GEOLOGIC MAPPING OF A TETHYAN OCEAN-CONTINENT TRANSITION DETACHMENT FAULT EXPOSED IN THE LIGURIDE COMPLEX OF SOUTHERN ITALY

The Liguride Complex of Southern Italy contains km-scale blocks of Tethyan ophiolite exposed in an accretionary-wedge scale mélange. These ophiolites have long been interpreted as dismembered fragments of ocean crust due to their incomplete sequence. We present new mapping of an ophiolite exposed at Timpa Pietrasasso near Terranova di Pollino, Basilicata that demonstrates a low-angle detachment fault that developed at an ocean-continent transition. This fault is responsible for the contact between mantle-derived serpentinite and gabbro with volcanic and sedimentary rocks.

The Timpa Pietrasasso ophiolite is comprised of deformed gabbro and serpentinite overlain by basalt and sedimentary units. The basalt unit consists of pillow basalt with sedimentary serpentinite deposited between pillows as well as in lenses. Depositional chert can be found locally between pillows. The basalt unit also contains a volcanic breccia. Pillows display a flattening foliation parallel to the sharp contact between basalt and gabbro. The gabbro has a strong mylonitic fabric overprinted by a late cataclastic texture. This unit is cut by undeformed basalt dikes which cross-cut mylonitic foliation. Underlying the gabbro is a serpentinite unit. This unit contains Hercynian blocks, dismembered rodingite dikes, and locally contains blocks of Miocene sandstone and shale encased within a serpentinite matrix.

At Timpa Pietrasasso the juxtaposition of deep mylonitic gabbro against shallow basalt and sedimentary units indicates a Tethyan-aged low-angle normal fault that accounts for the missing section in the ophiolite sequence. Although this area is affected by Cenozoic Alpine deformation, we believe the deformation is Jurassic Tethyan in age because undeformed basalt dikes cut the mylonitic gabbro, indicating that gabbro underwent brittle-ductile deformation before intrusion by basalt. The Hercynian-aged blocks in the serpentinite place the faulting in close proximity to a continental margin. We have yet to determine whether the sharp basalt to gabbro contact is due to faulting or if a depositional contact exists on the detachment fault surface.