Geological hostory of Christmas Island

To: "'Birding-aus'" <>
Subject: Geological hostory of Christmas Island
From: "Ross Macfarlane" <>
Date: Sun, 18 Dec 2011 07:31:34 +1100
Of passing interest:

Christmas Island seamounts: Is the mystery finally solved?

The evidence they brought back to the lab told an interesting story: The rocks' geochemical signatures didn't match those from mid-ocean ridges or hotspot volcanoes. Instead, they matched the signatures of continental rocks — in particular, rocks from northwestern Australia.

Using this clue and tectonic plate reconstructions, Hoernle's team traced the rocks back to the ancient supercontinent of Gondwana.

Around 150 million years ago, greater India, Australia and Burma — all once part of this supercontinent — began to rift away from each other. This created the spreading center (or mid-ocean ridge) that eventually formed the Indian Ocean. As this was happening, the bottom part of the continental crust delaminated, or "peeled off in a sheet," Hoernle said. "


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