A noritic clast from the Hedjaz chondritic breccia: implications for melting events in the early solar system

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Abundances of Na, Mg, Al, K, Ca, Sc, Cr, Fe, Co, Ni, Rb, Sr, Ba, REE, Ir, and Au were determined in a unique, noritic clast carrying a fractionated REE component from the Hedjaz (L) chondritic breccia by instrumental neutron activation analysis and isotope dilution mass spectrometry. The clast, previously described by Nakamura et al. (1990), consists of two lithologies, and is depleted in siderophile and moderately volatile lithophile elements when compared with its host meteorite. The REE abundance pattern of the clast is L-chondritic (1.4–1.6 × CI-chondrite) with a large (62%), positive Eu anomaly. Strontium is also enriched (3.2 × CI-chondrite) relative to trivalent REE. Chemical and petrologic data suggest that the elemental fractionations observed in the Hedjaz noritic clast could be accomplished in a single host-like parent body with several episodes of impact melting and heating. An impact melt enriched in feldspar components could have been generated in a neighboring region on a parent body, and then infiltrated into the precursor material of the clast. An enhancement of plagiophile elements would then be produced in the clast. Moderately volatile element and siderophile element fractionations could be related to gas/solid or gas/liquid processes and silicate/metal melt fractionations, respectively, which may have occurred during melting and formation of the clast.