Geological Survey of Denmark and Greenland

About: Geological Survey of Denmark and Greenland is a facility organization based out in Copenhagen, Denmark. It is known for research contribution in the topics: Greenland ice sheet & Ice sheet. The organization has 844 authors who have published 3152 publications receiving 104706 citations. The organization is also known as: Danmarks og Grønlands Geologiske Undersøgelse.

Rapid transition from continental breakup to igneous oceanic crust in the South China Sea

Abstract: Continental breakup represents the successful process of rifting and thinning of the continental lithosphere, leading to plate rupture and initiation of oceanic crust formation. Magmatism during breakup seems to follow a path of either excessive, transient magmatism (magma-rich margins) or of igneous starvation (magma-poor margins). The latter type is characterized by extreme continental lithospheric extension and mantle exhumation prior to igneous oceanic crust formation. Discovery of magma-poor margins has raised fundamental questions about the onset of ocean-floor type magmatism, and has guided interpretation of seismic data across many rifted margins, including the highly extended northern South China Sea margin. Here we report International Ocean Discovery Program drilling data from the northern South China Sea margin, testing the magma-poor margin model outside the North Atlantic. Contrary to expectations, results show initiation of Mid-Ocean Ridge basalt type magmatism during breakup, with a narrow and rapid transition into igneous oceanic crust. Coring and seismic data suggest that fast lithospheric extension without mantle exhumation generated a margin structure between the two endmembers. Asthenospheric upwelling yielding Mid-Ocean Ridge basalt-type magmatism from normal-temperature mantle during final breakup is interpreted to reflect rapid rifting within thin pre-rift lithosphere.

State of the Climate in 2013

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Structure of the SE Greenland margin from seismic reflection and refraction data: Implications for nascent spreading center subsidence and asymmetric crustal accretion during North Atlantic opening

Abstract: [1] Seismic reflection and refraction data from the SE Greenland margin provide a detailed view of a volcanic rifted margin from Archean continental crust to near-to-average oceanic crust over a spatial scale of 400 km. The SIGMA III transect, located ∼600 km south of the Greenland-Iceland Ridge and the presumed track of the Iceland hot spot, shows that the continent-ocean transition is abrupt and only a small amount of crustal thinning occurred prior to final breakup. Initially, 18.3 km thick crust accreted to the margin and the productivity decreased through time until a steady state ridge system was established that produced 8–10 km thick crust. Changes in the morphology of the basaltic extrusives provide evidence for vertical motions of the ridge system, which was close to sea level for at least 1 m.y. of subaerial spreading despite a reduction in productivity from 17 to 13.5 km thick crust over this time interval. This could be explained if a small component of active upwelling associated with thermal buoyancy from a modest thermal anomaly provided dynamic support to the rift system. The thermal anomaly must be exhaustible, consistent with recent suggestions that plume material was emplaced into a preexisting lithospheric thin spot as a thin sheet. Exhaustion of the thin sheet led to rapid subsidence of the spreading system and a change from subaerial, to shallow marine, and finally to deep marine extrusion in ∼2 m.y. is shown by the morphological changes. In addition, comparison to the conjugate Hatton Bank shows a clear asymmetry in the early accretion history of North Atlantic oceanic crust. Nearly double the volume of material was emplaced on the Greenland margin compared to Hatton Bank and may indicate east directed ridge migration during initial opening.