Experimental studies of trace-element partitioning applicable to igneous petrogenesis (original) (raw)
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Chemical Geology, 1994
In the 16 years since the Sedona Conference on the behaviour of trace elements in silicate systems, numerous studies providing new data have filled many of the gaps in knowledge of trace-element partitioning evident at that conference. The advent of new microbeam techniques for in situ trace-element analysis has provided great impetus for this work. For example, values for large ion lithophile element (LILE) and high field strength element (HFSE) partitioning between olivine, pyroxene, garnet, amphibole and titanate minerals and silicate liquids have been determined. When plotted on mantle normalizing geochemical diagrams, partition coefficients for the main mantle silicate minerals show steeply inclined patterns (over several orders of magnitude) from LILE to heavy rareearth elements (HREE). Amphibole, however, has a relatively flat pattern (though still favouring HREE over LILE by about an order of magnitude). Also, there is a notable flattening of the patterns for HREE in pyroxenes and garnet relative to olivine.
Geochimica Et Cosmochimica Acta, 1998
To constrain the trace element composition of aqueous fluids in the deep crust and upper mantle, mineral-aqueous fluid partition coefficients (D min/fluid) for U, Th, Pb, Nb, Ba, and Sr have been measured for clinopyroxene, garnet, amphibole, and olivine in experiments at 2.0 GPa and 900°C. Ciinopyroxeneand garnet-fluid partition coefficients are similar for Nb (0.01-0.7) and Ba ( ~ 10-4-10-5), whereas values of D cpx/ttuid for Sr (0.5-4), Th (0.6-9), and Pb (0.04-0.09) are -10× (Th, Pb) to ~ 1000× (Sr) higher than O garnet/fluid. At the same fO2 (FMQ + 1), garnet-fluid partition coefficients for U are -10× higher than those for clinopyroxene. Amphibole-fluid partition coefficients are uniformly high ( -1 ) for all elements studied, and, with the exception of Ba, interelement fractionations are similar to clinopyroxene. The olivine-fluid partition coefficient for Nb is similar to values measured for the other silicates, whereas D °~Vm~/~u~J for U, Th, Pb, Sr, and Ba are significantly lower.
Lithos, 2013
The partitioning of a number of trace elements (LILE, HFSE, REE, Cu, Pb, Co, Ni) between mantle minerals (olivine, pyroxenes and garnet) and silico-carbonate melts was experimentally studied at 6-12 GPa and 1300-1700°C. The starting compositions were model kimberlitic with~30 wt.% SiO 2 , which differentiated to carbonatite-like melts with b10 wt.% SiO 2 depending on the degree of crystallization. The melts were rich in CO 2 (up tõ 30 wt.%) and contained 0 to 30 wt.% H 2 O. Trace elements were added to the starting mixtures to levels of 100 ppm. They were analyzed by LA ICP MS in the products of 18 experiments. The partition coefficients of Ba, La, Ta, and Nb are very low for all phases (b0.01). These elements are especially susceptible to contamination in the experimental products. We suspect that some relatively high values obtained for these elements in previous studies are overestimated. Generally, the partition coefficients (D s/l ) of the moderately incompatible and compatible elements increase in the sequence olivine-low-Ca pyroxene-high-Ca pyroxene. Garnet shows maximum fractionation of the trace elements, such that D values for the highly incompatible elements are lower than those for pyroxenes and highest for the HREE, Sc, and V. The partition coefficients of a number of incompatible elements are rather insensitive to pressure, temperature, and melt composition. There is no correlation between the partition coefficients and the content of H 2 O, CO 2 and the overall content of trace elements. They are predominantly controlled by the composition of the crystalline phases. In particular, garnet-liquid partitioning is very sensitive to Ca in garnet, and pyroxene-liquid partitioning to Al in pyroxene. The comparison of the obtained partition coefficients with the compositions of likely kimberlite magmas shows that depleted and refertilized harzburgite from the continental lithospheric mantle is a viable candidate as the source material of kimberlites. The estimation of trace element characteristics of near-solidus mantle melts indicates that the most reliable indicator of carbonate melt metasomatism is depletion of Zr and Hf relative to Sm and Nd. Criteria based on the ratios of more incompatible elements (e.g. Nb/La) are very sensitive to the melting conditions and can be misleading.
Trace-element zoning in mantle minerals; metasomatism and thermal events in the upper mantle
1996
Studies of trace-element zoning in mantle-derived rninerals can provide important constraints on the nature and time scales ofmetasomatic processes and thermal events in the upper mantle, and on diffusion rates. Zoning data on garnet in peridotite xenoliths restrict some metasomatic processes to geologically short time-spans (10-1ff years) prior to the eruption of the host magmas, and suggest that the metasomatism is genetically connected to the magmatic events or their immediate prccursors. Such metasomatism effects major changes in both the major-element and trace-element composition of the rocks, and these xenoliths should not be used to represent large volumes in the mantle. Modeling of heating and cooling rates, based on Ni zoning in game! suggests that the heating observed in high-T xenoliths is a transient phenomenon associated with local intrusion of magrna bodies. The relative lengths ef 2ening profiles for various elements in single crystals of gamet suggest that diffirsion coefficients, over the temperatffe range 1200-1400oC, decrease in the order Ni) Fe, Mn > Ti, Zt > Y (and heavy ^REE") = Ca > Cr, G4 V. Analyses of zo.ing profiles in gamet cooled from a high temperature suggest that rates of Ni dilhrsion are equivalent to those of Fe-Mg down to temperatures neax 600oC. Pyroxene equilibration during thermal and metasomatic events probably involves volume diffrrsion over very short distances only, beween high-mobility paths such as cleavage planes. Kelwords : 2ening, mantle, difflrsion, metasomatism, pyrope-rich gamet. SoM:raans L'6tude de la zonation eil 6l6ments traces des min6raux du manteau peut permettre de mieux cemer la nature des ptocessus et des 6v6nements m6tasomatiques du manteau sup6rieur, l'6chelle de temps n6cessaire pour leur d6veloppement, et les taux de diffrrsion. Les donn6es sur le gre4at des x6nolithes p6ridotitiques indiqueraient que certains processus m6tasomatiques se sont deroul6s sur une echelle de temps relativement courte (10-1ff ann6es) pr6c6dant l'6ruption des magmas h6tes.
Journal of Petrology, 2000
protogranular, Cr-diopside-bearing harzburgite; (2) poikilitic, Studies of upper-mantle xenoliths in alkali basalts, Mg-augite-bearing harzburgite and cpx-poor lherzolite; (3) dunite kimberlites, lamproites and carbonatites have improved that contains clinopyroxene, spinel phlogopite, and rarely amphibole. our understanding of materials and processes involved Trace element data for rocks and minerals identify distinctive in the geochemical evolution of the mantle (e.g. Downes signatures for the different rock types and record upper-mantle & Dupuy, 1987; Chalot-Prat processes. The harzburgites reflect an initial partial melting event & Boullier, 1997). The variation and magnitude of followed by metasomatism by mafic alkaline to carbonatitic melts. geochemical heterogeneities in the lithospheric mantle The dunites were first formed by reaction of a harzburgite protolith reflect the composition of mantle melts and fluids and with tholeiitic to transitional basaltic melts, and subsequently the efficiency of heat and mass transfer. Mantle plumes developed metasomatic assemblages of clinopyroxene + phlogopite are important for initiating such transfer processes. ± amphibole by reaction with lamprophyric or carbonatitic melts. The Kerguelen plume is remarkable because of its We measured two-mineral partition coefficients and calculated volume, the persistence of volcanic activity for at least mineral-melt partition coefficients for 27 trace elements. In most 115 My, and its migration across diverse geotectonic samples, calculated budgets indicate that trace elements reside in environments through time as a result of spreading of the constituent minerals. Clinopyroxene is the major host for REE, the Indian Ocean .
Trace Element Contents of Mantle-Derived Magmas Through Time
Journal of Petrology, 2021
A large compilation of quality-curated major and trace element data has been assembled to investigate how trace element patterns of mafic and ultramafic magmas have varied with time through particular settings from the Archean to the Phanerozoic, the primary objective being to recognise at what times particular patterns of variation emerge, and how similar these are to baseline data sets representing tectonic settings in the modern Earth. The most informative element combinations involve Nb, Th and the REE, where REE are represented by ‘lambda’ parameters describing slope and shape of patterns. Combinations of the ratios of Th, Nb, La and lambda values from Archean and early Proterozoic basalts and komatiites reveal a distinctive pattern that is common in most well-sampled terranes, defining a roughly linear trend in multi-dimensional space from compositions intermediate between modern n-MORB and primitive mantle at one end, towards compositions approximating middle-to-upper contine...
Trace elements and Sr-isotopes in some mantle-derived hydrous minerals and their significance
Geochimica et Cosmochimica Acta, 1978
New analyses of K, Rb, Sr and Ba contents and the 87Sr/86Sr ratios of eight amphiboles, one phlogopite, two diopsides, and one host alkalic basalt for an amphibole are reported: The samples are mostly inclusions in alkalic basalts and occur in association with peridotite inclusions. Two of the samples are from alpine-type peridotite bodies -one from the Etang de Lhers massif in the French Pyrenees and the other from the Finer0 massif in the Ivrea zone in northern-Italy.
Chemical Geology, 1995
Trace-element abundances in coexisting clinopyroxenes and garnets from five suites of mantle-derived garnet pyroxenite and eclogite xenoliths and two suites of eclogite inclusion pairs in diamonds have been determined by electron microprobe (Ti) and proton microprobe (Ni, Zn, Ga, Sr, Y, Zr). The sample sets provide garnet--clinopyroxene pairs from a range of depths on contrasting geothermal gradients (40-90 mW m 2) from South Africa, and western and eastern Australia. These data are used to assess the effects of phase composition, pressure (P) and temperature (T) on the partitioning of each element between garnet and clinopyroxene.
Earth and Planetary Science Letters, 2005
Iron isotopic compositions potentially provide a powerful new tracer of planetary formation and differentiation processes and of secular and spatial changes in mantle oxidation state. However, the processes governing iron isotope fractionation in igneous rocks remain poorly understood. Here we show that there are significant variations in the iron isotope compositions (d 57/54 Fe) of mantle rocks (0.9x) and minerals (olivines 0.6x, clinopyroxenes 0.9x and orthopyroxenes 0.8x), with spinels showing the greatest total variation of 1.7x. Positive linear functional relationships with slopes that are, within error, equal to unity are found between the d 57/54 Fe values of coexisting orthopyroxene, clinopyroxene and olivine, strongly suggesting that the d 57/54 Fe values of these minerals reflect intra-sample mineral-mineral isotopic equilibrium. Positive correlations between the d 57/54 Fe values of silicate minerals and spinels also exist, although they are more scattered, which could be caused by late disturbance of mineral-spinel isotopic equilibrium. Bulk-rock, clinopyroxene and spinel d 57/54 Fe values correlate with chemical indices of both melt extraction and oxidation. Iron isotope fractionation during spinel-facies partial melting is investigated using simple models, which demonstrate that the maximum expected fractionation between melt and residue will be~0.5x, with the residue becoming isotopically light relative to the melt and to the initial source region. Hence melt extraction, in combination with significant changes in mantle oxidation state, may be an explanation for Fe isotopic variations in mantle peridotites. Metasomatism of the sub-arc mantle by iron-rich silicate melts originating from the subducting slab may also explain the light bulk-sample d 57/54 Fe values of some arc peridotites (À 0.2x to À 0.6x), but mass-balance calculations require these metasomatic agents to have extreme d 57/54 Fe values (e.g. À 3.0x). The large differences in the d 57/54 Fe values of garnet and spinel facies rocks are 0012-821X/$ -see front matter D (H.M. Williams). Earth and Planetary Science Letters 235 (2005) 435 -452
Geochimica et Cosmochimica Acta, 2006
Osmium, Ru, Ir, Pt, Pd and Re abundances and 187 Os/ 188 Os data on peridotites were determined using improved analytical techniques in order to precisely constrain the highly siderophile element (HSE) composition of fertile lherzolites and to provide an updated estimate of HSE composition of the primitive upper mantle (PUM). The new data are used to better constrain the origin of the HSE excess in Earth's mantle. Samples include lherzolite and harzburgite xenoliths from Archean and post-Archean continental lithosphere, peridotites from ultramafic massifs, ophiolites and other samples of oceanic mantle such as abyssal peridotites. Osmium, Ru and Ir abundances in the peridotite data set do not correlate with moderately incompatible melt extraction indicators such as Al 2 O 3 . Os/Ir is chondritic in most samples, while Ru/Ir, with few exceptions, is ca. 30% higher than in chondrites. Both ratios are constant over a wide range of Al 2 O 3 contents, but show stronger scatter in depleted harzburgites. Platinum, Pd and Re abundances, their ratios with Ir, Os and Ru, and the 187 Os/ 188 Os ratio (a proxy for Re/Os) show positive correlations with Al 2 O 3 , indicating incompatible behavior of Pt, Pd and Re during mantle melting. The empirical sequence of peridotite-melt partition coefficients of Re, Pd and Pt as derived from peridotites (D s=l Re < D s=l Pd < D s=l Pt < 1) is consistent with previous data on natural samples. Some harzburgites and depleted lherzolites have been affected by secondary igneous processes such as silicate melt percolation, as indicated by U-shaped patterns of incompatible HSE, high 187 Os/ 188 Os, and scatter off the correlations defined by incompatible HSE and Al 2 O 3 . The bulk rock HSE content, chondritic Os/Ir, and chondritic to subchondritic Pt/Ir, Re/Os, Pt/Re and Re/Pd of many lherzolites of the present study are consistent with depletion by melting, and possibly solid state mixing processes in the convecting mantle, involving recycled oceanic lithosphere. Based on fertile lherzolite compositions, we infer that PUM is characterized by a mean Ir abundance of 3.5 ± 0.4 ng/g (or 0.0080 ± 0.0009*CI chondrites), chondritic ratios involving Os, Ir, Pt and Re (Os/Ir PUM of 1.12 ± 0.09, Pt/Ir PUM = 2.21 ± 0.21, Re/Os PUM = 0.090 ± 0.002) and suprachondritic ratios involving Ru and Pd (Ru/Ir PUM = 2.03 ± 0.12, Pd/Ir PUM = 2.06 ± 0.31, uncertainties 1r). The combination of chondritic and modestly suprachondritic HSE ratios of PUM cannot be explained by any single planetary fractionation process. Comparison with HSE patterns of chondrites shows that no known chondrite group perfectly matches the PUM composition. Similar HSE patterns, however, were found in Apollo 17 impact melt rocks from the Serenitatis impact basin . Targeting the impactors: siderophile element signatures of lunar impact melts from Serenitatis. Earth Planet. Sci. Lett, 217-228.], which represent mixtures of chondritic material, and a component that may be either of meteoritic or indigenous origin. The similarities between the HSE composition of PUM and the bulk composition of lunar breccias establish a connection between the late accretion history of the lunar surface and the HSE composition of the Earth's mantle. Although late accretion following core formation is still the most viable explanation for the HSE abundances in the Earth's mantle, the ''late veneer'' hypothesis may require some modification in light of the unique PUM composition.