Carosi, R., Frassi, C., Iacopini, D. and Montomoli, C. 

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Post collisional transpressive tectonics in northern Sardinia (Italy)

R. Carosi

Università degli Studi di Pisa, Dipartimento di Scienze della Terra, via S. Maria 53, 56126 Pisa, Italy. Tel. 0039 050 2215727, Fax 0039 050 2215800

<carosi@dst.unipi.it>

C. Frassi

<frassi@dst.unipi.it>

D. Iacopini

<iacopini@dst.unipi.it>

C. Montomoli

<montomoli@dst.unipi.it>

Abstract

The aim of this work is to review and synthetize the geological and structural analysis performed in the Variscan Basement of Northern Sardinian during the last ten years and to add new preliminary data on the Anglona–SW Gallura area. A transpressive crustal-scale deformation (D2), is documented in the Variscan Basement of northern Sardinia. A shear deformation parallel to the belt, overprinting previous D1 structures related to a top-to-the S and SW nappe stacking, has been recognized. The L2 stretching lineation points to an orogen-parallel stretching and to a general change in the tectonic transport from D1 to D2 deformation phases. D1 phase developed during initial frontal collision whereas D2 deformation was characterized by dextral shearing. In this sector of the Variscan belt exhumation is due to continuing compression with an increasing component of horizontal displacement developed in a regime of decreasing pressure. The D2 transpressional deformation enhanced telescoping of the Barrovian isogrades and the exhumation of the low- to medium-grade metamorphic rocks. The overall change of the shortening direction in a large sector of an orogenic belt with the occurrence of increasing orogen-parallel displacement, may be regarded as a general mechanism affecting the exhumation of rocks and preventing the overthickened and thermally softened collisional crust from undergoing a diffused gravitational collapse. The rotation of nearly 90° of the tectonic transport in Sardinia during collisional and post-collisional stages could be related to paleoposition of the Corsica-Sardinia block, close to southeast France and northeast Spain, and to the development of the Ibero-Armorican arc.

Keywords: Variscan belt, transpression, vorticity analysis, shear zones, Sardinia

Table of Contents

Introduction
Geological setting
Structural pattern
Strain pattern of D1 deformation
Strain pattern of D2 deformation
D2 structures
D2 shear zones
Vorticity analysis
Method 1 (Gosh & Ramberg, 1976; Passchier, 1988)
Method 2 (Holcombe & Little, 2001)
Comparison of the data and discussion about the vorticity of the flow
Late folding
Relations between metamorphism and deformation
Timing of transpressional deformation
Discussion
Orogen-parallel tectonic transport in the southern Variscan belt
Conclusion
Acknowledgments
References
List of Figures
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