Finite element analysis of axisymmetric flow into partially penetrating wells

The finite element method was used to solve the problem of flow to a partially penetrating strainer well in a leaky confined aquifer under steady and unsteady conditions. Predictions of the model were compared with reported pumping test data. A good agreement was obtained between them. The effects of penetration and screen position on discharge through imperfect well were studied. Results were compared with analytical solutions and presented graphically.     

An application of R-mode factor analysis to the study of metamorphic petrogenesis

R-mode factor analysis of modal and chemical data clarifies the trends of mineralogical evolution and associated chemical variations in amphibolites from the Northwest Adirondack Mountains, New York and the Willyama Complex, Broken Hill District. In both areas the principal mineralogical reaction attending metamorphism, as described by the first factor, appears to have been Hornblende + Quartz → Calcic pyroxene + Orthopyroxene + Plagioclase. For the Adirondack amphibolites, the derived reaction coefficients viewed against the modal contents of the pyroxenes suggest another hornblende breakdown reaction producing calcic pyroxene, which is corroborated by the first appearance of the phase a little NE of Emeryville. The other factors extracted reveal the underlying parameters responsible for the development of biotite, sphene, opaques and quartz in the Adirondack metabasites and albite, anorthite, ilmenite and quartz in the Willyama Complex amphibolites.The analysis also demonstrates that the principal mineralogical reactions in both the areas have been combinations of thermal and ionic types and further that to decipher the net mineralogical changes in high grade metamorphic basic and pelitic rocks it is necessary to extend the integration of the ‘part reactions’ occurring in different domains to the level of a hand specimen.     

Coronas from the Thessaloniki gabbros,North Greece

Chemical composition of the phases occurring as corona structures in the Thessaloniki gabbros are subjected to algebraic method of treatment following Korzhinskii [1]. The analysis reveals that the mineralogical reactions responsible for the growth of the corona structures were possibly allochemical in nature in regard to the non-volatile components. The chemical similarity of the pyroxenes occurring within and beyond the corona structures in the gabbros appears compatible with such a model.     

Mixing behavior in quaternary garnet solid solution and an extended Ellis and Green garnet-clinopyroxene geothermometer

Applications of the different formulations of garnet-clinopyroxene geothermometers to crustal granulites and particularly to metamorphosed manganese formations show a wide scatter of estimates. This is primarily related to the uncertainty associated with the formulation of the activity-composition relationship in garnet solid solution besides that in the clinopyroxene solid solution. The largest uncertainty appears to have resulted from the adopted Mg-Mn interaction parameter in garnet which is yet to be experimentally determined. A fresh statistical regression of eleven pairs of garnet and clinopyroxene equilibrated at identical P-T conditions from a manganese formation in India yields W _Mg-Mn ^Gt (=W_Mn-Mg) value of 1600±500 cal/mols. An extension of the Ellis and Green (1979) geothermometer, known to work well in normal granulites, incorporating terms associated with the activity coefficients of the exchangeable cations, now yields consistent temperature estimation from normal granulites as well as from metamorphosed manganese formations. The geothermometer, however, will not work well for garnet having X_Fe0.65 and clinopyroxenes containing appreciable Na, Al and/or Fe³⁺.     

Effect of chlorine on near-liquidus phase equilibria of an Fe–Mg-rich tholeiitic basalt

The importance of Cl in basalt petrogenesis has been recognized, yet constraints on its effect on liquidus crystallization of basalts are scarce. In order to quantify the role of Cl in basaltic systems, we have experimentally determined near-liquidus phase relations of a synthetic Fe–Mg-rich basalt, doped with 0.0–2.5 wt% dissolved Cl, at 0.7, 1.1, and 1.5 GPa. Results have been parameterized and compared with previous data from literature. The effect of Cl on mineral chemistry and liquidus depression is dependent on the starting basaltic composition. The liquidus depression measured for a SiO₂-rich, Al₂O₃-poor basalt is smaller than that observed for a basaltic melt depleted in silica and enriched in FeO_T and Al₂O₃. The effect of Cl on depression of the olivine–orthopyroxene–liquid multiple saturation pressure does not seem to vary with the starting composition of the basaltic liquid. This suggests that Cl may significantly promote the generation of silica-poor, Fe–Al-rich magmas in the Earth, Mars, and the Moon.     

A refined garnet - biotite Fe−Mg exchange geothermometer and its application in amphibolites and granulites

A new formulation of garnet-biotite Fe–Mg exchange thermometer has been developed through statistical regression of the reversed experimental data of Ferry and Spear. Input parameters include available thermo-chemical data for quaternary Fe–Mg–Ca–Mn garnet solid solution and for excess free energy terms, associated with mixing of Al and Ti, in octahedral sites, in biotite solid solution. The regression indicates that Fe–Mg mixing in biotite approximates a symmetrical regular solution model showing positive deviation from ideality withW _FeMg ^bi =1073±490 cal/mol. H _r and S _r for the garnet-biotite exchange equilibrium were derived to be 4301 cal and 1.85 cal respectively. The resultant thermometer gives consistent results for rocks with a much wider compositional range than can be accommodated by earlier formulations.     

Geochemistry of braunite and associated phases in metamorphosed non-calcareous manganese ores of India

In the metamorphosed manganese oxide ores of India, braunite is ubiquitous in all assemblages from chlorite to sillimanite grades. Chemical analyses of braunite from different prograde assemblages confirm the presence of a fixed R²⁺ (=Mn²⁺+Mg+Ca) SiO₃ molecule in the mineral. Element partitioning between coexisting braunite and bixbyite indicates a near-ideal mixing of Fe⁺³/ -Mn⁺³ in the phases. This also indicates that braunite became relatively ferrian while equilibrating with associated phases such as bixbyite, hollandite and jacobsite during prograde reactions. Petrogenetic studies show that as a general trend, prograde lower oxide phases appeared by deoxidation of higher oxide phases. But braunite, a more reduced phase than bixbyite, appeared early from deoxidation of pyrolusite in presence of quartz. Bixbyite could appear later from the reacting pyrolusite-braunite-quartz assemblage. Inferred mineral reaction paths and the general trend of pro-grade deoxidation reactions suggest that the composition of ambient fluid phase was internally buffered during metamorphism.     

Evidence of Superposed Metamorphism from the Gokavaram Area, Eastern Ghats Belt, and its Relation with the Kemp Land Coast, East Antarctica

In this paper, we compare the petrological histories of the Kemp Land Coast (east Antarctica), and Gokavaram area (Eastern Ghats), that were supposed to have been juxtaposed. The area around Gokavaram is dominated by different varieties of paragneisses (pelitic, quartzofeldspathic, and calcareous composition) with relatively minor amounts of orthogneisses (mafic, enderbitic, and granitic composition). The rocks were involved in three major phases of deformation, and were finally affected by localised shear movement. On the basis of reaction textures, well preserved in high Mg-Al granulites, and calc-silicate granulites, and geothermobarometric data we deduce a polymetamorphic evolution of the rocks. Following an early M₁ metamorphism culminating at 9.2–9.4 kbar, > 950°C, the rocks cooled nearly isobarically down to 850°C. During a subsequent M₂ metamorphism, near isothermal decompression to 5–6 kbar occurred. This was followed by near isobaric cooling down to 600–650°C. M₃ is a weak amphibolite facies overprint, largely restricted to late shears, which involved hydration as well. Available radiometric data from this area can be interpreted in terms of partial resetting of U-Pb systematics in older sphenes due to M₃ metamorphism at ca. 550 Ma. Despite the absence of sufficient isotopic data on the Eastern Ghats granulites, we document a remarkable similarity in the petrological history of the two supposedly erstwhile neighbours.