Andesite Line

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andesite line

[′an·də‚zīt ‚līn]
The postulated geographic and petrographic boundary between the andesite-dacite-rhyolite rock association of the margin of the Pacific Ocean and the olivine-basalt-trachyte rock association of the Pacific Ocean basin.

Andesite Line


the line that separates the peripheral area of the Pacific Ocean, characterized primarily by the andesite composition of volcanic products, from the ocean’s internal area, where magmatic rocks of exclusively basaltic composition are prevalent. The line was established by the American geologist J. Marshall in 1911. In the east the andesite line follows along the coast of America; in the north it bends around the Aleutian Islands bow on the ocean side; in the west it bends around Kamchatka, the Kuril, Japanese, and Mariana islands and the islands of Melanesia and New Zealand. The region lying within the andesite line is generally considered the most ancient part of the Pacific Ocean. It has a typically oceanic crust that changes almost immediately to a continental crust in the south and a transitional crust in the east.