REVISION 1 1 2 3 4 Phosphate minerals in the H group of ordinary chondrites , and fluid activity recorded by 5 apatite heterogeneity in the Zag H 3-6 regolith breccia 6 7

28 29 Phosphate minerals in ordinary chondrites provide a record of fluids that were present 30 during metamorphic heating of the chondrite parent asteroids. We have carried out a 31 petrographic study of the phosphate minerals, merrillite and apatite, in metamorphosed H group 32 ordinary chondrites of petrologic type 4-6, in order to understand development of phosphate 33 minerals and associated fluid evolution during metamorphism. In unbrecciated chondrites, 34 apatite is Cl-rich and shows textural evolution from fine-grained apatite-merrillite assemblages 35 in type 4 towards larger, uniform grains in type 6. The Cl/F ratio in apatite shows a similar 36 degree of heterogeneity in all petrologic types, and no systematic change in compositions with 37 metamorphic grade, which suggests that compositions in each meteorite are dictated by localized 38 conditions, possibly because of a limited fluid / rock ratio. The development of phosphate 39 minerals in H chondrites is similar to that of L and LL chondrites, despite the fact that feldspar 40 equilibration resulting from albitization is complete in H4 chondrites but not in L4 or LL4 41 chondrites. This suggests that albitization took place during an earlier period of the metamorphic 42 history than that recorded by preserved apatite compositions, and chemical equilibrium was not 43 achieved throughout the H chondrite parent body or bodies during the late stages of 44 metamorphism. A relict igneous clast in the H5 chondrite, Oro Grande has apatite rims on relict 45 phenocrysts of (possibly) diopside that have equilibrated with the host chondrite. Apatite in the 46 Zag H3-6 regolith breccia records a complex fluid history, which is likely related to the presence 47 of halite in this meteorite. The porous dark H4 matrix of Zag, where halite is observed, has a 48 high apatite / merrillite ratio, and apatite is extremely Cl-rich. One light H6 clast contains 49 similarly Cl-rich apatite. In a second light H6 clast, apatite compositions are very heterogeneous 50 and more F-rich. Apatites in both H4 matrix and H6 clasts have very low H2O contents. 51 Heterogeneous apatite compositions in Zag record multiple stages of regolith processing and 52 shock at the surface of the H chondrite parent body, and apatite records either the passage of 53 fluids of variable compositions resulting from different impact-related processes, or the passage 54 of a single fluid whose composition evolved as it interacted with the chondrite regolith. 55 Unraveling the history of apatite can potentially help to interpret the internal structure of 56 chondrite parent bodies, with implications for physical and mechanical properties of chondritic 57 asteroids. The behavior of halogens recorded by apatite is important for understanding the 58 behavior of volatile elements in general: if impact-melt materials close to the surface of a 59 chondritic asteroid are readily degassed, the volatile inventories of terrestrial planets could be 60 considerably more depleted than the CI carbonaceous chondrite abundances that are commonly 61 assumed. 62 63