The alkaline rocks of the Motzfeldt Centre; progress report on the 1984 field season

C Bradshaw

doi:10.34194/rapggu.v125.7893

Abstract

The detailed mapping programme in the Motzfeldt Centre that commenced in 1982 with the Syduran project (Armour-Brown et al., 1983) continued in collaboration with the GGU Pyrochlore project in 1984 (Tukiainen, this report). The resuIts obtained during the 1982 field season enabled the various syenite units of the centre to be grouped (from older to younger) into Geologfjeld (GF), Motzfeldt Sø (MSF) and Flinks Dal (FDF) Formations (Tukiainen et al., 1984). The purpose of the work in 1984 was to study the structure and spatial distribution of the rock formations in the lesser known western and southern parts of the Motzfeldt Centre. The revised map is shown in Tukiainen (this report) and some of the more important observations are outlined below.

Highlights

The detailed mapping programme in the Motzfeldt Centre that commenced in 1982 with the Syduran project (Armour-Brown et al, 1983) continued in collaboration with the GGU Pyrochlore project in 1984 (Tukiainen, this report)
No clear cross-cutting relations were found, but the Geologfjeld Formation grades rapidly downwards from a white, coarse, homogeneous nepheline-free syenite into pink-brown feldspar-Iaminated syenite with conspicuous nepheline
The MSF/GF contact is well exposed in places and is found to be sharp with several pegmatitic apophyses extending into the Geologfjeld syenite

Summary

Colin Bradshaw

The detailed mapping programme in the Motzfeldt Centre that commenced in 1982 with the Syduran project (Armour-Brown et al, 1983) continued in collaboration with the GGU Pyrochlore project in 1984 (Tukiainen, this report). The resuIts obtained during the 1982 field season enabled the various syenite units of the centre to be grouped (from older to younger) into Geologfjeld (GF), Motzfeldt Sø (MSF) and Flinks Dal (FDF) Formations (Tukiainen et al, 1984). The purpose of the work in 1984 was to study the structure and spatial distribution of the rock formations in the lesser known western and southern parts of the Motzfeldt Centre. The revised map is shown in Tukiainen (this report) and some of the more important observations are outlined below

The boundary between the Geologfjeld and Motzfeldt Sø Formations

Motzfeldt Sø Formation

Lotte Melchior Larsen and Tapani Tokiainen

New observations