Publication Date

5-2011

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Geology

Department

Geosciences

Major Advisor

C. J. Northrup, Ph.D.

Abstract

The late Paleozoic Variscan Orogen of Europe represents one member of a composite Mountain belt (including the Allegenian, Southern Appalachan, and Mauratanides among others) that formed as a response to the closure of both the Rheic and Galacia/Southern Brittany oceans between the Gondwonan and Laurentian continents, marking the final amalgamation phase of Pangaea. Field investigations as well as data from bore holes has resolved that rocks deformed during the Variscan orogeny can be delineated into six tectonic zones (Figure 4). Of particular interest to this study are the Rock of the Southern European Variscides, the most intact (minimal Pyrenean and/or Alpine deformation) section of which is located throughout the Mediterranean island of Sardinia, Italy. Variscan rocks exposed in Sardinia have been further subdivided into four distinct tectono/metamorphic zones; Mid to High Grade metamorphic rocks of the Internal zone in the north, Internal Nappes bounded by thick (~10-30m) mylonitic boundaries, External Nappes delineated by more concise nappe boundaries, and the External zone which is identified by Carmignani (1992) classic fold-and-thrust belt.

To investigate timing of deformational features developed within Variscan rocks of Sardinia this paper examines rocks contained within the Extarnal Nappes, outcropping in the Lago Mulargia region near the villages of Siurgus/Donigala. A regional deformational sequence of events has been identified by Conti (1999) primarily consisting of a SSW shortening event followed by one 90° shift in shortening direction and again returning to a SSW directed shortening phase. Field investigations in the region along with previous mapped geology (Funedda et. al. 2010) illustrated that deformational structures in this region do not entirely fit within the context of the sequence of events identified by Conti (1999). In this study these structures are analyzed and placed within a locally defined deformational sequence, this local sequence is then placed into the context previously laid out by Conti (1999) and a new composite deformational history is created that takes into account the mapped relationships of deformational features within the Lago Mulargia region.

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