The internal structure of an active sea-floor massive sulphide deposit

The massive sulphide deposit on the Mid-Atlantic ridge is dependent on the presence of anhydrite and grows as an in situ breccia pile. This layer is formed during successive periods of hydrothermal activity that creates new hydrothermal precipitates and strengthens the previous deposit. During periods of hydrothermal inactivity, the brecciation of the deposits is initiated by the breakup of the sulphide chimneys, rupturing of anhydrite, and disordering by faulting. The high temperature within the mound is due to the hydrothermal circulation of the sea water through permeable ocean crust.