Aulacogen

In geology, an aulacogen is a failed arm of a triple junction of a plate tectonics rift system. A triple junction beneath a continental plate initiates a three way breakup of the continental plate. As the continental break-up develops one of the three spreading ridges typically fails or stops spreading. The resulting failed rift is called an aulac...
Found on http://en.wikipedia.org/wiki/Aulacogen

Aulacogen

In geology, an aulacogen is a sediment-filled trough in the continental crust representing the trace of an incipient rift which failed to develop.
Found on http://www.probertencyclopaedia.com/browse/HA.HTM
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