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- Green, P. F., et al.
(författare)
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Stratigraphic landscape analysis, thermochronology and the episodic development of elevated, passive continental margins
- 2013
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Ingår i: Geological Survey of Denmark and Greenland Bulletin. - : Geological Survey of Denmark and Greenland. - 1811-4598 .- 1604-8156 .- 1904-4666. ; :30, s. 4-150
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Tidskriftsartikel (refereegranskat)abstract
- The continental margin of West Greenland is similar in many respects to other elevated, passive continental margins (EPCMs) around the world. These margins are characterised by extensive regions of low relief at elevations of 1-2 kilometres above sea level sloping gently inland, with a much steeper, oceanward decline, often termed a 'Great Escarpment', terminating at a coastal plain. Recent studies, based on integration of geological, geomorphological and thermochronological evidence, have shown that the high topography of West Greenland was formed by differential uplift and dissection of an Oligo-Miocene peneplain since the late Miocene, many millions of years after continental break-up between Greenland and North America. In contrast, many studies of other EPCMs have proposed a different style of development in which the high plateaux and the steep, oceanward decline are regarded as a direct result of rifting and continental separation. Some studies assume that the elevated regions have remained high since break-up, with the high topography continuously renewed by isostasy. Others identify the elevated plains as remnants of pre-rift landscapes. Key to understanding the development of the West Greenland margin is a new approach to the study of landforms, stratigraphic landscape analysis, in which the low-relief, high-elevation plateaux at EPCMs are interpreted as uplifted peneplains: low-relief surfaces of large extent, cutting across bedrock of different age and resistance, and originally graded to sea level. Identification of different generations of peneplain (re-exposed and epigene) from regional mapping, combined with geological constraints and thermochronology, allows definition of the evolution leading to the formation of the modern-day topography. This approach is founded particularly on results from the South Swedish Dome, which document former sea levels as base levels for the formation of peneplains. These results support the view that peneplains grade towards base level, and that in the absence of other options (e.g. widespread resistant lithologies), the most likely base level is sea level. This is particularly so at continental margins due to their proximity to the adjacent ocean. Studies in which EPCMs are interpreted as related to rifting or break-up commonly favour histories involving continuous denudation of margins following rifting, and interpretation of thermochronology data in terms of monotonic cooling histories. However, in several regions, including southern Africa, south-east Australia and eastern Brazil, geological constraints demonstrate that such scenarios are inappropriate, and an episodic development involving post-breakup subsidence and burial followed later by uplift and denudation is more realistic. Such development is also indicated by the presence in sedimentary basins adjacent to many EPCMs of major erosional unconformities within the post-breakup sedimentary section which correlate with onshore denudation episodes. The nature of the processes responsible is not yet understood, but it seems likely that plate-scale forces are required in order to explain the regional extent of the effects involved. New geodynamic models are required to explain the episodic development of EPCMs, accommodating post-breakup subsidence and burial as well as subsequent uplift and denudation, long after break-up which created the characteristic, modern-day EPCM landscapes. © 2013 Pushpa Publishing House, Allahabad, India.
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| 2. |
- Japsen, P., et al.
(författare)
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From volcanic plains to glaciated peaks : BURIAL, uplift and exhumation history of southern East Greenland after opening of the NE Atlantic
- 2014
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 116, s. 91-114
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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