Structure of the Jotun Nappe Complex, Southern Norwegian Caledonides: Ambiquity of Gravity Modelling and Reinterpretation.
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Gravity studies have previously indicated a deep root zone (16 kmthick) below the outcropping pyroxene-granulites of the Jotun Nappe Complex in Norway. Combined interpretation of gravity and aeromagnetic data give re- sults that contradict these earlier gravity interpretations. The Jotun Nappe Complex is inferred to be less than 6 km thick at the deepests part, and the thickness changes abruptly across the Lærdal-Gjende fault which is clearly reflected in the magnetic and gravity maps. The Lærdal-Gjende fault penetra- tes at least down to the maximum depth of the Jotun Nappe Complex and con- tinuous further to the east than previously recognized. The astonishingly close correlation between surface geology and gravity and magnetic maps provide constraints on the gravity modelling. These constraints, in combination with new petrophysical data and an alternative regional- residual gravity separation, lead to a new geophysical model in agreement with the hypothesis that the Jotun Nappe was transported over a considerable distance from the northwest onto the Baltic shield. The emplacement of the dens Jotun rocks onto the Precambrian crust must have caused gravitational instability and regional isostatic adjustments associated with vertical tectonics. Gravitational subsidence provided a mechanism to preserve the thickest part of the massif in a depression or .....etc........