Chemical studies of L chondrites. III - Mobile trace elements and Ar-40/Ar-39 ages

Radiochemical neutron activation analysis has been used to determine the content of the mobile trace elements Ag, Au, Bi, Cd, Co, Cs, Ga, In, Rb, Se, Te, Tl, and Zn, in L4-6 chondrites with undisturbed Ar-40 release patterns or patterns showing some 4.4-4.6 Gyr plateau disturbance that indicates some shock-induced loss. The mean concentrations are significantly lower in 16 chondrites with disturbed patterns than in 4 with undisturbed ones, consistent with shock-induced mobilization. Significantly lower mean concentrations of nearly all trace elements in 26 strongly shocked chondrites than in 14 mildly shocked ones indicate loss in shock-formed FeS-Fe eutectic and/or by means of vaporization during cooling of shock-heated collisional debris.