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The mesozoic to cenozoic thermal history of south Norway as revealed by apatite fission track analysis (AFTA) and thermal modelling studies
ABSTRACTS M i o c e n e extension in the Betic Cordillera, SE S p a i n : Constraints from Fission Track Analysis.
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Kit Johnson, London Fission Track Research G r o u p , Birkbeck College, G o w e r St., London WCIE 6BT. The Betic Cordillera lies along the southern margin of the Iberian peninsular. Its northerly External Domain is an u n m e t a m o r p h o s e d fold and thrust belt consisting of Mesozoic and Tertiary sediments that were deformed during the late Oligocene - early Miocene. The southerly Internal Domain is a largely m e t a m o r p h o s e d sequence of Palaeozoic and Triassic sediments that n o w form a stack of different n a p p e complexes. In the Internal D o m a i n , rocks that were m e t a m o r p h o s e d at pressures corresponding to a crustal depth of -37kin are n o w within 6 k m structural thickness of o v e r l y i n g u n m e t a m o r p h o s e d rocks. This observation suggests that excision of crust by extensional tectonics has occurred along n a p p e contacts that had previously been interpreted as being entirely the result of compressional stacking. Apatite and zircon fission track analysis has been used to constrain the thermal history of samples taken from the different complexes in an a t t e m p t to establish the presence, extent, and timing of extensional tectonics within the Internal d o m a i n since the late Oligocene. Results f r o m three north-south transects indicate that rapid tectonic denudation and exhumation of the lowermost n a p p e complex occurred toward the end of the Serrevalian-beginning of the Tortonian (12-9 Ma BI') as evidenced by concordant ages and m e a n track lengths >14[Jm (apatite) and > l l l a m (zircon). The overlying complex has a more protracted low t e m p e r a t u r e cooling history with zircons and apatites yielding ages of -19Ma and ~14Ma respectively together with l o w e r mean track lengths of <1411m (apatite) and <101am (zircon).
THE MESOZOIC TO CENOZOIC THERMAL HISTORY OF SOUTH NORWAY AS REVEALED BY APATITE FISSION TRACK ANALYSIS (AFTA) AND THERMAL MODELLING STUDIES. M. Rohrman, P.A. van der Beek & P.A.M. Andriessen Vrije Universiteit, Institute of Earth Sciences, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands Southern Norway is part of the Fennoscandian shield, and consists of high-grade Precambrian rocks. The area is bound in the Northwest by Caledonian nappe-tectonics and in the East by the Permian Oslo rift. The last being one of the most recent visible geological event known onland, apart from some minor Jurassic dykes in the West. The history of the more recent evolution of Southern Norway has remained badly constrained throughout the years. Most of the present-day information comes from the surrounding sedimentary basins, which show complicated histories as evidenced by diverse rifting events (i.e. Norwegian-Greenlandsea, North sea), inversion tectonics and magmatism.
AF'rA can possibly fill the gap between the evolution of Southern Norway and its surrounding basins. This information can be important for the influence of this hinterland on the basins and hydrocarbon maturation. Preliminary results show decreasing ages from 240 Ma in the South to 160 Ma in the North. Length distributions provide evidence for a mixed-age interpretatior, of most of these ages. To gain more information, modelled thermal histories were calculated. The
first modelling results suggest a rapid cooling phase in the Tertiary for the Southernmost samples. This work forms part of ongoing research in Norway, its Atlantic margin and future work in the surrounding basins.
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Kit Johnson, London Fission Track Research G r o u p , Birkbeck College, G o w e r St., London WCIE 6BT. The Betic Cordillera lies along the southern margin of the Iberian peninsular. Its northerly External Domain is an u n m e t a m o r p h o s e d fold and thrust belt consisting of Mesozoic and Tertiary sediments that were deformed during the late Oligocene - early Miocene. The southerly Internal Domain is a largely m e t a m o r p h o s e d sequence of Palaeozoic and Triassic sediments that n o w form a stack of different n a p p e complexes. In the Internal D o m a i n , rocks that were m e t a m o r p h o s e d at pressures corresponding to a crustal depth of -37kin are n o w within 6 k m structural thickness of o v e r l y i n g u n m e t a m o r p h o s e d rocks. This observation suggests that excision of crust by extensional tectonics has occurred along n a p p e contacts that had previously been interpreted as being entirely the result of compressional stacking. Apatite and zircon fission track analysis has been used to constrain the thermal history of samples taken from the different complexes in an a t t e m p t to establish the presence, extent, and timing of extensional tectonics within the Internal d o m a i n since the late Oligocene. Results f r o m three north-south transects indicate that rapid tectonic denudation and exhumation of the lowermost n a p p e complex occurred toward the end of the Serrevalian-beginning of the Tortonian (12-9 Ma BI') as evidenced by concordant ages and m e a n track lengths >14[Jm (apatite) and > l l l a m (zircon). The overlying complex has a more protracted low t e m p e r a t u r e cooling history with zircons and apatites yielding ages of -19Ma and ~14Ma respectively together with l o w e r mean track lengths of <1411m (apatite) and <101am (zircon).
THE MESOZOIC TO CENOZOIC THERMAL HISTORY OF SOUTH NORWAY AS REVEALED BY APATITE FISSION TRACK ANALYSIS (AFTA) AND THERMAL MODELLING STUDIES. M. Rohrman, P.A. van der Beek & P.A.M. Andriessen Vrije Universiteit, Institute of Earth Sciences, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands Southern Norway is part of the Fennoscandian shield, and consists of high-grade Precambrian rocks. The area is bound in the Northwest by Caledonian nappe-tectonics and in the East by the Permian Oslo rift. The last being one of the most recent visible geological event known onland, apart from some minor Jurassic dykes in the West. The history of the more recent evolution of Southern Norway has remained badly constrained throughout the years. Most of the present-day information comes from the surrounding sedimentary basins, which show complicated histories as evidenced by diverse rifting events (i.e. Norwegian-Greenlandsea, North sea), inversion tectonics and magmatism.
AF'rA can possibly fill the gap between the evolution of Southern Norway and its surrounding basins. This information can be important for the influence of this hinterland on the basins and hydrocarbon maturation. Preliminary results show decreasing ages from 240 Ma in the South to 160 Ma in the North. Length distributions provide evidence for a mixed-age interpretatior, of most of these ages. To gain more information, modelled thermal histories were calculated. The
first modelling results suggest a rapid cooling phase in the Tertiary for the Southernmost samples. This work forms part of ongoing research in Norway, its Atlantic margin and future work in the surrounding basins.
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