Distribution and Origin of 36Cl In Allende CAIs
The abundance of short-lived radionuclides (SLRs) in early solar system materials provide key information about their nucleosynthetic origin and can constrain the timing of early solar system events. Excesses of {sup 36}S ({sup 36}S*) correlated with {sup 35}Cl/{sup 34}S ratios provide direct evidence for in situ decay of {sup 36}Cl ({tau}{sub 1/2} {approx} 0.3 Ma) and have been reported in sodalite (Na{sub 8}Al{sub 6}Si{sub 6}O{sub 24}Cl{sub 2}) and wadalite (Ca{sub 6}Al{sub 5}Si{sub 2}O{sub 16}Cl{sub 3}) in CAIs and chondrules from the Allende and Ningqiang CV carbonaceous chondrites. While previous studies demonstrate unequivocally that {sup 36}Cl was extant in the early solar system, no consensus on the origin or initial abundance of {sup 36}Cl has emerged. Understanding the origin of {sup 36}Cl, as well as the reported variation in the initial {sup 36}Cl/{sup 35}Cl ratio, requires addressing when, where and how chlorine was incorporated into CAIs and chondrules. These factors are key to distinguishing between stellar nucleosynthesis or energetic particle irradiation for the origin of {sup 36}Cl. Wadalite is a chlorine-rich secondary mineral with structural and chemical affinities to grossular. The high chlorine ({approx}12 wt%) and very low sulfur content (<<0.01 wt%) make wadalite ideal for studies of the {sup 36}Cl-{sup 36}S system. Wadalite is present in Allende CAIs exclusively in the interior regions either in veins crosscutting melilite or in zones between melilite and anorthite associated with intergrowths of grossular, monticellite, and wollastonite. Wadalite and sodalite most likely resulted from open-system alteration of primary minerals with a chlorine-rich fluid phase. We recently reported large {sup 36}S* correlated with {sup 35}Cl/{sup 34}S in wadalite in Allende Type B CAI AJEF, yielding a ({sup 36}Cl/{sup 35}Cl){sub 0} ratio of (1.7 {+-} 0.3) x 10{sup -5}. This value is the highest reported {sup 36}Cl/{sup 35}Cl ratio and is {approx}5 times greater than values for sodalite in some CAIs and chondrules. We report here new {sup 36}Cl-{sup 36}S isotope measurements of wadalite in two Type B CAIs (TS34 and Egg-6) and sodalite in a fine-grained CAI (Pink Angel) from Allende.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 973864
- Report Number(s):
- LLNL-PROC-421346; TRN: US201007%%410
- Resource Relation:
- Conference: Presented at: Lunar and Planetary Science Conference, Houston, TX, United States, Mar 01 - Mar 05, 2010
- Country of Publication:
- United States
- Language:
- English
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