Intercrystalline cation partitioning between minerals of the triplite-zwieselite-magniotriplite and the triphylite-lithiophilite series in granitic pegmatites

Minerals of the triphylite-lithiophilite, Li(Fe, Mn)PO₄, and the triplite-zwieselite-magniotriplite series, (Mn, Fe, Mg)₂PO₄F, occur in the late stage period of pegmatite evolution. Unfortunately, neither are the genetic relationships between these phosphates fully understood nor are thermodynamic data known. Consequently, phosphate associations and assemblages from 8 granitic pegmatites — Clementine II, Rubicon II and III, and Tsaobismund (Namibia); Hagendorf-Süd and Rabenstein (Germany); Valmy (France); Viitaniemi (Finland) — have been tested for compositional zoning and intercrystalline partitioning of main elements by electron microprobe techniques. Although the selected pegmatites display varying degrees of fractionation, and the intergrowth textures indicate different genetic relationships between the phosphates, the plots of mole fractions X _Fe=Fe/(Fe+Mn+Mg+Ca), X _Mn=Mn/(Fe+Mn+Mg+Ca), and X _Mg=Mg/(Fe+Mn+Mg+Ca) can be fitted relatively well with smooth curves in Roozeboom diagrams. Their deviations from symmetrical distribution curves are mainly dependent upon X _Mg or X _Ca, and upon non-ideal solutions. Surprisingly small differences between the partition coefficients were detected for intergrowths of different origin. However, the partitioning of shared components among coexisting phases is clearly dependent upon the conditions of formation. Compositional zoning is observed only when both Fe–Mn phosphates are intergrown mutually or with other Fe–Mn–Mg mineral solid-solutios. Thus, the zoning does not seem to be due to continuous crystallization, but to later diffusion processes. The triplite structure has preference for Mn, Mg, and Ca, while Fe prefers minerals of the triphylite series. A quantification of main element fractionation between minerals of the triphylite and the triplite series is possible in the cases where diffusion can be excluded. For the Fe/(Fe+Mn) ratios of core compositions an equation with a high correlation coefficient (R=0.988) was determined: Fe/(Fe+Mn)_Tr=[Fe/(Fe+Mn)_Li]/{2.737-(1.737)[Fe/(Fe+Mn)_Li]} (Tr=triplite series, Li=triphylite series). Consequently, the Fe/(Fe+Mn) ratio of the triplite series can now also be used in the interpretation of pegmatite evolution, just like that of the triphylite series which has been successfully applied in the past.     

Magma mixing,the petrogenetic link between anorthositic suites and rapakivi granites, Åland,SW Finland

Summary The Åland, rapakivi batholith consists of several granites that differ texturally and mineralogically from quartz-porphyritic varieties to rapakivi varieties with K-feldspar ovoids (wiborgites and pyterlites) and aplitic granites. Closely associated with the batholith there is a mafc magmatic series of dolerite dykes, norites, anorthosites and monzodiorites.The earliest major intrusive phase of the Åland, rapakivi batholith consists of quartzporphyritic hornblende rapakivi. This rock contains small amoeboidal mafc enclaves, labradorite megacrysts, quartz ocelli, amphibole-mantled xenoliths and irregular clots of granophyric granite. These disequilibrium features are products of mixing between basaltic and granitic magmas. Geochemical modelling indicates that the quartzporphyritic hornblende rapakivi is a mixture of 15% hi-Fe monzodiorite (mafic endmember) and 85% quartz-feldspar porphyry (felsic end-member). The monzodiorite is derived from a norite-anorthosite-monzodiorite series. The quartz-feldspar porphyry is produced by partial melting of the country rock caused by intrusions of hot basic magma.Structural, textural and geochemical features suggest that magma mixing was an important petrogenetic process in the formation of the earliest rapakivi granite intrusions in the Åland, rapakivi batholith. Petrographic evidence of magma mixing can also be found in the major intrusion of the batholith, the wiborgite rapakivi granites. Chemically the mixing is difficult to specify in these rocks because of a high proportion of felsic component. Zircon and apatite fractionation trends, however, indicate that the wiborgite rapakivis also contain components from a mixed source.

---

Magmamixing, die petrogenetische Verbindung zwischen Anorthositen und RapakiviGraniten, Åland, SW Finnland

Zusammenfassung Der Rapakivi Batholit von Åland besteht aus verschiedenen Graniten, die in ihrer Textur und Zusammensetzung das Feld von quarzporphyritischen über Rapakivigranite mit K-Feldspat-Ovoiden (Wiborgite und Pyterlite) und aplitischen Graniten abdecken. Eine mafische magmatische Serie von Dolerit-Gängen, Noriten, Anorthositen und Monzodioriten ist mit diesen Batholiten eng verbunden.Die erste größere Intrusivphase des Åland, Rapakivi Batholiten besteht aus quarzporphyritischem Hornblende Rapakivi. Dieses Gestein enhält kleine Amöboide, mafische Enklaven, Labradorit Megakristalle, Quarzocelli, Xenolithe mit Amphibolrändern und unregelmäßige Aggregate von granophyrischem Granit. Diese Produkte von Ungleichgewichts-Bedingungen gehen auf die Mischung zwischen basaltischen und granitischen Magmen zurück. Geochemische Modelle zeigen, daß der quarzporphyritische Hornblende-Rapakivi eine Mischung von 15%. eisenreichen Monzodiorit (mafisches Endglied) und 85% Quarz-Feldspatporphyr (felsisches Endglied) ist. Der Monzodiorit stammt von einer Norit-Anorthosit-Monzodiorit Serie. Der QuarzFeldspat-Porphyr entstand durch teilweise Aufschmelzung des Nebengesteines, die durch Intrusionen heißen basischen Magmas verursacht wurden.Strukturelle, texturelle und geochemische Daten zeigen, daß Magmamischung ein wichtiger petrogenetischer Prozeß der Bildung der frühesten Rapakivi-Granit-Intrusionen im Åland, Batholith waren. Petrographische Hinweise auf Magmamischung können auch in der größten Intrusion des Batholiths, dem Wiborg Rapakivi Granit, gefunden werden. Wegen des hohen Anteils felsischer Komponenten ist es schwierig, das Magmamixing in diesen Gesteinen chemisch zu quantifizieren. Zirkon- und Apatitfraktionierungs-Trends weisen jedoch darauf hin, daß auch die WiborgitRapakivis Komponenten aus einer gemischten Quelle enthalten.

---

---

With 5 figures     

Cyclic sedimentation and climatically caused sea-level changes in the Late Palaeozoic of Central Europe

Significant short-term fluctuations are characteristic of geological history since Precambrian times. Only the younger Quaternary climatic fluctuations are known in more detail as a result of a high grade time resolution. Climatic change can also be postulated with respect to older, cold periods during which polar inland ice sheets developed. From a discussion of endogene and exogene interpretations it is shown that global climatic changes, and the sea-level changes induced by them, as well as changes in the position and extent of climatic zones throughout the world provide a control mechanism for sedimentation which is consistent with cyclic sedimentation in Late Palaeozoic times, and also if the basin subsides non-cyclically. The model allows an explanation of the development of the Permo-Carboniferous sedimentary cycles without numerous short-term vertical oscillations of the earth's crust. In reality, exogene and endogene controls on sedimentation act together in great variety of combinations.     

Geochemical characteristics of Cocos Plate seamount lavas

A wide compositional continuum of basalts has been erupted from near-ridge seamounts constructed on the Cocos Plate between the Clipperton and Orozco Francture Zones. They range from highly evolved to moderately primitive (3.0–7.8% MgO), LREE-enriched alkali basalts, to moderately evolved to near-primary (5.2–9.5% MgO) tholeiites indistinguishable from N-type MORB. The data set of 159 quench glass analyses exhibits a remarkably consistent variation in both major and trace element composition that is keyed to variations in (La/Sm). Modeling of potential liquid lines of descent at pressures ranging from 1 bar to 8 kbar shows that this covariation is partially due to systematic differences in liquid lines of descent, where the alkaline lavas have undergone substantially more high pressure clinopyroxene fractionation and substantially less low pressure plagioclase fractionation than the tholeiites. In addition, systematic variation in the composition of the more primitive glasses indicates that they were derived from mixing of discrete enriched and depleted melts in the heterogenous seamount mantle source at pressures of 8–10 kbar and greater, and that clinopyroxene may be a residual phase during partial melting. These results show that porous media flow in the seamount mantle source is minor and that melt transport is accomplished primarily through cracking and diking. This study supports suggestions that the general homogeneity of basalt along the EPR is due to mixing in sub-axial magma chambers and mush zones, with additional mixing during partial mantle melting and melt segregation.     

Paleomagnetism of Lower Devonian volcanics and Devonian dykes from northcentral New Brunswick,Canada

Some 50 oriented samples (120 specimens) have been collected on eight sites of volcanic rocks from the Lower Devonian Dalhousie Group of northern New Brunswick and Devonian andesitic to basic dykes from central New Brunswick. Univectorial and occasional multivectorial components were extracted from the various samples. Results after AF and thermal demagnetization compare relatively well. In the volcanics and tuffs, two components of magnetization have been isolated: A (D = 33°, I = ?58°, α₉₅ = 7.3°, K = 236) for four sites and B (D = 66°, I = +53°) for three sites. The grouping of component A is improved after tilt correction but the fold test is not significantly positive at the 95% confidence level. Component A is interpreted as being primary while component B is unresolved and appears to be the resultant magnetization of a Late Paleozoic and a recent component. The pole position obtained for tilt corrected component A is 268°E, 1°S, d_p = 6.5°, d_m = 8.8°. The paleolatitude calculated for component A is 39°S. The paleopole of in situ component A is located close to those of the Early-Middle Devonian formations from Quebec, New Brunswick and New England states while the paleopole of tilt-corrected component A is similar to Lower Devonian poles of rock units from the Canadian Arctic Archipelago. If component A is primary (as we believe it to be), then the western half of the northern Appalachians had already docked onto the North American Craton by Early Devonian time. Alternatively, if component A is secondary the same conclusion applies but the juxtaposition took place in Middle Devonian time.     

A LABORATORY INVESTIGATION OF THE INDUCED POLARIZATION OF THE TRIASSIC SHERWOOD SANDSTONE OF LANCASHIRE AND ITS HYDROGEOLOGICAL APPLICATIONS*

The time-domain induced polarization (IP) of saturated Sherwood Sandstone correlates significantly with the intergranular permeability and the matrix conductivity but only at low electrolyte concentrations (< 500 p.p.m. NaCl). An increase in the magnitude of sandstone IP with increase in the valence of the electrolyte cation is pronounced but occurs only at intermediate concentrations, i.e., between 100 and 2500 p.p.m. Surface IP and resistivity depth sounding measurements, supplemented by data from laboratory measurements, can be used to estimate the groundwater conductivity and hence the salinity in a moderate to strongly saline sandstone aquifer.     

The use and waste of water in a third world city

All over the world, cities that are crossed by large rivers, have the great advantage of being able to meet their water needs. In the humid tropics, such cities should normally not experience water scarcity.Ilorin, the city under study is crossed by two fairly large rivers. The town is just about 100 km² in area with a population less than 500,000. 3km E of the city, is a dam with a storage capacity of 43 million m³. The daily water production to the city is 661/person. When it is realized that less than 25% of the houses in the city have modern sanitary conveniences, then 661/person per day borders on over supply. Yet there is the cry of inadequate water supply from sections of the city.The habits of the city dwellers make them waste water. For example, mouth brushing alone takes about 2.4 I/person when the tap runs continuously. Secondly a bath with a 221 bucket of water is adequate for an adult, but when a shower bath is taken, about 841 will be required for about 15 minutes.This paper has examined the use and waste of water among the physical strata in the city. These strata coincide with the socio-economic strata.For an affluent class, a threshold water requirement of 521 is manageable, whereas in the Government Reservation area, the average is 82 1 (often includes waste). For the indigenous area, about 351 per day for an individual is the need, though the demand might be much higher than this value.