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Constraining the early history of Solar system events from 26Al-26Mg isotope systematics in CAIs Ritesh Kumar Mishra and Marc Chaussidon
Centre de Recherches Pétrographiques et Géochimiques, CRPG CNRS, 15 rue Notre Dame des Pauvres, BP 20, 54501 Vandoeuvre les Nancy, France.
Sample and Analytical procedure: Different types of CAIs ( A, B, igneous, fine grained; Fig. 2) present in some of the least altered meteorite sample Efremovka,Vigarano and Axtell were analysed using secondary ion mass spectrometer (SIMS) 1270 at CRPG, Nancy. A ~ 20nA O-‐ primary beam accelerated at 13kV was used to obtain secondary posiVvely charged ions of 24Mg, 25Mg, 26Mg, and 27Al at a mass resoluVon of 2500 for isotopic analysis in a mulV-‐collecVon mode using FCs’ at L’2, C, H1 and H’2. The sample was kept at 10kV while an energy window of 50eV was used. The hydride contribuVon were suppressed by keeping vacuum > 3x10-‐9. Terrestrial standards of Burma spinel, MORB, San Carlos olivine, and syntheVc glass standards (BacaV, Px, An) with composiVon similar to analogous minerals in CAIs were analyzed at regular intervals to ascertain instrumental mass fracVonaVon during the analysis of meteoriVc sample. The instrumental mass fracVonaVon (1/β) varied between 0.511 -‐0.523 from one analyVcal session to another but was mostly in a narrow range during a given session (Fig. 1). The external reproducibility on δ26Mg was ~0.018 ‰ (σ/√n; n~12). Results:: IniVal δ26Mg and 26Al/27Al obtained for 10 CAIs from Vigarano; 5 CAIs, 1 AOA, and a chondrule from Efremovka and another CAI from Axtell are shown in Fig.3 & 4. Data obtained suggest that the analysed CAIs formed or were last melted during different high temperature events during the iniVal Vme period ranging upto ~1.5Myr. This Vme period is considerably longer than class 0 and I stage. Considering homogeneous distribuVon of isotopes during the early solar system, 2 CAIs (#Ei9, Axt#1) show δ26Mg* indicaVng condensaVon ~0.4Myr later than fiducial t0 when26Al/27Al was 5.25x10-5. The data obtained can be also interpreted to suggest that a significant level of heterogeneity >10% existed during the earliest stage .
0 1 2 3 4-0.3
0.0
0.3
0.6
0.9
1.2
27Al/24Mg
26 M
g (‰
)
[26Al/27Al]i= (3.77 ± 0.29) x 10-5 ( 2
Efremovka ( CV 3.1- 3.4 ) CAI #9
26Mg0= -(0.07±0.04) (‰)
0 5 10 15 20
0
1
2
3
4
5
6
7 Efremovka ( CV 3.1- 3.4 ) CAI #1
27Al/24Mg
26 M
g (‰
)
[26Al/27Al]i= (3.885 ± 0.076) x 10-5 ( 2
26Mg0= +(0.24±0.07) (‰)
Date ß 1/ß
29 March 1.9505 0.513
30 March 1.9382 0.516
1 April 1.9230 0.520
2 April 1.9478 0.513
log
(26M
g/24
Mg)
-0.900 -0.899 -0.898 -0.897
log (25Mg/24Mg)
-0.860
-0.858
-0.856
-0.854
Burma spinelSan Carlos OlivineMORBPyroxeneBacati
Fig. 1 Variation of Instrumental Mass Fractionation
[1] Bouvier & Wadhwa (2010) Nature geo. 3, 637-‐641. [2] Amelin et al. (2010) EPSL 300, 343-‐350. [3]Villeneuve et al. (2009) Science 325, 985-‐8. [4] Kita et al. (2010) LPSC 41 2154. [5] Davis et al. (2010) LPSC 41 2496. [6] MacPherson et al. (2010) ApJ 711, L117-‐121. . [7] Jacobsen et al. (2008) EPSL 272, 353-‐364. [8] Bizzarro et al., (2011) J. Anal. At. Spectrom. 26, 565-‐577. [9] Larsen K. K. et al. (2011) Ap. J. 735, 37-‐41. [10] Schiller M. et al. (2011) GCA 74, 4844-‐64.
Introduction: The earliest formed Solar system solids-‐ Calcium, Aluminum,-‐rich Inclusions (CAIs) with absolute age of ~4568 Myrs [1,2] are the most appropriate samples to study physico-‐chemical condiVons, events, processes, and their evoluVon in temporal and spaVal scale during the earliest stage of Solar system. The development of high precision analyVcal techniques now allow to discern difference at levels of sub permil and Vme duraVons of ≤100kyrs. These developments of high precision analyVcal techniques allows to invesVgate the veracity of hitherto assumpVons and understand and provide stringent constraints of the condiVons during the early Solar system [3-‐10]. To constrain the physico-‐chemical condiVons and their evoluVon during the neonatal stage of Solar system a systemaVcs high precision Al-‐Mg isotope systemaVcs study in a suite of CAIs was carried with the following specific objecVves. Obtain precise Vme of formaVon and iniVal δ26Mg* in various types of CAIs to address: 1) SpaVal and temporal scale of homogeneous distribuVon of isotopes (at least Mg and Al isotopes and by inference others elements) in early Solar system, 2) Elucidate existence (or non existence) of a single epoch leading to formaVon of a parVcular (or all) type(s) of CAIs, 3) Existence of epochs or conVnuum of high temperature events (condensaVon, reheaVng, shock waves) leading to constraints on their casuals'.
Fig.4
Fig.3
Fig.2
Mg Evolution Diagram
1 2 3 4 5
-0.1
0.0
0.1
0.2
0.3
0.4
0.5 Efremovka CAI Fine GrainedEfremovka AOAEfremovka CAI Spinel Vigarano CAI BVigarano CAI SpinelVigarano CAI Fine GrainedSemarkona ChondruleAngrites (Schiller et al. 2010)Efremovka ChondruleSolar (Jacobsen et al. 2008)
Axtell CAI B
26 M
g (‰
)
(26Al/27Al x 10-5
432
1
5
Time after CAI formation (Myr) T0 = 26Al/27Al = 5.25x10-5 0.29 1.02 0.59 1.75 0.05
Fig.4