Magnetite-rutile symplectite
Description
The textures and geochemical characteristics of the rocks in layered intrusions potentially provide insights into the physical and chemical processes that have taken place in mafic magma chambers. Diverse exsolution textures preserved by Fe-Ti oxides record the crystallization temperature and oxygen fugacity (fO2) within magma chambers. Here we investigated ilmenite-hematite solid solution (Ilmss) relationships evident in preserved intergrowths of magnetite-rutile and ilmenite-hematite in gabbros of the Xinjie layered intrusion. The crystallographic orientation and 3-D morphology of the two intergrowth types constrain the transformation mechanism of the exsolution textures from Ilmss. The results reveal that the magnetite-rutile symplectite can be transformed from Ti-rich ilmenite with Ilm≥0.85 above 550°C when the sub-solidus T-fO2 trend is buffered by the biotite-ilmenite-feldspar-ulvöspinel (KUIlB) mineral assemblages crystallized from hydrated mafic magmas. The magnetite-rutile symplectite in terrestrial and planetary (e.g. martian and lunar) rocks/ regolith can serve as a unique indicator of hydration during magma evolution.