Meteorite Ages & Timing of Solar System Processes

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1 Meteorite Ages & Timing of Solar System Processes 1

2 Isotope Systematics Object 0 CHUR 26 Mg 24 Mg 26 Mg 24 Mg 26 Mg 24 Mg Chemical fractionation 26 Al decay ( 26 Al/ 27 Al) t0 ( 26 Mg/ 24 Mg) t0 ( 26 Mg/ 24 Mg) t0 27 Al/ 24 Mg 27 Al/ 24 Mg 27 Al/ 24 Mg t 0 : formation of object 0 t 1 : formation of object 1 Present 26 Mg 24 Mg ( 26 Mg/ 24 Mg) t0 26 Mg 24 Mg 26 Mg 24 Mg 26 Al decay Chemical fractionation 26 Mg 24 Mg ( 26 Mg/ 24 Mg) t1 ( 26 Al/ 27 Al) t1 27 Al/ 24 Mg 27 Al/ 24 Mg 27 Al/ 24 Mg 27 Al/ 24 Mg CHUR Object 1 Slope gives 26 Al/ 27 Al. Intercept gives initial 26 Mg/ 24 Mg ( 26 Al/ 24 Mg). 2

Isotope Systematics δ 26 Mg* ( ) 3 2 1 Bulk isochron of CAIs (Jacobsen et al. 2008) 26 Al/ 27 Al 0 =(5.23±0.

O Ca δ 26 Mg* ( ) Internal isochron of a fine-grained CAI (MacPherson et al. 2010a) 15 10 5 26 Al/ 27 Al 0 =(5.27±0.

3 Isotope Systematics δ 26 Mg* ( ) Bulk isochron of CAIs (Jacobsen et al. 2008) 26 Al/ 27 Al 0 =(5.23±0.13) 10 5 Condensation of 1 10-μm dust from nebular gas O Mg Mg Ti Si O Ca Al Si Al/ 24 Mg 27 Al/ 24 Mg Al O Mg Agglomeration into mm cm-sized objects Si O Ca δ 26 Mg* ( ) Internal isochron of a fine-grained CAI (MacPherson et al. 2010a) Al/ 27 Al 0 =(5.27±0.17) 10 5 Different measuremen ts give similar 26 Al/ 27 Al values... < 50 kyr formation of CAIs and last Melting and crystallization δ 26 Mg* ( ) Internal isochron of an igneous CAI (MacPherson et al. 2010b) 26 Al/ 27 Al 0 =(5.17±0.31) 10 5 heating event took place within 50kyr Al/ 24 Mg 3

Isotope Systematics 0.5 cm 1,000 km Hf/W~3.5 Hf/W~0.8 Core formation t c Hf/W~0 Present Chondrite (representative of bulk Mars) Differentiated planet 1.8516 Mantle (Hf/W~3.5) 182 W/ 183 W 1.8514 1.

4 Isotope Systematics 0.5 cm 1,000 km Hf/W~3.5 Hf/W~0.8 Core formation t c Hf/W~0 Present Chondrite (representative of bulk Mars) Differentiated planet Mantle (Hf/W~3.5) 182 W/ 183 W Chondrite (Hf/W~0.8) ε 182 W = t c = 4.0 Myr Core (Hf/W~0) Time after solar system birth (Myr) 100 Core (metal) values yield chondritic value at time of segregation. 4

5 Relative Timing of Solar System Events Combined CAI isochron: m = (9.72±0.44) x 10-5 i = -3.28±0.12 MSWD = 0.6 t = ±0.7 Ma ε 182 W Hf/ 184 W Fig. 4. Combined Hf W isochron for CAIs. Symbols and regression as in Figs. 2 and 3. Grey triangles are data for different fractions from Allende CAI All-MS-1 (Kleine et al., 2005). Inset shows a magnification of the isochron with Hf W data for fractions with low 180 Hf/ 184 W. The absolute age is calculated relative to Pb Pb ages for angrites (for details see text). [Burkhardt et al., 2008] 5

6 Timing of Parent Body Formation/Differentiation Hvittis (EL6) Indarch (EH4) Abee (EH4) Enstatite chondrites Dhurmsala (LL6) b Dhurmsala (LL6) a St. Severin (LL6) a Tuxtuac (LL5) a Parnallee (LL3.6) a Dalgety Downs (L4) b Bruderheim (L6) a Homestead (L5) a Tennasilm (L5) a Bovedy (L3) a Ordinary chondrites Miles Arlington Watson Weekero Station IIE Kernouvé (H6) a Monroe (H6) a Richardton (H5) a Orchansk (H4) a Forest Vale (H4) a Bath (H4) a Bremervörde (H3.9) a Karoonda (CK4) a Acfer 114 (CR2) a Dar al Gani 188 (CO3) a Isna (CO3) a Banten (CM2) a Cold Bokkeveld (CM2) a Murray (CM2) a Nogoya (CM2) a Murchison (CM2) b Murchison (CM2) a Arch (CV3) a Bali (CV3) a Axtell (CV3) a Allende (CV3) c Carb. chondrites Toluca Seeläsgen Nagy Vaszony Mundrabilla Morasko Cranbourne Coolac Campo de Cielo Canyon Diablo Caddo County Negrillos Gibeon IAB IIICD IIAB IVA Allende (CV3) b Allende (CV3) a Orgueil (CI1) a ε 182 W ε 182 W [Kleine et al., 2009] 6

Differentiation of Iron Meteorite Parent Bodies [Burkhardt et al., 2008] Core formation ages for magmatic iron meteorites IC (-3.63 to -3.35) IIAB (-3.43 to -3.23) IID (-3.95 to -3.

7 Differentiation of Iron Meteorite Parent Bodies [Burkhardt et al., 2008] Core formation ages for magmatic iron meteorites IC (-3.63 to -3.35) IIAB (-3.43 to -3.23) IID (-3.95 to -3.24) Timing of events relative to CAI (oldest materials) will depend on how well we know the ε 182 W of CAI. IIIAB IIIE IIIF IVA IVB (-3.40 to -3.28) (-3.41 to -3.33) (-3.35 to -3.00) (-3.43 to -3.28) (-3.50 to -3.46) Age relative to CAIs (Ma) Early estimates had lower 182 W/ 184 W in irons than initial SS value..what? (extra 182 W from s and r processes!) Within error, data show that iron parent bodies formed very fast and on same timescale as chondrules...core formation within 2 Myr of SS formation. [Burkhardt et al., 2012] 7

8 Relative Timing of Solar System Events EARTH AND MOON Crystallization of lunar magma ocean (~70%) Giant Moonforming impact?63 % of Earth accreted W model ages for complete core formation MARS Mantle differentiation Accretion and core formation CHONDRITE PARENT BODIES Chondrules (carb. chondrites) Chondrules (ord. chondrites) high-t metamorphism (H chondrites) DIFFERENTIATED PLANETESIMALS Accretion and core formation (magmatic irons) Magmatism (eucrites, angrites, mesosiderites) Thermal metamorphism (eucrites) [Kleine et al., 2009] Time after CAI formation (Myr) 8

9 Relative Timing of Solar System Events T after CAIs (Myr) ? Parent bodies of magmatic iron meteorites Parent bodies of eucrites and angrites Probability density CAIs initial Oldest chondrule precursors Parent bodies of ordinary chondrites Parent body of CB chondrites 5.2x Al/ 27 Al Chondrules (n = 112) Unequilibrated ordinary chondrites Carbonaceous chondrites igure 6 9

10 Relative Timing of Solar System Events Class I Class II Class III Debris disk ,000 km 1,000 km 100 km Runaway, oligarchic growth Planetesimals Chaotic growth Mars Moon-forming (embryo) impact Earth (planet) 10 km Melting by 26 Al decay km Size (m) m 1 cm 1 mm Meter barrier Fragmentation Dust agglomeration Gravitational instability? Bouncing Melting of refractory inclusions Chondrule formation Dissipation of the gas μm Condensation of refractory dust Collision-induced dust 1 Myr 10 Myr 100 Myr Time after solar system birth (years) 10

11 Primitive Achondrites How do we tell primitive achondrites apart from magmatic achondrites (e.g., HEDs)? Mn is more compatible than Mg, so partial melts have higher Mn/Mg and residue has lower Mn/Mg. [McSween, 2010] Note that primitive achondrites have chondritic Mn/Mg values, indicating very low degrees of partial melting (but texture indicates they are achondrites). 11

12 Primitive Achondrites [McSween, 2010] Acapulocoites Similar to O chondrites, few relict chondrules. Major elements nearly chondritic. Depleted in sider./calc. elements: extraction of metal-sulfide melt. Lodranites More recrystallized, no chondrules. Greater degree of partial melting (extraction of basalt): bulk no longer chondritic 12

13 Primitive Achondrites Ureilites OL + PX and rich in C (graphite). Highly recrystallized. Depleted in lithophiles, indicating loss of basaltic melt. Residue from melting of carbonaceous chondrites? [McSween, 2010] 13

but Vesta (eucrite parent body) appears to have

14 Timing of Magmatic Processes Magmatic processes began relatively early in solar system history, but Vesta (eucrite parent body) appears to have had a protracted magmatic history. [McSween, 2010] 14

15 Timing of Primary Processes [McSween, 2010] 15

16 Timing of Secondary Processes [McSween, 2010] 16

17 Shock Ages of Ordinary Chondrites [Bogard, 1995] 17

Geol. 656 Isotope Geochemistry

Geol. 656 Isotope Geochemistry Lecture 23 Spring 23 Meteorites are our primary source of information about the early Solar System. ISOTOPE COSMOCHEMISTRY INTRODUCTION Figure 1. Photograph of the meteorite Allende, which fell in Mexico