Partial melting and melt migration in the acapulcoite-lodranite parent body

Graves Nunataks 95209: A snapshot of metal segregation and core formation

“…Instead, it appears likely that the metal-rich sheet was intruded into the current GRA 95209 matrix from a source region perhaps far removed on the parent body. McCoy et al (1997b) calculated that veins of molten metal-sulfide in the range of 1 mm to 1 cm wide migrating through a solid silicate matrix might reach lengths up to 1 km on asteroidal bodies where pressures would be negligible. Within GRA 95209, migration of Fe,Ni-FeS veins and dikes was more complicated than migration of a single, large dike.…”

“…One explanation for this may be in the relative temperatures of the two lithologies. Given that melt migration distances for a cm-wide metal-rich sheet might approach hundreds of meters (McCoy et al, 1997b), it is quite possible that this sheet originated in a portion of the parent body several hundred degrees hotter than the surrounding matrix and reactions at those higher temperatures produced the reduction now observed within the metal-rich sheet. In contrast, the matrix lithology reached a lower peak temperature and reduction did not occur.…”

“…This situation appears to be changing with the discovery of meteorites that experienced limited degrees of partial melting and melt migration, sometimes capturing this process frozen in time. Among the suite of acapulcoites and lodranites, Monument Draw preserves metal-sulfide-phosphate veins (McCoy et al, 1996) and Lewis Cliffs 86220 preserves metal-sulfide-gabbro melts inside an acapulcoite host (McCoy et al, 1997b). Unfortunately, the amount of material available for study from these two meteorites is extremely limited.…”

Anatomy of a Partially Differentiated Asteroid: A “NEAR”-Sighted View of Acapulcoites and Lodranites

“…1d). McCoy et al (1997b) interpreted this assemblage as a basaltic Fe,Ni-FeS melt which had migrated out of the lodranite source region and was trapped in a cooler acapulcoite source. A similar conclusion was reached based on trace element signatures in the minerals of this melt lithology (Floss 2000).…”

“…Modeling of dike propagation on the acapulcoite-lodranite parent body (McCoy et al 1997b) suggests that these veins might have high length/width ratios on the order of 100-1000. Thus, centimeter-wide veins might have lengths approaching several meters and meter-wide veins would have lengths approaching 1 km.…”