JUANCHENG


H5
standby for juancheng photo
Fell February 15, 1997
35° 32' N., 115° 23' E.

At 11:23 P.M. local time, a bright fireball exploded into a shower of stones, which fell with whistling noises in numerous villages in Juancheng County, Heze Prefecture of Shandong Province, China. The fall dispersion ellipse was ~10.5 km by ~4.3 km. More than a thousand stones fell, only one of which was reported to have damaged the roof of a farm building. The total weight of the fall was over 100 kg, with the largest fragment weighing only 2.6 kg.

standby for juancheng strewn field diagram
Diagram credit: Chen et al., MAPS, vol. 33, p. A177 (1998)

Juancheng is highly equilibrated, exhibiting a granular, recrystallized texture. Its constituents are olivine, low-Ca pyroxene, kamacite, troilite, and minor plagioclase. Calcium oxide enrichment in the plagioclase is thought to reflect a high-temperature thermal history. Thermal models utilizing the observed Fe–metal separation and diffusion characteristics has enabled Toplis et al. (2007) to estimate the depth of equilibration for the H5 chondrites to be ~30 km (given a parent body of 180 km in diameter).

A complex cooling history for the higher petrologic type H chondrites (5/6) was suggested from thermometric studies conducted by Ganguly et al. (2012). They reconciled data from calculations of two-pyroxene thermometers with the Ar–Ar, Pb–Pb, and Hf–W closure temperatures of select minerals to determine a cooling history consistent with very rapid cooling between ~800°C and 450°C, followed by a very slow cooling stage, and then another rapid cooling stage. By contrast, those H chondrites with lower petrologic types experienced a steady state of very rapid cooling. It was proposed that this scenario was more consistent with a collisional disruption and re-accretion of the parent body as opposed to a smoothly transitional "onion shell" model. A more in-depth discussion of the cooling history can be found on the Monahans (1998) page.

Juancheng has been very weakly shocked to stage S2. Cosmogenic nuclide data infer a pre-atmospheric diameter of 1.3–1.7 m and a CRE age of 5.3 m.y. The photo above shows a 4.7 g partial section of a small Juancheng individual.