Geophysical-petrological modelling of the East Greenland Caledonides – Isostatic support from crust and upper mantle (original) (raw)
Related papers
The East Greenland Caledonides—teleseismic signature, gravity and isostasy
The large-scale geological evolution of the North Atlantic Realm during the past 450 Myr is largely understood, but crucial elements remain uncertain. These involve the Caledonian orogeny, the formation of the North Atlantic and accompanying igneous activity, and the present-day high topography surrounding the North Atlantic. Teleseismic receiver function interpretation in the Central Fjord Region of East Greenland recently suggested the presence of a fossil Caledonian subduction complex, including a slab of eclogitised mafic crust and an overlying wedge of serpentinised mantle peridotite. Here we further investigate this topic using inverse receiver functions modelling. The obtained velocity models are tested with regard to their consistency with the regional gravity field and topography. We find that the obtained receiver function model is generally consistent with gravity and isostasy. The western part of the section, with topography of >1000 m, is clearly supported by the 40-km-thick crust. The eastern part requires additional buoyancy as provided by the hydrated mantle wedge. The geometry, velocities and densities are consistent with interpretation of the lithospheric structure as a fossil subduction zone complex. The spatial relations with Caledonian structures suggest a Caledonian origin. The results indicate that topography is isostatically compensated by density variations within the lithosphere, and that significant dynamic topography is not required at the present-day.
Crustal Structure in Central‐Eastern Greenland From Receiver Functions
Journal of Geophysical Research: Solid Earth, 2018
The crustal structure in the interior of Greenland is largely unknown because of its remote location below the up to 3.4-km-thick ice sheet. We present a model of the crustal velocity structure in central-eastern Greenland based on simultaneous inversion of P and S receiver functions for data acquired at 23 broadband stations between the coast and the center of the ice sheet. The area is believed to mainly include Precambrian basement and includes a part covered by Tertiary volcanic rocks and some sedimentary basins. Our results show a westward deepening Moho from less than 20 km at the coast to 50 km below central Greenland. Crustal S wave velocities are generally 3.75 km/s through the whole crust which may be relatively small for Precambrian areas, and V p /V s is generally around 1.73, although slightly higher in central Greenland. In the coastal area we observe anomalously low velocities at the top of the crust. In the volcanic area south of Scoresbysund Fjord this layer has very high V p /V s (>2), which indicates a high mafic content and the presence of water-filled cracks in the basaltic material. In the north, outside the volcanic area, V p /V s is normal and the low-velocity layer probably is instead related to the presence of sedimentary basins. At stations in the center of our study area we find low V s and high V p /V s in the lower crust. Based on the Moho topography, our results do not support Airy type isostasy as explanation of the high topography in eastern Greenland. Plain Language Summary Crustal structure in interior Greenland is largely unknown due to its inaccessibility. The origin of the mountains at the rim of Greenland is enigmatic, and cannot be explained by standard plate tectonic processes. We present the first crustal structure profile across the mountains and to the centre of Greenland which is needed for constraining the possible mechanisms that formed the mountains. We conclude that crustal isostasy cannot explain their presence.
Journal of Petrology, 2000
mantle melting zone, accompanied by an increase in the average Drilling along a 63°N transect off SE Greenland during Ocean degree of melting with time from >4% to >12%. These modest Drilling Program (ODP) Legs 152 and 163 recovered a succession degrees of melting imply mantle temperatures only >100°C hotter of volcanic rocks representing all stages in the break-up of the than normal upper mantle. Upwelling mantle must therefore have volcanic rifted margin. The rocks range from pre-break-up continental been fed dynamically to the melt zone to generate the igneous crust tholeiitic flood basalt, through syn-break-up picrite, to truly oceanic of 18 km thickness deduced from seismic and gravity studies. Nbasalt forming the main part of the seaward-dipping reflector MORB-like magmas dominated the earliest part of the succession sequence (SDRS). All the lava flows recovered from the transect although a few flows of 'Icelandic' basalt were erupted in the prewere erupted in a subaerial environment. 40 Ar-39 Ar dating shows break-up phase. In contrast, the post-break-up magmas had an that the earliest magmas were erupted at >61 Ma and has Icelandic mantle source. This suggests that the developing head of confirmed that the main part of the SDRS was erupted during C24r the ancestral Iceland plume was compositionally zoned, with a core (56-53 Ma) following continental break-up. Magma represented by of Icelandic mantle surrounded by a thick outer zone of hot, depleted the pre-break-up lava flows was stored in crustal reservoirs where upper mantle. it evolved by fractional crystallization and assimilation of continental crust. Trace element and radiogenic isotope data show that the contaminant changed, through time, from lower-crustal granulite to a mixture of granulite and amphibolite, suggesting storage of magma at progressively shallower levels in the crust. The degree of contamination declined rapidly as break-up proceeded, and the youngest rocks sampled in the transect are uncontaminated by continental basement. Variation of, for example, Sc/Zr and Sm/ KEY WORDS: flood basalt; geochemistry; Greenland; Palaeogene; Sr-Nd-Pb isotopes Lu through the succession suggests a shallowing of the top of the * Corresponding
Precambrian Research, 1995
Major and trace element chemistry and Rb-Sr isotope data are presented for Palaeoproterozoic basement gneisses within the Caledoni an fold belt of NorthEast Greenland. They indicate that these rocks represent remnants of a Palaeoproterozoic collisional orogen formed near the margin of an Archaean continent. Older tonalitic and granodioritic gneisses represent arc granitoids. Granitic rocks (sensu stricto) of two distinct kinds can be recognised: (1) collision-type granites; and (2) post-orogenic ("A-type") granites, which may have formed during collapse of this orogen. It is suggested that the Palaeoproterozoic gneisses of NorthEast Greenland, together with coeval granitoid rocks in Scandinavia and North America, form a T-shaped arrangement of orogenic belts. Similar patterns are also recognised for the later Grenvillian and Caledonian orogenic episodes. Orogenic activity of different ages in NorthEast Greenland overlaps in space, resulting in very complex geological relationships.
Post-collisional extension of the East Greenland Caledonides: a geophysical perspective
Geophysical Journal International, 2000
Crustal extension during and following continental collision is well documented in the Arctic Caledonian fold belt. However, models for the post-collisional extension of the Caledonides are mainly based on geoscientific data from Scandinavia. For a more complete understanding of the evolution of the Caledonides, knowledge of the crustal structure of East Greenland is vital. Seismic and gravity studies have revealed a pronounced Moho topography and a west-dipping lower crustal reflector beneath the fjord region of East Greenland. These deep crustal structures are related to Late Caledonian extensional structures at the surface. The observations can be satisfactorily explained by applying simple shear or eduction models proposed for upper crustal extension in Scandinavia to the complementing lower crustal structures in East Greenland. However, exhumation of the Caledonian Northeast Greenland eclogite province cannot be accomplished by these models. Instead, a synthesis of geoscientific data has shown marked differences in the crustal structure of East Greenland north and south of about 76°N, indicating a different crustal evolution of the northern and southern parts of the East Greenland Caledonides.
Geophysical Journal International, 1998
We present results from the ¢rst combined marine^land seismic refraction survey in the area of the East Greenland Caledonides, together with gravimetric measurements. The seismic and gravimetric models show a consistent picture of the crustal structures. In the western area, which is part of the Caledonian mountains of East Greenland, crystalline rocks with P-wave velocities of about 5.5 km s {1 occur at the surface. Seismic velocities increase continuously with depth and reach values of 6.6 km s {1 at 12 km. The total thickness of the crust as revealed by the seismic measurements reaches high values of up to 48 km in the southwestern part of the region (28 0 W). Gravity data, which also cover the region west of the seismic lines, indicate a possible further increase of the crustal thickness. These high values raise questions about whether they represent a Caledonide crustal root, which would stand in strong contrast to the ¢ndings in the Caledonian areas of Europe, or whether the crustal thickening represents a pre-Caledonian structure and is a¤ne rather to the older regions west of the Caledonides and adjacent to the Greenland inland ice. Towards the east crustal thickness decreases rapidly. It reaches a minimum of 22 km under the Late Palaeozoic^Mesozoic sedimentary basin of Jameson Land. The crustal thinning is the result of the stretching of East Greenland, which was produced by a general extensional tectonic regime and the collapse of the Caledonian mountain chain from Devonian time onwards. In the area of transition from thick to thin crust, the seismic data indicate a layered structure at the Moho. This region is interpreted as a zone of extensive intrusion or underplating during the rifting in the Tertiary.