Publication Date:
2014-10-27
Description:
A concordant body of presumably igneous, but deformed and at least partly recrystallized rocks, the Lac-Croche Plutonic Complex, consists of leuconoritic and mangeritic gneisses, and of monzonitic and granitic rocks. It is surrounded by gneisses, at least partly of sedimentary origin. Inclusions of the surrounding gneisses occur in the Complex. From the similarity in orientation of lineations in the Complex and surrounding gneisses, and of fold axes further away from the Complex, it is concluded that all rocks were deformed together, at least once. The study of the pre-tectonic history of the rocks is hampered by the strong overprint of regional metamorphism.
From a number of conceivable sequences of events, the two simplest are chosen: either the Complex was part of the basement on which sediments (now paragneisses) were deposited, or the parent magma of the Complex intruded the paragneisses. Most field evidence (mainly structural) fits either sequence, but the absence of folds formed by groups of inclusions, docs not fit the basement hypothesis. It is concluded that the Lac-Croche Plutonic Complex is younger than the “Grenville“ paragneisses and intrusive into them.
Repository Name:
National Museum of Natural History, Netherlands
Type:
Article / Letter to the editor
Format:
application/pdf
