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Japsen P.,Geological Survey of Denmark | Green P.F.,Geotrack International | Bonow J.M.,Geological Survey of Denmark | Bonow J.M.,Sodertorn University College | And 2 more authors.
Global and Planetary Change | Year: 2014

In southern East Greenland (68-70°N), voluminous flood basalts erupted onto a largely horizontal lava plain near sea level at the Paleocene-Eocene transition when sea-floor spreading started in the NE Atlantic. Based on synthesis of geological observations, stratigraphic landform analysis and apatite fission-track analysis data in 90 rock samples, we show how three regional phases of uplift and exhumation subsequently shaped the present-day margin and controlled the discontinuous history of the Greenland ice sheet. A late Eocene phase of uplift led to formation of a regional erosion surface near sea level (the Upper Planation Surface, UPS). Uplift of the UPS in the late Miocene led to formation of the Lower Planation Surface (LPS) by incision below the uplifted UPS, and a Pliocene phase led to incision of valleys and fjords below the uplifted LPS, leaving mountain peaks reaching 3.7. km above sea level. Local uplift affected the Kangerlussuaq area (~. 68°N) during early Eocene emplacement of the Kangerlussuaq Intrusion and during late Oligocene block movements, that may be related to the detachment of the Jan Mayen microcontinent from Greenland, while middle Miocene thermal activity, coeval with lava eruptions, heated rocks along a prominent fault within the early Cretaceous to Paleocene Kangerlussuaq Basin. The three regional uplift phases are synchronous with phases in West Greenland, overlap in time with similar events in North America and Europe and also correlate with changes in plate motion. The much higher elevation of East Greenland compared to West Greenland suggests support in the east from the Iceland plume. These observations indicate a connection between mantle convection, changes in plate motion and vertical movements along passive continental margins. © 2014 Elsevier B.V. Source

Chalmers J.A.,Geological Survey of Denmark | Green P.,Geotrack International | Japsen P.,Geological Survey of Denmark | Rasmussen E.S.,Geological Survey of Denmark
Journal of Geodynamics | Year: 2010

Nielsen et al. (2009a) suggested that the high mountains of southern Scandinavia are the result of protracted exhumation since the Silurian. The evidence cited by Nielsen et al. (2009a) in support of this hypothesis is, however, very selective and other published evidence shows that their hypothesis is untenable. We suggest that an objective review of available evidence shows that the mountains of Norway are the result of uplift resulting from Cenozoic tectonism amplified by the isostatic response to resulting erosion, similar to many other continental margins around the world. © 2010 Elsevier Ltd. Source

Japsen P.,Geological Survey of Denmark | Chalmers J.A.,Geological Survey of Denmark | Green P.F.,Geotrack International | Bonow J.M.,Geological Survey of Denmark
Global and Planetary Change | Year: 2012

Many studies of elevated, passive continental margins (EPCMs) assume that their characteristic, large-scale morphology with high-level plateaux and deeply incised valleys has persisted since rifting and crustal separation, and that the absence of post-rift sediments is evidence of non-deposition. The high mountains in West Greenland, however, expose evidence of km-scale, post-rift subsidence, and recent studies showed that typical EPCM morphology with elevated plateaux formed c. 50. Myr after breakup through a process of uplift and dissection of a regional, post-rift erosion surface. Since the West Greenland margin shares all the morphological characteristics of EPCMs, the results from West Greenland lead us to question the common assumption that EPCMs have remained high since the onset of continental separation. We present published evidence of post-rift burial followed by uplift and exhumation from a number of EPCMs and their adjacent basins to support the notion that EPCMs are not permanent highs and that their morphology is unrelated to rifting and continental breakup. Geodynamic models that explain EPCMs as permanent highs since the time of rifting require either no lithospheric mantle extension below extending crust or effective elastic thicknesses > 100. km. Such models are, however, not consistent with the subsidence history inferred from actual rifts and their margins. Geodynamic models using low elastic thicknesses and a much more uniform distribution of strain within the lithosphere are more consistent with observations of early post-rift behaviour, but some additional process is needed to uplift the margins later. We suggest that EPCMs represent anticlinal, lithospheric folds formed under compression where an abrupt change in crustal or lithospheric thickness occurs between cratons and rift basins. We propose that EPCMs are expressions of episodes of post-rift burial followed by compression-induced uplift and exhumation; one episode of uplift results in erosion of the region to produce a low-relief surface near the level of the adjacent, opening ocean, and a second (or more) episode(s) raises the plateau to its present elevation, after which the plateau is dissected by fluvial and possibly glacial erosion. © 2011 Elsevier B.V. Source

Green P.F.,Geotrack International | Japsen P.,Geological Survey of Denmark | Chalmers J.A.,Geological Survey of Denmark | Bonow J.M.,Geological Survey of Denmark
Journal of the Geological Society | Year: 2011

In central West Greenland, Palaeogene volcanic sequences deposited during post-rift subsidence are exposed in mountains reaching 2 km above sea level (a.s.l.), with Palaeocene marine deposits within this section at elevations up to 1.2 km a.s.l. This clearly shows that present-day elevated topography of the West Greenland margin is not a remnant of the rifting process but developed later. Integrating such geological constraints with landscape analysis and thermochronological data shows that mountain summits in central West Greenland represent an Oligocene-Miocene peneplain, which is the counterpart of a correlative unconformity offshore separating Eocene from Middle Miocene sedimentary units. Onshore the peneplain has been exhumed, uplifted to its present altitude and progressively dissected since the Late Miocene. Redfield (Journal of the Geological Society, London, 167, 261-271, 2010) questioned numerous aspects of this interpretation, suggesting that 'the AFT model-based hypothesis that [the elevated topography of West Greenland] was constructed in purely Neogene time remains an unproven speculation'. But as we illustrate here, evidence for Neogene uplift is provided by landscape analysis and geological evidence, as well as thermochronology, and integration of these independent lines of investigation provides a consistent synthesis that we regard as highly reliable. The resulting history of episodic burial and exhumation cannot be simply dismissed, and poses a major challenge to accepted tectonic and geomorphological models for the development of rifted continental margins: how do mountains form along passive continental margins millions of years after rifting and breakup?. © The Geological Society of London. Source

Japsen P.,Geological Survey of Denmark | Bonow J.M.,Geological Survey of Denmark | Green P.F.,Geotrack International | Cobbold P.R.,French National Center for Scientific Research | And 4 more authors.
Bulletin of the Geological Society of America | Year: 2012

It is a common assumption that elevated passive continental margins have remained high since rifting and breakup. Here, we show that the Atlantic margin of NE Brazil has under gone a more complex history. Our synthesis of geological data, landscape analysis, and paleothermal and paleoburial data reveals a four-stage history: (1) After Early Cretaceous breakup, the margin under went burial beneath a thick sedimentary cover; (2) uplift episodes in the Campanian and Eocene led to almost complete removal of these deposits; (3) the resulting large-scale, low-relief erosion surface (peneplain) was deeply weathered and finally reburied at the Oligocene-Miocene transition; and (4) Miocene uplift and erosion produced a new, lowerlevel peneplain by incision of the uplifted and re-exposed Paleogene peneplain. Previous studies have identified aspects of this interpretation, but we have defined the absolute timing and magnitude of discrete events of burial and exhumation that followed Early Cretaceous rifting and Eocene-Oligocene peneplanation. We suggest that a late sedimentary cover protected Paleogene weathering profiles until the present day. The uplift phases in Brazil are synchronous with uplift phases in Africa and the Andes. The Andean phases coincided with rapid convergence on the western margin of South America, and the Campanian uplift coincided with a decline in spreading rate at the Mid-Atlantic Ridge. Consequently, we suggest that both vertical movements and lateral changes in the motion of the plates have a common cause, which is lateral resistance to plate motion. © 2012 Geological Society of America. Source

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