Geology of the Kiglapait layered intrusion, coast of Labrador, Canada.

• Main Author: Morse, Stearns A. (Stearns Anthony), 1931-
• Format: Others
• Language: en
• Published: McGill University 1961
• Subjects: Geology.
• Online Access: http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=43594

A Precambrian layered gabbroic intrusion about 560 km('2) in area, of the Skaergaard type, crops out on the middle north coast of Labrador. Border zones and a Layered series are recognized, === and have the following characteristics and approximate mean thicknesses: (UNFORMATTED TABLE FOLLOWS) === Upper Border zone: grey gabbro 400 m === Upper zone d: larvikite 385 m === Upper zone a, b, c: olivine gabbro 1800 m === Lower zone troctolite 4500 m === Inner Border zone b: massive gabbro 180 m === Outer Border zone a: banded gabbro 485 m(TABLE ENDS) === The intrusion displays extreme fractionation resulting in larvikite consisting of mesoperthite, fayalite, ferroaugite, and ore as the uppermost differentiate. Mineral variation and differentiation are described by means of quantitative mineralogy. Plagioclase varies from An 78 to An 2, olivine from Fo 82 to Fo 7, and clinopyroxene from Ca(,45)Mg(,43)Fe(,12) to Ca(,46)Mg(,8)Fe(,46) toward the top of the intrusion. A study of plagioclase structural state shows this mineral to be partly and variably disordered. A pyroxene trend line and pyroxene-olivine tie lines are presented, and the pyroxene solvus is discussed. Local mineral variation is discussed in the light of cumulate solidification processes. === From modal and mineral analyses, the composition of the parent magma is estimated to have been alkali-basalt. The intrusion is unique for its type in having no free quartz in any rock. The compo- sitions of successive liquids are estimated, and variation diagrams are presented. The course of crystallization related to known and deduced phase equilibria is discussed, and layers of massive oxide ore are treated in the light of oxygen partial pressure variation. === Older migmatites and metasediments are described in Part I, along with younger intermediate and granitic intrusives. Two K-A dates for the younger rocks are reported. An appendix deals with refined mineralogical techniques and their precision.