Mg-Fe Mica and alteration minerals in gabbroic rocks from Atlantis Bank, Southwest Indian Ridge

Abstract

We report paregenesis and chemical compositions of Mg-Fe mica (biotite/aspidolite) and associated minerals in gabbroic rocks recovered from Atlantis Bank during IODP Expedition 360. Many Mg-Fe mica are deficient in Na and K, showing a mixing trend with chlorite. In addition, they show an interference color lower than that of typical biotite, suggesting submicroscopic interlayering with chlorite. A close association of the Mg-Fe mica with felsic veins suggests that metasomatism by siliceous fluids pervasively took place in the lower crustal gabbroic rocks of Atlantis Bank.