Late Miocene remagnetization within the internal sector of the Northern Apennines, Italy

Abstract

Paleomagnetic and geologic evidence indicates that Upper Jurassic radiolarian cherts of both the Tuscan Cherts Formation (continental margin, Tuscan Units) and the Monte Alpe Cherts Formation (oceanic crust, Ligurian Units) were remagnetized during Miocene orogenesis of the Northern Apennines of Italy. Characteristic overprint magnetizations with reversed polarities have been found over a large area within the internal sector of the Northern Apennines, including eastern Liguria, Elba Island and the Thyrrenian margin, and west of the Middle Tuscan Ridge. The reversed-polarity overprint (average direction: D = 177j, I = À 52j, a 95 = 15j) was most likely acquired during Late Miocene uplift and denudation of the orogenic chain, and thermochemical remagnetization was a probable consequence of increased circulation of orogenic fluids. Similarly, mostly reversed-polarity directions of magnetization have been found by other workers in overlying post-orogenic Messinian sediments (D = 177j, I = À 57j, a 95 = 3j), which show little counterclockwise (CCW) vertical-axis rotation with respect to stable Europe ( À 8 F 5j). The Monte Alpe Cherts sampled at sites in the external sector of the Northern Apennines, close to major tectonic features, have normal-polarity overprint directions with in situ W -SW declinations. Since the overlying post-orogenic Messinian sediments have not been substantially rotated about vertical axes, the evidence points to an earlier, pre-Late Miocene remagnetization in the external parts of the orogenic chain. D

Behaviour of minor arcuate shapes hosted in curved fold-and-thrust belts: an example from the Northern Apennines (Italy)

“…A similar ITC has been documented in other sites and sections from the Northern Apennines (e.g. Tarduno et al 1992;Aiello et al 2004;Satolli et al 2007. The pole position indicates the remagnetization was acquired during a Tertiary reversed polarity chron.…”

“…, or to external derived fluids (e.g. enhanced circulation of orogenic fluids during the uplift; Lu et al 1990;Aiello et al 2004).…”

Palaeomagnetism of Middle Triassic red bedded cherts from southwest Japan: equatorial palaeolatitude of primary magnetization and widespread secondary magnetization

“…An example of multiple pigmentation events with different magnetization ages has been reported by Park & Jefferson (1991). A widespread remagnetization recorded in radiolarian cherts has been reported from the Northern Apennines and Greece (Aiello et al 2004(Aiello et al , 2008. Its unblocking temperatures up to about 640 • C suggest that the remanence resides in haematite, which is considered by the authors to have precipitated in association with regional tectonics leading to fault-related crustal rotations (Aiello et al 2004(Aiello et al , 2008.…”

“…A widespread remagnetization recorded in radiolarian cherts has been reported from the Northern Apennines and Greece (Aiello et al 2004, 2008). Its unblocking temperatures up to about 640 °C suggest that the remanence resides in haematite, which is considered by the authors to have precipitated in association with regional tectonics leading to fault‐related crustal rotations (Aiello et al 2004, 2008). The example is similar to that of this study.…”