Abstract Angrite meteorites are samples of early planetesimal magmatic rocks, distinguished from more typical “basaltic eucrites” by compositions that are silica undersaturated, relatively oxidized, and with high CaO/Al 2 O 3 . The latter is not expected from nebular, chondritic materials that might form a primitive mantle, such as a source enriched in refractory inclusions with fixed CaO/Al 2 O 3 (e.g., CV chondrite). Here we present results of “reversal” crystallization experiments for two possible parental angrite compositions (approximating the D'Orbigny meteorite) to investigate the role of spinel as a sink for Al 2 O 3 . This mineral has previously been produced with angritic melts during “forward” melting of CV chondrite and may be abundant in the angrite source. At oxidizing conditions, we confirm that spinel is a liquidus phase and that angritic magmas form near the olivine‐anorthite‐spinel‐liquid peritectic. A stability gap separates Al‐rich liquidus spinels and lower temperature spinels, the latter of which are similar to those in basaltic eucrites. Al‐rich spinel is likely more abundant in the angritic source than other Fe‐rich core‐forming components such as metal or sulfide, and a CV chondrite‐like composition generates most features of angrite magmas by fractionation of observed olivine and liquidus spinel. Direct CaO excess, via carbonate addition, is therefore limited. In this model, discrepancies remain for Li, Sc, Cr(‐Al), and Ba, which may record local accretion conditions or early processing. The possible role of spinel as a sink for 26 Al may have strong influence on the thermal evolution of the angrite parent body.
Abstract. The New England Orogen, Eastern Australia, was established as an outboard extension of the Lachlan Orogen through the migration of magmatism into the forearc basin and accretionary prism. Widespread S-type granitic rocks of the Hillgrove and Bundarra Supersuites represent the first pulse of magmatism, followed by I- and A-types typical of circum-Pacific extensional accretionary orogens. Associated with the former are a number of small tholeiite-gabbroic to intermediate bodies of the Bakers Creek Suite, which are a heat source for production of granitic magmas and potential tectonic markers indicating why magmatism moved into the forearc and accretionary complexes, rather than rifting the old Lachlan Orogen arc. The Bakers Creek suite gabbros capture an early (~ 305 Ma) forearc basalt-like component with low Th/Nb and with high Y/Zr and Ba/La, recording melting in the mantle wedge with little involvement of a slab flux and indicating forearc rifting. Subsequently, arc-backarc like gabbroic magmas (305–304 Ma) were emplaced followed by diverse magmatism of mixed compositions leading up to the main S-type granitic intrusion (~ 290 Ma). This trend in magmatic evolution implicates forearc and other mantle wedge melts in the heating and melting of fertile accretion complex sediments and relatively long (~ 10 Myr) timescales for such melting.
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