Philip E. Janney

• PhD, Scripps Institution of Oceanography-UC San Diego (1996)
• Professor and Head of Department at University of Cape Town

We present a chemical and stable and radiogenic isotope data set for carbonatite, aillikite (ultramafic lamprophyre) and olivine melilitite from the Zandkopsdrift carbonatite complex in Namaqualand, South Africa. This carbonatite complex is associated with the ≈500-km-long, NE-SW oriented, age-progressive (40–80 Ma) Namaqualand-Bushmanland-Warmbad...

Controversies surround the origin of kimberlite megacrysts, including whether and how they are genetically related to their host kimberlites, the relationship between the Cr-poor and Cr-rich suites and the dominant processes responsible for elemental and isotopic variations of megacrysts from a given kimberlite. We present new in-situ major and tra...

Kimberlites are ultrabasic, Si-undersaturated, low Al, low Na rocks rich in CO2 and H2O. The distinctive geochemical character of kimberlite is strongly influenced by the nature of the local underlying lithospheric mantle. Despite this, incompatible trace element ratios and radiogenic isotope characteristics of kimberlites, filtered for the effects...

MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside) and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks occur as mantle-derived xenoliths in kimberlites and other alkaline volcanic rocks. Both rock types are alkaline and ultramafic in composition. The H 2 O and alkali metal enrichments in MARID and PIC rocks, reflected in abundant phlogopite, have been s...

Long-lived (>2.5 Ga) cratons usually preserve ancient cold and refractory mantle roots, but how the deep roots survive from recycling back to the convective mantle remains open to debate. Here, the mechanism for preservation of Archean mantle roots is explored using the major-, trace-element and Sr-Nd isotopic systematics of kimberlites, the asthen...

The diamond potential of kimberlites is generally determined using indicator minerals (i.e., xenocrysts), entrained by the parent magma while ascending through the sub-continental lithospheric mantle (SCLM). It is becoming increasingly apparent that olivine can also be used to understand mantle sampling depth, using the Al-in-olivine thermometer, a...

The elemental and isotopic properties of garnet pyroxenites can yield information on lithospheric mantle composition, thermal state, and evolution. The 34Ma Kakanui Mineral Breccia in New Zealand contains spectacular but little-studied mantle peridotite and pyroxenite xenoliths that yield new insights into the evolution of a portion of the underlyi...

Diamonds can form within eclogite (remnants of ancient subducted oceanic crust) in the subcontinental lithospheric mantle (SCLM), pieces of which may then be transported to the surface as xenoliths in kimberlites. These diamond-bearing xenoliths offer a rare opportunity to study diamonds in their host lithology. The morphology and surface features...

One of the fundamental constraints on the carbon content in the Earth’s mantle comes from depleted mid-ocean ridge basalts (D-MORB) that experienced minimal CO2 degassing. The CO2/Ba ratio of 120 ± 20 in these D-MORB have been used to estimate the CO2 content in more enriched MORB (e.g., N- and E-MORB) that have lost CO2 through degassing. However,...

Midcrustal rocks in retrograde metamorphic settings are typically H2O-undersaturated and fluid-absent and have low permeability. Exhumed continental retrograde faults, nonetheless, show evidence for the operation of fluid-mediated weakening mechanisms during deformation at midcrustal conditions. To explore the origin and effects of fluids in retrog...

With exception of Maluma (1979) and Musambachime (2016, 2017), there have been no archaeometallurgical publications on the technology and culture of iron production in Zambia. This paper presents archaeological and archaeometallurgical evidence of a technology of iron production in Chongwe in terms of spatial organization, the process of metal prod...

Text: A large major and trace element data set has been obtained on clinopyroxene (cpx), ilmenite and garnet (as well as minor orthopyroxene (opx) and olivine) in mineral concentrates from the Mbuji-Mayi and Tshibwe kimberlites (Mbuji Mayi kimberlite field, Archean-Paleo-proterozoic Kasai Block, Congo Craton, DRC; Demaiffe et al, 1991) and the Kund...

MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside) and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks are unusual mantle samples entrained by kimberlites and other alkaline volcanic rocks. The formation of MARID rocks remains hotly debated. Although the incompatible element (for example, large ion lithophile element) enrichment in these rocks suggests...

The Saltpeterkop Complex (SPKC), Northern Cape, South Africa, contains carbonatite, potassic trachyte, olivine melilitite and ultramafic lamprophyre magmas that were erupted through the crystalline basement of the Proterozoic Namaqua-Natal mobile belt at ~74 Ma and occur primarily as shallow intrusive features. Isolated subvolcanic intrusions and e...

The Saltpeterkop Carbonatite Complex is a Late Cretaceous (≈76 Ma) volcanic and shallow intrusive magmatic feature located approximately 20 km southeast of Sutherland in the Northern Cape. It is unusual among southern African carbonatite complexes in that it has not been deeply eroded, and retains a significant vestige of its original volcanic f...

Detailed petrologic, geochemical and isotopic analyses of a new FUN CAI from the Allende CV3 meteorite (designated CMS-1) indicate that it formed by extensive melting and evaporation of primitive precursor material(s). The precursor material(s) condensed in a ¹⁶O-rich region (δ¹⁷O and δ¹⁸O ∼ -49‰) of the inner solar nebula dominated by gas of solar...

We present the results of laboratory experiments in which a forsterite-rich melt estimated to be a potential precursor of Allende CMS-1 FUN CAI was evaporated into vacuum for different lengths of time at 1900°C. The evaporation of this melt resulted in residues that define trajectories in chemical as well as magnesium, silicon and oxygen isotopic c...

___________________________________________________________________________ Controversy surrounds the relationship between megacrysts and their host kimberlites. Garnet and clinopyroxene (cpx) megacrysts from four Cambrian to Late Cretaceous southern African kimberlites representative of Group I and Group II varieties have been selected for a compa...

Lithium concentration and isotopic fractionation profiles across augite grains from two Martian meteorites - MIL 03346 and NWA 817 - were used to determine their thermal history and implications for their geologic setting. The iron-magnesium zoning and associated magnesium isotopic fractionation of olivine grains from NWA 817 were also measured and...

We present here analyses of mass-independent effects in the Ti isotope ratios of 17 coarse-grained (compact Type A and Type B) calcium–aluminum-rich inclusions (CAIs) from the Allende CV3 chondrite utilizing a method developed for rapid measurement of Ti isotopes by laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-...

The short-lived radionuclide 26 Al existed throughout the solar nebula 4.57 Ga ago, and the initial abundance ratio (26 Al/ 27 Al) 0 , as inferred from magnesium isotopic compositions of calcium–aluminum-rich inclusions (CAIs) in chondritic meteorites, has become a benchmark for understanding early solar system chronology. Internal mineral isochron...

Magnesium isotope ratios are known to vary in solar system objects due to the effects of 26Al decay to 26Mg and mass dependent fractionation, but anomalies of nucleosynthetic origin must also be considered. In order to infer the amount of enhancement of 26Mg/24Mg due to 26Al decay or to resolve small nucleogenetic anomalies, the exact relationship...

Laboratory experiments were used to determine the thermal (Soret) isotopic fractionation of lithium and potassium in a basalt melt, which adds elements with ionic charge +1 to the list of elements for which thermal isotopic fractionations in silicate liquids have been previously reported (i.e., Ca, Mg, Fe, Si, O, Sr, Hf, and U). The new experiments...

Oxygen isotopes are useful tracers of silicate melt generation processes because of the relatively constant abundance of oxygen in silicate reservoirs and the large isotopic fractionation that can occur between 18O and 16O during low (< 350°C) and high (> 350°C) temperature alteration processes at Earth’s surface. Studies of oceanic island basalts...

Fe and Ni isotope measurements across zoned metal grains from three CBb meteorites (QUE 94411, HaH 237, and MAC 02675) are used as constraints on their origin.

In situ Mg-isotopic data for CMS-1 are reported along with a new set of vacuum experiments that were performed on its estimated precursor composition.

Results on vacuum evaporation experiments of Mg- and Si-rich CMAS melts are used to discuss evolution of chemical and isotopic compositions of FUN CAIs.

Several recent studies found large lithium isotopic fractionations correlated with concentration gradients in pyroxene minerals from lava flows and mantle nodules that were interpreted as indicating diffusion of lithium into the grains. Motivated by these findings experiments were undertaken in which powdered spodumene (LiAlSi2O6) or Li2SiO3 was us...

FUN (Fractionation and Unidentified Nuclear) calcium-, aluminum-rich inclusions (CAIs) have large mass-dependent fractionations of silicon, magnesium, and oxygen isotopes (up to δ29Si ˜15‰ and δ25Mg ˜40‰), and mass-independent isotopic anomalies in many elements. To test the proposition that the mass-fractionation effects of all three isotopic syst...

We report here Al-Mg systematics for a coarse-grained CAI from the NWA 6991 CV3 chondrite for which we have previously reported an internal Pb-Pb isochron age.

Magnesium and silicon isotopic profiles across melilite grains in two type B1 and two type B2 calcium-aluminum-rich inclusions (CAIs) reveal differing but constant enrichments in heavy isotopes everywhere except ≤1000 μm from the CAI margins. There is no close correlation in the B1s or the B2s between isotopic composition and åkermanite content of...

Results of new evaporation experiments with Fo-rich melts are discussed in terms of temperature and composition effects on fractionation of Si and Mg isotopes.

We present the 60Fe-60Ni isotope systematics of individual chondrules from three unequilibrated ordinary chondrites measured by MC-ICPMS. The data are used to estimate a Solar System initial 60Fe/56Fe of ~10-8 .

FUN CAIs preserve large isotopic anomalies in several neutron-rich isotopes including 50Ti, as well as extreme mass-dependent fractionations in Mg and Si. We report on the Ti, Si and Mg isotopic compositions of a new Allende FUN CAI designated CMS-1.

High precision SIMS 26Al-26Mg isotope analyses were performed for a pristine Type B1 CAI Leoville 3535-1 on multiple mineral phases that include aluminum-rich zoned melilite mantle (Åk20-Åk60), magnesium-rich melilite (Åk70), fassaite, spinel and anorthite in the core. The data yield a well-defined internal isochron with an inferred initial 26Al/27...

Laboratory experiments demonstrating isotopic fractionation of lithium diffused into an augite grain are in good agreement with the lithium abundance and isotopic profiles in an augite grain from martian meteorite MIL 03346.

We report on the in situ measurement of titanium isotope ratios by LA-MC-ICPMS in nine Allende CAIs. Matrix-matched glass standards were synthesized and used for the correction of matrix-effects and isobaric interferences.

We present first results on texture and isotopic compositions of residues produced by cooling Fo-rich materials in vacuum. The results show that it is evaporation that controls the textures and Mg- and Si-isotopic compositions of crystallized phases.

We present preliminary data on the solar wind Mg isotopic composition in Genesis collectors to quantify the isotopic fractionation between solar wind and the Sun’s photosphere.

New Pb-Sr-Nd-Hf isotope data for Cr-poor and Cr-rich clinopyroxene megacrysts from southern African kimberlites strongly support a genetic link between megacrysts and kimberlites and further indicate that the isotopic differences between the two are largely explained by assimilation-fractional crystallization processes that occur as sub-lithospheri...

FUN inclusion Vigarano 1623-5 shows the first unequivocal correlated petrologic and isotopic evidence for volatilization. O-, Si-, and Mg-isotopic compositions reveal that 1623-5 has experienced several evaporation events and an isotopic exchange of O.

In order to deduce the isotopic compositions in the solar nebula of volatile elements, e.g., noble gases, O, and N, from analyses of the solar wind (SW), we must understand the magnitude of mass-dependent fractionation between the SW and the photosphere. With the exception of evaporation effects in CAIs, mass-dependent fractionation of Mg isotopes...

Abstract– Evaporation rates of K2O, Na2O, and FeO from chondrule-like liquids and the associated potassium isotopic fractionation of the evaporation residues were measured to help understand the processes and conditions that affected the chemical and isotopic compositions of olivine-rich type IA and type IIA chondrules from Semarkona. Both types of...

We report initial results from LA-MC-ICPMS analyses of Mg isotopes in selected chondrules in Allende and Semarkona, which suggest these chondrule formed no earlier than ~1 Ma and no later than ~3 Ma after CAIs.

Laboratory evaporation residues are used to test the proposition that combining the measured bulk and isotopic composition of the residues allows one to accurately determine the composition of the precursor.

We present a study of the 60Fe-60Ni chronometer in D’Orbigny and other angrites. Whole-rock samples and mineral separates from D’Orbigny define a precise 60Fe-60Ni isochron, which is used to estimate the initial solar system abundance of 60Fe.

We report composition-dependent matrix effects in the in-situ measurement of Mg and Si isotope ratios by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) in natural and synthetic silicate glasses. These were determined using two 193nm wavelength excimer laser ablation-multicollector ICPMS systems, one employing a double-focusi...

A mineral chemistry and whole-rock major element, platinum group element (PGE), and Re^Os isotope dataset is presented for a large suite of mantle xenoliths from 13 kimberlites that erupted through the Proterozoic mobile belts surrounding the Archean Kaapvaal craton of South Africa. The peridotites have compositions that are unusually infertile com...

High precision SIMS internal isochron of Leoville 3535-1 type B1 CAI indicates that it melted 30-40 k.y. after the formation of first solids in the solar system from refractory precursor solids and possibly it melted multiple times.

We report oxygen isotope data for the residues produced by evaporation of Mg- and Si-rich CMAS-liquids. The results on oxygen together with Mg- and Si-isotopes in the experimental run products are used to estimate the isotopic compositions of natural FUN CAIs.

Evaporation experiments using chondrule-like liquids as starting compositions are used to place constraints on the processes and conditions for the origin and evolution of Type IA and Type IIA chondrules.

A new 238U/235U ratio for the pyroxene fraction of the D'Orbigny angrite adjusts the previously reported Pb-Pb age of -0.6±0.3 Ma. This adjustment affects all short-lived chronometers anchored to D'Orbigny and reconciles some discrepancies in early solar system materials.

How to Get a Date Radiometric dating relies on measuring the abundance of a radioactive isotope and/or its decay products. By knowing a decay rate and an isotopic starting abundance—both assumed to be constant—an age is determined. Using high-resolution mass spectrometry, Brennecka et al. (p. 449 , published online 31 December; see the Perspective...

In-situ Mg and Si isotope measurements by laser ablation-multicollector mass spectrometry (LA-MC-ICPMS) are important tools for investigating topics ranging from the timescales and conditions of formation of refractory inclusions in meteorites to paleo-environmental studies. However, due to the small number of widely available and well-characterize...

Calcium-, aluminum-rich inclusions (CAIs) are often enriched in the heavy isotopes of magnesium and silicon relative to bulk solar system materials. It is likely that these isotopic enrichments resulted from evaporative mass loss of magnesium and silicon from early solar system condensates while they were molten during one or more high-temperature...

Asuka 881394 is a unique basaltic meteorite that originated in the crust of a differentiated planetesimal in the early Solar System. We present high precision Pb, Mg, and Cr isotopic compositions of bulk samples and mineral separates from this achondrite. A 207Pb–206Pb internal isochron obtained from the radiogenic pyroxene and whole-rock fractions...

We report on an investigation of the 26Al–26Mg isotope systematics in the D’Orbigny and Sahara 99555 angrites. High precision Mg isotope compositions and Al/Mg ratios were measured in mineral separates and whole rock samples from D’Orbigny and Sahara 99555 using multiple-collector inductively coupled plasma mass spectrometry (MC-ICPMS). Plagioclase...

Samples produced in piston cylinder experiments were used to document the thermal isotopic fractionation of all the major elements of basalt except for aluminum and the fractionation of iron isotopes by chemical diffusion between a natural basalt and rhyolite. The thermal isotopic fractionations are summarized in terms of a parameter Ωi defined as...

We present the results of our experiments on evaporation kinetics of forsterite-rich melts in vacuum. The results are used to place constraints on the thermal history of FUN CAIs.

Isotopic profiles of Mg and Si in melilite were measured within three Type B Ca-Al-rich inclusions from the CV3 chondrites Allende (USNM-3529.16 and AL-4884) and Leoville (USNM-3535.1) by secondary ion mass spectrometry.