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| Titel |
Construction and differentiation of the ferroan (A-type) Sveconorwegian (=Grenvillian) Kleivan intrusion |
| VerfasserIn |
J. Vander Auwera, O. Bolle, J.-P. Liegeois, J. Schittekat, B. Charlier |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060265
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| Zusammenfassung |
| It was recognized that two important boundaries, the Farsund-RAP shear zone and the
Sveconorwegian (=Grenvillian) opx-in isograd, controlled the composition of the
post-collisional magmatism of southern Norway (0.97 to 0.92 Ga) (Vander Auwera et al.,
2011). The Farsund-RAP shear zone (Bolle et al., 2010), a boundary between two contrasted
lithothectonic units, separates magmatic bodies with different isotopic compositions mainly
due to different contaminants. During the regional metamorphism (1.035 to 0.97 Ga: i.e.
Bingen et al., 2005), southern Norway lower crustal segments were variably modified, with
granulite facies conditions prevailing in the westernmost part of the orogen and producing
dehydrated lower crustal sources west of the opx-in isograd, and more hydrated
sources east of this isograd. The small Kleivan intrusion (- 20 km2, 930 ± 7 Ma,
Rb-Sr; Pedersen & Falkum, 1975), located in the eastern hydrated part of the orogen,
confirms these interpretations. This pluton contains two different trends. The main
trend displays, from North to South and with increasing SiO2, a gradual variation
from opx-bearing charnockites to amphibole-bearing and finally biotite-bearing
granites (Petersen, 1980), in which titanite is absent. In the subsidiary Hbl+Tit trend,
titanite is present, opx is absent and amphibole is the dominant ferromagnesian.
The main trend has a significantly higher Fe# than the Hbl+Tit trend, echoed by
higher Fe# in amphiboles and accompanied by a larger range in SiO2 (63.9 to 77%
in the main trend; 63.5 to 68.9% in the Hbl+Tit trend). Both trends are ferroan
and have overlapping compositions for trace and other major elements. The bulk
magnetic susceptibility (Km) is higher in the Hbl+Tit trend, reflecting its higher
magnetite/ilmenite ratio. The two trends have similar initial Sr, Nd and Pb isotopic
compositions indicating contamination by the eastern crustal contaminant only, in agreement
with the emplacement of the Kleivan intrusion east of the Farsund-RAP shear zone.
Experimental data (Bogaerts et al., 2006) indicate a lower H2O content (5.5 wt%
H2O). In addition, higher magnetite/ilmenite ratio and titanite occurrence within
the Hbl+Tit trend agree with a higher fO2. The presence of two trends differing
by their H2O content and fO2 is here related to straddling of the opx-in isograd
(Sveconorwegian metamorphism) by the Kleivan intrusion (Vander Auwera et al.,
2011).
It is also worth noting that, despite similar rheologies (similar major elements
composition and temperature), the two trends did not mix, preserving their characteristics
towards their level of emplacement (3.5 to 5 kbar) through differentiation and upward
migration from the lower crust. |
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