Martian Geochronology from Meteorites and Crater Counts

Transcription

1 Martian Geochronology from Meteorites and Crater Counts L. E. Nyquist KR NASA Johnson Space Center, Houston, TX, USA Acknowledgments: C.-Y. Shih, D. Bogard, J. Park

2 Introduction and Overview Current status of Martian meteorite (MM) ages Methods, examples, and factors No old shergottites Comparisons to cratering chronologies Hartmann/Neukum S. Werner s 2005 Ph. D. thesis Stöffler-Ryder derived curve Implications for meteorite source regions Possibilities for calibrating the cratering curve Possibilities for dating secondary mineralization Example: Nakhlite iddingsite. VERY preliminary Rb-Sr studies of sulfates Some analytical requirements for in situ age dating Mostly for Rb-Sr, Sm-Nd

3 N(1) (km -2 ) Martian and Lunar Meteorite Ages and Cratering Chronology EN MN LN EH LH EA MA LA Lunar Meteorites Werner (2005) Mars 4 Neukum et al. (2001) Moon Lunar data (Stoeffler & Ryder, 2001) Mars = 1.55 x Lunar data Autolycus 3 AAa2n ~AEC2 Werner (2005) Time before Present (Ga) 2 Martian Meteorites Aristillus 1 0 FH 2 boundaries Period EN ~1% MN/LN ~19% H~21% EA ~9% MA ~5% LA ~2% % Surface Area

4 S Cerberus Plains Zunil Crater AEC2 Olympus Mons AAa2n AAa1n Elysium Mons Werner (2005), Fig Geologic map from Tanaka et al. (2005) with numbered units for crater size-frequency distribution measurements by Werner.

5 Adapted from S. Werner (Thesis, 2005)

6 Adapted from Ph. D. Thesis of S. Werner (2005; Fig )

7 From S. Werner (Thesis, 2005, Fig )

8 Radiometric Lunar and Martian Surface Ages and Impact Chronology N(1) (km -2 ) Ka 009 A Werner (2005) Mars Dho287A 3 Y86032 LAP Time before Present (Ga) 2 Neukum et al. (2001) Moon Lunar data Martian Meteorites (Stoeffler & Ryder, 2001) Hartmann (2005):? log N shallow, M = (N M /N m ) T, 2<D<50 = 1.55 NWA Lunar Meteorites Mars = 1.55 x Lunar data Autolycus AAa2n ~AEC2 Werner (2005) Aristillus EN ~1% MN/LN ~19% H~21% EA ~9% MA ~5% LA ~2% % Surface Area

9 Impact Chronology of Mars 30 Nyquist (2005) : Revised Martian Crater Curve (= Stoeffler & Ryder (2001) Lunar x 1.55) Surface Area (Vol. %) Martian Meteorites (solid symbols) NDDS melts unsampled EN LN/MN Hesperian A Time before Present (Ga)

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11 30 Percentage of Exposed Volcanics on Modern Mars in Each Epoch Noachian Hesperian Amazonian 25 Surface Area % Hartmann/Ivanov Neukum/Ivanov 5 H A 0 N Time before Present (Ga)

12 NWA 1460 Basaltic Shergottite

13 87 Sr/ 86 Sr Basaltic Shergottite - NWA 1460 Leach WR2(l) interior Opq(r) WR2(r) WR2 Plag1,2(r) fines T=336±15 Ma I(Sr)= ±30? Sr Pxf(r) Rb/ 86 Sr Px2a(r) +15 Ma -15 Ma Px2(r) Px1(r) Rb/ 86 Sr

14 143 Nd/ 144 Nd Basaltic Shergottite - NWA 1460 Leach WR2(l) interior T=350±16 Ma? Nd =+10.6±0.5 WR2 Plag(r) Plag2(r) fines Opq(r)? Nd Px2a(r) Px1(r) WR(r) Px2(r) Sm/ Nd Ma +16Ma Sm/ 144 Nd

15 Basaltic Shergottite - NWA NWA Plag 6-98% 39 Ar 40 Ar/ 36 Ar-Trap Age = 353±16 Ma ( 40 Ar/ 36 Ar) Tr =372±98 36 Ar/ 37 Ar= Age = 334±19 Ma ( 40 Ar/ 36 Ar) Tr =434±97 36 Ar/ 37 Ar= Ar/ 36 Ar -Trap

16 40 Ar / 36 Ar Zagami FG-Plag 0-25% % 25-54% Ar / 36 Ar Bogard & Park (2008) Slide courtesy of J. Park Isochron Age =?300 Myr 40Ar xs is distributed through the lattice Larger 40Ar xs (at intermediate temp extractions 23-54% of 39Ar ) hump : 40Ar/36Ar=?1000 (could be Martian atm in a shock produced phase)

17 Excess 40Ar in Zagami Mineral Separates Phase 40Ar xs % total CG-Plag 15.7x 10-7 cm 3 32 FG-Plag* 23.4 (17.9)x 10-7 cm 3 54 CG-Px2 10.8x 10-7 cm 3 85 FG-Px 2 9.2x 10-7 cm 3 86 FG-Px x 10-7 cm 3 89 (*Second value for FG-Plag subtracts the trapped component with 40Ar/36Ar=1000.) Bogard & Park (2008) suggest 40Ar xs =?1-2x10-6 (in cm 3 STP/g) Similar 40Ar excesses are also observed in other shergottites (Bogard, Park & Garrison, 2008, submitted. Courtesy of J. Park) Values calculated by subtracting from measured 40Ar, the amount of 40Ar* in situ, assuming Zagami formation age of 170 Myr. No significant difference between CG & FG, nor between Plag & Pyx

18 For Nakhlites: Common Age; No Evidence of Significant Excess 40 Ar Nakhlites MIL03346 NWA-998 Y Isochron Age =1325 ±18 Myr R 2 = Nakhla K ppm Gov. Valadares Lafayette Chassigny E E E E E E E E E-0 Total 40 Ar cm 3 /g Courtesy D. Bogard

19 Common Age and x10-7 cm 3 /g Magma-Derived 40 Ar Shergottites All 170 Myr Isochrons Zagami Los Angeles NWA3171 [ K ] ppm Shergotty NWA2975, 1068 Y-00097, EET High-K Plag Low-K Pyx Mid-K WR Total 40 Ar, 10-7 cm 3 /g glass Courtesy of D. Bogard

20 1.0 Basaltic & Lherzolitic Shergottites? =5 207 Pb/ 206 Pb T=700 Ma T=173 Ma? =10 Blanks MT?=8?=8 EETA Sh,Za Y79 LA?=6?=6? =4 Sh Phos (SIMS) Zagami Chen & Wasserburg (1986) Bouvier et al. (2005) Borg et al. (2005) Shergotty Chen & Wasserburg (1986) Sano et al. (2000) wtd avg. Los Angeles Bouvier et al. (2005) EETA Chen & Wasserburg (1986) Y Misawa et al. (1997) Ga 173 Ma 204 Pb/ 206 Pb

21 Shergottites 1.0 Zagami Mask. leach (Bouvier et al. 2005) Shergotty Zagami LA MT ( 207 Pb/ 206 Pb) i % conf. intervals Assimilant range 0.4 "4.0" Ga line ( 204 Pb/ 206 Pb) i

22 0.08 LA Zagami Shergottites Chen & Wasserbug ; Borg et al ( 204 Pb/ 206 Pb) i Bouvier et al ~0.064 Assimilant range Shergotty 95% conf. intervals 0.05 ~0.725 Assimilant range ( 87 Sr/ 86 Sr) i

23 ~2.6 Ga ~1.6 Ga ~0.3 Ga Spirit Opportunity Figure 1 from Nimmo and Tanaka (2005) Ann. Rev. Earth Planet. Sci., 33, Surface ages from Hartmann et al. (1981)

24 Young Elysium Volcanics ~100 Ma Apollinaris Patera 3.7 to ~3.1 Ga 10 S Gusev X Spirit ~3.6 to ~1.8 Ga 15 S >3.7 Ga 170 E 175 E Gusev Crater with Apollinaris Patera Image and Age Ranges Courtesy of K. Tanaka 180 E

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26 143 Nd/ 144 Nd Nakhlite - MIL T=1.36±0.03 Ga? Nd =+15.2±0.2 Gl Ol Ol2 Cpx2(l) WR(l) WR1? Nd Cpx1 Cpx3-0.4 WR1,2(r) 147 Sm/ 144 Nd Ma Cpx2(r) -30Ma 147 Sm/ 144 Nd

27 0.708 Nakhlite - Lafayette T= Ga I Sr = WR(l) 87 Sr/ 86 Sr Px(r) Id2(r) WR2 WR1 WR(r) Ol(r) Px(l) Ol(l) Id1(r) Id2(l) Id1(l) T idd? =~680 Ma Rb/ 86 Sr Shih et al. (1998)

28 Kuebler et al. (2003) A study of olivine alteration to iddingsite using Raman spectroscopy. LPSC34. Iddingsite...a catch-all term to describe reddish alteration products of olivine...an Å-scale intergrowth of goethite and smectite (saponite)... Alteration conserves Fe (albeit oxidized), but requires addition of Al and H 2 O and removal of Mg and Si. Kuebler et al. (2003), Fig. 2.

29 Orthopyroxenite ALH Sr/ 86 Sr Silicates T = Ga I Sr = S6 Carbonates T = Ga I Sr = S S Rb/ 86 Sr Borg et al. (1999) The age of the carbonates in Martian Meteorite ALH Science, 286,

30 Clark et al. (2005) Chemistry and mineralogy of outcrops at Meridiani Planum. EPSL 240, Fig. 12 showing the modeled mineral components of outcrops at Endurance, Fram, and Eagle Craters from the APXS and MB instruments. Modeled total sulfate abundance is 35 % for SO 3 = 20%.

31 Outcrop sulfates at the Opportunity Site, Meridiani Planum (Mini-TES; Glotch et al. (2006) JGR 111, E12SO3) Mineral Base Model Terr. Rb-Sr Na-jarosite NaFe 3 (SO 4 ) 2 (OH) 6 10% (5%?) Y K-jarosite KFe 3 (SO 4 ) 2 (OH) 6 (5%?) Y Kieserite MgSO 4. H 2 O 20% Y Anhydrite CaSO 4 10 % Gypsum CaSO 4. 2H 2 O Y Terrestrial sulfate samples courtesy of R. Morris Sample LNVJAR1-FP GCJAR1-FP KIEDEI WD164A1

32 Preliminary Rb-Sr Study of Terrestrial Sulfates K-Jarosite KFe 3 (OH) 6 (SO 4 ) 2 (15 mg) GCJAR1-FP (New Mexico) Readily soluble in HF+HNO 3 Na-Jarosite NaFe 3 (OH) 6 (SO 4 ) 2 (16 mg) LNVJAR1-FP (Nevada) Readily soluble in HF+HNO 3 Gypsum CaSO 4. 2H 2 O (16 mg) WD164A1 (Italy) Insoluble in hot water, soluble in 1N HCl Kieserite MgSO 4. H 2 O (26 mg) KIEDEI (Germany) Insoluble in room temperature H 2 O (15 min) Soluble in hot H 2 O (1 hr)

33 0.708 Hypothetical Sr-Isotopic Evolution in Ancient Sulfates with Terrestrial-Sample Rb/Sr ratios 87 Sr/ 86 Sr Ancient alteration T=4.56 Ga Gypsum (WD164A1) Na-Jarosite (LNVJAR1) Kieserite (KIEDE1) T=4.56 Ga K-Jarosite (GCJAR1) Rb/ 86 Sr

34 Mauna Kea Basaltic Tephra & Jarosite Altered tephra Fresh tephra Nd (ppm) Jarosite Sm (ppm)

35 143 Nd/ 144 Nd Mauna Kea Basaltic Tephra & Jarosite Altered tephra Maximum Jarosite Age T=~400 Ka;?Nd=+6.5 Basalt age T(Ar-Ar)=400±26 Ka (Sharp et al. 1996) Jarosite Fresh tephra Tephra-Jarosite errorchron T=230±140 Ma Sm/ 144 Nd

36 Mauna Kea Basaltic Tephra & Jarosite Maximum Jarosite Age T=~400 Ka; I(Sr)= Jarosite 87 Sr/ 86 Sr fresh tephra altered tephra Basalt age T(Ar-Ar)=400±26 Ka (Sharp et al. 1996) Tephra alteration errorchron T=5.1±1.8 Ma Rb/ 86 Sr

37 143 Nd/ 144 Nd Basaltic Shergottite - NWA 1460 Bulk Rock Acid-leaching Experiment interior T=354±22 Ma? Nd =+10.5±0.5 WR WR(l) Acid-leachates fines? Nd WR(r) Acid-residues 147 Sm/ 144 Nd Ma Ma Sm/ 144 Nd

38 Basaltic Shergottite - NWA 1460 Bulk Rock Acid-leaching Experiment interior fines T(Min.)=336±15 Ma I(Sr)= ±30 87 Sr/ 86 Sr WR leachates T(WR)=170±36 Ma I(Sr)= ± WR WR residues Rb/ 86 Sr

39 0.76 Martian Meteorites Orthopyroxenite T=~4.56 Ga 87 Sr/ 86 Sr Nakhlites T=~1.3 Ga Shergottites T=~165 Ma Depleted shergottites T= Ma 87 Sr/ 86 Sr errors Olivine-shergottites T= ~165 Ma ±1% ± Rb/ Sr errors ±10% ±5% Rb/ 86 Sr

40 Martian Meteorites 143 Nd/ 144 Nd Nakhlites T=~1.3Ga Orthopyroxenite T=~4.56 Ga Shergottites Olivine-shergottites T= ~165 Ma Depleted shergottites T= Ma 143 Nd/ 144 Nd errors ±1 ±1% 147 Sm/ 144 Nd errors ±10% ±5% Sm/ 144 Nd

41 Summary and Conclusions Large inherent uncertainty in cratering chronologies Date an Early-Mid Amazonian (~1-3 Ga) surface to calibrate. Gusev-like site probably OK Absolute dating of the Hesperian/Noachian also desirable. Better for life, late heavy bombardment issues. Meridiani-like site may be OK Dating aqueous activity/secondary minerals/life habitats Hard, even for laboratory-based geochronology. Isochron methods (esp. Rb-Sr) look promising Ar-Ar techniques also should be investigated. Micro-beam techniques available for a returned sample. SIMS: shergottite phosphates, baddeleyite; nakhlite phos. In Situ Dating Hard to impossible by traditional methods Best bet: redundant methods K-Ar with gas source mass spectrometer Automated chemistry lab for simple leaching, etc., with solids source mass spec (TIMS)

42 Outcrop sulfates at the Opportunity Site, Meridiani Planum (Mini-TES; Glotch et al. (2006) JGR 111, E12SO3) Mineral Base Model Terr. Rb-Sr Na-jarosite NaFe 3 (SO 4 ) 2 (OH) 6 10% (5%?) Y K-jarosite KFe 3 (SO 4 ) 2 (OH) 6 (5%?) Y Kieserite MgSO 4. H 2 O 20% Y Anhydrite CaSO 4 10 % Gypsum CaSO 4. 2H 2 O Y Terrestrial sulfate samples courtesy of R. Morris Sample LNVJAR1-FP GCJAR1-FP KIEDEI WD164A1

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44 Mauna Kea Basaltic Tephra and Jarosite (Two End-member Mixing Model) Marine aerosol (contaminant) For Sr : Jarosite=~75% Marine aerosol + ~25% Tephra 87 Sr/ 86 Sr % 95% 90% % of Marine aerosol in Tephra 80% 70% 50% 30% 10% Jarosite (~75% aerosol) Sr (ppm) Fresh Tephra

45 Mauna Kea Basaltic Tephra and Jarosite (Two End-member Mixing Model) 143 Nd/ 144 Nd Jarosite (~50% aerosol) % 99% 90% 70% 60% 80% 40% For Nd : Aerosol Jarosite=~50% Marine aerosol (contaminant) + ~50% Tephra Nd (ppm) 30% 20% % of Aerosol in Tephra Fresh Tephra 10%

46 87 Sr/ 86 Sr "Iddingsite" T=650±80 Ma >3.95(l) Cpx(r) WR(r) Nakhlite - Y WR1 Ol(l) >3.95(r) WR(l) Cpx(l) NM(l) Cpx2(l) Ol(r) Ol(residues) T=614±29 Ma NM(r) Cpx2(r) T=1.30±0.02 Ga I(Sr)= ± Rb/ 86 Sr Misawa et al. (2005) Antarct. Met. Res., Fig. 3

47 Lunar Mare Basalt Meteorite - Kalahari T=4.30±0.05 Ga? Nd,CHUR =+0.83±0.47 Px2(r) 143 Nd/ 144 Nd ? Nd,HEDR =-0.04±0.47 Leach WR(l) Plag(r) WR? Nd 1 0 Px1(r) 147 Sm/ 144 Nd Ma HEDR CHUR -1-52Ma Sm/ 144 Nd

48 Crystallization and Ejection Ages of Martian Meteorites Compared to Martian Epochs with Hartmann/Neukum (2001) Ages Crystallization Age (Ga) Lyon Hypothesis H/N A84 EA MA Nakhlites & Chassigny DaG, Y98 Dho NWA /1460, QUE LA 1068 Local Stratigraphy? EET BU PE A77, LEW, Y79 Zag, She, LA, Ejection Age (Ma) Basaltic shergottites Lherzolitic shergottites Clinopyroxenites (Nakhlites) Dunite (Chassigny) Orthopyroxenite

49 Hypothetical Sr-Isotopic Evolution in Sulfates with Terrestrial-Sample Rb/Sr ratios Basalt crystallization T=180 Ma Recent alteration T=10±1.4 Ma 87 Sr/ 86 Sr Kieserite Na-Jarosite Gypsum WR K-Jarosite Rb/ 86 Sr