What is Andesite Line in Geography?

Andesite is a grey igneous rock consisting of 52-65% silica. It is in the form of tiny crystals embedded in a glassy groundmass. Andesite Line is a petrological boundary in the Pacific Ocean, that can be traced from Alaska, Japan, the Marianas, the Bismarck Archipelago, Fiji and Tonga to the east of New-Zealand. To the west of the andesite line the rocks have 52-65% silica (andesite, dacite, rhyolite); to the east they consists less than 52% silica (basalt, trachyte, olivine).