International Geologiical Congress - Oslo 2008

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EUR-06 Collisional orogeny in the Caledonian-Appalachian Orogen

 

In search of the Alleghanian Orogeny - must sediments lie?

 

Scott Samson, Syracuse University (United States)
Jack Hietpas, Syracuse University (United States)
David Moecher, University of Kentucky (United States)
 

 

Clastic sedimentary rocks have the potential to hold vast amounts of information about the past tectonic history of orogenic regions, including the timing of major deformational/metamorphic events, relationships between distinct terranes, the paleogeographic origin of terranes, and the timing of accretion. Unlocking this vault of information requires the successful interrogation of clastic sedimentary rocks within orogenic belts. Determining the ages of detrital zircon has become an increasingly frequent method of trying to understand the evolution of mountain belts. And although determining the ages of the most resistant of orogenic progeny has produced a wealth of information for some regions other regions have proven that our interrogation methods are clearly lacking. A particularly stark and disturbing example of this comes from the almost complete lack of Appalachian orogenic events that are recorded in syn-tectonic sedimentary rocks.
The most spectacular example of a missing tectonic record is the lack of Alleghanian-age zircon in Pennsylvanian-Permian sedimentary rocks in the southern Appalachians. This lack of an orogenic "high fidelity" signal appears to partially be a result of inappropriate analytical protocols combined with a misunderstanding of which suspects to interrogate. We demonstrate that analyzing the metamorphic rims of zircon, rather than the traditional analysis of detrital cores, provides a more accurate view of past tectonic events. Determining the ages of detrital monazites is even more successful, and may prove to be the closet thing to a tectonic truth serum that we can use in the sedimentary record.

 

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