Late Miocene-Early Pliocene Out-of-Sequence Thrusting in the Southern Apennines (Italy)

Abstract

We present a structural study on late Miocene-early Pliocene out-of-sequence thrusts affecting the southern Apennine orogenic belt. The analyzed structures are exposed in the Campania region (southern Italy). Here, thrusts bound the N-NE side of the carbonate ridges that form the regional mountain backbone. In several outcrops, the Mesozoic carbonates are superposed onto the unconformable wedge-top basin deposits of the upper Miocene Castelvetere Group, providing constraints to the age of the activity of this thrusting event. Moreover, a 4-km-long N-S oriented electrical resistivity tomography profile, carried out along the Caserta mountains, sheds light on the structure of this thrust system in an area where it is not exposed. Further information was carried out from a tunnel excavation that allowed us to study some secondary fault splays. The kinematic analysis of out-of-sequence major and minor structures hosted both in the hanging wall (Apennine Platform carbonates) and footwall (Castelvetere Group deposits and Lagonegro-Molise Basin units) indicates the occurrence of two superposed shortening directions, about E-W and N-S, respectively. We associated these compressive structures to an out-of-sequence thrusting event defined by frontal thrusts verging to the east and lateral ramp thrusts verging to the north and south. We related the out-of-sequence thrusting episode to the positive inversion of inherited normal faults located in the Paleozoic basement. These envelopments thrust upward to crosscut the allochthonous wedge, including, in the western zone of the chain, the upper Miocene wedge-top basin deposits.

Crustal structure in the Campanian region (Southern Apennines, Italy) from potential field modelling

“…To the East, the Adria plate represents the foredeep and foreland region of the orogenic belt 26 – 28 . The northern Apennines is characterized by a regular, in-sequence system of N and NE-verging thrust imbricates 3 , while the Southern Apennines consist of ENE and E-verging thrusts which possesses duplex geometries and out-of-sequence trusting 1 , 3 , 29 , 30 . The central Apennines display N-verging and NE to ENE-verging thrust faults that dissect the tectonic edifice into several, small-scale tectonic slices 3 , 31 .…”

Structural and Stratigraphic Setting of Campagna and Giffoni Tectonic Windows: New Insights on the Orogenic Evolution of the Southern Apennines (Italy)

“…On the other hand, thick-skinned tectonics, defined by high-angle thrusts, played a significative role in the crustal shortening during the Pliocene-Middle Pleistocene; they were nucleated at deeper structural levels showing smaller displacements (e.g., [1,4,7,8]). Thick-skinned tectonics has probably acted through the positive inversion of pre-existing normal faults located in the Permo-Triassic rocks of the downgoing Adria inversion of pre-existing normal faults located in the Permo-Triassic rocks of the downgoing Adria plate [3], likely triggered by the buttressing of the thick Apulian Mesozoic carbonates against the allochthonous wedge in the early Pliocene [6,11]. The fault inversion generated deep-seated envelopment thrusts [12,13] that crosscut upward the already formed orogenic wedge and presently appear as out-of-sequence structures (Figure 1b; [11,14,15]).…”

“…Thick-skinned tectonics has probably acted through the positive inversion of pre-existing normal faults located in the Permo-Triassic rocks of the downgoing Adria inversion of pre-existing normal faults located in the Permo-Triassic rocks of the downgoing Adria plate [3], likely triggered by the buttressing of the thick Apulian Mesozoic carbonates against the allochthonous wedge in the early Pliocene [6,11]. The fault inversion generated deep-seated envelopment thrusts [12,13] that crosscut upward the already formed orogenic wedge and presently appear as out-of-sequence structures (Figure 1b; [11,14,15]). In the axial sector of the southern Apennine chain, these ramp-dominated thrusts have formed several anticlines within the buried Apulian carbonates that originated hydrocarbon traps presently drilled and exploited (e.g., [16]).…”

“…In the axial sector of the southern Apennine chain, these ramp-dominated thrusts have formed several anticlines within the buried Apulian carbonates that originated hydrocarbon traps presently drilled and exploited (e.g., [16]). These envelopment thrusts are widespread in the southern Apennines (e.g., [11,14,15,17]), frequently deforming the upper Miocene-Middle Pleistocene wedge-top basin deposits both in the western and eastern sectors of the chain. However, few studies have provided information about the orientation, structural style, kinematics, and age of these out-of-sequence structures (e.g., [11,14,15]).…”

“…These envelopment thrusts are widespread in the southern Apennines (e.g., [11,14,15,17]), frequently deforming the upper Miocene-Middle Pleistocene wedge-top basin deposits both in the western and eastern sectors of the chain. However, few studies have provided information about the orientation, structural style, kinematics, and age of these out-of-sequence structures (e.g., [11,14,15]). In this work, we analyzed the tectonic windows of Giffoni and Campagna in the southern Apennines (Figure 1a), where in-and out-of-sequence thrusts and related structures are remarkably exposed.…”