Ordinary chondrites (OCs) are classified into three groups, according to their oxidation state, which increases from the H to L to LL groups. This is demonstrated by the decrease in metal content (H = similar to 8 vol%, L = similar to 4 vol%, and LL = similar to 2 vol%), and by a positive correlation between Delta O-17 and %Fa through the OC sequence. Compared to other chondrites, OCs exhibit the largest variation in oxidation state, but there is an ongoing debate on the processes that control this variation. To constrain the causes of the variations in the oxidation state with respect to the associated nebular versus parent bodies processes, we investigated the elemental and isotopic variations of germanium (moderately siderophile and volatile) in the bulk sample, as well as in the metal, silicate and sulfide phases, over a range of petrographic types for the H, L, and LL ordinary chondrites. We found that delta Ge-74/70(metal) is a proxy for the delta Ge-74/70(bulk) composition and that each OC group is distinguishable by their delta Ge-74/70(metal), which increases from -0.51 +/- 0.09 parts per thousand for H chondrites, -0.31 +/- 0.06 parts per thousand for L chondrites, and, finally, to -0.26 +/- 0.09 parts per thousand for LL chondrites (2 sigma SD). Additionally, the OC sequence exhibited a positive correlation, from H to L to LL, between delta Ge-74/70(metal) and %Fa, as well as oxygen isotopes (delta O-17, delta O-18 and Delta O-17), that was not a consequence of a "size sorting effect" on chondrules (i.e., chondrule mixing) or metamorphic processes in the parent bodies but, rather, was the result of nebular processes. We propose that the correlation between the delta Ge-74/70 values and %Fa, Delta O-17, delta O-18 can be explained by an increasing proportion of accreted hydrated phyllosilicates, from the H, L to LL groups, with high delta Ge-74/70 and Delta O-17. We found that 10 to 15% of phyllosilicates, with a composition of [Ge] = 4-7 ppm and delta Ge-74/70 = 3-2.5 parts per thousand, is needed to change the delta Ge-74/70 from H to LL, which corresponds to a Delta O-17 approximate to 8-7 parts per thousand. This value agrees with the Delta O-17 approximate to 7 parts per thousand composition of the accreted nebular component reported by Choi et al. (1998). During thermal metamorphism, phyllosilicates destabilize, liberating germanium that will be incorporated in the metal, then leading to its high delta Ge-74/70 signature. High-temperature metamorphism can explain the lack of delta Ge-74/70(metal) variation with the petrologic type in the OC, even for the type 3 chondrites (T approximate to 675 degrees C), implying a complete reaction even at low petrologic types. In addition, metal-silicate re-equilibration in response to thermal metamorphism results in a decrease in Delta Ge-74/70(metal-silicate) from 0.33 parts per thousand to 0.06 parts per thousand, within the H chondrite group, which is interpreted as the result of delta Ge-74/70(silicate) variation. The mean positive Delta Ge-74/70(metal-silicate) fractionation factor of +0.22 +/- 0.36 parts per thousand (error propagation on individual error) also displays a remarkable similarity to the direction of isotopic fractionation with other germanium isotopic metal-silicate datasets, such as the magmatic iron meteorites, the Earth silicate reservoirs. We propose that the Delta Ge-74/70(metal-silicate) and the negative delta Ge-74/70 values of OCs are inherited from metal-silicate melting and partial exchange before planetesimal accretion in a light isotope-enriched gas. Finally, the delta Ge-74/70(metal)-Delta O-17(silicate) correlation between the IIE iron meteorites and OCs, provides new evidence for the existence of a highly reduced HH group. (C) 2019 Elsevier Ltd. All rights reserved.
