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Showing 1 to 12 of 12 for “"compositional zoning"”.
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Understanding the evolution of compositional zoning in San Juan Volcanic Field ignimbrites using iron isotope ratios
… of many large calderas. Ignimbrites include both compositionally zoned rhyolitic to dacitic eruptions as well as monotonous intermediates. However, the petrogenetic origin of the volcanic field and the mechanisms of magma compositional evolution within magma chambers prior to eruptions remain …
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A Study of Compositional Zoning in Garnets From the Ducktown Mining District, Tennessee: Implications for Mathematical Modelling of Garnet Growth
… the Ducktown mining district were examined for compositional zoning. Unzoned garnets are common in the sphalerite rich areas--the garnets are 50% spessartine--and in the calc-silicate nodules--the garnets show extreme sieve texture. Normal (convex manganese profile) zoning is prevalent among …
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Titanite zoning and magma mixing
… evidence of magma-mixing processes within its compositional zoning. Titanite from the Ross of Mull Granite displays a large variety of textural features, both with respect to crystal shape and compositional zoning. The variation of the trace elements observed in titanite is a direct reflection …
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Petrology of the Taconian-Acadian Overlap Zone, Hartland Belt, Western Connecticut
… in western Connecticut. Mineral equilibria and compositional zoning studies for pelitic units of the Ratlum Mountain and Rowe Formations indicate that garnet porphyroblast rims equilibrated with matrix minerals at P-T conditions that are consistent with an Acadian (Devonian) metamorphic field …
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Metamorfismo varisico dell’Unità tettonica del Monte Grighini,Sardegna centrale
… analyses shown that garnet of Toccori has compositional zoning in fact, almandine and pirope increasing and grossular and spessartin decrease, from the core to the rim (mineral association: Grt + Wmca + Bt + Qtz ± St ± And). A rare heuedral garnet without compositional zoning was observed …
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Variations in δ56Fe during magma differentiation at Cedar Butte volcano: signatures of thermal diffusion?
… Butte is a SRP volcanic complex which erupted a compositional progression of lavas from initial high silica rhyolite to final basaltic trachyandesite in the late pleistocene (~0.4 Ma). The lavas form a curved array on a MgO vs SiO2 diagram, ruling out a primary role for mixing in producing this …
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Experimental studies of iron-magnesium order-disorder in orthopyroxene: Equilibrium, kinetics, and applications
… rate constant as (fO₂)¹/⁶. The temperature and compositional dependence of the disordering rate constant, K⁺, can be expressed as: ln K⁺(Ord) = - [(36420)/T(K)] min⁻¹ + 29.03 + 4162(XFe) where XFe is the Fe molar fraction of the sample. The thermodynamic and kinetics data of Fe-Mg order-disorder …
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Petrologic and Fluid Inclusion Constraints on the Tectonic Evolution of the Manhattan Prong, Southeastern New York
… the presence of Ky+Sta along with the slight compositional zoning of garnets in Peach Lake samples suggests that the contact assemblage may have been modified by a later metamorphism. Manhattan Schist collected adjacent to ~350 Ma granites (Brock, 1993) has been partially modified by contact …
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Gold mineralization in the Um El Tuyor area, South Eastern Desert, Egypt
… locally attained under high fluid/rock ratios. Compositional zoning of the auriferous pyrite and arsenopyrite crystals, along with the presence of patchy pyrrhotite and sphalerite inclusions in these crystals, and the absence of these features in pyrite and arsenopyrite of the late sulphide …
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Trace element distributions and partitioning trends in hydrothermal base metal sulphide ores comprising sphalerite, galena, chalcopyrite and tetrahedrite-tennantite
… mapping also reveals oscillatory and sector compositional zoning of various elements in galena for the first time. It is inferred that the partitioning of certain minerals between galena and sphalerite pairs is both predictable and systematic. This systematic partitioning is explored and it …
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Kinematic evolution, metamorphism, and exhumation of the Greater Himalayan Series, Sutlej River and Zanskar regions of NW India
… thermodynamic and diffusion modeling indicates compositional zoning preserved in garnet has remained unmodified since growth and can be related directly to the P--T--X evolution of rocks from this zone. Classic porphyroblast--matrix relationships coupled with the above models provide a …
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Vorticity of Flow, Deformation Temperatures, and Strain Symmetry of the Moine Thrust Zone, NW Scotland: Constraining the Kinematic and Thermal Evolution of a Collisional Orogenic System
… Moine thrust, subhedral garnets with prograde compositional growth zoning yield peak temperatures (grt-bio) of 440-492 °C at 4.5-6.0 kbars from Creagan Meall Horn to northern Assynt. Three samples collected at similar structural positions along the leading edge of the Moine nappe yield …