The palaeomagnetism of Lesbos, NE Aegean, and the eastern Mediterranean inclination anomaly

Abstract

SUMMAR YPalaeomagnetic results for 44 sites in 16-22 Ma volcanic rocks from Lesbos, NE Aegean, yield a mean pole at 81.8uN, 178.1uE, K=9.0, A 95 =7.6u. The mean direction for these sites (D=4.3u, I=48.5u, k=10.8, a 95 =6.9u) is 5.9ut6.1u shallower than the reference direction for Miocene Lesbos calculated from Besse & Courtillot (1991). Combining these new data with previous work yields a mean inclination that is 5.6ut4.7u too shallow. Experimental problems, magnetic anisotropy, the magnetic terrain effect, geomagnetic anomalies, and problems with the reference path all seem unable to account for this observation. Shallow inclinations are a common feature of the Aegean region: 17 of 18 palaeomagnetic studies on Cenozoic igneous rocks have returned an inclination that is shallower than expected. Northward motion of the Aegean block by y500 km with respect to northern Europe would account for this observation.

Shallow bias in Mediterranean paleomagnetic directions caused by inclination error

“…Beck et al [9] report data from Lesbos with a mean inclination of 51.7j (a 95 = 6.89), which is consistent with the inclination expected for that location by BC02 (53.9j, a 95 = 4.5). [Beck et al used an earlier version of the European pole paths to calculate the expected inclination, which was a degree or so steeper than that predicted by BC02.]…”

“…A total of 87% of all studies with N = 20 sites have average inclinations that are below the GAD expectation, while 100% of all studies with N = 500 did. However, the magnitude of the bias is certainly largest with studies with fewer sites and can be more than 6j very shallow with the number of sites typical of the studies cited by Beck et al [9] (see Fig. 5a).…”

“…Hence, application of inaccurate structural tilt corrections leads to a shallow bias in inclinations. Therefore, it is perhaps not surprising that the tilt adjusted mean value of Beck et al [9] is shallower than the unadjusted mean, bolstering their argument for anomalous geomagnetic fields. We find no support for such an interpretation.…”

“…Nevertheless, it has often been argued that inclination flattening cannot explain the anomalously shallow inclinations observed in volcanic rocks [8,45]. Consequently, the tectonic explanation, including accommodation of f 500 km northward displacement with respect to Europe was recently put forward again by Beck et al [9] on the basis of paleomagnetic results from igneous rocks of Lesbos.…”

Exhumation with a twist: Paleomagnetic constraints on the evolution of the Menderes metamorphic core complex, western Turkey

“…Arrows represent a selection of the most important reported paleomagnetic declinations with respect to south, giving the outline of the Aegean orocline, which runs from northern Albania to the Isparta Angle. White arrows represent directions measured in lower Miocene and older rocks, and gray arrows represent late Miocene and younger directions: 1, Apulian platform, no or little rotation since Eocene [Tozzi et al, 1988;Scheepers, 1992;Speranza and Kissel, 1993]; 2, Dinarids, no rotation since the Cretaceous ; 3, Albania, ∼50°of rotation since the early Miocene [Speranza et al, 1992Mauritsch et al, 1995Mauritsch et al, , 1996; 4, western Greece and Peloponnesus, ∼50°c lockwise rotation since the early Miocene Freeman, 1982, 1983;Kissel et al, 1984Kissel et al, , 1985Kissel and Laj, 1988;Márton et al, 1990;Morris, 1995;van Hinsbergen et al, 2005b]; 5, Moesian platform and Rhodope, no significant post-Eocene rotation with respect to the Eurasian APWP ; 6, Lesbos, no significant rotation of Miocene volcanics [Kissel et al, 1989;Beck et al, 2001]; 7, Crete, local, variable, strike-slip-related post-Messinian counterclockwise rotations [Duermeijer et al, 1998]; 8, Rhodos, Pleistocene counterclockwise rotation, without rotation between early Miocene and Pleistocene [Laj et al, 1982;van Hinsbergen et al, 2007]; 9, Bey Dağları, ∼20°counterclockwise rotations [Kissel and Poisson, 1987;Morris and Robertson, 1993;van Hinsbergen et al, 2010]; 10, Isparta Angle, no Pliocene or younger rotations in its center [Kissel and Poisson, 1986]; 11, clockwise rotations between the Eocene and Miocene of the eastern limb of the Isparta Angle, delimiting the eastern edge of the Aegean orocline ; 12, post-early Miocene clockwise rotation of the volcanic fields of Afyon [Gürsoy et al, 2003]. VAN …”