XENOCRYSTIC OLIVINE AND SPINEL IN THE ASUKA 12209 ANGRITE

Of all the early Solar System planetesimal crustal rocks, angrite meteorites stand out from their more common basaltic equivalents. They have low silica contents (lacking low-Ca pyroxene), are rich in refractory elements (e.g. Ca, Al, and Ti, resulting in ‘fassaite’ pyroxene), and depleted in most alkali elements (Na, K, Rb) [e.g. 1]. Their parent body is covered by volcanic angrites [2] that host large, rounded olivine and spinel grains of different core compositions, and strong chemical zoning at irregular, resorbed margins (groundmass overgrowth and ~1-10 µm diffusion profiles) [e.g. 3, 4]. Such characteristics indicate that they were not in equilibrium with their host magmas, but are captured xenocrysts, from the angritic mantle or an isotopically similar source (suggested by oxygen isotope systematics, especially Δ17O; [5]). The new Asuka (A)12209 angrite [6], probably paired with the smaller A 881371, contains many large olivines and spinels, and provides an opportunity to characterize this possible mantle material in more detail.

Jaar van publicatie:2016