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1.
Summary The 100 m thick and 700 m long Nadezhda sill-like gabbronorite body, emplaced in the mafic-ultramafic Lukkulaisvaara layered intrusion, is associated with Cu-Ni-PGE mineralization that is mostly confined to mottled anorthosites developed from host gabbronorites and norites along the margin of the entire body. PGE and Au show distinct positive correlation with Cu, Ni and S suggesting that the noble metals are mainly controlled by sulphides. A mineralized layer about 1 m thick contains on average 0.74 wt.% S, 1.77 ppm Pt and 7.96 ppm Pd. Marginal location of PGE-rich sulphides and their absence in the Nadezhda body suggest that the mineralizing process must have been gravity-independent and not related to the bulk saturation of the magma in sulphides. We propose that the Nadezhda Cu-Ni-PGE mineralization formed as a result of local sulphide saturation that was achieved in situ at the margins as a result of the flux of ore-bearing fluids from the interior of the body towards its margins. The sulphides became PGE-rich due to interaction with a large volume of ore-bearing fluids that were introduced into the Nadezhda body during a juvenile stage of its development as a conduit through which a large volume of magma has passed on its way to the main chamber. Authors’ addresses: R. M. Latypov and S. Yu. Chistyakova, Kola Science Centre, Geological Institute, Fersman Str. 16, 184200 Apatity, Russia; Present address: Department of Geosciences, University of Oulu, P. O. Box 3000, Oulu, FIN-90014, Finland; T. T. Alapieti, Department of Geosciences, University of Oulu, P. O. Box 3000, Oulu, FIN-90014, Finland  相似文献   

2.
Summary The 100 m thick and 700 m long Nadezhda body in the Lukkulaisvaara layered intrusion exhibits concentric zonation with an inward progression from a 0.5 to 1.0 m thick marginal layer of medium- to coarse-grained norites and gabbronorites that abruptly give way to fine-grained oikocrystic gabbronorites composing the rest of the body. The concentric zonation is additionally emphasized by well-developed alignment of plagioclase laths and orthopyroxene oikocrysts parallel to the outer contacts of the body, pegmatitic gabbronorite segregations in the centre of the body and slight inward decrease in whole-rock Mg# and Cr and increase in incompatible elements. The body has distinctly higher whole-rock Mg# and lower concentrations of all incompatible components than its host rocks. It is enveloped by highly altered marginal anorthosites belonging to host norites and gabbronorites. We interpret the Nadezhda body as a portion of high Mg# (∼75%) and incompatible element-poor (∼20 ppm, Zr; ∼10 ppm, total REE; ∼0.20 wt%, TiO2) magma that replenished the evolving chamber and became trapped within the cumulate pile. Recrystallization of adjacent rocks by volatiles exsolved from the magma upon emplacement resulted in formation of marginal anorthosites. Upon cooling the magma started to crystallize medium- to coarse-grained norites along its margins, but subsequent decompression and loss of volatiles led to rapid crystallization of magma into fine-grained oikocrystic gabbronorites. Solidification of the remaining residual liquid gave rise to pegmatitic gabbronorite segregations. Supplementary material to this paper is available in electronic form at Tables 3–6 available as electronic supplementary material Authors’ addresses: R. M. Latypov, S. Yu. Chistyakova, Kola Science Centre, Geological Institute, Fersman Str. 16, 184200 Apatity, Russia; Present address: Department of Geosciences, University of Oulu, P.O. Box 3000, Oulu, FIN-90014, Finland; T. T. Alapieti, Department of Geosciences, University of Oulu, P.O. Box 3000, Oulu, FIN-90014, Finland  相似文献   

3.
Summary An unusually thick sulfur-poor mineralized zone enriched in platinum-group elements (PGE) is described in the Hanumalapur Complex, Shimoga District, Karnataka State, India. This promising occurrence was discovered in the early 1990s and the best samples at the time of writing have yielded Pt+Pd concentrations in excess of six ppm. The western part of the area concerned belongs to the late Archaean Dharwar Super Group (3000–2500 Ma), while the eastern part is occupied predominantly by a granite-gneiss terrain ∼3000 Ma in age. Ten mafic-ultramafic complexes which host interesting vanadium-bearing titanomagnetite occurrences are encountered in the western part, one of which is the Hanumalapur Complex. The PGE mineralized zone in this complex may be divided into four mineralogically distinctive types, which are, in descending order of PGE content: 1) a silicate-hosted Pd type, 2) a silicate-hosted Pt type, 3) a base-metal sulfide-hosted Pd type, and 4) an oxide-hosted PGE type. The genesis of the mineralization is somewhat unclear at this point of investigation, especially because of complete re-crystallization, but the evidence gathered so far suggests something different than a traditional orthomagmatic model requiring magma mixing processes and resulting in sulfide immiscibility. This is backed-up by the general lack of base metal sulfides in favor of chromite, although pure chlorite-amphibole and chlorite-albite-epidote-amphibole rocks may contain significant PGE concentrations regardless of the amount of chromite. The PGM textures show little evidence of hydrothermal alteration and remobilization, but the PGE mineralogy itself displays some characteristics of fluid action, as it seems that there are some OH-bearing Pt and Pd minerals present. The first author was Deceased Author’s address: R. J. Kaukonen, Department of Geosciences, University of Oulu, Oulu, P.O. Box 3000, FIN-90014 Finland  相似文献   

4.

Report

III. International Drumlin Symposium 26.6. – 2.7.1990 Oulu, Finland  相似文献   

5.
 The average strength, s, of the bonded interactions comprising a cation containing oxide anion coordination polyhedron and the value of the electron density, ρ(r c ), at the bond-critical points are inversely correlated with bond length. In each case, the observed bond lengths, R, were modeled with power-law expressions defined in terms of s/r and ρ(r c )/r, respectively, where r is the Periodic Table row number of the cation involved in the bonded interaction. On the basis of the close connection between bond strength and the value of the electron density at the bond-critical point, we conclude that bond strength is a direct measure of bond type; the greater its value, the greater the localization of electron density in the binding region and the greater the shared–electron covalent character of the bonded interaction. Received: 15 October 2002 / Accepted: 17 February 2003 Present address:G. V. Gibbs in care of M. Spackman Department of Chemistry, University of New England, Armidale 2351, Australia Acknowledgements The NSF is thanked for supporting this study with grant EAR–9627458. The paper was written while GVG was a Visiting NSF Scholar at The University of Arizona. The faculty and graduate students of the Department of Geosciences and Bob Downs and Marelina Stimpf in particular are thanked for making the visit great fun.  相似文献   

6.
The chilled margins of the Michikamau, Muskox, Skaergaard, and Bushveld intrusions were experimentally remelted over a range of f O 2. The observed primary phases, at certain values of f O 2 (generally 10–12 to 10–8 atm) correspond with the reported mineralogy of the earliest cumulates. Previous investigations appear to have been conducted at higher values of f O 2 (>10–6 atm) at which the experimental mineralogy did not relate to the cumulates.October 1973 to October 1974 at Division of Tribophysics, C.S.I.R.O., P.O. Box 4331, Melbourne, Victoria 3001, Australia.  相似文献   

7.
Petrology of the Partridge River Intrusion, Duluth   总被引：2，自引：1，他引：2  
Drill core DDH-221 was drilled for the Minnamax Project by AMAX Exploration, Inc., as part of the exploration for Cu-Ni sulfidesin the basal rocks of the northwestern margin of the DuluthComplex. The drill core intersects 525 m of the Partridge RiverIntrusion before passing into the Virginia Formation footwall.The rocks in the drill core comprise plagioclase and olivinecumulates, with troctolite and olivine gabbro as the most commonrock types. Sulfide- and oxide-bearing gabbros are present inthe lowest 100 m of the core where decreases in the crystalsizes of plagioclase and olivine, and the appearance of ophitictextures adjacent to the footwall, indicate that the chilledmargin of the intrusion has been preserved (Chalokwu & Grant,1990). The concentrations of incompatible elements in the wholerocks and the iron contents of olivine and pyroxenes all increasesharply in the lowest 100 m of the drill core (Chalokwu &Grant, 1990), and are interpreted as the downward increase inintercumulus liquid now preserved as intercumulus phases, andthe reaction of this liquid with olivine and pyroxenes. Mass, balance calculations for rocks containing widely differentvolumes of intercumulus phases show that the intercumulus liquidwas a chemically uniform ferrodiorite that can be derived fromKeweenawan high-alumina olivine tholeiite by plagioclase (An63),clinopyroxene (En50Fs10Wo40), and olivine (Fo71) fractionation. Initial 87Sr/86Sr values for plagioclase range between 0–704764and O-706335, with the highest values occurring adjacent tothe footwall Virginia Formation, and the lowest at intermediatedepths in the core. These variations are similar to 87Sr/86Srvalues reported earlier by Grant & Moiling (1981) From theadjacent core DDH-295, although the values are all greater thanpublished initial ratios for the least altered Keweenawan lavas.We attribute the isotopic variations in core DDH-221 to isotopicheterogeneities in the Partridge River Intrusion magmas, andto limited assimilation of the Virginia Formation within 50m of the footwall. Rare-earth and other trace elements in the intercumulus liquidfrom core DDH-221 have similar distributions to the same elementsin Keweenawan basic to intermediate lavas. We conclude that the rocks of the Partridge River Intrusionsampled in drill core DDH-221 comprise a mechanical mixtureof cumulus plagioclase and olivine and intercumulus liquid thatwere not in equilibrium with each other, and that the intercumulusliquid was broadly consanguineous with Keweenawan high-aluminaolivine tholeiite lavas, but was modified to a greater extentby assimilative exchange with continental crust. After emplacement,the crystal-liquid mixture was modified by flotation of thecumulus plagioclase out of the basal zone, and by limited —but not ubiquitous — assimilation of footwall VirginiaFormation.  相似文献   

8.
The intercumulus liquid of a crystal mush fills pore spaces,and typically solidifies to form overgrowths on cumulus grainsand poikilitic post-cumulus minerals. If the liquid is immobile,solidification produces zoned intercumulus minerals, as a resultof progressive fractionation of the residual liquid. Convectionwithin the mush results in buffering of the liquid composition,and thus limits mineral zonation. For fully solidified cumulates,‘fossil’ changes in liquid composition or porosityare difficult to identify. However, detailed study of immobileminor components of plagioclase overgrowth rims can provideinformation about the progressive solidification of intercumulusmaterial. Ti contents of plagioclase overgrowths, in samplesfrom the lowermost parts of the Skaergaard Intrusion, show strongvariations with anorthite content. With decreasing XAn, Ti concentrationsfirst rise and then fall, consistent with changing TiO2 contentsof the intercumulus liquid during solidification. TiO2 in plagioclasedecreases sharply at An55, reflecting local saturation of Fe–Tioxides. Ti in clinopyroxene oikocrysts also falls rimward, butzoning in faster diffusing species (Fe, Mg) is limited. Otherthan slight reverse zones that may occur on the plagioclasemargins, XAn falls continuously during crystallization. Thereverse zoning is interpreted as the result of compaction-drivendissolution and reprecipitation of plagioclase. The continualdecrease in XAn is exploited, together with back-scattered electronimages of the cumulates, to produce calibrated images showingregions of progressive crystallization. This allows the regionscrystallizing at each stage of solidification to be visualized.These images show that the final remnants of interstitial meltwere present in triangular pockets and as thin grain-boundarymelt films. This approach can provide information about theprogressive reduction of porosity during cumulate solidification. KEY WORDS: residual liquid; cumulate; plagioclase; porosity; Skaergaard  相似文献   

9.
The Mordor Alkaline Igneous Complex (MAIC) is a composite intrusion comprising a body of syenite and a funnel-shaped layered mafic–ultramafic intrusion of lamprophyric parentage, the Mordor Mafic–Ultramafic Intrusion or MMUI. The MMUI is highly unusual among intrusions of lamprophyric or potassic parentage in containing primary magmatic platinum-group element (PGE)-enriched sulfides. The MMUI sequence consists largely of phlogopite-rich pyroxenitic cumulates, with an inward dipping conformable layer of olivine-bearing cumulates divisible into a number of cyclic units. Stratiform-disseminated sulfide accumulations are of two types: disseminated layers at the base of cyclic units, with relatively high PGE tenors; and patchy PGE-poor disseminations within magnetite-bearing upper parts of cyclic units. Sulfide-enriched layers at cycle bases contain anomalous platinum group element contents with grades up to 1.5 g/t Pt+Pd+Au over 1-m intervals, returning to background values of low parts per billion (ppb) on a meter scale. They correspond to reversals in normal fractionation trends and are interpreted as the result of new magma influxes into a continuously replenished magma chamber. Basal layers have decoupled Cu and PGE peaks reflecting increasing PGE tenors up-section, due to increasing R factors during the replenishment episode, or progressive mixing of between resident PGE-poor magma and more PGE-enriched replenishing magma. The presence of PGE enriched sulfides in cumulates from a lamprophyric magma implies that low-degree partial melts do not necessarily leave sulfides and PGEs in the mantle restite during partial melting. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

10.
江苏省新沂市马陵山地区的4个神秘的印记,传统上被解释为“李存孝打虎处”的“虎爪印”和“人足迹”,重新将其解释为大盛群田家楼组恐龙足迹。这些足迹中只有一个最深的“虎爪印”保存了可识别的趾印,表明它是一个有着后内侧拇趾印的兽脚类恐龙左足迹,是一道单步约50cm的直线行迹的一部分;另一种解释是该足迹为小型蜥脚类恐龙的右后足迹,形成行迹的右侧部分,其左侧部分没有保存。马陵山足迹点提供了恐龙足迹如何影响中国民间传说的另一个案例。  相似文献   

11.
The Ultramafic Series of the Stillwater Complex in the MountainView area of the intrusion consists of 17 cyclic units thathave been numbered stratigraphically. A typical unit has olivinecumulates at the base, olivine–bronzite cumulates at intermediatelevels, and bronzite cumulates at the top. Most cyclic unitsalso have chromite-rich layers near their base, the thickestbeing the G and H chromitite zones in units 10 and 11. The Gand H zones are each separated from the top of the underlyingcyclic unit by 1–3 m of coarse-grained olivine cumulateand pegmatite; and they are both succeeded by thinner chromititezones, respectively called the hanging wall G (HWG) and thehanging wall H (HWH) zones, situated {small tilde}20 m and 5m above them. The G and H chromitite zones feature rhythmicsequences of thin layers that tend to progress upward from massivechromitite through chromite–olivine cumulate to olivine–chromitecumulate (the last with the minerals in approximately cotecticproportions of about 98:2). In cyclic units 10 and 11, variationsof Mg/Fe in the olivine and bronzite, and of Ni in the olivine,are small and show no clear stratigraphic fractionation trends.The abundance of Cr in the chromite in unit 10 does have a fractionationtrend, however, being generally highest at the bottom of theunit and lowest at the top, with a regression at the HWG zone.In general, Cr in chromite is highest at the base of a rhythmicunit and decreases upward, but it shows no overall decline throughsuccessive rhythmic units; Fe3 exhibits opposite variation,being lowest in the massive chromite, and highest in the disseminatedgrains. The G and H chromitite zones, in the Mountain View area, eachcontain enough chromite to form a single layer of massive chromitite{small tilde} 1 m thick. If their formation involved removalof only 30% of the Cr in the parental magmatic liquid (estimatedconcentration, 600 ppm), then this liquid could have amountedvolumetrically to an areally equivalent layer at least 2000m thick. Model calculations demonstrate that such a large volumeof liquid is consistent with the small variations of Mg/Fe inthe pyroxenes and olivines in the Stillwater cyclic units. We postulate that the G and H chromitite zones and cyclic unitsthat host them formed in response to the entry of new pulsesof primitive magmatic liquid into the Stillwater chamber. Fromexperimental observations, we infer that these pulses producedfountains in which the primitive liquid mixed with residualfractionated liquids, yielding hybrids that were compositionallywithin the chromite liquidus field (or volume) and that weresupercooled (supersaturated ) with respect to the oxide mineral.These effects may have been enhanced by low fO2 (oxygen fugacity)in the primitive liquid and(or) by high fO2 of the fractionatedliquid. The hybrid liquids probably collected at the bottomof the chamber in a zoned layer that then divided into double-diffusiveconvecting layers. In these circumstances, the lowest chromite-richlayer in a rhythmic sequence could have formed from the lowestdouble-diffusive liquid layer, and the next could then haveformed when this liquid mixed with the liquid layer above it—andso on up the sequence. We argue that the thick G and H chromititezones are situated toward the top of the Ultramafic Series becausethat level marks when the compositional contrasts between theinjected primitive liquid and the residual fractionated liquidsin the chamber were greatest.  相似文献   

12.
In this article, the shear behavior of discontinuities caused by bedding planes of weakness between two different rock types with high strength difference is investigated. The effect of roughness and compressive strength of joint wall in such discontinuities are studied. The designed profiles consist of two regular and three irregular artificial joints molded by three types of plaster mortars with different uniaxial compressive strengths. Firstly, it is demonstrated that the shear behavior of discontinuities with different joint wall compressive strengths (JCS) is different from rock joints with identical wall compressive strengths by showing that Barton’s empirical criterion is not appropriate for the former discontinuities. After that, some correlation equations are proposed between the joint roughness coefficient (JRC) parameter and some surface statistical/fractal parameters, and the normal stress range of Barton’s strength criterion is also modified to be used for such discontinuities. Then, a new empirical criterion is proposed for these discontinuities in such a way that a rational function is used instead of JRC log10(JCS/σ n) as i 0(σ c/σ n)a/[b + (σ c/σ n) a ] by satisfying the peak dilation angle boundary conditions under zero and very high normal stress (physical infinite normal stress causing zero peak dilation angle). The proposed criterion has three surface parameters: i 0, a, and b. The reason for separation of i 0 from JRC is indicated and the method of its calculation is mentioned based on the literature. The two remaining coefficients (a and b) are discussed in detail and it is shown that a shows a power-law relationship with b, introducing the coefficient c through b = c a . Then, it is expressed that a is directly related to discontinuity surface topography. Finally, it is shown that the coefficient c has higher values in irregular profiles in comparison with regular profiles and is dominated by intensity of peak dilation angle reduction (majorly related to the surface irregularity and minorly related to roughness). The coefficient c is to be determined by performing regression analysis on experimental data.  相似文献   

13.
To constrain the tectonic and metamorphic history of the GrenvilleProvince of southern Ontario we have quantitatively evaluatedchanges in peak metamorphic pressures and temperatures in theregion. Pressures increase northwest from the Frontenac Axistowards the Grenville Front, and they increase from 4–6kb near Madoc to 10–11 kb south of North Bay. Furtherto the north pressures decrease to 8–9 kb in the GrenvilleFront Tectonic Zone north of the French and Mattawa Rivers.Temperatures form a broad high, reaching 800?C northeast ofParry Sound, and decreasing to 400–500?C in the HastingsLow near Madoc, 600–650?C east towards the Ottawa River,and 650–700?C near Sudbury. This regional P-T distributionis in good agreement with constraints available from the distributionof aluminosilicate polymorphs. Comparison of thermobarometric results with regional tectonicfeatures shows a sharp discontinuity across the Mattawa andFrench Rivers, with a 1–2-kb pressure drop to the north.This implies that the major movement along this zone since theGrenville event was ‘south-side-up’ rather than‘north-side-up’ as suggested by Lumbers (1971).Large P-T discontinuities are not apparent across the domainboundaries mapped by Davidson and co-workers east of Parry Sound,but small discontinuities may exist. Sparse data may indicatethat the Central Metasedimentary Belt equilibrated at 1–2kb lower pressures than the Central Gneiss Terrane. Zoning profiles in garnet-pyroxene pairs have been used to placeconstraints on the metamorphic pressure-temperature-time pathin the Parry Sound, Port Severn, Bancroft, and Mattawa areasof the Grenville Province, Ontario. A nonlinear fitting routinewas used to obtain best-fit core and rim analyses for garnetsand pyroxenes. These results were combined with plagioclasecore/rim analyses to obtain estimates of peak and retrogradeconditions. The resultant retrograde P-Tpath has a slope of7 ? 10 b/?C, and involves pressure changes of 0?6–2?1kb for temperature changes of 60–130?C. Present address: Department of Geosciences, University of Arizona, Tucson, Arizona 85721  相似文献   

14.
The 160 km2 Caledonian Fongen-Hyllingen complex is an extremelydifferentiated, layered, basic intrusion, synorogenically emplacedat 5–6 kb in the allochthonous Trondheim nappe complex,situated in the Trondheim region of Norway. A zone of gabbroic rocks without rythmic layering usually occursalong the margin and a supposed feeder to at least part of thecomplex is preserved. A wide variety of magmatic sedimentarystructures are present in the c. 10,000 m thick sequence ofrhythmically layered rocks which vary from olivine-picotitecumulates at the base to quartz-bearing ferrosyenites at thetop. Mineral compositions, fractionation trends, and the compositionof feeder rocks suggest a tholeiitic parent. Mineral compositions cover extreme ranges. Olivine varies fromFo86·2 to Fo0·2 with a hiatus between about Fo71and Fo61. Plagioclase ranges from An79·5 to An1·5,albite coexisting with orthoclase microperthite in the finaldifferentiates. Cumulus Ca-poor pyroxene (Wo2.4En66.8Fs30.8-Wo2·0En17·0Fs81·0)first shows sporadic inversion from pigeonite at the Fe-richcomposition of Fs67 and the final Ca-poor pyroxenes are replacedby magmatic grunerite which reaches an Mg: Fe ratio of 12:88.Ca-rich pyroxenes (Wo44·7En43·8Fs11·5-Wo47·0En0Fs53·0)are highly calcic and have a slight Ca-minimum in the earlystages, unrelated to the disappearance of Ca-poor pyroxene.Calcic amphibole, a constant intercumulus phase in most of thecomplex, becomes a cumulus phase in the later stages and variesfrom titanian-pargasite to ferro-edenite. Magnetite and ilmenitejoin the cumulate assemblage at Fo55 and ilmenite persists intothe final quartz-bearing ferrosyenite where it shows replacementby sphene. Apatite, biotite, zircon, quartz, K-feldspar andallanite join the final extreme differentiates in the namedsequence. The fractionation trend is, in many respects, transitionalbetween those typical of the tholeiitic and calc-alkaline series,and is interpreted as reflecting crystallization under moderate,increasing PH2O. Cryptic layering shows several reversals to higher temperatureassemblages with increasing stratigraphic height. Successivereversals are to irregular compositions and measured in termsof olivine composition, can be up to about 30 mole per centFo. The minimum stratigraphic thickness to include the entirefractionation range is reduced to about 2200 m after ‘removal’of the compositional overlaps due to the reversals. Thus roughlythree-quarters of the present cumulate stratigraphic sequencerepresents magma replenishment. A mechanism involving the mixingof fresh magma batches with the residual, differentiated magmafrom the previous influx, is envisaged. The periodic influxof fresh magma took place into a chamber which was probablyclosed to the exit of material.  相似文献   

15.
Adcumulate formation in mafic layered intrusions is attributed either to gravity-driven compaction, which expels the intercumulus melt out of the crystal matrix, or to compositional convection, which maintains the intercumulus liquid at a constant composition through liquid exchange with the main magma body. These processes are length-scale and time-scale dependent, and application of experimentally derived theoretical formulations to magma chambers is not straightforward. New data from the Sept Iles layered intrusion are presented and constrain the relative efficiency of these processes during solidification of the mafic crystal mush. Troctolites with meso- to ortho-cumulate texture are stratigraphically followed by Fe–Ti oxide-bearing gabbros with adcumulate texture. Calculations of intercumulus liquid fractions based on whole-rock P, Zr, V and Cr contents and detailed plagioclase compositional profiles show that both compaction and compositional convection operate, but their efficiency changes with liquid differentiation. Before saturation of Fe–Ti oxides in the intercumulus liquid, convection is not active due to the stable liquid density distribution within the crystal mush. At this stage, compaction and minor intercumulus liquid crystallization reduce the porosity to 30%. The velocity of liquid expulsion is then too slow compared with the rate of crystal accumulation. Compositional convection starts at Fe–Ti oxide-saturation in the pore melt due to its decreasing density. This process occurs together with crystallization of the intercumulus melt until the residual porosity is less than 10%. Compositional convection is evidenced by external plagioclase rims buffered at An61 owing to continuous exchange between the intercumulus melt and the main liquid body. The change from a channel flow regime that dominates in troctolites to a porous flow regime in gabbros results from the increasing efficiency of compaction with differentiation due to higher density contrast between the cumulus crystal matrix and the equilibrium melts and to the bottom-up decreasing rate of crystal accumulation in the magma chamber.  相似文献   

16.
Summary Oxygen isotope ratios of igneous zircon from magmatic rocks in Finland provide insights into the evolution and growth of the Precambrian crust during the Svecofennian orogeny. These data preserve magmatic δ18O values and correlate with major discontinuities in the lower crust. Oxygen isotope ratios of zircon across the 1.88–1.87 Ga Central Finland granitoid complex (CFGC) range from 5.50‰ to 6.84‰, except for three plutons in contact with the adjacent greenstone and metasedimentary belts (δ18O(Zrc) = 7.60‰–7.78‰). There is a systematic variation in δ18O(Zrc) with respect to geographic location in the CFGC, ranging from 6.60±0.23‰ (σ) in the northeast to 5.90±0.40‰ in the west-southwest. These values correlate with a change in crustal thickness and shift in geochemical composition. The oxygen isotope composition of the 1.65–1.54 Ga rapakivi granites and related rocks in southern Finland show a decreasing trend from north to south, independent of their emplacement age. The southern anorogenic granite group has an average δ18O in zircon of 6.14±0.07‰ and the northern anorogenic group has an average δ18O in zircon of 8.14±0.59‰. This difference reflects the boundary between island arc terrains accreted during the Paleoproterozoic. Deceased  相似文献   

17.
The basal area and productivity of managrove wetlands are described in relation to selected soil properties to understand the general pattern of optimum forest stature at the mouth of estuaries in the Everglades, such as the Shark River Slough, Florida (U.S.). The basal area of mangroves decreases from 40.4 m2 ha−1 and 39.7 m2 ha−1 at two stations 1.8 km and 4.1 km from the estuary mouth to 20.7 m2 ha−1 and 19.6 m2 ha−1 at two sites 9.9 km and 18.2 km from the mouth, respectively. The gradient in basal area at these four sites is mostly the result of approximately 34 yr of growth since Hurricane Donna. Wood productivity is higher in the lower estuary (10.7 Mg ha−1 yr−1 and 12.0 Mg ha−1 yr−1) than in the upper estuary (3.2 Mg ha−1 yr−1 and 4.2 Mg ha−1 yr−1). Porewater salinity among these four mangrove sites during seasonal sampling in 1994 and 1995 ranged from 1.6 g kg−1 to 33.5 g kg−1, while sulfide was generally<0.15 mM at all sites. These soil values indicate that abiotic stress cannot explain the decrease in forest structure along this estuarine gradient. Concentrations of nitrogen (N) and phosphorus (P) are more closely related to patterns of forest development, with higher soil fertility at the mouth of the estuary as indicated by higher concentrations of extractable ammonium, total soil P, and available P, along with higher ammonium production rates. The more fertile sites of the lower estuary are dominated by Laguncularia racemosa, whereas the less fertile sites in the intermediate and upper estuary are dominated by Rhizophora mangle. Relative N mineralization per unit of total N is higher in the lower estuary and is related positively to concentrations of available P, indicating the importance of turnover rates and nutrient interactions to soil fertility. Concentrations of Ca-bound P per volume soil in the lower estuary is 40-fold higher than in the upper estuary, and along with an increase in residual P in the upper estuary, indicate a shift from mineral to organic P along the estuarine gradient. Mineral inputs to the mouth of Shark River estuary from the Gulf of Mexico (rather than upland inputs) apparently control the patterns of mangrove structure and productivity.  相似文献   

18.
Initial 87Sr/86Sr ratios down a 2,315 foot-long core (DDH-295) through the Partridge River Troctolite are lower in the depth range 710–1,410 feet (0.70443±22) than in the underlying and overlying rocks (0.70500±18). These initial ratio variations define three zones (I, II, and III) thought to be three intrusive units within the troctolite. The best estimate of the Rb-Sr age of the troctolite is 1,050±105 m.y. The olivine compositions and the abundances of the incompatible trace elements Zr, Y, and Rb show identical variations down the core, with downward repetitions of olivine iron-enrichment and incompatible trace element enrichments. Discontinuities in the olivine compositions and incompatible trace element abundances match the initial 87Sr/86Sr ratio discontinuities in the core. The strontium isotope data imply that involatile components of the Proterozoic Virginia Formation and other Archaean rocks were not significantly assimilated by the troctolites, for only three out of the twenty-three initial 87Sr/86Sr ratios depart from normal magmatic values. These three anomalous ratios are not systematically related to the Cu-Ni sulphide mineralization and may be the result of secondary calcite in the troctolite. The strontium isotope systematics of the Virginia Formation xenoliths and underlying hornfelses are highly disturbed as a result of Rb loss. The apparently inverted fractionation sequences in the troctolites are interpreted in terms of downward increases in intercumulus liquid in repeated magma batches and controlled by plagioclase flotation. The amount of intercumulus liquid is estimated to range from 7 to 61 weight per cent. The Cu-Ni sulphides are concentrated in the lower 250 feet of zone I (immediately above the Virginia Formation) and through 400 feet of core across the contact between zones I and II, more than 750 feet above the base. Because the sulphide-bearing troctolites are not systematically related to disturbances in the magmatic initial 87Sr/86Sr ratios, the mineralization probably involved the volatile transfer of sulphur derived from dehydration reactions in the underlying Virginia Formation.  相似文献   

19.
Recent low temperature, adiabatic calorimetric heat capacity measurements for grossular have been combined with DSC measurements to give entropies up to 1000 K. In conjunction with enthalpy of solution values for grossular, these data have yielded H f o (298.15K) and G f o (298.15K) values of –1583.2 ± 3.5 and –1496.74 ± 3.7 kcal mol–1 respectively. For 15 reactions in the CaO-Al2O3-SiO2-H2O system, thermodynamically calculated P-T curves have been compared with experimental reversals and have shown good agreement in most cases. Calculations indicate that gehlenite is probably totally disordered. Estimates of zoisite and lawsonite entropies are consistent with the phase equilibrium and grossular data, but estimates of the entropies of pyrope and andradite show large discrepancies when compared with experimental reversals.Contribution no. 600 from the Mineralogical Laboratory, The Department of Geology and Mineralogy, The University of Michigan, Ann Arbor, Michigan 48109, USA  相似文献   

20.
Summary The Neoproterozoic Bou Azzer ophiolite complex hosts numerous, small lenticular bodies of massive and disseminated chromite. Metallurgical-grade high-Mg and high-Cr spinels (cores with 48–62 wt% Cr2O3) reveal complex alteration patterns of successive Cr and Mn enrichment and loss of Al towards the rims, while the Mg# ratios [(Mg/(Mg + Fe2+)] remain almost constant. Concentration patterns of platinum-group elements are typical for ophiolitic chromitite poor in sulfides, with predominance of the IPGE, variable Rh, and low Pt and Pd. The most abundant platinum-group mineral is Rh-bearing laurite that occurs either included in spinel or in silicate matrix, whereas Os-Ir-Ru alloy is always included in spinel. Laurite inclusions reveal complex intergrowth textures with Rh-Ru-Pt rich alloy, and with Rh-rich sulfide. Most laurites display trends to sulfur-poor compositions leading to local formation of very fine-grained Ru-Os-Ir alloy phases. Ni-Co-Fe sulfides, arsenides and sulfarsenides devoid of PGE are associated with the alteration of chromite. Textural position and chemical composition of the base metal inclusions, as well as comparison of alteration features between chromite and accessory chromian spinel in the Co-Ni-As ores of the Bou Azzer ophiolite indicate a close connection. It is suggested that hydrothermal fluids percolated through the marginal zones of the ophiolite belt during greenschist facies metamorphism and deposited Ni-Co-Fe arsenides, sulfarsenides and minor sulfides as accessories within altered chromitites, and also in structurally favourable zones as Ni-Co-As ores. Author’s address: Dr. Frank Melcher, Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover, Germany  相似文献   

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