoic crustal sources, whereas the lower ε_Hf and higher T ^C values for zircons suggest the contribution of the Archean crustal source to the formation of their magmatic precursors. Thus, at the Paleoproterozoic stage of evolution of the southwestern margin of the Siberian craton, both crustal recycling and crustal growth through the contribution of juvenile material took place. On the southwestern margin of the Siberian craton, detrital zircons with ages of ~ 2.3–2.4 and 1.95–2.0 Ga are widespread in Paleoproterozoic paragneisses of the Irkut and Angara–Kan terranes and in terrigenous rocks of the Urik–Iya graben, which argues for their common and, most likely, proximal provenances. In the time of metamorphism (1.88–1.85 Ga), the age of Paleoproterozoic detrital zircons (2.4–2.0 Ga), and their Lu–Hf isotope composition (ε_Hf values ranging from positive to negative values) the paragneisses of the southwestern margin of the Siberian craton are similar to the metasedimentary rocks of the Paleoproterozoic orogenic belts of the North China Craton. In the above two regions, the sources of detrital zircons formed by both the reworking of the Archean crust and the contribution of juvenile material, which is evidence for the crustal growth in the period 2.4–2.0 Ga.     

Influence of emission from copper–nickel smelters on the chemical composition of lake water: Acidification forecast

The influence of the emission of sulfur dioxide and solid substances from Pechenganickel and Severonickel copper–nickel combines (Murmansk oblast) on the chemical compositions of lake water and the development of acidification is analyzed. The temporal dynamics of ∼100 lakes, studied in 1990, 1995, 2000, 2005, 2009, and the response of the chemical composition of the lake water to the impact of acid-forming substances depending on the load level (the distance of combines), geologically controlled sensitivity of catchment areas of the lakes studied to acid deposition, and the lake areas is discussed. The likely further changes in sulfate concentration and pH value in the lake water under the scenarios of increase/decrease of sulfur dioxide emissions from smelter are estimated.

     

Effects of errors and biases on the scaling of earthquake spatial pattern: application to the 2004 Sumatra–Andaman sequence

This study discusses the scaling properties of the spatial distribution of the December 26, 2004, Sumatra aftershocks. We estimate the spatial correlation dimension D ₂ of the epicentral distribution of aftershocks recorded by a local network operated by Geological Survey of India. We estimate the value of D ₂ for five blocks in the source area by using generalized correlation integral approach. We assess its bias due to finite data points, scaling range, effects of location errors, and boundary effects theoretically and apply it to real data sets. The correlation dimension was computed both for real as well as synthetic data sets that include randomly generated point sets obtained using uniform distributions and mimicking the number of events and outlines of the effective areas filled with epicenters. On comparing the results from the real data and random point sets from simulations, we found the lower limit of bias in D ₂ estimates from limited data sets to be 0.26. Thus, the spatial variation in correlation dimensions among different blocks using local data sets cannot be directly compared unless the influence of bias in the real aftershock data set is taken into account. They cannot also be used to infer the geometry of the faults. We also discuss the results in order to add constraints on the use of synthetic data and of different approaches for uncertainty analysis on spatial variation of D ₂. A difference in D ₂ values, rather than their absolute values, among small blocks is of interest to local data sets, which are correlated with their seismic b values. Taking into account the possible errors and biases, the average D ₂ values vary from 1.05 to 1.57 in the Andaman–Nicobar region. The relative change in D ₂ values can be interpreted in terms of clustering and diffuse seismic activity associated with the low and high D ₂ values, respectively. Overall, a relatively high D ₂ and low b value is consistent with high-magnitude, diffuse activity in space in the source region of the 2004 Sumatra earthquake.

     

Character of spatiotemporal variations in the chemical composition of lake water under the influence of emission from copper–nickel plants: Prediction of acidification

In this paper, we analyze the influence of variations in the emission of sulfur dioxide and solid substances by the Pechenganikel and Severonikel copper–nickel plants in Murmansk oblast on the chemical composition of lake water and development of acidification. The dynamics of ~100 lakes examined in 1990, 1995, 2000, 2005, and 2009 and response of the chemical composition of the lake waters on the impact of acidifying substances was explored depending on the magnitude of load (distance from the plants), geologically controlled vulnerability of the lake catchments to acid precipitation, and the size of the lakes. Possible further changes in the sulfate concentration and pH values of lake waters were estimated for scenarios assuming an increase or a decrease in sulfur dioxide emission from the plants. It was shown that, in the zone of maximum and high load, a 20% change in sulfur dioxide emission will result in a mean change in sulfate concentration of ±8 μeq/L (which is comparable with the regional background) and a change in pH value of ±0.1 in acid-sensitive lakes and will have almost no effect on these parameters in lakes insensitive to acid precipitation.     

Variations in the Pb isotope composition in polyformational magmatic rocks of the Ketkap–Yuna igneous province of the Aldan Shield: Evidence for mantle–crust interaction

The Pb isotope composition of polyformational Mesozoic igneous rocks of the Ketkap–Yuna igneous province (KYIP) and lower crustal metamorphic rocks of the Batomga granite–greenstone area (the complex of the KYIP basement) of the Aldan Shield was studied for the first time. Based on the data obtained, several types of material sources participating in petrogenetic processes were distinguished. The mantle source identified as PREMA is registered in most of the igneous formations and predominates in mafic alkaline rocks. According to the isotope characteristics, the upper crustal source corresponds to a source of the “Orogen” type by the model of “plumbotectonics” or to the average composition of the continental crust by the Stacey–Kramers model. The lower crust is the third material source; however, the type of lower crustal protolith involved in the igneous process is still not defined, which makes difficult to estimate its role in the petrogenetic processes.     

U–Pb dating,geochemistry, and Sr–Nd isotopic composition of a granodiorite porphyry from the Jiadanggen Cu–(Mo) deposit in the Eastern Kunlun metallogenic belt,Qinghai Province,China

The Jiadanggen porphyry Cu–(Mo) deposit is newly discovered and located in the Eastern Kunlun metallogenic belt of Qinghai Province, China. Here, we present a detailed study of the petrogenesis, magma source, and tectonic setting of the mineralization causative granodiorite porphyry. The new data indicate that the granodiorite porphyry is characterized by high SiO₂ (68.21–70.41 wt.%) and Al₂O₃, relatively high K₂O, low Na₂O, and low MgO and CaO concentrations, and is high-K calc-alkaline and peraluminous. The granodiorite porphyry has low Mg^# (38–46) values that are indicative of no interaction between the magmas and the mantle. The samples that we have examined have low Nb/Ta (9.17–10.3) and Rb/Sr (0.28–0.39) ratios, which are indicative of crustal-derived magmas. Source region discrimination diagrams indicate that the magmas that formed the granodiorite porphyry were derived from melting of a mixed amphibolite source in the lower crust. The samples have I_Sr values of 0.70954–0.70979, ε_Nd(t) values of − 8.3 to − 7.9, and t_2DM ages ranging from 1644 to 1677 Ma. These indicate that the magmas that formed this intrusion were generated by melting of Mesoproterozoic lower crustal material. Higher K(Rb) contents of the samples indicate that the magma source is high potassium basaltic material in the lower crust, which could be derived from an enriched mantle source. LA-ICP-MS zircon U–Pb dating of the granodiorite porphyry yields a late Indosinian age (concordia age of 227 ± 1 Ma; MSWD = 0.31), which is close to the molybdenite Re–Os isochron age (227.2 ± 1.9 Ma), indicating further the close relationship between the granodiorite porphyry and the Cu–(Mo) mineralization. These samples are LREE and LILE (e.g., Rb, K, Ba, and Sr) enriched, and HFSE (e.g., Nb, Ta, P, and Ti) depleted, especially in P and Ti, similar to the characteristics of volcanic arc magmas. This intrusion most likely formed during the later stage of Indosinian deep subduction of oceanic slab. This was associated with underplating of mantle-derived magmas, which provided heat for crustal melting. Similar to the Jiadanggen granodiorite porphyry, Indosinian hypabyssal intermediate-felsic intrusive rocks, formed under subduction tectonism or a transitional regime from subduction to syn-collision, make up the most important targets for porphyry Cu(Mo) deposits in the Eastern Kunlun metallogenic belt.     

Petrogenesis of Dashenshan I-type granodiorite: implications for Triassic crust–mantle interaction,South China

Triassic granodiorites in South China (SC) provide an opportunity to examine crust–mantle interactions that may have been caused by a mantle plume. Here we present a combined study of chronological, geochemical, and Sr–Nd–Hf isotopic compositions for Dashenshan granodiorites. These are high-K, calc-alkaline, I-type granodiorites that yield a U–Pb zircon age of 211 ± 3 Ma. They are metaluminous to weakly peraluminous (A/CNK < 1.1), with 3.04–3.89 wt.% Na₂O and 3.24–3.86 wt.% K₂O, and Na₂O/K₂O ratio ranging from 0.79 to 1.11. These granodiorites contain 67.7–72.6 wt.% SiO₂ but show moderate Mg^# values (44.2–57.8) and variable contents of Ni (3.6–29.9 ppm) and Cr (7.6–53.5 ppm). They exhibit light rare earth element (REE) enrichment and flat, heavy REE patterns with negative Eu anomalies (Eu/Eu* = 0.52–0.87). They also display strongly negative Ba, Sr, Nb, Ta, P, and Ti anomalies and positive Rb, Th, K, and Pb anomalies. Dashenshan granodiorites have high whole-rock initial ⁸⁷Sr/⁸⁶Sr ratios (0.7121–0.7172), negative ε_Nd (t) values (–8.8 to –6.8), and negative zircon ε_Hf (t) values (–6.6 to –3.3). These results suggest that the Dashenshan granodiorites were generated by a mixing between crustal melt and mantle-derived magma in an extensional setting. We conclude that generation of the Dashenshan pluton may reflect an interaction between a mantle plume and the overlying SC crust.     

Copper-gold endoskarns and high-Mg monzodiorite–tonalite intrusions at Mt. Shea,Kalgoorlie, Australia: implications for the origin of gold–pyrite–tennantite mineralization in the Golden Mile

Five Cu–Au epidote skarns are associated with the Mt. Shea intrusive complex, located in the 2.7–2.6 Ga Eastern Goldfields Province of the Archean Yilgarn craton, in greenstones bounded by the Boulder Lefroy and Golden Mile strike-slip faults, which control the Golden Mile (1,435 t Au) at Kalgoorlie and smaller “orogenic” gold deposits at Kambalda. The Cu–Au deposits studied are oxidized endoskarns replacing faulted and fractured quartz monzodiorite–granodiorite. The orebodies are up to 140 m long and 40 m thick. Typical grades are 0.5% Cu and 0.3 g/t Au although parts are richer in gold (1.5–4.5 g/t). At the Hannan South mine, the skarns consist of epidote, calcite, chlorite, magnetite (5–15%), and minor quartz, muscovite, and microcline. Gangue and magnetite are in equilibrium contact with pyrite and chalcopyrite. The As–Co–Ni-bearing pyrite contains inclusions of hematite, gold, and electrum and is intergrown with cobaltite and Cu–Pb–Bi sulfides. At the Shea prospect, massive, net-textured, and breccia skarns are composed of multistage epidote, actinolite, albite, magnetite (5%), and minor biotite, calcite, and quartz. Gangue and magnetite are in equilibrium with Co–Ni pyrite and chalcopyrite. Mineral-pair thermometry, mass-balance calculations, and stable-isotope data (pyrite δ³⁴S_CDT = 2.5‰, calcite δ¹³C_PDB = −5.3‰, and δ¹⁸O_SMOW = 12.9‰) indicate that the Cu–Au skarns formed at 500 ± 50°C by intense Ca–Fe–CO₂–S metasomatism from fluids marked by an igneous isotope signature. The Mt. Shea stock–dike–sill complex postdates the regional D1 folding and metamorphism and the main phase of D2 strike-slip faulting. The suite is calc-akaline and comprises hornblende–plagioclase monzodiorite, quartz monzodiorite, granodiorite, and quartz–plagioclase tonalite porphyry. The intrusions display a wide range in silica content (53–73 wt% SiO₂), in ratio (0.37–0.89), and in ratio (0.02–0.31). Chromium (62–345 ppm), Ni (23–158), Sr (311–1361 ppm), and Ba (250–2,581 ppm) contents are high, Sr/Y ratios are high (24–278, mostly >50), and the rare earth element patterns are fractionated . These features and a negative niobium anomaly relative to the normal mid-ocean ridge basalt indicate that the suite formed by hornblende fractionation from a subduction-related monzodiorite magma sourced from metasomatized peridotite in the upper mantle. The magnesian composition of many intrusions was enhanced due to hornblende crystallization under oxidizing hydrous conditions and during the subsequent destruction of igneous magnetite by subsolidus actinolite–albite alteration. At the Shea prospect, main-stage Cu–Au epidote skarn is cut by biotite–albite–dolomite schist and by red biotite–albite replacement bands. Post-skarn alteration includes 20-m-thick zones of sericite–chlorite–ankerite schist confined to two D3 reverse faults. The schists are mineralized with magnetite + pyrite + chalcopyrite (up to 0.62% Cu, 1.6 g/t Au) and are linked to skarn formation by shared Ca–Fe–CO₂ metasomatism. Red sericitic alteration, marked by magnetite + hematite + pyrite, occurs in fractured porphyry. The biotite/sericite alteration and oxidized ore assemblages at the Shea prospect are mineralogically identical to magnetite–hematite-bearing gold lodes at Kambalda and in the Golden Mile. Published fluid inclusion data suggest that a “high-pressure”, oxidized magmatic fluid (2–9 wt% NaCl equivalent, , 200–400 MPa) was responsible for gold mineralization in structural sites of the Boulder Lefroy and Golden Mile faults. The sericite–alkerite lodes in the Golden Mile share the assemblages pyrite + tennantite + chalcopyrite and bornite + pyrite, and accessory high-sulfidation enargite with late-stage sericitic alteration zones developed above porphyry copper deposits.     

Cretaceous sedimentary–volcanogenic complexes of the Kamchatka Isthmus: Structure,composition and geodynamic formation conditions

New data on the chemical and rare-element composition and age of the rocks referred earlier to the Iruney suite of the Kamchatka Isthmus are received. In the recent structure these rocks compose the structural–strata complexes of the nappe-folded Lesnovsky Rise. Radiolarian analysis data substantiate that the deposits belonging to the Ening series and the middle and upper parts of the Iruney suite were formed in a single sedimentation basin in the Campanian time. The discovery of a new occurrence of Prunobrachidae representatives on the Kamchatka Peninsula allows us to draw wide interregional correlations and reconstruct the sedimentation conditions. The studied volcanites relate to different igneous series and were formed in geodynamic conditions of the marginal sea and the volcanic arc. The igneous rocks of the Ening stratum are similar to the N-MOR and OI basalts that were formed within the marginal sea (Iruney Marginal Sea) basin. The Upper Cretaceous formations of the eastern slope of the Sredinny Range were formed within the volcanic rise with the island-arc type of volcanism. The younger Eocene igneous rocks of the neo-autochthon (granites and granodiorites) and the volcanic rocks of the Kinkil suite mark a new orogenic stage of development of the Kamchatka margin.     

Determining the composition of C–H–O liquids following high-pressure and high-temperature diamond-trap experiments

Here, we present the first analytical technique (the quartz tube system technique—QTS) to directly analyze H₂O and CO₂ contents in liquids following high-pressure, high-temperature experiments in capsules containing mantle minerals and a diamond layer serving as a fluid/melt trap. In this technique, the capsule is frozen prior to opening; the diamond trap is cut out of the capsule and placed inside a N₂-filled quartz tube. The diamond trap is heated up to 900 °C to release the gases to an Infrared Gas Analyzer, which determines the CO₂ and H₂O contents. Three sets of experiments containing SiO₂ and CaCO₃ powders were performed at 6 GPa and 1,000 °C in order to calibrate and validate the technique. These experiments demonstrated that when samples are prepared in a N₂ environment, CO₂ and H₂O can be directly measured with an accuracy and precision of 2–3 and 3–4 %, respectively. The QTS technique (for H₂O and CO₂ determination) together with the cryogenic technique (total dissolved solids content) can be applied to diamond-trap capsules following HP–HT experiments in order to provide direct and complete liquid compositions coexisting with mantle material. The principal advantage of the QTS technique of direct analysis of volatile content in liquids over the indirect approach of mass balance calculations is the possibility of studying carbonated and hydrous liquid compositions in equilibrium with mantle material regardless of chemistry and pressure–temperature experimental conditions.