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The use of 187Re-187Os isotopes in revealing magmatic processes on Mars

  • November 2016
  • Conference: NERC Isotope Workshop
  • Volume: 1
Authors:
Nicola Mari at University of Pavia
Nicola Mari
L. J. Hallis at University of Glasgow
L. J. Hallis
Amy Riches at University of Edinburgh School of Geoscience and SETI Institute
Amy Riches
  • University of Edinburgh School of Geoscience and SETI Institute
M. R. Lee at University of Glasgow
M. R. Lee
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Abstract

Rhenium and osmium are highly siderophile elements (HSE) that can help in revealing the genesis of asteroidal and planetary cores and mantles. In particular, the 187Re-187Os isotope system can be used to answer key issues in planetology and cosmochemistry, as insights on core formation, early differentiation, and late accretion events in terrestrial planets (Shirey and Walker, 1998; Righter et al., 2000). Studying the Re-Os systematics on Martian meteorites is critical for an understanding of the mantle evolution of Mars, and to constrain whether one or more magmatic reservoirs derived from crystallization of a magma ocean. The similar content in Os in terrestrial and Martian basalts would argue that the sources for both planets had the same abundances in Os and HSE, this is also true for ultramafic rocks on Mars and Earth (Birck & Allegre, 1994; Warren & Kallemeyn, 1996). Thus, Os isotopes can be used to obtain the relative abundance of Re and Os on Earth as well on Mars, assuming the very similar HSE content of both mantles (Shirey & Walker, 1998).
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1st NERC IAPETUS Isotope Workshop, University of Glasgow (23rd- 24th November 2016)
The use of 187Re-187Os isotopes in revealing magmatic processes on
Mars
N. M a r i 1, L . H a l l i s 1, A . R i c h e s 2, M . L e e 1
1Sc h o o l o f G e o g r a p h ic al and Earth Sciences, U n i v ers ity of Glasgow, UK ; 2Department
of E a r t h S c i e n c e s , Dur ham University, UK
Rhenium and osmium are highly siderophile elements (HSE) that can help in revealing
the genesis of asteroidal and planetary cores and mantles. In particular, the
187Re-187Os isotope system can be used to answer key issues in planetology and
cosmochemistry, as insights on core formation, early differentiation, and late accretion
events in terrestrial planets (Shirey and Walker, 1998; Righter et al., 2000).
Studying the Re-Os systematics on Martian meteorites is critical for an understanding
of the mantle evolution of Mars, and to constrain whether one or more magmatic
reservoirs derived from crystallization of a magma ocean. The similar content in Os in
terrestrial and Martian basalts would argue that the sources for both planets had the
same abundances in Os and HSE, this is also true for ultramafic rocks on Mars and
Earth (Birck & Allegre, 1994; Warren & Kallemeyn, 1996). Thus, Os isotopes can be
used to obtain the relative abundance of Re and Os on Earth as well on Mars,
assuming the very similar HSE content of both mantles (Shirey & Walker, 1998).
References
Shirey S. B. & Walker R. J., 1998. The Re-Os isotope system in cosmochemistry and high-
temperature geochemistry. Annu. Rev. Earth Planet. Sci., vol. 26, pp. 423-500.
Righter K., Walker R. J., and Warren P. H., 2000. Significance of highly siderophile elements and
osmium isotopes in the lunar and terrestrial mantles. Origin of the Earth and Moon (R. M. Canup and
K. Righter, eds.), pp. 291-322, University of Arizona press.
Birck J. L., Allegre C. J., 1994. Contrasting Re/Os magmatic fractionation in planetary basalts. Earth
Planet. Sci. Lett., vol. 124, pp. 139-48.
Warren P. H., Kallemeyn G. W., 1996. Siderophile trace elements in ALHA84001, other SNC
meteorites and eucrites: evidence of heterogeneity, possibly time-linked, in the mantle of Mars.
Meteor. Planet. Sci., vol. 31, pp. 97-105.
ResearchGate has not been able to resolve any citations for this publication.
Significance of Highly Siderophile Elements and Osmium Isotopes in the Lunar and Terrestrial Mantles
Article
  • Jan 2000
Analytical and experimental advances in the past decade have increased our understanding of the highly siderophile elements (HSE) and the 187Re-187Os and 190Pt-186Os isotopic systems in terrestrial, meteoritic, and planetary materials. Analyses of a broad range of natural materials and experiments on natural analogs have demonstrated that HSE reside primarily in metal alloys, sulfides, and oxides. These elements will be strongly partitioned into a metallic core during planetary differentiation, leaving low concentrations (
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Siderophile trace elements in ALH84001, other SNC meteorites and eucrites: Evidence of heterogeneity, possibly time-linked, in the mantle of Mars
Article
  • Dec 1995
We report neutron activation analyses, including radiochemical determination of trace siderophile elements (Au, Ge, Ir, Ni, Os and Re), for three SNC/martian meteorites, and Os and Re results for numerous eucrites. Ratios such as Ga/Al in the SNC orthopyroxenite ALH84001 confirm its martian affinity—its many distinctive characteristics, most notably its near-primordial age, notwithstanding. To the list of ALH84001's idiosyncrasies can now be added extraordinarily low concentrations of Au, Ni and, especially, Re (17 pg/g), for a martian meteorite. We consider several possible origins for the anomalously low Re content in ALH84001, including metasomatism or alteration. The pyroxene-cumulate nature of this rock probably does not account for its low Re content. Other SNC meteorites are also cumulates. An examination of Re-Nd variations among terrestrial basalts and komatiites suggests that Re is compatible with mantle minerals in general and only incompatible with olivine (however, olivine dominates the mantle residuum, especially during komatiite genesis). Our preferred model is that the ALH84001 parent melt formed in a mantle source region that was far more Re-depleted, and/or at a substantially lower oxygen fugacity, than the sources of the young SNC meteorites. Such a contrast is consistent with models that replenish siderophile elements in planetary mantles by gradual admixture of late-accreting matter and similarly derive most planetary water (which serves as an oxidant) very late in accretion. According to this model, ALH84001 formed before the siderophile-rich matter and water had been mixed well into the martian interior. Possibly the martian mantle never became generally as Re-rich and/or oxidized as the source region(s) of the younger SNCs.
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The Re-Os isotope system in cosmochemistry and high-temperature geochemistry
Article
  • May 1998
The Re-Os isotope sytem, based on the long-lived β − transition of 187 Re to 187 Os, has matured to wide use in cosmochemistry and high-temperature geochemistry. The siderophilic/chalcophilic behavior of Re and Os is different from that of the elements that comprise most other long-lived radiogenic isotope systems. Mag-matic iron meteorites (IIIAB, IIAB, IVA, and IVB) have Re-Os isochrons that indicate asteroidal core crystallization within the first 10–40 million years of Solar System evolution. Rocks from Earth's convecting mantle show generally chondritic Re/Os evolution throughout Earth history that is explained by the ad-dition of highly siderophile elements to the mantle after core formation via late accretion. Oceanic basalts have Os-isotope systematics that improve the detailed geological interpretation of extant mantle components. Some portions of ancient subcontinental lithospheric mantle are severely depleted in Re and have corre-spondingly subchondritic 187 Os/ 188 Os, indicating long-term isolation from the convecting mantle during the Archean-Proterozoic. Magmatic ore deposits have differences in initial Os isotopic composition traceable to the crustal vs mantle sources of the platinum-group elements and base metals.
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Contrasting Re/Os fractionation in planetary basalts
Article
This work reports the first ReOs isotopic results for lunar basalts and eucrites. Both Re and Os concentrations are found to be very low and Re/Os ratios are close to chondritic. This contrasts with the much higher than chondritic Re/Os ratio of terrestrial basalts. Osmium displays a rather uniform solid/liquid fractionation in different planetary bodies (Moon, Earth, Eucrite Parent Body, Mars), whereas rhenium is about three orders of magnitude more incompatible in terrestrial basalt genesis. We argue that this is a function of oxygen fugacity in the source regions of basalts.
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