Mineralogical, REE and 146Sm-142Nd isotopic systematics of the earliest solar condensates in unequilibrated Enstatite chondrites

• Applicant: Professor Dr. Ahmed El Goresy (†)
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2012 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 211141497

Enstatite chondrites store chemical and isotopic signatures reflecting formational conditions at low oxygen fugacity. There is however no agreement on their birth place, history and locality of formation: (1) While the majority of scholars agree on their formation in the earliest episodes of the solar nebula, (2) Several scholars in the USA advocate for their evolution by impact melting in pre-existing asteroids. It is also disputed if the two subgroups: EH (high iron) and EL (low iron) emerged from the same parental asteroids. A further uncertainty is if individual EH, on the one hand and individual EL chondrites on the other came from different asteroids or from the same parent body. Bulk mineralogy and mineral chemistry in EH and EL chondrites are different and allow a clearcut recognition of EH from EL. The condensation scheme considers oldhamite (CaS) to be one of the earliest condensates at C/O ratios from > 0.83 < 0.95. CaS incorporated the majority of the REE and Actinides during condensation as sulfides. In contrast, the impact melting model considers CaS to have formed by impact melting. A mineralogical study of oldhamite and associated minerals, their REE patterns, their 146Sm/142Nd isotopic system (T1/2 = 103 Myr) and Pb-Pb ages of oldhamite and other sulfide generations in individual EH- and EL-chondrites is being conducted. Aims of this multitask scrutiny are to uncover: (1) REE signatures and 146Sm/142Nd isotopic systematics of oldhamites in EH-3 and in EL-3 chondrites, and if they are different (2) chronological details of condensation and/or accretionary and parent body events in earliest episode of the solar nebula, (3) C-, N- and H-isotopic investigations of different graphite types in EL-3 and of N in sinoite (Si2N2O) in the EL-3 in Almahata Sitta CT3 asteroid. Mineralogical, petrological and isotopic investigations of the newly recovered differentiated meteorite NWA7325 that was presumably ejected from the planet Mercury.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1385: The first 10 Million Years of the Solar System - A Planetary Materials Approach
• Participating Person: Professor Dr. Leonid Dubrovinsky