Composition and origin of hydrothermal ironstones from central Pacific seamounts
Abstract
Ironstones recovered from five Late Cretaceous seamounts in the central Pacific region probably formed during late-stage edifice-building volcanism. Ironstones are dense and compact with the appearance of brown chert. The ironstones are characterized by a goethite mineralogy with FeOOH contents up to 88%, extreme fractionation of Fe and Mn, low trace-element and rare earth element abundances, low Co/Zn ratios, and isotopic equilibration temperatures of about 20-45 °C. These characteristics indicate that the ironstones formed from hydrothermal fluids. Ironstones probably formed below the seawater-seafloor interface, as indicated by their occurrence as a proximal hydrothermal deposit, presence of primary goethite cement, pervasive replacement of rocks by goethite, and absence of interbedded pyro-clastic beds.
- Publication:
-
Geochimica et Cosmochimica Acta
- Pub Date:
- January 1994
- DOI:
- 10.1016/0016-7037(94)90455-3
- Bibcode:
- 1994GeCoA..58..179H