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