Happy Birthday Earth (at 9 a.m.): Birthday Cake Served Up on a New Plate

     Archbishop Ussher declared today, October 23rd, 4004 B.C. (at 9 a.m.) to be the Earth's birthday. Geologists everywhere will raise a glass this evening to celebrate. . .and serve up a piece of birthday cake on a "brand new" tectonic plate, the Malpelo plate, off the coast of Ecuador. The Malpelo plate is that thumb-like protrusion on the northeast corner of the Nazca Plate (seen below in light blue).

      "Researchers led by Rice University geophysicist Dr. Richard Gordon discovered the microplate while analyzing the junction of three other plates in the eastern Pacific Ocean. Their research is published in Geophysical Research Letters.

     The Malpelo plate, named for an island and an underwater ridge it contains, is the 57th tectonic plate to be discovered and the first in nearly a decade. "Mal pelo" means "bad hair" in Spanish (making the Malpelo plate the patron saint of bad hair days?)

     How do geologists discover a plate? In this case, they carefully studied the movements of other plates and their evolving relationships to one another as the plates move at a rate of millimeters to centimeters per year.

     The Pacific lithospheric plate that roughly defines the volcanic Ring of Fire is one of about 10 major rigid tectonic plates that float and move atop Earth's mantle, which behaves like a fluid over geologic time. Interactions at the edges of the moving plates account for most earthquakes experienced on the planet. There are many small plates that fill the gaps between the big ones, and the Pacific Plate meets two of those smaller plates, the Cocos and Nazca, west of the Galapagos Islands.

     One way to judge how plates move is to study plate-motion circuits, which quantify how the rotation speed of each object in a group (its angular velocity) affects all the others. Rates of seafloor spreading determined from marine magnetic anomalies combined with the angles at which the plates slide by each other over time tells scientists how fast the plates are moving."

      When you add up the angular velocities of these three plates, they ought to sum to zero," Dr. Gordon said. "In this case, the velocity doesn't sum to zero at all. It sums to 15 millimeters a year, which is huge."

       That made the Pacific-Cocos-Nazca circuit a misfit, which meant at least one other plate in the vicinity had to make up the difference. Misfits are a cause for concern -- and a clue.

      Knowing the numbers were amiss, the researchers drew upon a Columbia University database of extensive multibeam sonar soundings west of Ecuador and Colombia to identify a previously unknown plate boundary between the Galapagos Islands and the coast. The Malpelo plate is moving independently of the Nazca plate.

     "Since we're trying to understand global deformation, we need to understand where the rest of that velocity is going," he said. "So we think there's another plate we're missing."

      Let's discover yet another tectonic plate today to serve up that birthday cake! Enjoy, bad or good hair day!
Steph