A rock- and palaeomagnetic study ofgeologically recent lavas and 1995 volcanic glass on Fogo (Cape Verde Islands)

Bulletin of the Geological Society of Denmark

Milàn, J.¹  Gierlinski, G. 2004–10–22:¹ 

[1] A probable thyreophoran (Dinosauria, Ornithischia) footprint from the Upper Triassic of southern Sweden. Bulletin of the Geological Society of Denmark, Vol. 51, pp. 71–75, Copenhagen. © 2004 by the Geological Society of Denmark. ISSN 0011–6297.

关键词: Footprint;    Thyreophoran dinosaur;    Late Triassic;    Scania;    Sweden.;   

学科分类：地球科学(综合)

来源: Dansk Geologisk Forening

【 摘 要 】

Fogo is the only island in the Cape Verde archipelago with accounts of historical volcanic activity. Here we present palaeomagnetic data from seven geologically recent lava flows on Fogo, including one glassy, volcanic flow from the eruption in 1995. Almost all samples behaved well during alternating-field (AF) and thermal demagnetisation, and the characteristic remanent magnetisations (ChRMs) were generally easily isolated. The dominant magnetic mineral in all flow units, including the glassy flow, is titanomagnetite with a varying titanium content. The non-glassy flow units alldisplay pseudo-single-domain (PSD) behaviour, whereas the hysteresis parameters for the glassy flow unit tend to plot in a region associated with mixtures of superparamagnetic (SP) and single-domain (SD) grains. Despite historical accounts of the eruptive activity on Fogo it was impossible toobtain unique correlations between the historical flow flelds and the non-glassy flow units presented in this study. One of six non-glassy flow units yields a direction consistent with existing approximative reference curves for the historical secular variation on Fogo. Consequently, we suspect that some of the non-glassy flow units have been subjected to post-cooling block rotation. The glassy flow from 1995 proved to be a reasonable recorder of the geomagnetic fleld, yielding a direction (dec = 353.8° and inc = 12.9°), quite similar to the International Geomagnetic Reference Field(1995) for this site location (dec = 346.8° and inc = 14.4°).

【 授权许可】

Unknown