Palaeomagnetism of the Lisbon Volcanics

From Lisbon to the World...

Aikali.feldspars from the Crowsnest Volcanics, Atberta

Alkali-feldspar occurs in the Crowsnest Volcanics as phenocrysts and as free euhedra in the pyroclastics and their re-worked derivatives. Composition varies from 6O/p to 95/6 Or-molecule and 2V f.rom 50'[-f (010)] to 35'[ll(010)l' Individual crystals show a range of 2Zvalues, but only rarely contain more than one K-rich phase. Optics indicate that most of the K-feldspar is intermediate between ...

Palaeomagnetism of the Ordovician dolerites of the Crozon Peninsula (France)

In order to obtain a Lower Palaeozoic pole for the Armorican Massif and to test the origin of the Ibero-Armorican arc, the Ordovician dolerites of the Crozon peninsula have been palaeomagnetically studied. The samples show a multicomponent magnetization which has been revealed by AF and thermal demagnetization and thoroughly investigated with rock magnetic experiments, polished section examinat...

Volcanics from the Sierra Leone Rise

-THE Sierra Leone Rise, located in the east equatorial Atlantic. forms a discontinuous chain of seamounts as shallow as 2 km extending with a general NE-SW trend from near the Sierra Leone Coast of Africa, to the St Paul fracture zone near the Mid-Atlantic Ridge (Fig. 1). The origin of this feature has remained a topic of discussion. Sheridan et al.' have hypothesised that the Sierra Leone Rise...

Palaeomagnetism of the Bay an Gol Formation , western Mongolia

Oriented samples of the Lov.'er Cambrian Sayan Go! Formation from Salaany Go!, Mongolia, were collected at roughly 5 m stratigraphic intervals for palaeomagnetic analysis. Progressive alternatingfield and thermal demagnetization isolated two magnetic components: a present-field overprint, typically removed by 10 mT fields and -200 °C heating: and a high-coercivity, high-unblocking-temperature (...