Geochemistry of lewisian fe diorites north of laxford front (nw scotland): tectonic implications
Abstract
The geochemical signatures of diorites from the Northern Region of the mainland Lewisian Complex are the focus of this work. This type of rocks has not received special attention up to now. Also, we compare our results with those of similar lithologies from the Central and Southern regions. There are some differences bewteen the basic lithologies of the three regions. The Fe-diorites of the northern region show intrusive relationships with the tonalites (TTG) and are associated to granitic rocks. Also, from a geochemical point of view, the diorites show calc-alcaline and tholeiite affinities. In major elements geochemistry, the most significant difference with the basic lithologies of the other regions in the Lewisian is the SiO_2, and K_2O contents. The rocks of the Central Region have less SiO_2 and K_2O contents than the rocks of the Northern and Southern regions. On the other hand, the Fe-diorites of the Northern Region are slightly enriched in alkalis. The most important difference between basic lithologies of the Lewisian Complex is an increase of LREE contents from south to north. There are models to explain the origin of the mainland Lewisian Complex. According to a group of them, this domain was part of a single crustal block during the Archaean and it was reworked in the Proterozoic (Sutton &Watson, 1951). On the contrary, Kinny &Friend (1997) established a different origin for the regions of the mainland Lewisian complex, such that they consider each region as a different crustal block. This model best explain the differences studied in our work. Sutton, J. &Watson, J. 1951. The pre-Torridonian metamorphic history of the Loch Torridon and Scourie areas in the North-West Highlands and its bearing on the chronological classification of the Lewisian. Journal of the Geological Society, London 106, 241-296. Kinny, P.D. &Friend, C.R.L. 1997. U-Pb isotopic evidence for the accretion of different crustal blocks to form the Lewisian Complex of northwest Scotland. Contributions to Mineralogy and Petrology, 129, 326-340.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....7345L