Iron deficiency in pyrrhotite of suevites from the Chesapeake Bay impact crater, USA—A consequence of shock metamorphism?

摘要: Abstract– Pyrrhotite from suevite of the 35 Ma Chesapeake Bay impact structure (CBIS) shows a shock metamorphism and we report on several mineralogical magnetic features. strong brittle deformation with high density stacking faults, twinning parallel to hexagonal (001) planes average fault distances in order 10 nm. Although determination superstructure was not possible due lattice defects, reflections NiAs subcell, which is typical all pyrrhotite modifications, were clearly detected. This phase ferrimagnetic Curie temperature (TC) between 350 365 °C, this does show 34 K transition. The most peculiar feature low metal/sulfur ratio 0.81, indicates distinctly higher vacancy concentration than for 4C composition close smythite (Fe9S11). carries stable natural remanent magnetization relatively hard magnetic. Steep inclinations vector, however, suggest that has been remagnetized by drilling process. A explanation domain size faultless areas about 10 nm diameter, at lower limit single near threshold, below superparamagnetic behavior occurs. thermal stability excludes postshock heating above 300 °C CBIS. Our results imply iron-deficient produced metamorphism, although an iron loss never reported before pyrrhotite.