Sardinian and Corsican Islands Geomorphology


A detailed study of the magnetic -bearing granites of the Sardinian and Corsican islands notes a number of anomalous features.


Bulk susceptibility and AMS parameters: ...Most samples have susceptibility above 0.5 mSI, indicating that ferromagnetism is dominant with respect to diaand paramagnetism (Rochette et al. 1992). These granitoids clearly belong to the magnetite-bearing granitoids (Ishihara 1977). It is noteworthy that such high magnetic susceptibilities are absent in many of the other granitoids of the Hercynian belt (Table 2). The vast majority of Hercynian granites from the Pyrenees, Massif Central, Vosges, Central Iberia, Alps, Maures and Armorican Massif (see inset in Fig. 1 for location) have susceptibilities lower than 1 mSI, and most of them exhibit paramagnetic behaviour with susceptibility lower than 0.5 mSI. Moreover, in areas where ferromagnetic granitoids can be found they are a minority compared with paramagnetic ones (35% in the Berarde granite, 7% in the Rochail granite for instance). In fact, only the Flamanville granite in the Armorican Massif, which is a post-orogenic bubble-like intrusion, and the northern Vosges granites and granodiorites have a clear ferromagnetic behaviour. In Sardinia (F. Speranza, pers. comm.), some ferromagnetic granitoids can be found 50 km south of our study area (Monte di Ala area), whereas only paramagnetic granitoids have been found 100 km south of our study area (Nuoro area). Therefore, ferromagnetic granitoids are rare within the SW European Hercynian belt and are predominant, to our knowledge, only in the area studied in this paper. This suggests a peculiar orogenic context within the Hercynian belt (Ishihara 1977) and would deserve further attention.


The syntectonic character of most granitoid intrusions is widely reported in tensional as well as contractional tectonic settings (e.g. Hutton 1997).


It is interesting to note that U2a and U2b granitoids display orthogonal lineations but were emplaced in the same regional strain field. This is strongly supported by the slightly younger dyke swarm direction compatible with the stretching direction inferred from the petrofabric of the granitoids. This compatibility makes very improbable a scenario that would imply emplacement of U2a and U2b granitoids in contrasting strain regimes.


The magnetic mineralogy is dominated by multidomain magnetite grains and most granitoids exhibit ferromagnetic behaviour. This makes them very unusual within the western European Hercynian belt and suggests a peculiar orogenic context. Despite a few local exceptions, the coherent lineation and foliation patterns confirm that AMS is a powerful proxy for strain trajectories in apparently isotropic granitoids.


Another interesting feature is that the absence of a sigmoidal lineation pattern within U2b intrusions seems to indicate that the strike-slip component of the late Hercynian faults cross-cutting the whole Corsica-Sardinia batholith had little effect on the emplacement of these granitoids. To confirm this point, additional work on other leucogranitic intrusions in Corsica and Sardinia is required.


From: Magnetic fabric of granitoids from Southern Corsica and Northern Sardinia and implications for Late Hercynian tectonic setting
Journal of the Geological Society, Mar 2004 by Gattacceca, J, Orsini, J-B, Bellot, J-P, Henry, B, Et al

The examination of the geological structure of the Mediterranean Sea in the course of this work has identified the two Islands of Sardinia and Corsica as PZ Mega Ejecta emplacements. They arrived in one single divot unit, after having been excised from central Africa. We suggest that this emplacement would create a very enigmatic situation, with the normal geologic explanations failing to provide good explanation for anomalies such as those identified in the current research by others.

Here is a Google Earth composite with the generic PZ ejecta outline offering hinting. Click for a higher resolution view. The GE KMZ file is available on the KMZ Downloads page.

sardinia_corsica_emplacement_sm
PZ
The mega PZ ejecta divot was ejected from the Azaouka PZ terminal crater in central West Africa. The Azkouka Series is available for review in the Proofs section. A Google Earth trajectory composite is shown here for reference.

azaouka_sardina_trajectory_sm

The distance of the loft is measured as 2,700 km.

Summary:



By demonstrating collaborating evidence of PZ ejecta structural shape matching and correlating the emplacement with a well-defined PZ Crater structure, we feel that the Corsican and Sardinian geologic formations are of PZ Ejecta emplacements. The dating of the event has not been established at this time. We do note that the Trans- Mediterranean PZ Trench crater is tentatively identified as having excavated this area prior to the emplacement, which provides some sequencing information. The Islands were settled remarkably late, in the 6,000 BC to 5,500 BC timeframe, offering yet another data point and helps confirm the PZ Ejecta definition. A history of Sardinia is available at Sardegna.net

The review at Sardegna.net notes an abundance of astronomical monoliths on the island dating from the early settlement times.