An occurrence of grandidierite,kornerupine, and tourmaline in southeastern Ontario,Canada     

Steven W. Lonker 《Contributions to Mineralogy and Petrology》1988,98(4):502-516

Grandidierite, kornerupine, and tourmaline occur in high-grade pelitic gneisses from southeastern Ontario, Canada. The kornerupine occurs in quartz-bearing layers associated with biotite, cordierite, garnet, ilmenite, K-feldspar, magnetite, quartz, and, less commonly, sillimanite. Grandidierite is found in quartz-poor, cordierite+sillimanite segregations in contact with biotite, cordierite, ilmenite, K-feldspar, magnetite, sillimanite, and, more rarely, garnet. Tourmaline is sporadically distributed in all compositional layers, but is not in contact with the other borosilicates. There is no textural evidence for a reactive relationship among the three borosilicates. Neither chemical or textural equilibrium has been achieved on the scale of a thin section.It is proposed that the granite, K-feldspar-rich leucosomes, and different borosilicate assemblages in adjacent compositional layers evolved along a path of decreasing pressure and increasing temperature. The P-T path intersected a series of dehydration and melting reactions. This P-T path indicates that uplift had occurred before cooling had started and before the maximum temperature was reached. Corona and symplectite textures developed at various times during uplift both before and after cooling had started.  相似文献   

Major's Creek,N.S.W., Australia — A Devonian epithermal gold deposit     

B. A. Wake  G. R. Taylor 《Mineralium Deposita》1988,23(4):239-246

Mineralized veins at Major's Creek consist of preponderant quartz and carbonate gangue with gold, Au-Ag tellurides and base metal sulphides within silicified and sericitized dykes or granodiorite of the Braidwood Granite. Fluid inclusion studies indicate deposition throughout the range 350–80°C by low salinity fluids. Significant Au-Ag telluride mineralization took place at a temperature of about 155°C. Mineral deposition was due to the separation of a liquid CO₂ phase from an originally CO₂-rich aqueous fluid. Observed argillic alteration is a consequence of acid leaching above the boiling zone. Mineralization is epithermal in character and probably formed during the existence of a hydrothermal convective system. A relationship with similar epithermal gold deposits in the adjacent Eden-Yalwal Rift zone is inferred.  相似文献   

Chronology of the pressure-temperature history recorded by a granulite terrain   总被引：5，自引：1，他引：5  

A. S. Cohen  R. K. O'Nions  R. Siegenthaler  W. L. Griffin 《Contributions to Mineralogy and Petrology》1988,98(3):303-311

Coronite-bearing anorthositic granulites consisting of olivine, orthopyroxene, clinopyroxene, garnet and plagioclase assemblages are particularly well preserved at Gaupås and Holsnöy in the Bergen Arc of West Norway. The coronites are considered to have formed near T= 900° C and P=10 Kb by two stages of subsolidus reaction from an anorthositic gabbro parent. The first reaction involved ol+plagcpxI+opxI+sp and the second cpxI+opxI+sp+plcpxII+opxII+gn. The incomplete reaction products are preserved to varying extents in different corona structures. Sm-Nd isotopic data for each of four coronas yield precise isochrons, and demonstrate isochronism both between the constituent phases of the corona assemblages and dispersed ground mass phases. Three individual coronas not associated with shear zones yield ages of 907±9 my, 912±18 my and 905±37 my. Eclogite facies mineralogy is developed locally in shear zones, which are shown by Sm-Nd and Rb-Sr analyses to be Caledonian in age. Where relict corona structures survive unsheared within these zones, Nd exchange between the constituent phases cannot be resolved. This observation together with sympathetic Ca/Mg and Sm/Nd zoning preserved at T900° C in the garnet mantles of coronites places a limit on the diffusivity of Nd in pyropic garnets which is no higher than published experimental values for Mg in pyrope-almandine garnets. Consequently even in slowly-cooled granulite terrains, garnet grains are expected to yield Sm-Nd chronologies very close to the time of mineral growth.  相似文献   

Compositional variation in pyrochlores from the Mt Weld carbonatite laterite,Western Australia     

B. G. Lottermoser  B. M. England 《Mineralogy and Petrology》1988,38(1):37-51

Summary Pyrochlore is present as a residual mineral within a Mesozoic-Cainozoic laterite overlying and derived from a Proterozoic carbonatite intrusion. Leaching of the A-site ions Na and Ca from the pyrochlore structure occurred during weathering and the vacant sites were subsequently occupied by Sr and Ce. In addition, leaching of strongly-bonded Nb led to B-site vacancies, which were subsequently filled by Fe³⁺. The pyrochlore mineral chemistry changes markedly with depth in the weathering profile and the sequence: Na-Ca pyrochlore, strontian pyrochlore, strontiopyrochlore, ceriopyrochlore, cerian strontiopyrochlore and strontian ceriopyrochlore occurs between the fresh carbonatite/laterite interface and the top of the profile. This vertical zonation in pyrochlore mineral chemistry is the result of leaching and reprecipitation processes and the associated fractionation and differential mobility of individual elements during weathering.

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Variierende Zusammensetzungen in Pyrochlor in Lateriten des Mt Weld Karbonatits, West-Australien

Zusammenfassung Pyrochlor befindet sich in einem mesozoischen-känozoischen Laterit, der sich durch Verwitterung einer proterozoischen Karbonatitintrusion bildete. Das Lösen von A-Ionen, Na and Ca, aus der Pyrochlor-Struktur erfolgte während der Verwitterung; die freien Stellen wurden von Sr und Ce besetzt. Der Verlust von stark gebundenem Nb führte zu freien Stellen in der B-Position, die von F³⁺-Ionen besetzt wurden. Die Pyrochlor Zusammensetzung ändert sich deutlich mit der Verwitterungstiefe und entwickelt sich von der Karbonatit/Laterit-Grenze zum obersten Teil des Lateritprofils wie folgt: Na - Ca-Pyrochlor, strontian Pyrochlor, Strontiopyroehlor, Ceriopyrochlor, cerian Strontiopyrochlor bzw. strontian Ceriopyrochlor. Diese vertikale Zonierung in der Pyrochlorchemie ist das Resultat der Auslaugungs- und Wiederausfällungsprozesse während der Verwitterung und der damit verbundenen Fraktionierung und unter-schiedlichen Mobilität von einzelnen Elementen.

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The Perseverance Ultramafic Complex, Western Australia: The Product of a Komatiite Lava River   总被引：3，自引：0，他引：3  

BARNES  STEPHEN J.; HILL  ROBIN E. T.; GOLE  MARTIN J. 《Journal of Petrology》1988,29(2):305-331

The Perseverance ultramafic complex is a body of olivine-richkomatiitic rocks spatially associated with the Agnew nickeldeposit, in the Agnew-Wiluna greenstone belt of the ArchaeanYilgarn Block in Western Australia. The complex consists ofa central lenticular body, up to 700 m thick, of olivine adcumulates,flanked by laterally extensive sheet-like bodies of olivineorthocumulates and spinifextextured komatiite flows. Rocks progressivelyfurther away from the central lens have chemical compositionsreflecting higher original proportions of komatiite liquid tocumulus olivine. Parent liquids had MgO contents between 25and 32% MgO, approximately chondritic Al/Ti ratios and HREEpatterns, and moderate depletion in LREE. Olivines within the adcumulate lens show a progressive increasein forsterite content from Fo₉₃ at the bottom to Fo_94?5, atthe top. Calculated original olivine compositions in the flankingrocks are similar to those at the base of the central lens.Original olivine nickel contents show a symmetrical variationfrom maximum values of 3500 ppm at the top of the central lens,through minimum values of 1000 ppm at the base and margins ofthe central lens to intermediate values in the distal rocks.The complex as a whole shows evidence for nickel depletion relativeto other komatiite suites. These observations are explained in terms of prolonged eruptionand flow of komatiitic lava down a major flow channel or lavariver. Adcumulates crystallized on the floor and sides of thecentral channel, which was formed at an early stage by thermalerosion of floor rocks. Episodic overflow of the central channelproduced distal ‘flood plain’ rocks consisting ofolivine orthocumulates and layered flows. Lavas became moremagnesian and nickel-rich with time, giving rise to the observedspatial variation in primary olivine composition. Nickel depletionof the earliest lavas is attributed to pre-eruption segregationof large volumes of immiscible Fe-Ni-sulfide, which were concentratedto form the underlying Agnew nickel deposit.  相似文献   

Stand-level dieback etiology and its consequences in the forests of Papua New Guinea     

F. Arents 《GeoJournal》1988,17(2):209-215

Stand-level dieback inNothofagus, mangrove andEucalyptus deglupta forests is examined. InNothofagus and mangrove forests, groups of largely even-aged trees die simultaneously, possibly triggered by drought stress which may directly affect the trees inNothofagus forests or indirectly increase water salinity in mangroves. Lightning strikes may be an additional dieback trigger in mangroves. Crown decline only was observed inE. deglupta forests and this may be associated with water-logging during periods of exceptionally high rainfall. Examination of rainfall records shows that severe droughts occur periodically in association with El Nino Southern Oscillations in the Pacific Ocean.  相似文献   

Book reviews     

John S. Perry  A. Henderson-Sellers  P. M. Morrisette 《Climatic change》1989,15(3):487-494

The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

The significance of “diagenetic crystallization rhythmites” at the Nanisivik Pb-Zn-Ag deposit,Baffin Island,Canada     

D. C. Arne  S. A. Kissin 《Mineralium Deposita》1989,24(3):230-232

Conclusions Rhythmically banded ore textures at the Nanisivik Pb-Zn-Ag deposit are identical to those commonly referred to as diagenetic crystallization rhythmites or DCRs. The presence of such textures in a demonstrably epigenetic orebody indicates that their formation is not necessarily indicative of early diagenetic sulfide mineralization. Although the development of such textures may occur in near-surface and/or early diagenetic environments, their presence alone is not a compelling constraint on the timing of ore formation.  相似文献   

Activity-composition relations in FeTiO3-MnTiO3 ilmenite solid solutions from EMF measurements at 1050–1300 K     

Hugh St. C. O'Neill  Mark I. Pownceby  Victor J. Wall 《Contributions to Mineralogy and Petrology》1989,103(2):216-222

The activity of FeTiO₃ in the binary ilmenitepyrophanite (FeTiO₃-MnTiO₃) solid solution has been determined for the temperature range 1050–1300 K by displacement of the reaction: 2 FeTiO₃=2 Fe+2 TiO₂+O₂ in T-O₂ space, using an electrochemical technique with calcia- and yttria-stabilized zirconia solid electrolytes. The activities show small positive deviations from ideality, which, although the data are unusually precise, may be perfectly described by the simple regular solution model, with an interaction parameter, W _Fe-Mn ^ilm , of 2.2±0.3 kJ g-atom^–1, which is independent of temperature. This value, together with the experimental data on the partitioning of Fe and Mn between ilmenite and garnet (Pownceby et al. 1987), gives W _Fe-Mn ^gt =1.2±0.5 kJ g-atom^–1 for the almandine-spessartine (Fe₃Al₂Si₃O₁₂-Mn₃Al₂Si₃O₁₂) solid solution.  相似文献   

Dynamic recrystallization and chemical evolution of clinoamphibole from Senja,Norway   总被引：4，自引：0，他引：4  

R. J. Cumbest  M. R. Drury  H. L. M. van Roermund  C. Simpson 《Contributions to Mineralogy and Petrology》1989,101(3):339-349

Clinoamphibole from a mylonitic amphibolite exhibits microstructures characteristic of dynamic recrystallization, including porphyroclasts in a finer grained matrix of needle-shaped amphibole. The matrix amphibole defines an LS fabric and porphyroclasts have core and mantle structures with a core containing undulose to patchy extinction and (100) deformation twinning surrounded by a mantle of recrystallized grains. In addition intragranular grains also occur within the cores. TEM analyses of the porphyroclasts reveal that they contain a wide variety of lattice defects including high densities (5 × 10⁸cm^–2) of free dislocations and dislocation arrays, dissociated dislocations, stacking faults, and (100) micro-twins. TEM also shows that matrix grains and intragranular grains have relatively low defect densities, and that the intragranular new grains occur at localities in the porphyroclasts characterized by high densities of dislocations. These observations along with the chemical and orientation relationships between the recrystallized grains and porphyroclasts indicate that the new grains may have formed by heterogeneous nucleation and that further growth probably occurred by both strain assisted and chemically induced grain boundary migration or liquid film migration. This recrystallization event is interpreted to be synkinematic based on the fact that no recrystallization textures are present in the matrix grains and that the matrix grains define an LS fabric. However, the low defect densities in the matrix grains and the lack of intracrystalline strain in other phases indicate that post-kinematic recovery processes were active.  相似文献