We conducted a series of melting experiments in the join forsterite–diopside–leucite under 0.1 and 2.3 GPa and in the join forsterite–leucite–åkermanite under 2.3 GPa to understand paragenetic relationships amongst different types of lamproitic and lamprophyric magmas with K-rich mafic and ultramafic volcanic (kamafugitic) rocks. Both the joins were studied in the presence of excess water. The experimental results of the join forsterite–diopside–leucite at 0.1 GPa show that the five-phase point of forsterite (Fo)ss + diopside (Di)ss + leucite (Lc)ss + liquid (Liq) + vapour (V) (equivalent to ugandite lava) occurs at Fo2Di50Lc48 at 880 ± 5 °C. Phlogopite appears as the last phase at 830 ± 15 °C. The final crystalline assemblage of forsteritess + diopsidess + leucitess + phlogopite is similar to the phenocryst assemblage of missourite lava. Present study suggests that an olivine leucitite (ugandite) can be derived from an olivine italite, a slightly potassic peridotite and a leucitite magma.
A study of the join Fo–Di–Lc [P(H2O) = P(Total)] at 2.3 GPa shows that liquid compositions penetrate the primary phase volumes of forsteritess, phlogopitess, kalsilitess, K-feldsparss and diopsidess. It has the following three five-phase points: 1) one occurring at Fo9Di49Lc42 and 1005 ± 5 °C, where liquid and vapour coexists with forsteritess, phlogopitess and diopsidess (phlogopite-bearing madupite), 2) the second one at Fo4Di50Lc46 and 990 ± 10 °C, where diopsidess, K-feldsparss and phlogopitess coexist with liquid and vapour (pyroxene-bearing minette), and 3) the third one at Fo3Di21Lc76 and 775 ± 5 °C, where phlogopitess, kalsilitess and K-feldsparss are in equilibrium with liquid plus vapour (kalsilite-bearing minette).
The experimental results of the join Fo–Lc–åkermanite (Ak) show that the join 40 penetrates the primary phase volumes of forsteritess, phlogopitess, kalsilite, K-feldsparss, diopsidess and merwinitess. The data indicate the presence of four five-phase points: 1) one occurring at Fo7Lc42Ak51 and 1165 ± 5 °C, where phlogopitess, forsteritess, diopsidess coexists with liquid and vapour (olivine-bearing madupite), 2) the second one at Fo3Lc49Ak48 and 1140 ± 10 °C, where a liquid is in equilibrium with phlogopitess, K-feldsparss, diopsidess and vapour (pyroxene-bearing minette), 3) the third one at Fo18Lc21Ak61 and 1255 ± 10 °C, where merwinitess, forsteritess and diopsidess are in equilibrium with liquid and vapour (merwinite-bearing wherlite), and 4) the fourth one at Fo5Lc73.5Ak21.5 and 770 ± 5 °C, where kalsilitess, phlogopitess and K-feldspar coexist with liquid and vapour (kalsilite-bearing minette). The present data suggest that high pressure heteromorphic equivalent of a katungite magma is represented by a kalsilite-bearing minette, a pyroxene-bearing minette, or an olivine-bearing madupite. 相似文献
Inversion codes are the most useful tools to infer the physical properties of the solar atmosphere from the interpretation of Stokes profiles. In this paper, we present the details of a new Stokes Profile INversion code (SPIN) developed specifically to invert the spectro-polarimetric data of the Multi-Application Solar Telescope (MAST) at Udaipur Solar Observatory. The SPIN code has adopted Milne–Eddington approximations to solve the polarized radiative transfer equation (RTE) and for the purpose of fitting a modified Levenberg–Marquardt algorithm has been employed. We describe the details and utilization of the SPIN code to invert the spectro-polarimetric data. We also present the details of tests performed to validate the inversion code by comparing the results from the other widely used inversion codes (VFISV and SIR). The inverted results of the SPIN code after its application to Hinode/SP data have been compared with the inverted results from other inversion codes. 相似文献
Experimental studies have been performed on an olivine tholeiite and tholeiitic picrite at pressure and temperature ranges of 20–40 kb and 1200–1300°C. The lower and upper limits of basalt-eclogite transition zone for tholeiitic picrite are 23 kb and 31·67 kb at 1200°C, and 24·67 kb and 33·67 kb at 1300°C, whereas for olivine tholeiite, these are 27 kb and 32·33 kb at 1200°C, and 28·70 kb and 33·70 kb at 1300°C. While the assemblages for both samples below the transition region are Pl+Px+Mt, they are Pl+Gt+Px+Mt within it. The eclogite field has Gt+Px+Mt. The ratio of garnet to plagioclase increases from the transition zone to the eclogite field and with the disappearance of plagioclase, the percentage of garnet increases to 30 in the eclogite field. Comparison of our results with previous studies on basalt-eclogite transition shows that the transition zone found by us occurs at higher pressure-temperature conditions. Seismic studies of the region below the Deccan Traps show an increase in velocity (1–4%) at depth. It is suggested that after partial melting, during ascent of the basaltic liquid, a significant portion of it crystallizes within the upper mantle as pockets of eclogite. As eclogite is more dense than peridotite, their presence should cause a similar increase in the seismic velocity below the Deccan area. 相似文献
A centrographic method for analysing mineral deposit clusters is illustrated using the komatiite-hosted Kambalda nickel sulphide deposit cluster, Yilgarn craton, Western Australia. In this method, the standard distance circle divides the cluster into a more endowed inner part and a less endowed peripheral part. The standard deviational ellipse, another centrographic object, depicts the preferred northwest–southeast trend of nickel orebodies at Kambalda. Weighted centrography shows that nickel endowment is greater in the eastern than western part of the cluster. The spatio-geometric interaction of the circle and ellipse splits the cluster into several partitions. The relative concentration of nickel orebodies or endowment within a partition in relation to their concentration within the entire cluster is termed ‘capture efficiency’. Komatiite areal trace exhibits higher nickel orebody capture efficiency than spatio-geometric partitions; however, some spatio-geometric partitions exhibit nickel endowment capture efficiencies comparable to that of komatiite. Furthermore, nickel orebody and endowment capture efficiencies of komatiite are elevated only within the standard distance circle. These results suggest that at Kambalda, (i) the standard distance circle is a prime window for understanding the komatiite-hosted nickel system, and (ii) spatio-geometric partitions are plausible locales for spatial analysis of nickel orebodies and endowment. The proposed centrographic method is potentially useful in mineral resource estimations and mineral exploration targeting. 相似文献
Bayesian weight-of-evidence and logistic regression models are implemented in a GIS environment for regional-scale prospectivity modeling of greenstone belts in the Yilgarn Craton, Western Australia, for magmatic nickel sulfide deposits. The input variables for the models consisted of derivative GIS layers that were used as proxies for mappable exploration criteria for magmatic nickel sulfide deposits in the Yilgarn. About 70% of the 165 known deposits of the craton were used to train the models; the remaining 30% was used to validate the models and, therefore, had to be treated as if they had not been discovered. The weights-of-evidence and logistic regression models, respectively, classify 71.4% and 81.6% validation deposits in prospective zones that occupy about 9% of the total area occupied by the greenstone belts in the craton. The superior performance of the logistic regression model is attributed to its capability to accommodate conditional dependencies amongst the input predictor maps, and provide less biased estimates of prospectivity. 相似文献
The use of mineral deposit density regression models to estimate the number of undiscovered deposits is gaining acceptance in mineral resources assessments. The deposit density regression models currently in use are based on well-established power law relationships between deposit density (deposits/km2) and the areal extent of the host rocks in well explored regions (control areas) worldwide. Although these generalized or global deposit density models can generate guideline estimates that are useful at the terrane scale, locally-derived terrane-based deposit density regression models may potentially yield more relevant estimates at the terrane scale. Using 12 selected komatiite-defined control areas in the Kalgoorlie Terrane, Western Australia, we found that the size (km2) of the control areas had power law relationships with (i) nickel sulphide deposit density, and (ii) nickel endowment density (nickel metal/km2). Regression analyses showed that both power law relationships are statistically significant at the 5% level. This suggests that nickel sulphide deposit and endowment density models could be used to estimate the number of undiscovered nickel sulphide deposits and amount of nickel metal endowment in less explored komatiites in the Kalgoorlie Terrane. This study shows that global geological relationships can be viably downscaled onto local geological terranes thereby supporting the hypothesis that the processes of mineral deposit formation and preservation are scale-independent and self-similar. 相似文献
Significant uncertainties are associated with the definition of both the exploration targeting criteria and computational algorithms used to generate mineral prospectivity maps. In prospectivity modeling, the input and computational uncertainties are generally made implicit, by making a series of best-guess or best-fit decisions, on the basis of incomplete and imprecise information. The individual uncertainties are then compounded and propagated into the final prospectivity map as an implicit combined uncertainty which is impossible to directly analyze and use for decision making. This paper proposes a new approach to explicitly define uncertainties of individual targeting criteria and propagate them through a computational algorithm to evaluate the combined uncertainty of a prospectivity map. Applied to fuzzy logic prospectivity models, this approach involves replacing point estimates of fuzzy membership values by statistical distributions deemed representative of likely variability of the corresponding fuzzy membership values. Uncertainty is then propagated through a fuzzy logic inference system by applying Monte Carlo simulations. A final prospectivity map is represented by a grid of statistical distributions of fuzzy prospectivity. Such modeling of uncertainty in prospectivity analyses allows better definition of exploration target quality, as understanding of uncertainty is consistently captured, propagated and visualized in a transparent manner. The explicit uncertainty information of prospectivity maps can support further risk analysis and decision making. The proposed probabilistic fuzzy logic approach can be used in any area of geosciences to model uncertainty of complex fuzzy systems. 相似文献
In the present study authors have attempted to prepare a forest composition cover type map using landsat Thematic Mapper (T.M.) False colour Composite (F.C.C.) on 1:3n250,000 scale synthesized by combining band 2, 3 & 4 pertaining to study area. Landsat T.M.F.C.C. have been visually interpreted for delineation of forest cover type identified on the basis of tone/colour, texture, pattern & phenology and correlated with geographical location for drawing the final inferences. Limited field checks were done and types identified were correlated at some conspicuous identifiable location on image and ground and the informations were extrapolated for the whole study area. The forested area have been stratified into broad forest composition types as per Champion & Seth’s classification scheme. Temperate forest consisting of Oak forest and Deodar/mixed conifers could easily be separated due to sharp tonal contrast, however sub-tropical Chirpine and Northern tropical miscellaneous forest could be identified after having much correlation with the geographical location. The broad composition types were further classified into two density classes and the area under each category have been worked out using dot grid. 相似文献