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This investigation illustrates the use of major and trace elements to evaluate the petrogenetic evolution of the Late Jurassic Russian Peak Plutonic Complex in the Klamath Mountains Province, northern California, U.S.A. The two principal plutons in the complex consist of quartz diorite and granodiorite, both of which were most likely derived by partial melting of amphibolitic oceanic crustal sources and ultimately emplaced at a shallow level of ~10 km (Ptotal ~ 3 kbar). The major-element compositional variations in quartz diorite are consistent with crystallization of plagioclase (45 %) and amphibole (69 %) and resorption of clinopyroxene (-14 %). Major-element variations in granodiorite could have resulted from crystallization of plagioclase (60 %), amphibole (26 %), and biotite (14 %). Trace elements in whole-rocks and amphibole record different degrees of fractional crystallization, whole-rocks reflecting differentiation on a plutonic scale, and amphibole crystals reflecting differentiation on the scale of an individual sample. Quartz diorite experienced 10% fractional crystallization for the suite as a whole and 45% for individual samples; in contrast, granodiorite experienced 40% crystallization for the suite and 80% for individual samples. For both quartz diorite and granodiorite, comparisons of whole-rock REE patterns with those for melts calculated to be in equilibrium with amphibole demonstrate that the whole-rock REE compositions represent a combination of crystals and melts from evolving magmas, rather than melts alone. [ABSTRACT FROM AUTHOR]

The Padrť Stock is a small (~5 km²) intrusion located near the SE margin of the Teplá-Barrandian Unit, Bohemian Massif, several kilometers away from the NW periphery of the Central Bohemian Plutonic Complex. On outcrops, which are all located close to the contact of the stock with Neoproterozoic sedimentary rocks, two types of granitoids were detected, fine- to medium-grained hornblende-biotite Padrť granodiorite, and, along its SW margin, fine- to medium-grained partly porphyritic biotite Teslíny leucogranite. The U-Pb zircon dating of the more voluminous Padrť granodiorite by laser ablation ICP-MS yielded a magmatic age of 342.8 ± 1.1 Ma, which is slightly lower than are the published age data for the nearby Blatná suite granitoids of the plutonic complex. The Re-Os dating of molybdenite occurring in quartz veins within a quartzite lens in close exocontact yielded ages of 337.2 ± 2.4 Ma and 339.8 ± 2.5 Ma (two samples). The data indicate that the formation of molybdenite postdated that of the magmatic rock. This is in agreement with relatively low-temperature deposition of quartz related to formation of the molybdenite, as indicated by the fluid inclusions (280 to 300 °C). [ABSTRACT FROM AUTHOR]

Internal texture and contents of trace elements Al, B, Ba, Be, Cr, Fe, Ge, Li, Mn, Nb, P, Pb, Rb, Sn, Sr and Ti in quartz from the granite, graphic and core zone of the Vĕžná I pegmatite (SW Moravia, Czech Republic) were studied using panchromatic cathodoluminescence (CL) and laser-ablation ICP-MS (LA-ICP-MS), respectively. Quartz from all textural zones of the pegmatite is homogeneous and exhibit no CL. Aluminum contents increase from the granite zone to the quartz core in range 52 - 252 ppm, while the Ti contents increase from the granite to the graphic zone (26 - 34 ppm → 35 - 46 ppm), and subsequently decrease to the core (→ 15 - 31 ppm). Boron, Ba, Be, Cr, Ge, Fe, Mn, Nb, Pb, Rb, Sn and Sr contents reach their maximum in the pegmatite core; distribution of Li and P is heterogeneous. In general, the chemical composition of quartz from Vežná I pegmatite is well comparable with published data from the primitive (barren) pegmatites in Norway and beryl-columbite pegmatites in Borborema, Brazil. [ABSTRACT FROM AUTHOR]

A small and isolated hydrothermal vein-type Sb deposit is hosted by a lamprophyre dike which penetrated Neoproterozoic to early Cambrian volcanosedimentary successions near Chříč in the Teplá-Barrandian Unit, Czech Republic. Hydrothermal minerals were formed in several consecutive mineralization stages, separated by long pauses in hydrothermal fluid flow. Early Stage I is characterized by the formation of carbonates of dolomite-ankerite series (Carb I) and arsenopyrite with an imprecise Re-Os age of ~570 to 510 Ma. Stage I was followed by tectonic movements and brecciation. The second mineralization stage (Stage II) is characterized by the precipitation of quartz (Qtz I) and Sb minerals (predominantly stibnite) while the third stage (Stage III) is marked by the presence of carbonates of dolomite-ankerite series (Carb II) and quartz (Qtz II) along with Cu, Zn, Pb, Ag and Fe sulfides. Lead isotope data of galena indicate a Variscan age of Stages II-III. These stages were followed by precipitation of another generation of carbonate of dolomite-ankerite series (Carb III, Stage IV), quartz (Qtz III, Stage V) and formation of Sb supergene minerals. The earlier reported occurrence of gold was not confirmed in the studied rock samples but three types of gold particles of variable fineness, with one of them indicating a local origin, were found in the heavy mineral concentrate from a local creek. Elevated Au concentrations were found in arsenopyrite and pyrite. The ore-forming hydrothermal fluid of the mineralization stage III was of H2O-CO2 type with minor CH4 admixture, medium salinity, and temperatures in the range of 258-350 °C with an observed temperature decrease from Stage II to Stage V. Oxygen isotope data of Carb II correspond to high d18Ofluid values (~ +7.5 = VSMOW) with a decrease in the fluid d18O to later stages. An important part of the carbonate carbon was derived from decomposition of organic matter or its high-temperature reaction with hydrothermal fluid. Considering the wide variation in d34S values of sulfides and elevated Sb contents in the TBU black shales, we anticipate that the origin of the Chříč mineralization is closely associated with a metal and carbon-sulfur remobilization from the TBU volcanosedimentary successions in response to Cadomian and Variscan tectonothermal events. [ABSTRACT FROM AUTHOR]

New field, petrographic, geochemical and geochronological data from the Togtokhinshil Complex (western margin of the Lake Zone, Central Asian Orogenic Belt) reveal the presence of two separate Early Palaeozoic magmatic pulses: Mid-Ordovician and Late Devonian. The Mid-Ordovician (c. 460 Ma) magmatism produced various types of mafic plutonic rocks (gabbro-diorite suite) emplaced into the volcanosedimentary sequence of the Baatar Fm. Gabbros to gabbrodiorites have metaluminous and mostly low to normal-K calc-alkaline or possibly tholeiitic character. The majorand trace-element as well as Nd isotopic signatures suggest its magmatic-arc geotectonic setting and imply the derivation either exclusively from the mantle or in part from the juvenile mafic crust. The Late Devonian (c. 376 Ma) granite suite intruded the rocks of both the gabbro-diorite suite and the Baatar Fm. Granites are subaluminous and have a high-K calc-alkaline to shoshonitic character. Their magmatic arc-like geochemical signature is interpreted as inherited from the recycled arc-related crustal source. The granite suite seems a product of extensive mantle heat-induced crustal anatexis. The Depleted Mantle Nd model ages (c. 0.75 Ga) indicate derivation of the magmatic rocks of the both suites from relatively juvenile, and geochemically immature, sources. These results provide a clear evidence of the Mid-Ordovician arc-related magmatism in the western part of the Lake Zone. They thus prolong the assumed period of magmatic-arc activity and constrain onset of accretionary processes in this part of the Central Asian Orogenic Belt. The gabbro-diorite suite represents either part of a long-lived magmatic-arc or, more likely, a member of multiple island-arc system along the western margin of the Lake Zone. Newly described Late Devonian magmatism in the Togtokhinshil Complex provides further evidence of tectono-thermal event that was widespread in the Central Asian Orogenic Belt. The geodynamic cause for this event remains uncertain, but effects of lithospheric thinning and/or asthenospheric mantle upwelling are considered the most likely. [ABSTRACT FROM AUTHOR]

At Vítkov, sparse molybdenite occurs within tungsten mineralization hosted by topaz greisen in orthogneiss in the envelope of the Variscan Krkonoše-Jizera granite Pluton (northern Bohemian Massif). Mineralogical study showed that sulfide mineralization started with precipitation of arsenopyrite followed by molybdenite, tungstenite, transitional Mo- and W-dominated disulfides and concluded by pyrite. Textural relationships between molybdenite and tungstenite imply that tungstenite was formed during several stages related to molybdenite bending and fracturing. Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) analyses of Re-poor (< 0.3 ppm) molybdenite showed extreme concentrations of W (up to 26 558 ppm) accompanied by Ag, As, Bi, Pb, Se, Te and other metals. Electron microprobe analyses of inclusions-free molybdenite confirmed the abundance of W (~0.5 wt. %) and tungstenite showed ~4 wt. % Mo, indicating a substitution of Mo4+ for W4+. Stability and phase relationships between molybdenite and tungstenite and locally identified transitional Mo- and W-dominated disulfidic phases suggest that tungstenite crystallization was triggered by a decrease in fO2 below WO2-WO3 buffer that followed after molybdenite precipitation. Tungstenite zoning and sharp tungstenite-molybdenite contacts indicate disequilibrium during their formation. [ABSTRACT FROM AUTHOR]

Pyroxenites occur as rare, but important, mantle xenoliths within Cenozoic volcanic rocks of the Central European Vol¬canic Province (CEVP). We report the petrography, geothermobarometry, mineral chemistry as well as clinopyroxene trace-element and Sr-Nd isotopic compositions of six pyroxenite xenoliths hosted by Tertiary-Quaternary volcanic rocks from Kozákov (NE Bohemia), Dobkovičky and Kuzov (Ohře/Eger Rift), and Lutynia (SW Poland). Three Kozákov xenoliths record a complex nature and evolution. As suggested by contrasting estimated temperatures (596-663°C and 1008-1067°C) and textures, olivine clinopyroxenite and one websterite were likely derived from different depths and may represent crystallization products of transient melts. Another websterite contains symplectite pseudomorphs after garnet which originated by exsolution from highly aluminous clinopyroxene, and the garnet breakdown was associated with melt introduction. This websterite P-T conditions (17.3 to 21.4 kbar and 1080-1200°C) correspond to derivation from depths of 55-69 km. The composition of websterite from Dobkovičky suggests its origin as a cumulate from melt derived from a highly depleted mantle source with a composition similar to Depleted MORB Mantle (DMM). The posi¬tion and petrological significance of websterite from Kuzov remains unclear because of a lack of data from associated peridotites. At Lutynia, cryptic metasomatism of peridotites by a CO2-bearing alkaline melt was described previously, and the composition of melt calculated to be in equilibrium with Lutynia websterite clinopyroxene is very similar to that in equilibrium with metasomatized amphibole-bearing peridotite. Therefore, the Lutynia websterite may represent a cumulate from percolating melt that metasomatized the lithospheric mantle in this area. [ABSTRACT FROM AUTHOR]