1. Jeff TaylorAges, Mantle Sources, Differentiation1 SNC Ages, Mantle Sources, and the Differentiation of Mars Crystallization ages of Martian meteorites –Mostly young, but initial differentiation very early Isotopic record of the time of formation of source regions in the Martian mantle –At least three mantle reservoirs –Preserved for 4.5 billion years –No recycling of crust Magma ocean modeling

2. Complications in Age Determinations Jeff TaylorAges, Mantle Sources, Differentiation2 Weathering on Mars and Earth Shock effects during launch from Mars

3. Jeff TaylorAges, Mantle Sources, Differentiation3

4. Jeff TaylorAges, Mantle Sources, Differentiation4 Age of QUE 94201 Borg et al. (1997)

5. Jeff TaylorAges, Mantle Sources, Differentiation5 Age of QUE 94201 Borg et al. (1997)

6. Jeff TaylorAges, Mantle Sources, Differentiation6 Age of DaG 476 Sm-Nd age well defined (474 Gy), though affected a bit by terrestrial weathering, as shown by mixing line with clays etc. Rb-Sr system is disturbed and gives no age info. However, can get initial Sr by assuming Sm-Nd age and using low Rb maskelynite Borg et al. (2003)

7. Jeff TaylorAges, Mantle Sources, Differentiation7 Ages of Dated Martian Events Borg and Drake (2005) 4091 ±30 Ma

8. The Old-Shergottite Interpretation Jeff TaylorAges, Mantle Sources, Differentiation8 Bouvier et al. (2005)

9. Jeff TaylorAges, Mantle Sources, Differentiation 9 Shergottite Age Conundrum Pb isotopic data indicate old ages for Martian meteorites, including shergottites. But internal isochrons suggest young ages for shergottites. (From Borg et al., 2003, GCA, v. 67(18), p. 3519-3536.)

10. The Old-Shergottite Interpretation Jeff TaylorAges, Mantle Sources, Differentiation10 Moser et al. (2013)

11. Jeff TaylorAges, Mantle Sources, Differentiation11 Martian Meteorites Imply Early Global Differentiation 165-212 Ma 327-575 Ma 1300 Ma 4500 Ma Ages 87 Rb  87 Sr Earth (recycling and smaller range in Sr composition) enriched depleted No recycling on Mars Borg et al (1997, 2003)

12. Jeff TaylorAges, Mantle Sources, Differentiation12 165-212 Ma 327-575 Ma 1300 Ma 4500 Ma Ages 87 Rb  87 Sr enriched depleted 4.49 Ga mixing line Rb-Sr whole rock mixing diagram Two reservoirs established at ~4.5 Ga: No recycling on Mars Earth (recycling) Borg et al (1997, 2003)

13. Jeff TaylorAges, Mantle Sources, Differentiation13 Independent Support for Early Differentiation 147 Sm  143 Nd (t 1/2 =106 Gy) 146 Sm  142 Nd (t 1/2 = 103 My) These can be used together to determine time of differentiation if that happened early enough (before 142 Nd decayed away) Graph at right shows that SNCs lie along a line indicating initial fractionation of Sm from Nd took place 4.5 Gy ago Borg and Drake (2005), based on Borg et al. (2003), and Foley et al (2005)

14. Hf-W and Core Formation 182 Hf decays to 182 W with a half life of 9 My During core formation, W goes into core (Hf/W in core is 0), while remaining Hf stays in mantle (Hf/W is >10. 142 Nd is also shortlived Assuming a 2-stage model, the apparent isochron suggests age of 11.6 ± 0.4 My after beginning of solar system. Jeff TaylortAges, Mantle Sources, Differentiation14 Foley et al. 2005

15. Jeff TaylorAges, Mantle Sources, Differentiation15 Dating core formation: - W goes into core - Hf does not - 182 W in mantle indicates amount decayed after core formed - Hf-W data from Martian meteorites indicate core formation by 11.6 My after solar system formation - Other work suggests 2-4 My

16. Jeff TaylorAges, Mantle Sources, Differentiation16 Depleted and Enriched Shergottites Depleted Enriched

17. Jeff TaylorAges, Mantle Sources, Differentiation17 Earth Courtesy of Lars Borg 0.0 0.4 0.8 1.2 1.6 0.695 0.705 0.715 0.725 Shergotty LEW ALH77 EETA/B QUE DaG Zagami Initial 87 Sr/ 86 Sr Nakhlites La/Yb Shergottite Mixing: Two Ancient Reservoirs mixing Long-term incompatible-element enriched. Long-term incompatible-element depleted. depleted enriched

18. Jeff TaylorAges, Mantle Sources, Differentiation18 Earth Jones (1989) Longhi (1991) Borg et al (1997, 2003) mixing depleted enriched Long-term incompatible-element enriched. Long-term incompatible-element depleted.

19. Jeff TaylorAges, Mantle Sources, Differentiation19 Oxidation State of Reservoirs We can determine oxygen fugacity (fO 2 ) from that amount of Fe 2+ and Fe 3+ in ilmenite and coexisting spinel, or among spinel,olivine, and pyroxene Basic relation: 6Fe 2 SiO 4 + O 2 = 3Fe 2 Si 2 O 6 + 2Fe 3 O 4 oliv pyrox spinel fO 2 = Fe 3 O 4 (sp)*Fe 2+ (pyx)/Fe 2+ (oliv) Has been calibrated experimentally Ilm = ilmenite; TMt = titanomagnetite

20. Jeff TaylorAges, Mantle Sources, Differentiation20 Uncertainties Some concern that use of oxides does not reflect temperature of magma because of lower- T requilibration –Use of olivine and pyroxene avoids that problem Electron microprobe analyses must be “perfect” and so must the minerals because amount of Fe 3+ is calculated from stociometry of minerals Chris Herd, who has done most of this for SNCs, estimates that uncertainty in fO 2 is ±0.5 log units

21. Jeff TaylorAges, Mantle Sources, Differentiation21 Oxidation state of Sources Meenakshi Wadhwa (ASU) measured Eu and Gd in pyroxenes in Martian basaltic meteorites, using ion microprobe Found correlation with initial Sr D Eu related to fO 2 (experiments) So initial Sr isotopic composition related to fO 2 Was first to show this Laboratory experiments (in G. McKay’s Lab at JSC) calibrate Eu partitioning as Function of fO 2

22. Jeff TaylorAges, Mantle Sources, Differentiation22 log fO 2 (relative to QFM) La/Yb Oxidation states inherited from source regions Herd et al (2002) Goodrich et al (2003) Olivine-Phyric Basaltic Shergottites Enriched (“crust”) Depleted (“mantle”) No correlation with type of shergottite

23. Jeff TaylorAges, Mantle Sources, Differentiation23 1. Formation of 2 reservoirs at ~4.5 Ga: “Crust-like”:high La/Yb low Sm/Nd (-e Nd ) high Rb (high 87 Sr/ 86 Sr) oxidized “Mantle-like”:lowLa/Yb high Sm/Nd (+ e Nd ) low Rb (low 87 Sr/ 86 Sr) reduced Martian differentiation history 2.No significant recycling 3.Later magmatism samples mixtures of 2 reservoirs

24. Jeff TaylorAges, Mantle Sources, Differentiation24 Diversity of Mantle Sources Calculated 147 Sm/ 144 Nd in sources for shergottites have a big range Ditto for 87 Rb/ 86 Sr This means that almost all of the meteorites must come from separate sources –Exceptions: nakhlites and chassigny, and EET 79001 A and B Implies a complicated mantle

25. Jeff TaylorAges, Mantle Sources, Differentiation25 Insert diagram of martian mantle/crust with amphibole layer Reduced basalt (mantle characteristics) e.g., QUE 94201 CRUSTCRUST MANTLEMANTLE Long-term, incompatible element depletion Oxidized basalt (crustal characteristics) e.g., Shergotty Long-term, incompatible element enrichment Alteration Upper Mantle Source ~ IW (~QFM - 3.5) Herd et al (2002) Alteration Assimilation of Altered Crust

26. Jeff TaylorAges, Mantle Sources, Differentiation26 Insert diagram of martian mantle/crust with amphibole layer Reduced basalt (mantle characteristics) e.g., QUE 94201 CRUSTCRUST MANTLEMANTLE Long-term, incompatible element depletion Oxidized basalt (crustal characteristics) e.g., Shergotty Long-term, incompatible element enrichment Upper Mantle Source ~ IW (~QFM - 3.5) Herd et al (2002) Hydrous Minerals Hydrous Assimilation of Hydrous Minerals Throughout Crust

27. Jeff TaylorAges, Mantle Sources, Differentiation27 Heterogeneous Mantle Model (Magma Ocean) Insert diagram of martian mantle/crust with amphibole layer CRUST Long-term, incompatible element depletion Oxidized basalt (crust-like characteristics) e.g., Shergotty Reduced basalt (mantle characteristics) e.g., QUE 94201, Dhofar 019 Long-term, incompatible element enrichment ~ IW MANTLE Herd et al (2003)

28. So which one, crustal assimilation or differences in the mantle? Consensus is that the mantle dominates and that it all involves the magma ocean No correlation with petrographic type—both basaltic and olivine-phyric shergottites are in enriched and depleted, and in between, categories No strong correlation between indices of differentiation (SiO 2 concentrations, Mg/(Mg+Fe) and trace element or isotopic ratios (see next slide) Jeff TaylorAges, Mantle Sources, Differentiation28

29. Mantle Sources Jeff TaylorAges, Mantle Sources, Differentiation29 Calculated mantle sources assuming differentiation at 4.513 Ga No Correlation with SiO 2

30. Nakhlite and Sherg Souces Are Different Jeff TaylorAges, Mantle Sources, Differentiation30 Foley et al. (2005)

31. Mantle Sources Jeff TaylorAges, Mantle Sources, Differentiation31 “Enriched” Shergottites “Depleted” Shergottites Taylor et al. (2008)

32. Mantle Sources Jeff TaylorAges, Mantle Sources, Differentiation32 Taylor et al. (2008) - Plots at left show that nakhlite source regions are distinct from those of shergottites. - The Ba/La plot has both nakhlites and shergottites above the chondrite line, indicating that there must be an additional (low Ba/La) region in the mantle. - Plots at left show that nakhlite source regions are distinct from those of shergottites. - The Ba/La plot has both nakhlites and shergottites above the chondrite line, indicating that there must be an additional (low Ba/La) region in the mantle.

33. Jeff TaylorAges, Mantle Sources, Differentiation33 Magma Ocean Geochemical Modeling In contrast to modeling the lunar magma ocean, we have to take into account high-pressure phases on Mars This cross section assumes Dreibus-Wänke bulk composition (high FeO) and is based on experiments by Bertka and Fei. Majorite has garnet structure but pyroxene composition

34. Evidence for a Martian Magma Ocean Early differentiation Rapid accretion Jeff TaylorAges, Mantle Sources, Differentiation34 Dauphas and Pourmand (2011)

35. Jeff TaylorAges, Mantle Sources, Differentiation35 Magma Ocean Geochemical Modeling Borg and Draper (2003) have modeled crystallization of magma ocean from expected crystallization sequence of bulk Mars composition Results are reasonable and when assorted cumulates are remelted, SNC parent magmas are produced, including high Ca/Al Elements that do not fit very well: Rb, U, Ta, light REE Borg and Draper (2003)

36. Jeff TaylorAges, Mantle Sources, Differentiation36 Mantle Turn Over after Magma Ocean Crystallization

37. Jeff TaylorAges, Mantle Sources, Differentiation37 Density

38. Jeff TaylorAges, Mantle Sources, Differentiation38 One Layer

39. Jeff TaylorAges, Mantle Sources, Differentiation39 Making a Complicated Mantle

40. Jeff TaylorAges, Mantle Sources, Differentiation40 Styles of Differentiation

41. Jeff TaylorAges, Mantle Sources, Differentiation41 Styles of Differentiation Moon has much lower K/Th than Mars, but also much larger range in both elements (cumulates, highly evolved materials, KREEP) Implies that on Mars: no large areas dominated by cumulates or highly evolved magmatic products Does this mean Mars had no magma ocean, or different magma ocean processes? Th on the Moon Th on Mars

42. Jeff TaylorAges, Mantle Sources, Differentiation42 Styles of Differentiation Mars: no magma ocean? Maybe, but: –Meteorite data show that there was an early, extensive differentiation event –Processes in Martian magma ocean might have been different than in lunar magma ocean (hydrous? Choked with crystals?) If no magma ocean –Accreting planetesimals were not substantially melted –Not enough 26 Al to cause substantial melting.