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Using global multiresolution topography, we estimate new transform-fault azimuths along the Cocos-Nazca plate boundary and show that the direction of relative plate motion is 3.3 degrees 1.8 degrees (95% confidence limits) clockwise of prior estimates. The new direction of Cocos-Nazca plate motion is, moreover, 4.9 degrees 2.7 degrees (95% confidence limits) clockwise of the azimuth of the Panama transform fault. We infer that the plate east of the Panama transform fault is not the Nazca plate but instead is a microplate that we term the Malpelo plate. With the improved transform-fault data, the nonclosure of the Nazca-Cocos-Pacific plate motion circuit is reduced from 15.0mm a(-1)3.8mm a(-1) to 11.6mm a(-1)3.8mm a(-1) (95% confidence limits). The nonclosure seems too large to be due entirely to horizontal thermal contraction of oceanic lithosphere and suggests that one or more additional plate boundaries remain to be discovered.

Plain Language Summary The central tenet of plate tectonics is that the tectonic plates are rigid. In sharp conflict with this assumption is the prior result that the relative motions between the Cocos, Nazca, and Pacific tectonic plates, which lie in the Pacific Ocean basin, do not sum to zero as expected if the plates are indeed rigid. From an analysis of plate-motion data, we show that part of the traditionally defined Nazca plate, which lies off the west coast of South America, is really a separate tectonic plate, which we refer to as the Malpelo plate. Recognition of this new tectonic plate reduces the inconsistency in the plate-motion circuit, but a large and significant inconsistency remains. This remaining inconsistency suggests that there may be one or more plate boundaries still remaining to be discovered within these three plates.