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3 years ago in StructuralAnalysis , Tectonics By Paula

What type of geological structures (features) can be inferred from a zone between extensional and compressional stress regimes?

I'm interpreting a complex fault zone where early normal faults appear reactivated and folded. This suggests a shift in the regional stress field over time. To build a robust kinematic model, what suite of structures should I be specifically looking for to confidently identify such a transitional tectonic phase in the rock record?

 

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By Fathima M Answered 3 years ago

I've mapped several basins that underwent this inversion. You'll typically find a nested set of structures. First, look for the original extensional architecture grabens or half-grabens now preserved as a hanging wall. The key indicators are the reactivation of those older normal faults; they often become reverse or oblique-slip faults, with slickenside lineations showing a composite slip history. You'll also see forced folding of the earlier syn-rift sediments above the reactivated fault tips. Finally, look for positive flower structures or broad, asymmetric anticlines developing in the cover, indicating transpressional squeeze. The structural overprint is rarely neat, but those reactivated faults are the definitive signature.

 

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