Late Neogene kinematics of intra‐arc oblique shear zones: The Petilia‐Rizzuto Fault Zone (Calabrian Arc, Central Mediterranean)

Abstract

The kinematics of intra‐arc shear zones play a key role in the secondary shaping of orogenic arcs such as the Calabrian Arc (central Mediterranean). Comparison of the Neogene structural development of the Petilia‐Rizzuto Fault Zone and the basement structure of the bordering Sila massif reveals that the fault zone is the surface expression of a deep NW–SE trending sinistral crustal oblique shear zone. This shear zone continues over a length of more than 130 km across the northern segment of the Calabrian Arc and shows a post‐Eocene sinistral displacement of about 50 km. The late Neogene forearc basin development and syndepositional tectonics along the fault zone are reconstructed in great detail by analyzing the middle Miocene‐Recent tectonic sequence stratigraphy. A strike‐slip cycle can be recognized whereby the subsequent activity of Riedel shears, tensional faults, and P shears, positive flower structures and principle displacement wrench faults, can accurately be traced in time. Observed phenomena are discussed in terms of the activity of a conjugate system of oblique thrust zones within the growing accretionary complex. The evolution of special types of thrust belt basins is illustrated. These include oblique thin‐skinned pull‐apart basins, oblique rhomboidal “harmonica” basins, and “detached slab” basins (new terms introduced here), evolving one into the other. A new feature illustrated is the recurrent basin inversion which generated passive roof duplexes through back‐shear motion and out‐of‐sequence thrusting along the wedge. The fault patterns and the style of inversion tectonics imply an E–W directed axis of effective compressive stress in this part of the arc. This resulted from an interaction of (1) local E–W directed compression related to a differential displacement of two parallel segments of the arc (generated by the migration to the southeast of the Calabrian Arc and opening of the Tyrrhenian backarc basin); (2) alternating NW–SE directed compression and extension (related to pulsating thrust wedge dynamics with phases of accretion and underthrusting respectively) and (3) regional, compressive interplate stress (middle Messinian‐middle Pliocene). All structures are overprinted by post middle Pleistocene extensional faulting (related to rapid uplift of intra‐arc massifs) and reversal along thrust planes and transcurrent faults. This extensional collapse reflects isostatic adjustments in response to plate rupture which was provoked by regional compressive stress.

Volcanic facies architecture of an intra-arc strike-slip basin, Santa Rita Mountains, Southern Arizona

“…These faults commonly form in the thermally weakened crust of the arc, particularly on continental crust, which is weaker and better coupled to the subducted slab than oceanic-arc crust (Dewey 1980;Jarrard 1986a;Ryan and Coleman 1992;Smith and Landis 1995). Strike-slip faults, transtensional faults, and block rotations play an important role in modern volcanic arcs; examples include the Central American arc (Burkhart and Self 1985;Jarrard 1986b;Weinberg 1992); the Trans-Mexican Volcanic belt (IsradeAlcantara and Garduno-Monroy 1999); the Andean arc of southern Chile and Patagonia (Cembrano et al 1996;Thomson 2002); the Sumatra arc (Bellier and Sebrier 1994); the Aeolian arc (Gioncada et al 2003); the Calabrian arc (Van Dijk 1994); the Aleutian arc (Geist et al 1988); the Taupo Volcanic Zone (Cole and Lewis 1981); the central Philippine arc (Sarewitz and Lewis 1991); and others. Strike-slip basins are the most tectonically active type of basin (Nilsen and Sylvester 1995), so the effects of strike-slip faulting on the development of volcanic successions within arcs must be profound.…”

Neotectonic rotations in the Calabrian Arc; implications for a Pliocene-Recent geodynamic scenario for the Central Mediterranean

“…Royden et al, 1987;see Van Dijk and Okkes, 1988,199O;Patacca and Scandone, 1989). Its cover and slices of its basement are now present in the thrust sheets of the Calabrian Arc as "Apenninic Platform Units" (Apennines), Stilo-Tiriolo-Serre Units (Tyrrhenian vergent units in Calabria; see Van Dijk, 1994), and Panormide Platorm Units (Sicily).…”

“…Fore-arc basins. The fore-arc basins are situated upon the internal slope of the Calabrian accretionary thrust wedge, and are of various types (strike-slip, pull-apart, piggy-back, "detached-slab" and "harmonica" basins; see Van Dijk, 1994). These are all special types of thrustbelt basins showing several kilometres of Neogene deposits.…”

“…Along the boundaries of the segments, within NW-SE trending shear zones, small strike-slip basins are present (Meulenkamp et al, 1986;Okkes, 1990,1991). Along the external margin of Calabria, the thrust-belt basins can be regarded as piggy-back basins and "harmonica basins" upon the accretionary thrust wedge (Van Dijk and Okkes, 1988,199O;Van Dijk, 1994). The CrotoneSpartivento Basin, along the external margin of Calabria, is a typical fore-arc basin (Rossi and Sartori, 1981;Van Dijk, 1990.…”

Extensional and Transtensional Continental ARC Basins: Case Studies from the Southwestern United States

“…This is because (1) oblique convergence is far more common than orthogonal convergence, and at most continental arcs, an obliquity of only 10 degrees off orthogonal results in the formation of strike-slip faults in the upper plate; and (2) faults are concentrated in the thermally weakened crust of arcs, particularly on continental crust, which is weaker and better coupled to the subducting slab than oceanic arc crust (Dewey, 1980;Jarrard, 1986;McCaffrey, 1992;Ryan and Coleman, 1992;Smith and Landis, 1995). Strike-slip faults were described from a number of modern continental arcs, including the TransMexican Volcanic belt (van Bemmelen, 1949), the Andean arc (Cembrano et al, 1996;Thomson, 2002), the Sumatra arc (Bellier and Sebrier, 1994), the Aeolian arc (Gioncada et al, 2003), the Calabrian arc (Van Dijk, 1994), and the central Philippine arc (Sarewitz and Lewis, 1991). However, studies of intra-arc strike-slip basins remain sorely lacking, relative to studies of strike-slip basins along transform margins (Busby and Bassett, 2007).…”