STRUCTURAL ANALYSIS OF THE VARISCAN NAPPE ZONE, PORTO CORALLO, SARDINIA, ITALY

1:10,000 scale mapping and structural analysis in the nappe zone of the Variscan orogen, in the area of Porto Corralo, Sardinia, Italy, suggests a polyphase deformational history involving both contractional and extensional components. Lower Paleozoic rocks in the area contain a strong penetrative foliation and have been affected at the km-scale by at least two generations of thrusting, alternating with at least two generations of folding. Early thrusts (D1), were affected by NE-trending folds (D2), which were in turn truncated by later thrusts (D3). E-W trending upright folding (D4) affected the entire Variscan nappe stack. Due to reorientation by folding, the original thrust vergence is difficult to interpret at the scale of the study area; however, regional relationships suggest SW-directed transport. Folding is present at a variety of scales, ranging from cm to km. The youngest group of structures in the area (D5) includes NE-striking normal faults, some of which may represent reactivated older thrusts. The complex deformational history is consistent with early, polyphase Variscan contraction, followed by later orogenic extension. The absolute timing and tectonic mechanisms of the extension are not well constrained, and could be related to either: 1) local extensional modification of the Variscan nappe stack while overall contraction continued elsewhere or at a deeper structural level; or 2) post-orogenic extension due to gravitational instability of the nappe stack and/or changes in far-field plate interactions.