engleski

Changes of magnetic properties of Permian clastic deposits upon heating - effects on the AMS and palaeomagnetic results

A sequence of Permian red bed deposits(siltstones and sandstones) as well as accompanying conglomerates from the Velebit Mountain (Croatia) have their rock magnetic properties and AMS fabric studied for fresh samples and for subsequently heated in air or in argon. Hematite rich fresh samples of clastic deposits revealed a great potential for a growth of secondary magnetite (mostly SP) upon heating depending on the state of the sample (powdered or solid) and air/argon atmosphere. Magnetic susceptibility was strongly increased upon heating above 600 ◦C in K(T) experiments for powdered samples in argon as well as during a typical thermal demagnetization of paleomagnetic samples. SIRM(T) experiments for solid samples (previously heated in air) revealed a moderate increase in intensity due to growth of secondary SD magnetite. Paleomagnetic samples heated above 600 ◦C showed a great potential for acquiring viscous remanence (by strong enhancement of minor SP magnetite phase that existed in samples) that may strongly affect stepwise demagnetization results. For almost all sites such heating resulted in thermal enhancement of AMS (increase of P’) that mimics the AMS for fresh samples except one site. We will discuss the effects of the SP magnetite fraction on the AMS and paleomagnetic results.

palaeomagnetism; anysotropy of magnetic susceptibility; Permian; Croatia

nije evidentirano