Abstract

Ordovician rocks of the Lachlan fold belt contain a continental-margin submarine fan that in its undeformed state has a minimum area of 1.2 x 106 km2, comparable to the size of the Bengal Fan. Cambrian and Ordovician mafic volcanic seamount chains in the Lachlan fold belt are analogous to the Ninetyeast Ridge and other seamounts associated with the Bengal Fan in the northeastern Indian Ocean. Basement of the Lachlan fold belt, by analogy with that of the Bengal Fan, may have been ocean floor with an overlying continental-rise prism that developed after the breakup of Laurentia and eastern Gondwana to form the ancestral Pacific Ocean in the latest Precambrian. The continental-rise prism was imbricated during Silurian-Devonian deformation to form the lower crust that provided source rocks for the Silurian to Carboniferous granites.

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