Search results for "Biotite"
showing 10 items of 25 documents
The effect of microscale pore structure on matrix diffusion—a site-specific study on tonalite
1997
Abstract The matrix diffusion of non-sorbing tracers was studied in rocks from the Syyry area, Central Finland (SY1). The effect of alteration and weathering on rock matrix porosity and on the available pore space, which affects diffusivity, are discussed. The main rock type in the crystalline bedrock of Syyry is a slightly foliated, gray tonalite with mica gneiss inclusions as well as minor, more mafic inclusions. The total porosity and the spatial porosity distribution and microstructure of the rocks were investigated using infiltration of carbon- 14-methylmethacrylate, electron microscopy and Hg-porosimetry. The laboratory-scale diffusion experiments were performed using (1) the out-leac…
Long-term stability of alpha particle damage in natural zircon
2005
Abstract We report the first discovery of radiation damage haloes generated by alpha particles in zircon. Proterozoic zircon crystals from a potassium-rich leucogranite from the Adirondack Mountains, New York State, have interior regions that are generally low in actinide elements (UO 2 + ThO 2 ≤ 0.02 wt.%) but show a remarkable pattern of heterogeneous metamictisation. The degree of radiation damage in these regions is not uniformly low, as would be expected if it corresponded to the observed actinide distribution patterns and age of the crystals. Rather, radiation damage is significantly increased in the outermost micro-areas of the low-actinide regions. The additional radiation damage …
Impact of Coseismic Frictional Melting on Particle Size, Shape Distribution and Chemistry of Experimentally-Generated Pseudotachylite
2020
In natural friction melts, or pseudotachylites, clast textures and glass compositions can influence the frictional behavior of faults hosting pseudotachylites, and are, in turn, sensitive to the processes involved in pseudotachylite formation. Quantification of these parameters in situations where the host rock composition and formation conditions are well-constrained, such as analogue experiments, may yield calibrations that can be employed in analysis of natural pseudotachylites. In this paper, we experimentally-generated pseudotachylites in granitoid rocks (tonalite and Westerly granite) at Pconf= 40 MPa and slip rates of ∼0.1 m s−1, comparable to the conditions under which natural pseud…
Experimental alteration of granitic rocks: Implications for the evolution of geothermal brines in the Upper Rhine Graben, Germany
2020
Abstract Geothermal energy exploitation in the Upper Rhine Graben (URG) chiefly has targeted faults and fractures within or connected with the crystalline basement, where hot fluids of c. 200 °C circulate at depths of c. 5 km. Formation fluids of the crystalline basement are highly saline, NaCl-dominated brines, whereas shallow crystalline basement water ( The trace element concentrations of the leachates are hereby related to the composition and stability of minerals in the rocks and can be directly linked to the proposed and observed dissolution processes at the different temperatures. In experiments with pure water at 70 °C, representing the recharge or infiltration conditions, water-roc…
Flame foliation: Evidence for a schistosity formed normal to the extension direction
2007
Abstract Foliations are normally thought to develop approximately parallel to the XY-plane of the finite strain ellipsoid, i.e., perpendicular to the main shortening direction. We present a new type of schistosity named “flame foliation” that forms orthogonal to the main extension direction, approximately parallel to the YZ-plane of finite strain. Flame foliation consists of anastomosing biotite-rich selvedges overprinting S1 in pelitic layers of metaturbitites in NW Namibia. The biotite crystals in the selvedges are peculiar because they are oriented oblique or orthogonal to the flame foliation itself and parallel to the previous S1 cleavage, a feature no other foliation shows. In some cas…
Evolution of the middle Paleozoic magmatism in the Chinese Altai: Constraints on the crustal differentiation at shallow depth in the accretionary oro…
2019
Abstract The Chinese Altai underwent intensive mafic and felsic magmatism in the middle Paleozoic, which was the most important magmatic event in the region. It is still unclear for the role of the event in formation of the crust that is thick (∼56 km) and has structure of three-layer stratification. In this study, the data for the middle Paleozoic mafic rocks and granites are comprehensively compiled and integrated with new geochronological, petrological, geochemical and Sr-Nd-Pb isotopic data for gabbroic rocks from Keketuohai area and tonalite and biotite granites from Habahe area. The middle Paleozoic mafic rocks exhibit two evolutionary trends, which can be defined as high-Al and low-A…
Evolution of mica fish in mylonitic rocks
2003
Abstract Mineral fish are lozenge-shaped porphyroclasts, single crystals in a finer grained matrix, which occur in ductile shear zones and which are commonly used as shear sense indicators. Mineral fish of biotite, tourmaline, K-feldspar, garnet, hypersthene and quartz occur in mylonites but most common are white mica fish. These mica fish can be subdivided into six morphological groups that develop by different mechanisms determined by different initial shapes and orientations. The principal mechanisms of formation are intracrystalline deformation combined with rigid body rotation. Concomitant selective grain size reduction occurs by recrystallisation, cataclastic separation, pressure solu…
U–Pb SIMS dating of synkinematic granites: timing of core-complex formation in the northern Anatolide belt of western Turkey
2005
Secondary ion mass spectrometry (SIMS) U–Th–Pb dating of magmatic zircon from the synkinematic Egrigoz and Koyunoba granites and a leucogranite dyke dates core-complex formation in the northern Anatolide belt of western Turkey at 24–19 Ma. The granites intrude into the footwall of the Simav detachment and are strongly elongated in the NNE direction parallel to tectonic transport on the detachment. Although large parts of the granites are undeformed, localized mylonitic to ultramylonitic deformation occurs directly beneath the Simav detachment and preserves evidence of progressive deformation from ductile to brittle conditions. Oscillatory zoned rims of long-prismatic zircon from the Egrigoz…
Influence of pH and temperature on the early stage of mica alteration
2012
Mineral dissolution and precipitation reactions actively participate in controlling fluid chemistry during water–rock interaction. In this study, the changes in the biotite and muscovite basal surface nano-morphology were evaluated during interaction with fluids of different pH (pH = 1.1, 3.3 and 5.7) at different temperatures (T =2 5, 120, and 200 C). Results show that at the nanometre scale resolution of the atomic force microscope (AFM), dissolution generates etch pits with a stair-shaped pattern over the (0 0 1) surface. The flux of dissolved elements decreases when pH increases. However, at pH 5.7, a change was found in the flux after 42 h of reaction when abundant gibbsite and kaolini…
Geochronology and Nd-Sr systematics of Lusatian granitoids: significance for the evolution of the Variscan orogen in east-central Europe
1994
A variety of pre-Variscan granitoids and two Variscan monzogranites occurring in the central and western parts of the Lusatian Granodiorite Complex (LGC), Saxonia were dated by the single zircon evaporation method, complemented by whole rock Nd isotopic data and Rb —Sr whole rock and mineral ages. The virtually undeformed pre-Variscan granitoids constitute a genetically related, mostly peraluminous magmatic suite, ranging in composition from two-mica granodiorite, muscovite-bearing biotite quartz diorite (tonalite) and granodiorite to biotite granodiorite and monozogranite.