Tourmalines of the Velence Granite Formation and the surrounding contact slate, Velence Mountains, Hungary

Three distinct paragenetic and compositional types of tourmaline were described from the Velence Granite and the surrounding contact slate. Rare, pitch-black, disseminated tourmaline I (intragranitic tourmaline) occurs in granite, pegmatite, and aplite; very rare, black to greenish-gray, euhedral tourmaline II (miarolitic tourmaline) occurs in miarolitic cavities of the pegmatites; abundant, black to gray, brown to yellow or even colorless, acicular tourmaline III (metasomatic tourmaline) occurs in the contact slate and its quartz-tourmaline veins. Tourmaline from a variety of environments exhibits considerable variation in composition, which is controlled by the nature of the host rock and the formation processes. However, in similar geologic situations, the composition of tourmaline can be rather uniform, even between relatively distant localities. Tourmaline I is represented by an Al-deficient, Fe3+-bearing schorl, which crystallized in a closed melt-aqueous fluid system. Tourmaline II is a schorl-elbaite mixed crystal, which precipitated from Li- and F-enriched solutions in the cavities of pegmatites. Tourmaline III shows an oscillatory zoning; its composition corresponds to schorl, dravite, and foitite species. It formed from metasomatizing fluids derived from the granite. This is the most abundant tourmaline type, which can be found in the contact slate around the granite.

Geology, physical-chemical and geodynamic conditions for the formation of Sokolovsk and Krasnokamensk granitoid massifs (South Ural)

The article describes the geological structure of the Sokolovsk and Krasnokamensk massifs located in the central part of the Western subzone of the Chelyabinsk-Adamovka zone of the Southern Urals. They are of Lower Carboniferous age and break through the volcanogenic-sedimentary deposits of the Krasnokamensk (D3kr) and Bulatovo (S1-D1bl) strata. It was found that these intrusions belong to the gabbro-syenite complex and are composed of gabbroids (phase I) and syenites, quartz monzonites, less often monzodiorites (phase II). The rocks of the second phase predominate (90–95%). Gabbros belong to the normal alkaline series of the sodium series and are close to tholeiitic mafic rocks, the formation of which is associated with riftogenic structures; syenites correspond to moderately alkaline series with K-Na type of alkalinity. It has been proved that in terms of their petrographic, petrochemical, geochemical, and metallogenic features (content of TiO2, K2O, Na2O, Rb, Sr, distribution of REE, the presence of skarn-magnetic mineralization), the rocks of the massifs under consideration undoubtedly belong to the gabbro-granite formation. Crystallization of the Sokolovsk and Krasnokamensk intrusions occurred at a temperature of 880–930 °С in the mesoabyssal zone at a depth of about 7–8 km (P = 2.2–2.4 kbar). At the postmagmatic stage, the transformation parameters of the initially igneous rocks were, respectively, T = 730–770 °C, P = 4.0–4.2 kbar. The fact that these massifs belong to the gabbro-granite formation makes it possible to include them, together with Bolshakovsk, Klyuchevsky, Kurtmaksky and Kambulatovo, into the Chelyabinsk-Adamovka segment of the South Ural Early Carboniferous rift system.

Tonalite-trondjemite-granodiorite formation of the Archaean. Special features of composition and conditions of formation, Ukrainian Shield as an example

Tonalite-trondjemite-granodiorite formation (TTG) produces the main volume of acidic rocks of the continental crust. Similar rocks are never met later. Therefore the problems of their production are directly connected with the problem of the crust and mantle formation. The structure of the Archean TTG formation of granite-gneiss area of the Bug megablock and granite-grrenstone area of the Middle Dnieper megablock (MDMB) has been considered. Similar and different features have been found. The analysis of these data resulted in a conclusion that within the MDMB, West Periazovian and Khashchevate-Zavalie block of the Middle Bug area the events of formation of the Archean granite-greenstone area were similar, however these three blocks of the Ukrainian Shield demonstrate different levels of erosion damage reflected in PT-conditions of metamorphic transformations. The rocks of TTG formation are a part of complex structured stratum appeared as a result of impregnation (migmatization) by quartz-albite melt of the primary crust and/or of more ancient strata of predominantly basic composition. In the middle-lower crust a partial replacement of the primary crust occurred and in the upper one — the deposition of new portions of the melt on the earlier ones, piercement of granite masses and migmatization of volcanogenic stratum. During the Archean these events happened repeatedly, that resulted in partial replacement of the primary crust with plagiogranites. Modern notions have been considered on the processes of producing of TTG granite formation. It has been shown that according to thermal model distribution of temperatures in the crust does not cross the line of basalt water solidus. That is why the appearance of granite melts could not be the result of submergence to big depths (ultrametamorphism). Chronological and genetic relation with mantle melting, of which komatiites and spilites of green-stone structures were crystallized, assumed convective flows in the mantle. To explain the formation of tonalite and trondjemite melt a model of two-leveled crystallization differentiation of ultrabasic melt has been used. However appearance of primary basalt replacement in such a scale and assimilation of green-stone roots by granite melt are possible only in case of interaction of mantle fluids with the rocks of primary crust. An assumption has been made that the composition of some part of these fluids could be close to composition of granite (trondjemite). According to the author’s opinion such assumption confirms a hypothesis of V. Griffin and N. Pirson about formation of crystalline mantle on the border between the Archean and Proterozoic.

Fracture Electric Field: A Synthetic Model for Seismogenic Process and its Relationship with Preseismic Electric Anomalies and Earthquakes

Unobservability of the seismogenic process in a causative fault that makes earthquake (EQ) prediction difficult. Although the relationship between the preseismic electric anomaly (PSEA) and the mainshock indicates that both the PSEA and EQ may originate from same course proceeding in the seismogenic zone, as evidenced by experiments on stressed granite, geological interpretation of those observations, and experiments was limited by the traditional granite formation theory. Based on new information from studies of granite genesis and geotransects, we present a synthetic model, the fracture electric field (FEF), to elucidate the seismogenic process on a causative fault and its logical linkage with the PSEA and EQ. The model is constrained with various data from the 1975 Haicheng EQ and verified by survey data from an FEF monitor station constructed in 2012 in Guangzhou, China. The main conclusions are as follows:(1) An uneven or undulant fault-plane is the prerequisite for stress-accumulation in the locality of the plane to form a seismogenic zone;(2) The position of the continental seismic layer corresponds to that of the crustal granite layer, suggesting that the seismogenic process of any causative fault in continents may produce the PSEA;(3) A normal FEF exists in a causative fault and can be measured beyond the preseismic situation. Thus, it is possible to detect the seismogenic process of a fracture through monitoring the variation of its FEF when the fracture enters a preseismic situation.

History of the formation of the early Carboniferous gabbro-granite formation, Southern and Middle Urals

The article presents new data on the geology and petrogeochemistry of the Magnitogorsk, Nepljuevsk and Kanzafarov rock complexes. Their belonging to the gabbro-granite formation has been proved. These data give opportunity to combine the South Ural and Middle Ural segments of the Early Carboniferous subduction rift into a single submeridional structure. Its formation took place at the Devonian island arc rear basin. The arc was overthrusted on the western edge of the East Ural Rise during the collision stage of the Southern Urals development. The Cu-Mo specialization of granitoids of the Magnitogorsk and Nepljuevsk complexes has been established.