排序方式： 共有40条查询结果，搜索用时 15 毫秒
1.
M. T. McCulloch T. K. Kyser J. D. Woodhead L. Kinsley 《Contributions to Mineralogy and Petrology》1994,115(3):303-312
A comprehensive Sr–Nd–Pb–O isotopic study is reported for rhyolites from the Maroa Volcanic Centre in the Taupo Volcanic Zone (TVZ) of New Zealand. The Sr–Nd isotopic compositions of the rhyolites (87Sr/86Sr=0.705236 to 0.705660 and Nd = 2.0 to 0.2) are intermediate between those of primitive basalts (87Sr/86Sr=0.70387 and Nd = 5.3) and the Torlesse basement (87Sr/86Sr=0.709 and Nd = -4.5). The relatively low mantle-like oxygen isotopic compositions of 18 O = 7 ± 0.5 are consistent with the Nd-Sr isotopic constraints in that they can be accounted for by 15% to 25% crustal contamination of a basaltic parent by relatively 18 O-rich Torlesse metasediment. High precision Pb isotopic analyses of plagioclase separates from the Maroa rhyolites show that they have essentially the same compositions as the Torlesse metasedimentary terrane which is itself distinctive from the Western or Waipapa metasediments. Due to the high concentration of Pb in the Torlesse metasediments (>20 ppm) compared to the basalts (<2 ppm), the Pb isotopic composition of the volcanics may be controlled by relatively small amounts (>10%) of crustal contamination. All these results are shown to be consistent with derivation of the rhyolites by 15% to 25% contamination of relatively primitive basaltic magmas with Torlesse metasedimentary crust, followed by extensive, essentially closed system fractionation of the basalt to a magma of rhyolite composition. It is argued that the processes of assimilation and fractionation are separated in both space and time. The voluminous high silica rhyolites, which make up >97% of the exposed volcanism in the continental margin back-are basin environment of the TVZ, therefore appear to be a product of predominantly new additions to the crust with assimilation-recycling of pre-existing crust being of secondary importance. 相似文献
2.
The effects of liquid immiscibility and thermal diffusion on oxygen isotopes in silicate liquids 总被引：2，自引：1，他引：1
Differences between the δ18O values of Si- and Fe-rich immiscible liquids in the system Fe2SiO4-KAlSi2O6-SiO2 (Fa-Lc-Q) in isothermal experiments at 0.1 MPa have been determined experimentally to be 0.6 permil. The observed partition
of 18O into the Si-rich liquid is consistent with previous experience with the preferential partition of 18O into Si-rich minerals in isothermal equilibrium with minerals of less polymerized structure. Crystallochemical principles
affect the distribution of oxygen isotopes in coexisting isothermal liquids in the same way as they apply to isothermally
coexisting crystals. The effects of Soret (thermal) diffusion on the distribution of oxygen isotopes in silicate liquids above
the solvus in the system Fa-Lc-Q under conditions of an imposed temperature gradient of ca. 250 °C over 4 mm and at 2 GPa
have also been investigated experimentally. Both the magnitude and the direction of separation of oxygen isotopes as a result
of Soret diffusion are unexpected. For each of the silicate liquids, the cold end of the charge is enriched in 18O by up to 4.7 permil, and the highest δ18O values are associated with the most silica-poor compositions. The distribution of oxygen isotopes appears to be similar
in each liquid, regardless of their chemical compositions, which is in contrast to the behaviour of cations whose distributions
are compositionally dependent and characterized by strong crystallochemical effects wherein network-forming species such as
Si and Al separate to the hot end and Mg, Fe and Ca are segregated preferentially to the cold end. Structural units in the
melts are evidently less selective between oxygen isotopes than between cations, because oxygen redistribution over all possible
sites in these units proceeds according to mass. Self-diffusion coefficients of oxygen in basaltic liquids estimated from
the Soret experiments are in accord with those from other isotope tracer experiments, and comparable to those of Si. The possible
effects of Soret diffusion on the oxygen isotopic composition of metasomatic veins in the mantle are examined in light of
these data, and indicate that decay of the thermal gradients in the veins exceeds that of the diffusion of oxygen needed to
produce variations in the δ18O values of mantle minerals. Variations in oxygen isotope ratios in most natural systems as a result of Soret effects are
unlikely.
Received: 6 January 1997 / Accepted: 28 June 1998 相似文献
3.
4.
The Valhalla uranium deposit, located 40 km north of Mount Isa, Queensland, Australia, is an albitite-hosted, Mesoproterozoic
U deposit similar to albitite-hosted uranium deposits in the Ukraine, Sweden, Brazil and Guyana. Uranium mineralisation is
hosted by a thick package of interbedded fine-grained sandstones, arkoses and gritty siltstones that are bound by metabasalts
belonging to the ca. 1,780 Ma Eastern Creek Volcanics in the Western Succession of the Mount Isa basin. Alteration associated
with U mineralisation can be divided into an early, main and late stage. The early stage is dominated by laminated and intensely
altered rock comprising albite, reibeckite, calcite, (titano)magnetite ± brannerite. The main stage of mineralisation is dominated
by brecciated and intensely altered rocks that comprise laminated and intensely altered rock cemented by brannerite, apatite,
(uranoan)-zircon, uraninite, anatase, albite, reibeckite, calcite and hematite. The late stage of mineralisation comprises
uraninite, red hematite, dolomite, calcite, chlorite, quartz and Pb-, Fe-, Cu-sulfides. Brannerite has U–Pb and Pb–Pb ages
that indicate formation between 1,555 and 1,510 Ma, with significant Pb loss evident at ca. 1,200 Ma, coincident with the
assemblage of Rodinia. The oldest ages of the brannerite overlap with 40Ar/39Ar ages of 1,533 ± 9 Ma and 1,551 ± 7 Ma from early and main-stage reibeckite and are interpreted to represent the timing
of formation of the deposit. These ages coincide with the timing of peak metamorphism in the Mount Isa area during the Isan
Orogeny. Lithogeochemical assessment of whole rock data that includes mineralised and unmineralised samples from the greater
Mount Isa district reveals that mineralisation involved the removal of K, Ba and Si and the addition of Na, Ca, U, V, Zr,
P, Sr, F and Y. U/Th ratios indicate that the ore-forming fluid was oxidised, whereas the crystal chemistry of apatite and
reibeckite within the ore zone suggests that F− and were important ore-transporting complexes. δ18O values of co-existing calcite and reibeckite indicate that mineralisation occurred between 340 and 380°C and involved a
fluid having δ18Ofluid values between 6.5 and 8.6‰. Reibeckite δD values reveal that the ore fluid had a δDfluid value between −98 and −54‰. The mineral assemblages associated with early and main stages of alteration, plus δ18Ofluid and δDfluid values, and timing of the U mineralisation are all very similar to those associated with Na–Ca alteration in the Eastern
Succession of the Mount Isa basin, where a magmatic fluid is favoured for this style of alteration. However, isotopic data
from Valhalla is also consistent with that from the nearby Mount Isa Cu deposit where a basinal brine is proposed for the
transport of metals to the deposit. Based on the evidence to hand, the source fluids could have been derived from either or
both the metasediments that underlie the Eastern Creek Volcanics or magmatism that is manifest in the Mount Isa area as small
pegmatite dykes that intruded during the Isan Orogeny. 相似文献
5.
Charles R. Stern Fred A. Frey Kiyoto Futa Robert E. Zartman Zicheng Peng T. Kurtis Kyser 《Contributions to Mineralogy and Petrology》1990,104(3):294-308
The Pliocene and Quaternary Patagonian alkali basalts of southernmost South America can be divided into two groups. The cratonic basalts erupted in areas of Cenozoic plateau volcanism and continental sedimentation and show considerable variation in 87Sr/86Sr (0.70316 to 0.70512), 143Nd/144Nd (Nd) and 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios (18.26 to 19.38, 15.53 to 15.68, and 38.30 to 39.23, respectively). These isotopic values are within the range of oceanic island basalts, as are the Ba/La, Ba/Nb, La/Nb, K/Rb, and Cs/Rb ratios of the cratonic basalts. In contrast, the transitional basalts, erupted along the western edge of the outcrop belt of the Pliocene and Quaternary plateau lavas in areas that were the locus of earlier Cenozoic Andean orogenic arc colcanism, have a much more restricted range of isotopic composition which can be approximated by 87Sr/86Sr=0.7039±0.0004, Nd, 206Pb/204Pb=18.60±0.08, 207Pb/204Pb=15.60±0.01, and 208Pb/204Pb=38.50±0.10. These isotopic values are similar to those of Andean orogenic are basalts and, compared to the cratonic basalts, are displaced to higher 87Sr/86Sr at a given 143Nd/144Nd and to higher 207Pb/204Pb at a given 208Pb/204Pb. The transitional basalts also have Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios higher than the cratonic and oceanic island basalts, although not as high as Andean orogenic are basalts. In contrast to the radiogenic isotopes, 18O values for both groups of the Patagonian alkali basalts are indistinguishable and are more restricted than the range reported for Andean orogenic are basalts. Whole rock 18O values calculated from mineral separates for both groups range from 5.3 to 6.5, while measured whole rock 18O values range from 5.1 to 7.8. The trace element and isotopic data suggest that decreasing degrees of partial melting in association with lessened significance of subducted slabderived components are fundamental factors in the west to east transition from arc to back-arc volcanism in southern South America. The cratonic basalts do not contain the slab-derived components that impart the higher Ba/La, Ba/Nb, La/Nb, Cs/Rb, 87Sr/86Sr at a given 143Nd/144Nd, 207Pb/204Pb at a given 208Pb/204Pb, and 18O to Andean orogenic arc basalts. Instead, these basalts are formed by relatively low degrees of partial melting of heterogeneous lower continental lithosphere and/or asthenosphere, probably due to thermal and mechanical pertubation of the mantle in response to subduction of oceanic lithosphere below the western margin of the continent. The transitional basalts do contain components added to their source region by either (1) active input of slab-derived components in amounts smaller than the contribution to the mantle below the arc and/or with lower Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios than below the arc due to progressive downdip dehydration of the subducted slab; or (2) subarc source region contamination processes which affected the mantle source of the transitional basalts earlier in the Cenozoic. 相似文献
6.
207Pb/204Pb versus 206Pb/204Pb model ages using Shonkin Sag data and published analyses for magmas of the Cenozoic Wyoming-Montana alkaline province (WYMAP) provide evidence of an Archean age for the subcontinental lithospheric mantle (SLM) associated with the Wyoming craton. The SLM imprint on magmas is expressed as Ba, Ta, Nb and Ti "anomalies" which correlate with radiogenic isotopic data, and it resembles a subduction imprint on Cenozoic south-western USA basalts (SWUSAB). However the latter give Proterozoic Pb isotope model ages. Although the Archean and Proterozic model ages may represent mixing lines, the fact that they resemble the ages for continental crust cut by WYMAP and SWUSAB respectively indicates that the age of the underlying SLM helped control the "isochron" slopes and inferred "ages". Lower 143Nd/144Nd and 206Pb/204Pb but comparable 87Sr/86Sr for WYMAP suggest that SLM associated with Archean cratons has lower Sm/Nd, U/Pb and Rb/Sr ratios than SLM associated with SWUSAB Proterozic terranes, regardless of when the subduction imprint or imprints developed. WYMAP magmas have high Pb/Zr ratios indicating that Archean SLM, like Archean continental crust, is enriched in Pb compared to Proterozoic SLM. If the enrichment was Archean, it implies that higher Archean heat flow enhanced Pb transfer from the subducting slab to overlying lithospheric mantle and crust. A subducted sediment imprint on the SLM is also consistent with high i18O values for the Shonkin Sag. Low TiO2 in WYMAP may reflect a residual mantle TiO2 phase. If so, the Nb "missing" from crustal and oceanic mantle reservoirs may reside in rutile of Archean SLM. Isotopic similarities between WYMAP and EM1 oceanic island basalts may reflect the presence of delaminated, Archean SLM in the oceanic mantle, although low Pb/Zr ratios and a lack of Ti, Nb and Ta anomalies in oceanic island basalts deserve further investigation. 相似文献
7.
T. K. Kyser W. E. Cameron E. G. Nisbet 《Contributions to Mineralogy and Petrology》1986,93(2):222-226
18O values of unaltered olivine and pyroxene phenocrysts in boninites from several areas range from 5.8 to 7.4 and indicate that the source for most boninites is more 18O-rich than MORBs and other oceanic basalts. The source for oxygen and other major elements is most likely a refractory portion of the mantle having a
18O value of up to 7.0 to which must be added a small amount of H2O-rich fluid to induce partial melting. This fluid, which is derived from subducted crust, is the vehicle for LREEs including Nd. The variable, normally low
Nd values typical of boninites do not correlate with the
18O values.Post eruptive exchange of oxygen in the glass of boninites with that of sea water at low temperatures (<150° C) produces
18O values of >10 in optically fresh glass. Hydration of the glass has increased the water contents of most boninites from estimated magmatic values of 1–2 wt% to 2–4 wt% and produced D values of < –80, which may be lower than the original magmatic D values. In contrast to most submarine pillow basalts, the magmatic volatile composition of boninite lavas has been extensively modified as a result of post eruptive interaction with seawater. 相似文献
8.
Robert T. Gregory Hugh P. Taylor Jr. T. Kurtis Kyser James R. O'Neil Ian S. E. Carmichael 《Contributions to Mineralogy and Petrology》1986,93(1):114-119
Kyser, O'Neil, and Carmichael (1981, 1982) measured the
18O values of coexisting minerals from peridotite nodules in alkali basalts and kimberlites, interpreting the nodules as equilibrium assemblages. Using Ca-Mg-Fe element-partition geothermometric data, they proposed an empirical18O/16O geothermometer: T(°C)=1,151–173–68
2, where is the per mil pyroxene-olivine fractionation. However, this geothermometer has an unusual crossover at 1,150 °C, and in contrast to what might be expected during closed-system equilibrium exchange, the most abundant mineral in the nodules (olivine) shows a much greater range in
18O (+4.4 to +7.5) than the much less abundant pyroxene (all 50 pyroxene analyses from spinel peridotites lie within the interval +5.3 to +6.5). On
18O-olivinevs.
18O-pyroxene diagrams, the mantle nodules exhibit data arrays that cut across the
18O=zero line. These arrays strongly resemble the non-equilibrium quartzfeldspar and feldspar-pyroxene
18O arrays that we now know are diagnostic of hydrothermally altered plutonic igneous rocks. Thus, we have re-interpreted the Kyser et al. data as non-equilibrium phenomena, casting doubt on their empirical geothermometer. The peridotite nodules appear to have been open systems that underwent metasomatic exchange with an external, oxygen-bearing fluid (CO2, magma, H2O, etc.); during this event, the relatively inert pyroxenes exchanged at a much slower rate than did the coexisting olivines and spinels, in agreement with available exchange-rate and diffusion measurements on these minerals. This accounts for the correlation between
18O pyroxene-olivine and the whole-rock
18O of the peridotites, which is a major difficulty with the equilibrium interpretation.Contribution No. 3978, Publications of the Division of Geological and Planetary Sciences, California Institute of Technology 相似文献
9.
Summary Zippa Mountain pluton is a Mesozoic concentrically-zoned intrusion, located within the Canadian Cordillera of British Columbia.
An extensive phase of K-feldspar bearing syenite grades towards its margins to mela-syenite and clinopyroxenite. This simple
pattern of petrological zonation is overprinted by localised occurrences of silica-undersaturated, peralkaline rock types.
High-purity wollastonite skarns occur within and peripheral to the intrusion and result from extensive interaction between
intrusion-related fluids and Permian limestone/marble, at shallow crustal levels. Field, chemical and isotopic studies provide
insights into interaction between a parental syenitic magma and these country rocks. To achieve this, petrological studies
of four of the skarn bodies present have been combined with chemical and isotopic data from the pluton, and from drill core
through the skarn into the pluton, to reconstruct the stages in the development of wollastonite skarn and progressive magma-country
rock interaction. Derivation of peralkaline compositions from the syenitic magma requires either a loss of Si and Al, or addition
of Na and/or K. Our studies preclude the addition of alkali elements but highlight extensive Si-infiltration into the limestone,
while the conversion of marble to grossular-andradite skarn, indicates Al-infiltration. Fluid egress resulted in de-silicification/de-alumination
of the Zippa Mountain magmas, and increased peralkalinity; wollastonite and garnet-bearing skarn formed as a by-product. Hence,
the development of peralkaline rock compositions at Zippa Mountain required a parental syenitic magma, and reaction and/or
interaction with calcareous country rocks.
Present address: Institut für Geowissenschaften, Universit?t Tübingen, Tübingen, Germany 相似文献
10.
To trace the fluid history of sedimentary basins requires integration of relatively diverse sub-disciplines including sedimentology, stratigraphy, tectonics, structural geology, petrography, geochemistry and geophysics. These aspects of basin evolution are interrelated and thus all are required to understand the source, character and distribution of fluids associated with ore deposits hosted in basins. Fluids are strategically associated with both the formation and preservation of almost every type of economic ore deposit in basins. As such, knowledge of the geochemical and physical characteristics, timing, origin, reactivity and flow histories of fluids are basic to formulating effective exploration strategies. 相似文献