Model of crustal formation in Iceland, and application to submarine mid-ocean ridges

Abstract

During the early 1960s, when the idea of seafloor spreading was crystallizing out of geophysical data gathered over oceanic areas, similar ideas were beginning to take shape in Icelandic geology, but on the basis of a different kind of data. Geological studies of the structure of the eastern Iceland Tertiary lava pile led Walker (1959, 1960) to suggest that regional dips of the lavas were due to sagging accompanying lava deposition in the active volcanic zone. These ideas were further elaborated by Bodvarsson and Walker (1964), who tried to estimate the amount of crustal drift that might have accompanied the injection of dikes as observed in the eastern Iceland lava pile, taking into account the increase in dike fraction with depth in the crust. Subsequent studies of the Tertiary lava pile in other parts of Iceland have essentially confirmed a structure analogous to that given by Walker for eastern Iceland (Saemundsson, 1978). Observations from two distinct geological regions can be brought to bear on the process of crustal accretion in Iceland. One region is the present active zone of rifting and volcanism, the axial rift zone. The other region is the flanking Tertiary lava pile where the internal structure of the uppermost well-developed crust can be observed to a depth of 1–1.5 km in valleys that have been carved into the crust by glacier action. In the axial rift zones the constructional processes of extrusive volcanism, faulting, and Assuring take place as discrete but closely associated events.

Evolution of the Vøring Volcanic Margin

“…For example, it is known from Iceland that the constructional process of crustal accretion includes discrete but closely associated events of extrusive volcanism, faulting, and fissuring, creating overlapping spreading centers, transient fissure swarms, and central volcanoes (Palmason, 1988). We have assumed an analog situation at the Wring Plateau, noting that a single drill hole only samples one locality, whereas the geophysical surface data represent an integrated pattern.…”

Crustal structure along the Leg 152 drilling transect

“…Below these sediments, the SDRS and its source region are present (crustal unit 3). As pointed out by Larsen and Jakobsdóttir (1988), it is inherent in the Pálmason (1986) model for SDRS type crust that this volcanic cover is replaced downward by a sheeted dike complex. However, neither the model for crustal accretion in Iceland nor our observations constrain the thickness of this dike complex.…”

“…This provides us with the possibility to estimate the position of the continent-ocean boundary within the upper crust (i.e., the outer limit of the COT). Application of the kinematic model for crustal accretion in Iceland (Pálmason, 1986) to the southeast Greenland SDRS shows that lavas now located shallow in the crust stem from a fairly narrow rift zone 4−10 km wide and located around 25 km in the down-dip direction (Larsen and Jakobsdóttir, 1988). A more distal origin would, for simple geometric reasons, require continuation of the lavas to unrealistically great depths (see Larsen and Jakobsdóttir, 1988, and Larsen and Saunders, this volume).…”

“…Larsen and Jakobsdóttir (1988) interpreted the main part of southeast Greenland SDRS as subaerially erupted lavas that emanated from a fairly narrow, Icelandic-type spreading center. This implies that the SDRS crust represents Icelandic-type oceanic (igneous) crust (Pálmason, 1986) with the continent-ocean transition (COT) located below the inner part of the SDRS. Testing these interpretations by borehole data was one of the major tectonic objectives of Ocean Drilling Program (ODP) Leg 152.…”

Crustal accretion of thick mafic crust in Iceland: implications for volcanic rifted margins

“…[Colour online. ] accommodated by subsidence centered on the axis and diminishing off axis with progressive spreading (Bodvarsson and Walker 1964;Pálmason 1986). Although lavas on Iceland typically do not dip more than 20°, lavas on the East Greenland margin bend downward to nearly vertical, demonstrating that larger rotations are possible at deeper structural levels.…”