Graduate Thesis Or Dissertation
 

A study of the chemical composition of Ca-Al-rich inclusions from the Allende Meteorite

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  • Nine Ca-Al-rich inclusions and one olivine inclusion from Allende meteorite were studied for Ti, Al, Fe, Mg, Ca, Na, Cl, K, Sc, V, Cr, Mn, Co, Ni, Zn,Hf, W, Ir, Au, Ta, and Re -via INAA (instrumental neutron activation analysis) and REE, Ba, Sr via RNAA (radiochemical NAA). The inclusions were classified according to the scheme of Martin and Mason (1974). It was found that Group I inclusions have lower volatile element content (Na, K, Zn, Cl, Mn and Fe) and light REE and higher refractory element content than Group II inclusions. Group III inclusions are intermediate between Group I and Group II. The siderophile elements Ir and Re are correlated; W does not correlate with Ir and from thermodynamic calculations, W is predicted to condense as WO2 at 1380°K instead of the metallic form at higher temperatures. The Ca-Al-rich inclusions exhibit the REE patterns defined by Martin and Mason (1974). Group I is flat and 10-12X chondrites. Also classified in this group is an inclusion (A-2) with depleted Gd to Er and Lu relative to the rest of the REE. Group II contains patterns with flat light REE and severely fractionated heavy REE with positive Tm and Yb anomalies relative to their neighboring Er and Lu but normal Tm relative to La-Sm. The element Tm correlates with Ta along the line defined by cosmic ratios. Group III shows flat REE patterns with negative Eu and Yb anomalies. A new REE pattern has been found with a negative Ce anomaly in an inclusion, tentatively classified as a Group I inclusion. The approximate character of the REE patterns of Group II and III may be predicted from thermodynamic calculations. All of the inclusions studied have covariant Eu and Sr abundances which are nearly equal on a chondritic normalized basis, suggesting extensive divalent behavior of Eu. All the fractionated patterns observed have nearly equal chondritic normalized Eu and Yb which is unexpected and not predicted from thermodynamic calculations. The REE patterns observed appear to support gaseous condensation models and demonstrate the complex nature of their origin.
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