Читать книгу Biogeography in the Sub-Arctic - Группа авторов - Страница 22

Volcanism preceding continental break‐up is generally confined to a narrow zone along which new oceanic crust is generated and is typically subdued. Although phenomena comparable to that of the North Atlantic area are known from some other oceanic openings (e.g. the Red Sea), such voluminous magmatism is the exception rather than the rule. For the North Atlantic the huge quantities of intrusive and extrusive igneous rocks that heralded the opening of the new ocean are now attributed to the ascent within a few million years of abnormally hot proto‐Icelandic plume. The contrast between the much smaller degree of magmatism attending the southern parts of the Atlantic and that attending the North Atlantic opening is ascribed to the major influence of a mantle plume in the latter. The opening of the North Atlantic, and Baffin Bay, was presaged by magma generation along the zones attenuated as a result of Mesozoic continental extension. Whilst the surviving volcanic products can be seen in the eastern coastal regions of Greenland, the Faeroes, north‐western UK as well as in central West Greenland and eastern Baffin, most of the basaltic rocks are submerged and lie off the Greenland and Norwegian shelves, the Faeroe and Rockall plateaux and the Jan Mayen ridge (Figure 8, see Plate section).

Figure 8 Distribution of the early Paleogene lavas, subaerial and submarine. The current spreading centres are marked in red.

Source: Based on Larsen et al. (1994).

The magmatism occurred in two principal periods, (a) 62–58 Ma and (b) 56–52 Ma (Saunders et al. 1997; Fitton and Larsen 2001). The latter period was characterized by higher eruption rates and greater magmatic volumes, accompanied by rapid thinning and rupture of the continental lithosphere. The bulk of the magmatism may have been accomplished within only two to three million years (White 1988).

The start of magmatism in the early stages of the first period typically involved sediments rich in volcanic particles (i.e. volcanogenic sedimentation) and the accumulation of sequences of pillow lavas and hyaloclastite breccias in shallow (non‐marine) waters. Subsequently, sub‐aerial eruptions dominated. During the earlier period a large volume of basalt lavas was erupted in West Greenland and Baffin Island, but within the Northern Irish and Hebridean region activity was more subdued. Eroded remnants of the prodigious quantities of lavas erupted in the second period are preserved along much of the coastal region of East Greenland between latitudes 67.5° and 75°N (Figure 8) and on the Faeroe Islands.