Elements In Olivine Research Articles

Relict olivine grains, chondrule recycling, and implications for the chemical, thermal, and mechanical processing of nebular materials

Chondrules and isolated forsterites in five low-subtype ordinary chondrites [NWA 3127 (LL3.1), Sahara 97210 (LL3.2), Wells (LL3.3), Chainpur (LL3.4), and Sahara 98175 (LL3.5)] were studied using petrographic, EMPA, and SIMS techniques to better constrain the origin of chondrules and the olivine grains within them. Our results imply that igneous crystallization, vapor fractionation, redox effects, and open-system behavior were important processes. All olivine grains, including normal, relict, and isolated forsterite grains, show evidence for igneous fractionation under disequilibrium conditions, with olivine crystallizing during rapid cooling (closer to 2000 °C/h than to 100 °C/h). Vapor fractionation is manifested by anti-correlated abundances between refractory elements (Al, Sc, Y, Ti, Ca, V) and volatile elements (Cr, Mn, P, Rb, Fe) in olivine. Redox effects are evidenced in various ways, and imply that Fe, Co, Ni, and P were partitioned more into metal, and V was partitioned more into olivine, under reducing conditions in the most FeO-poor melts. There is no obvious evidence for systematic variations in olivine composition according to meteorite subtype, but shock melting in Sahara 97210 resulted in the injection of glass-derived melt into olivine, resulting in artificially high abundances of Ba, Sr, Na, Ti, and some other incompatible elements in olivine. Terrestrial weathering in a hot desert environment may have mobilized Ba and Sr in some glasses. Our data suggest that chondrules in ordinary chondrites experienced repeated thermal, chemical, and mechanical processing during a “recycling” process over an extended time period, which involved multiple episodes of melting under fluctuating redox and heating conditions, and multiple episodes of chondrule break-up in some cases. Forsterite grains, including normal grains in forsterite-bearing type I chondrules, the cores of isolated forsterites, and relict forsterite in type II chondrules, all crystallized from similar, refractory melts under reducing conditions; relict Mg-olivine and isolated forsterite grains were thus derived from type I chondrules. Olivine in type II chondrules, including normal grains and ferroan overgrowths on relict Mg-olivine, crystallized from more volatile-rich, oxidized, and relatively unfractionated melts. Relict dusty olivine grains in type I chondrules were derived from type II chondrules during incomplete melting episodes involving reduction and some vaporization, with clear (non-dusty) grains in dusty olivine-bearing chondrules crystallizing from the reduced and partly vaporized melts. Melt compositions parental to normal olivine grains in type I and II chondrules are systematically enriched in refractory elements compared to bulk chondrule compositions, implying that chondrules often experienced open-system exchange with more volatile-rich surroundings after some olivine had crystallized, possibly while the chondrules were still partly molten. Type II chondrules could have been derived from type I chondrules by the addition of relatively volatile-rich material, followed by re-melting and little evaporation under oxidizing conditions. In contrast, type I chondrules could have been derived from type II chondrules by re-melting involving more-or-less evaporation under reducing conditions. Chemical, oxygen isotope, and petrographic data are best accommodated by a model in which there were several (>2–3, sometimes ⩾4–5) melting episodes for most chondrules in ordinary chondrites.

Significance of the concentration gradients associated with dunite bodies in the Josephine and Trinity ophiolites

Detailed transects were sampled across dunite bodies in the Josephine and Trinity ophiolites. The major peridotite lithologies sampled in the Josephine transect are a sequence of dunite and harzburgite and in the Trinity transect a sequence of dunite, harzburgite, lherzolite, and plagioclase lherzolite (DHL‐PL). Major, minor, and selected trace element abundances in olivine, orthopyroxene, clinopyroxene, and spinel were measured. The composition profile from the Josephine transect has revealed a concentration gradient near the dunite‐harzburgite contact. The composition profile from the Trinity transect has revealed several concentration gradients: two within the dunite, one in the harzburgite, and at least two in the plagioclase lherzolite. The composition profiles record complex histories of melt transport, melt‐rock reaction, and subsequent subsolidus reequilibration. Analyses of closure distance suggest that compositional variation trends for a majority of major and minor elements in olivine, clinopyroxene, orthopyroxene, and spinel reported in this study were magmatic in origin. Subsolidus reequilibration may reduce the range or magnitude of variations for the 2+ cations such as Fe and Mg in olivine and spinel and significantly redistribute Ca and Li in coexisting minerals. Numerical simulations exploring the coupling of diffusion and advection in a porous matrix were used to explain compositional variations across the peridotite sequences. Melt flow from the host harzburgite into the dunite produces composition gradients near the dunite‐harzburgite contacts similar to those from the Josephine transect. In contrast, melt flow from the dunite into the surrounding peridotite lithologies can produce concentration gradients similar to those observed in the Trinity transect. At least two chemically distinct episodes of melt flow within the same dunite channel system are proposed. Results from this study show that concentration gradients developed around the dunite‐harzburgite and DHL‐PL sequences can be used to infer part of the melt flow history of the dunite channel systems in the mantle. Results from this study and those from other ophiolite studies also demonstrate that concentration profiles in dunite and the surrounding peridotite lithologies are highly variable even among differing peridotite sequences within the same ophiolite, suggesting that the composition of instantaneous melt flowing through individual dunite channels is quite variable and the mantle source regions are heterogeneous.

Partitioning of trace elements among coexisting crystals, melt, and supercritical fluid during isobaric crystallization and melting

The distribution of trace elements among coexisting crystals, melt, and supercritical fluid during melting and crystallization is a critical constraint for understanding the evolution of magmatic systems, including the origin and development of continental and oceanic crust. Although trace-element partitioning between crystals and melt during Rayleigh fractional crystallization or melting is well-known, partitioning among co-existing melt, crystals, and supercritical fluid during anatexis or crystallization is less explored despite the ubiquity of magmatic fluids. Here we develop the trace-element differential equations governing solid-melt-fluid equilibria for melting and crystallization under fluid-present conditions and provide analytical solutions for fractional and equilibrium crystallization and melting. A compilation of solid-fluid and melt-fluid distribution coefficients for about 30 trace elements in olivine, clinopyroxene, garnet, plagioclase, alkali feldspar, biotite, amphibole, apatite, and silicic melts is provided. Forward modeling demonstrates the conditions under which fluid-melt-solid partitioning will impact trace-element signatures in magmatic systems. We show that for trace elements soluble in aqueous fluids, the composition of a melt derived by fluid-present fractional crystallization or by fluid-present fractional melting will be significantly different than in otherwise comparable fluid-absent systems. Ignoring the partitioning of soluble elements into the fluid phase leads to large errors in concentrations (over 100%) and ratios and consequent misinterpretation of the trace-element character of source material and/or the processes of fractional crystallization and melting. Although significant in any setting involving fluid-present equilibria, this analysis may have a most profound influence on fluid-present subduction zone magma generation and the evolution of shallow level fluid-saturated silicic magmatic systems.

Survival times of anomalous melt inclusions from element diffusion in olivine and chromite

The chemical composition of basaltic magma erupted at the Earth's surface is the end product of a complex series of processes, beginning with partial melting and melt extraction from a mantle source and ending with fractional crystallization and crustal assimilation at lower pressures. It has been proposed that studying inclusions of melt trapped in early crystallizing phenocrysts such as Mg-rich olivine and chromite may help petrologists to see beyond the later-stage processes and back to the origin of the partial melts in the mantle. Melt inclusion suites often span a much greater compositional range than associated erupted lavas, and a significant minority of inclusions carry distinct compositions that have been claimed to sample melts from earlier stages of melt production, preserving separate contributions from mantle heterogeneities. This hypothesis is underpinned by the assumption that melt inclusions, once trapped, remain chemically isolated from the external magma for all elements except those that are compatible in the host minerals. Here we show that the fluxes of rare-earth elements through olivine and chromite by lattice diffusion are sufficiently rapid at magmatic temperatures to re-equilibrate completely the rare-earth-element patterns of trapped melt inclusions in times that are short compared to those estimated for the production and ascent of mantle-derived magma or for magma residence in the crust. Phenocryst-hosted melt inclusions with anomalous trace-element signatures must therefore form shortly before magma eruption and cooling. We conclude that the assumption of chemical isolation of incompatible elements in olivine- and chromite-hosted melt inclusions is not valid, and we call for re-evaluation of the popular interpretation that anomalous melt inclusions represent preserved samples of unmodified mantle melts.

Defining the mechanisms that disturb the Sm-Nd isotopic systematics of the Martian meteorites: Examples from Dar al Gani 476 and Allan Hills 77005

Microbeam studies of Martian meteorites Dar al Gani (DaG) 476 and Allan Hills (ALH) 77005 have been conducted to identify potential causes of disequilibrium exhibited in their Sm-Nd isotopic systematics. Olivine and maskelynite mineral fractions on the DaG 476 isochron are displaced relative to their positions as dictated by measured mineral compositions. The olivine mineral fractions from ALH 77005 not only have a relatively low Sm/Nd ratio, but appear to contain an unradiogenic component that shifts the olivine mineral fraction off the isochron defined by the pyroxene and maskelynite mineral fractions. Trace components such as melt inclusions, impact melt, high-Si mesostasis, and altered olivine were analyzed using scanning electron microscopy, quantitative electron microscopy, and secondary ion mass spectrometry to determine their potential for disturbing the isotopic systematics of the mineral fractions, assuming that the mineral fractions were not completely pure. Mixing models indicate that the presence of melt inclusions in the DaG 476 olivine mineral fraction lowered its Sm/Nd ratio. The maskelynite mineral fraction contains a related but more evolved mesostasis component that raised the Sm/Nd ratio of the fraction. The position of two olivine mineral fractions below the ALH 77005 isochron is interpreted to reflect small additions of impact melt with a light rare earth element enriched pattern and a non-indigenous, unradiogenic Nd component. Furthermore, the presence of rare earth elements in olivine and maskelynite from both igneous and non-igneous components such as melt inclusions, mesostasis, and impact melt is observed on a fine (<30 μm) scale. Despite the addition of this material, the Sm-Nd ages are not affected. This study demonstrates that detailed mineral separation procedures as employed by modern geochronology laboratories permit reliable ages to be derived from shocked and altered samples.

Short time scales of magmatic assimilation from diffusion modeling of multiple elements in olivine

Open-system processes have a large capacity to modify magma compositions during differentiation. Obtaining the rates of such processes is essential to understanding and constraining the evolution of magmatic systems. Here we quantify the time scales for magmatic assimilation of hydrous mafic to ultramafic cumulates by ascending basalts using the zoning patterns of olivine xenocrysts. Robust diffusion modeling results have been obtained by treating multiple compositional profiles for multiple elements (Fe-Mg, Ni, Mn, Ca) on multiple crystals from multiple flows. We find that the time between assimilation and eruption ranges from a few months to ∼25 yr, although 80% of the results are <10 yr. These ranges are shorter than either magma transport times from the mantle to the surface or typical repose periods of arc volcanoes. Thus, modification of the geochemical and mineralogical features of basalts by assimilation of plutonic rocks is a fast and probably unavoidable magmatic process.

Abundance and Partitioning of OH in a High-pressure Magmatic System: Megacrysts from the Monastery Kimberlite, South Africa

Concentrations of OH, and major and trace elements were determined in a suite of mantle-derived megacrysts that represent the crystallization products of a kimberlite-like magma at ~5 GPa and ~1400–1100°C. OH concentrations, determined by single-crystal Fourier transform infrared spectroscopy, display the following ranges (ppmw H2O): olivine 54–262, orthopyroxene 215–263, garnet 15–74, clinopyroxene 195–620, and zircon 28–34. High OH concentrations in olivine imply mantle conditions of origin, with limited H loss during ascent. OH is consistently correlated with megacryst composition, exhibiting trends with Mg-number that are similar to those of other minor and trace elements and indicating a record of high-pressure magmatic evolution. H substitution is not coupled to minor elements in olivine, but may be in ortho- and clinopyroxene. The OH–Mg-number trends of garnet and clinopyroxene show inflections related to co-precipitation of ilmenite, suggesting minor element (Ti) influence on OH partitioning. During differentiation, relative OH enrichment in clinopyroxene and olivine is consistent with proportional dependence on water activity, whereas that in garnet suggests a higher power-law dependence and/or influence of temperature. Inter-mineral distribution coefficients for OH between cpx, opx, olivine and zircon are thus constant, whereas partitioning between these minerals and garnet shows a factor 4–10 variation, correlated regularly with composition (and temperature). Calculation of solid–melt partition coefficients for H at 5 GPa over a range of magmatic evolution from 1380 to 1250°C yields: ol 0·0053–0·0046, opx 0·0093–0·0059, cpx 0·016–0·013, gt 0·0014–0·0003, bulk (garnet lherzolite–melt) 0·0063–0·0051. These are consistent with experimental studies and similar to values inferred from mid-ocean ridge basalt geochemistry, confirming the moderate incompatibility of H in mantle melting.

Minor elements in olivine from spinel lherzolite xenoliths: implications for thermobarometry

AbstractThe proton microprobe has been used to determine contents of Ca, Ti, Ni, Mn and Zn in the olivine of 54 spinel lherzolite xenoliths from Australian and Chinese basalts. These data are compared with proton-probe data for Ni, Mn and Zn in the olivine of 180 garnet peridotite xenoliths from African and Siberian kimberlites. Fe, Mn, Ni and Zn contents are well-correlated; because the spinel lherzolite olivines have higher mean Fe contents than garnet peridotite olivines (average Fo89.6vs. Fo90–92) they also have lower Ni and higher Mn contents. Zn and Fe are well-correlated in garnet peridotite olivine, but in spinel peridotites this relationship is perturbed by partitioning of Zn into spinel. None of these elements shows significant correlation with temperature. Consistent differences in trace-element contents of olivines in the two suites is interpreted as reflecting the greater degree of depletion of Archean garnet peridotites as compared to Phanerozoic spinel lherzolites. Ca and Ti contents of spinel-peridotite olivine are well correlated with one another, and with temperature as determined by several types of geothermometer. However, Ca contents are poorly correlated with pressure as determined by the Ca-in-olivine barometer of Köhler and Brey (1990). This reflects the strong T-dependence of this barometer: the uncertainty in pressure (calculated by this method) which is produced by the ±50°C uncertainty expected of any geothermometer is ca ± 8 kbar, corresponding to the entire width of the spinel-lherzolite field at 900–1200°C.

Does diffusion change the rare earth patterns of igneous rocks?

We examined the possibility of diffusion-controlled fractionation of the rare earth elements during igneous processes on the basis of lattice diffusion, by using available sets of diffusivity data on olivine and melilite. During partial melting of olivine, it is shown with a simple model that Fe and Mn are more enriched in the early stage liquid phase, while Ca, with lower diffusivity, is less enriched in the liquid. This implies that, during partial melting of olivine, the heavy rare earth elements with ionic radius similar to that of Mn can be more enriched in the early stage liquid phase relative to the light rare earth elements with ionic radius similar to that of Ca, contrary to what would be expected from equilibrium partition. Low inter-diffusivity of Mg + Si and Al + Al pairs in akermanitic melilite suggests that diffusivities of the rare earth elements in olivine are low, and that the effect of diffusion would continue for a longer period of time for trivalent rare earth elements than for divalent cations. Eu2+ also possibly behaves quite differently from trivalent rare earth elements during diffusion, and thus may produce Eu anomalies that are not expected by equilibrium partition. Diffusion can produce widely different distributions of the rare earth and other trace elements even in a single system depending on the time scale of the diffusion process. However, since natural systems are much more complicated than models, it is not clear whether the calculated results have practical significance in explaining the distribution of trace elements in nature.

Metasomatic origin for Fe-Ti-rich multiphase inclusions in olivine from kimberlite xenoliths

Because solid-solution trace elements in olivine have significant influence on upper mantle rheology, it is important to establish whether inclusions in olivine are exsolved from an intrinsic solid solution or are introduced by metasomatism. In a study of olivine in hot deformed peridotite xenoliths from kimberlites, we have found a new type of multiphase inclusion that contains Fe-Ti-rich and Si-Fe-Al-rich phases. Microstructural relations indicate that these inclusions form by a process involving metasomatic fluid infiltration along a fine network of cracks shortly before entrainment of the xenoliths, followed by crack healing during xenolith transport in the magma. The high trace-element content of Ti, Ca, Al, and Na found in Fe-Ti-rich, hot deformed olivine is related to metasomatic enrichment that occurred shortly before kimberlite eruption. Assessment of the effects of the Fe-Ti metasomatism indicates that the Cr-C-rich inclusions found in olivine from other hot deformed xenoliths are formed by precipitation from an intrinsic solid solution in olivine that has not been affected by Fe-Ti-rich metasomatism.

Lherzolite xenoliths in kimberlites and basalts: petrogenetic and crystallochemical significance of some minor and trace elements in olivine, pyroxenes, garnet and spinel

ABSTRACTElectron and ion microprobe analyses for P, Si, Ti, Al, Cr, V, Sc, Fe, Mn, Mg, Ni, Co, Ca, Sr, Na, K and Li in olivine, pyroxenes and garnet in forty-two cold and twelve hot garnet lherzolites from kimberlites, nine spinel lherzolites from kimberlites and eighteen from alkali basalts, and one cold garnet lherzolite from the Malaita alnöite, are compared with published data for minerals occurring in lherzolite, harzburgite and eclogite xenoliths, for silicate megacrysts in kimberlites, and for silicate inclusions in diamonds. Despite wide ranges in the chemistry of minerals from garnet and spinel lherzolites, there are distinct regions in composition space that would enable determination of the parent lithology of disaggregated minerals in kimberlites and alkali basalts. Titanium correlates with Fe3+ in garnets. Chromium, Al, V and Sc are distributed similarly between silicates in lherzolites. Sodium correlates with trivalent ions in olivine, and increases with temperature. The distribution of Na, but not of K and Li, between olivine and clinopyroxene correlates with temperature. The regular partitioning of Ti, Mn and Ni places constraints on crystal-liquid partition coefficients. Above the stability temperature of mica, ‘metasomatising fluids’ may scavenge Cr and other trivalent ions as they increase Ti in silicates.

MINOR ELEMENTS IN MARJALAHTI OLIVINE

Precise microprobe determinations of minor elements in olivine from Marjalahti show averages of 0.067% CaO; 0.0211% Cr2O3; less than 0.0045% TiO2; 0.288% MnO; and 30 ppm Ni. The calcium is as high as in some terrestrial plutonic olivines (e.g. Stillwater) but lower than in terrestrial nodule (high‐temperature mantle?) olivines, consistent with very slow cooling to low temperatures. The chromium is discrepant with some earlier determinations, and possibly chromium is zoned in most pallasitic olivines. The Ti, Mn, and Ni data are consistent with previous determinations.

Diffusion compensation in natural silicates

The temperature dependence of diffusion is usually found to follow the Arrhenius law: D = D 0 e − E/ RT Winchell (1969) showed that there is commonly an inter-dependence between D 0 and E (for diffusion in silicate glasses), such that diffusion of different species show a positive correlation on a log D 0 vs E plot. A similar effect was noted by Hofmann (1980) for cation diffusion in basalt. This implies that diffusion rates of different species tend to converge at a particular temperature; this effect is known as the ‘compensation effect’. I will show that this effect is also present for diffusion in feldspars and olivines. The equations for the compensation lines (with E given in kcal/mol) are: basalt— E = 50 + 7.5 log D 0 feldspar— E = 50.7 + 3.4 log D 0 olivine— E = 78.0 + 7.5 log D 0 The convergence, or crossover, temperatures for diffusion in various materials are: obsidian—3400°C basalt—1370°C olivine—1360°C feldspar—460°C Compensation plots are useful for evaluating and comparing experimental diffusion data (though of limited usefulness in a predictive sense) and for understanding ‘closure temperatures’ for diffusion in petrogenetic processes (since closure temperature, the temperature at which natural diffusion processes are frozen in, is dependent on E, log d 0, and cooling rate). I show that most diffusing species in feldspar have a closure-temperature close to the crossover or convergence temperature, implying that all species in feldspars can be expected to ‘freeze-in’ simultaneously at temperatures in the range 400–600°C (for cooling rates in the range 10 1–10 5°C/myr). Closure temperatures of various species in olivine, on the other hand, span a much larger range (800°C) for a similar range in cooling rates, implying that different elements in olivine will record different time-temperature stages in petrogenetic processes.

Fertile and barren Al [sbnd]Cr-spinel harzburgites from the upper mantle: Ion and electron probe analyses of trace elements in olivine and orthopyroxene: Relation to lherzolites

Ion and electron microprobe analyses of twenty-one Cr Al-spinel harzburgite xenoliths from southern African kimberlites show two chemical groups. Orthopyroxenes from “fertile” harzburgites have higher CaO (mean of 11, 0.95 wt.%), Al 2O 3 (3.05 wt.%), Cr 2O 3 (0.85 wt.%) and Li (0.8 ppmw) than those from “barren” harzburgites (mean of 10, CaO 0.24 wt.%, Al 2O 3 1.10 wt.%, Cr 2O 3 0.35 wt.%, Li 0.3 ppmw). Olivines from all harzburgites have similar chemistry except that mean values of Li and Na are higher for barren than fertile harzburgites (Li 0.9 vs. 0.4 ppmw; Na 2O 16 vs. 7 ppmw). Orthopyroxenes from fertile harzburgites are chemically distinct from those in garne lherzolites from southern Africa and spinel lherzolites from southwest U.S.A., but orthopyroxenes from barren harzburgites are indistinguishable from those in many coarse garnet lherzolites. Chromium, Ca, Ni, Na and Li in coexisting olivines and orthopyroxenes from the above rock types show complex patterns, which for Ca, Cr and Ni can be related to pressure and temperature. Temperatures from an empirically calibrated thermometer based on Ni-Mg exchange between olivine and orthopyroxene, measured modes of harzburgites (fertile, mean of 10: ol 68, opx 31, spinel-silicate intergrowth <0.5; barren, mean of 8: ol 76, opx 23, spinel and spinel-silicate intergrowth 1), and high-pressure experimental studies suggest (a) that harzburgites are residues of partial melting, (b) that barren harzburgites were melted to a greater extent at a higher temperature (though probably at a similar depth) than fertile harzburgites, and (c) that incomplete reequilibration during retrograde metamorphism has led to development of complex inter- and intragranular textures, probably in the range ∼700–900°C.

Distribution of REE and other trace elements between phenocrysts and peralkaline undersaturated magmas, exemplified by rocks from the Gardar igneous province, south Greenland

Partition coefficients for iron-rich olivine and pyroxene, sanidine, nepheline and apatite are reported from peralkaline trachytic to phonolitic dyke rocks and the agpaitic Ilímaussaq intrusion. Partition coefficients for many elements in olivine and pyroxene decrease with increasing peralkalinity and undersaturation of the magma, i.e. with decreasing polymerisation. The REE partition coefficients for olivine and pyroxene also show dependence on the mineral chemistry, i.e. the iron content. Probably due to the larger lattice sites in the iron end-members the heavy REEs enter the small six-coordinated lattice sites with increasing ease as the iron content of the mineral increases. La and Ce partition coefficients for apatite increase with increasing peralkalinity; this condition seems to stabilise a Na-REE-phosphate component in the mineral.

Statistical Classification of Garnets from Kimberlite and Associated Xenoliths: Addendum

Previous articleNext article No AccessStatistical Classification of Garnets from Kimberlite and Associated Xenoliths: AddendumJ. B. Dawson and W. E. StephensJ. B. Dawson Search for more articles by this author and W. E. Stephens Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 84, Number 4Jul., 1976 Article DOIhttps://doi.org/10.1086/628216 Views: 4Total views on this site Citations: 18Citations are reported from Crossref Copyright 1976 University of ChicagoPDF download Crossref reports the following articles citing this article:Agnes T. Fung, Stephen E. Haggerty Petrography and mineral compositions of eclogites from the Koidu Kimberlite Complex, Sierra Leone, Journal of Geophysical Research: Solid Earth 100, no.B10B10 (Sep 2012): 20451–20473.https://doi.org/10.1029/95JB01573Doris V. Hills, Stephen E. Haggerty Petrochemistry of eclogites from the Koidu Kimberlite Complex, Sierra Leone, Contributions to Mineralogy and Petrology 103, no.44 (Jan 1989): 397–422.https://doi.org/10.1007/BF01041749J.B. Dawson, J.V. Smith Relationships between eclogites and certain megacrysts from the Jagersfontein kimberlite, South Africa, Lithos 19, no.3-43-4 (Oct 1986): 325–330.https://doi.org/10.1016/0024-4937(86)90031-9M. Ito Kimberlites and their ultramafic xenoliths from western Kenya, TMPM Tschermaks Mineralogische und Petrographische Mitteilungen 35, no.33 (Jan 1986): 193–216.https://doi.org/10.1007/BF01082085R. L. Hervig, J. V. Smith, J. B. Dawson Lherzolite xenoliths in kimberlites and basalts: petrogenetic and crystallochemical significance of some minor and trace elements in olivine, pyroxenes, garnet and spinel, Transactions of the Royal Society of Edinburgh: Earth Sciences 77, no.33 (Nov 2011): 181–201.https://doi.org/10.1017/S026359330001083XColin H. Donaldson Kinetics of pyrope megacryst reactions in ascending basaltic magma – relevance to high-pressure magmatic crystallization at Elie Ness, East Fife, Geological Magazine 121, no.66 (May 2009): 615–620.https://doi.org/10.1017/S0016756800030752 References, (Jan 1984): 435–466.https://doi.org/10.1016/B978-0-444-42273-6.50037-7 References, (Jan 1984): 361–393.https://doi.org/10.1016/B978-0-444-42274-3.50036-6 Suzanne Mahlburg Kay , William T. Snedden , Brayton P. Foster , and Robert W. Kay Upper Mantle and Crustal Fragments in the Ithaca Kimberlites, The Journal of Geology 91, no.33 (Sep 2015): 277–290.https://doi.org/10.1086/628771SUZANNE Y. WASS, J. D. HOLLIS Crustal growth in south-eastern Australia?evidence from lower crustal eclogitic and granulitic xenoliths, Journal of Metamorphic Geology 1, no.11 (Mar 1983): 25–45.https://doi.org/10.1111/j.1525-1314.1983.tb00263.xD.B. Clarke, G.G. Pe-Piper Multiply exsolved clinopyroxene megacrysts from the Frank Smith Mine, Cape Province, South Africa, Lithos 16, no.11 (Jan 1983): 75–84.https://doi.org/10.1016/0024-4937(83)90036-1R.L. Hervig, J.V. Smith, I.M. Steele, J.B. Dawson Fertile and barren AlCr-spinel harzburgites from the upper mantle: Ion and electron probe analyses of trace elements in olivine and orthopyroxene: Relation to lherzolites, Earth and Planetary Science Letters 50, no.11 (Oct 1980): 41–58.https://doi.org/10.1016/0012-821X(80)90118-1N. P. Lock, J. B. Dawson Garnet-olivine reaction in the upper mantle: evidence from peridotite xenoliths in the Letseng-la-Terae kimberlites, Lesotho, Transactions of the Royal Society of Edinburgh: Earth Sciences 71, no.11 (Nov 2011): 47–53.https://doi.org/10.1017/S0263593300013481J. B. DAWSON, J. V. SMITH, J. S. DELANEY Multiple spinel–garnet peridotite transitions in upper mantle: evidence from a harzburgite xenolith, Nature 273, no.56655665 (Jun 1978): 741–743.https://doi.org/10.1038/273741a0F.C. Bishop, J.V. Smith, J.B. Dawson Na, K, P and Ti in garnet, pyroxene and olivine from peridotite and eclogite xenoliths from African kimberlites, Lithos 11, no.22 (Apr 1978): 155–173.https://doi.org/10.1016/0024-4937(78)90006-3J. B. Dawson, J. S. Delaney, J. V. SmitH Aspects of the mineralogy of aln�itic breccia, Malaita, Solomon Islands; comparison with continental kimberlites, Contributions to Mineralogy and Petrology 67, no.22 (Jan 1978): 189–193.https://doi.org/10.1007/BF01046575 W. E. Stephens , and J. B. Dawson Statistical Comparison between Pyroxenes from Kimberlites and Their Associated Xenoliths, The Journal of Geology 85, no.44 (Sep 2015): 433–449.https://doi.org/10.1086/628317

Compositional characteristics of olivines from Apollo 12 samples

The olivine phenocrysts of four basalts (12004, 12008, 12009 and 12022) are concentrically zoned and have core compositions about as magnesian as experimentally produced liquidas olivines, features which suggest fractional crystallization and absence of Fe-Mg reequilibration. In the magnesium- and olivine-rich granular basalt 12035, the olivines are either unzoned or are zoned toward adjacent grains and have compositions more iron-rich than either cumulus olivines or liquidus olivines (should the rock represent the composition of a melt), features which suggest extensive Fe-Mg re-equilibration. If one assumes that concentrations of minor elements at crystallization have also been preserved in the Mg-rich centers of olivines in the basalt porphyries, identification of two possible comagmatic pairs can be made: 12004 and 12009 (lower Ti and higher Cr in olivines), and 12008 and 12022 (higher Ti and lower Cr in olivines). Correlations are observed between the Fe-Mg proportions and the concentrations of minor elements in olivine (Ti, Mn and Ca all follow Fe, Cr follows Mg).