Exotic terranes

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A schedule of arrivals of incoming exotic terranes will account-as a simple continent-to-continent collision cannot do-for the long spreads of time between one and another of the Appalachian mountain-building pulses. As someone once compacted it for me, “you sweep the New Zealands and Madagascars out of the ocean and then you close it with the Alleghenian Orogeny.” Disagreeing interpreters see terranes of highly varied dimension. Nominated as the terrestrial remains of one exotic block is the whole of New England from Williamst own eastward, arriving in the Ordovician to lift the Taconic mountains. Exotic terranes and their effects represent only one of the responses of plate-tectonic theorists to the embarrassment caused by the failure of Exhibit A among intercontinental collisions to exhibit a finite suture. Another response conference room leeuwarden has been the notion that when two continents collide there is every possibility that one will split the other, like an axe blade entering cedar; if so, you would find the invaded country rock both above and below the invader. The concept is known as flake tectonics. Its message to Vibroseis is to stop
shaking and go home. With a little erosion and flake tectonics, you can have the native rock reaching far under the rock from across the sea. Even so, the bunching of exotic terranes seems to solve more problems than flake tectonics does. Exotic terranes not only explain the intervals of time involved in the Taconic, Acadian, Alleghenian orogenies, they suggest as well why Taconic deformation occurred in the nmthem but not the southern Appalachians. Shortening collisional boundaries, they restore some dignity to the Brevard suture. Anita turned on the windshield wipers and wiped an April shower. Beside the interstate, the Pocono Devonian roadcuts were of much the same age and character as ones we had seen before. We conference room eindhoven passed them by. “Better not to do geology in the rain,” Anita said. “It’s unfair to the rocks.” With regard to the possibility of exotic terranes having added themselves to eastern North America, she said, “If you stretch out the overthrusts in the Appalachians, they show that-before the mountain building began-the continent was much larger than it is now, not smaller.”

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