Emplacement, petrology and geochemistry of ultrabasic to basic intrusives at Aillik Bay, Labrador

Hawkins, David W. (1976) Emplacement, petrology and geochemistry of ultrabasic to basic intrusives at Aillik Bay, Labrador. Masters thesis, Memorial University of Newfoundland.

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Abstract

Intrusive into the Archean Hopedale Complex and Proterozoic Aillik Group in the vicinity of Aillik Bay, Labrador, are a suite of Mesozoic basic to ultrabasic dykes exhibiting the compositions minette, monchiquite, kimberlite, micaceous kimberlite, alnöite and carbonatite. The dykes were emplaced along several well developed joint directions and exhibit a variety of emplacement and/or internal features which are interpreted to be the result of liquid immiscibility, flow differentiation, multiple intrusion, supercooling, carbonatitization and forceful injection. The monchiquites, kimberlites and carbonatites are usually banded and are gradational in composition along strike. -- The kimberlites are clinopyroxene-bearing and contain two generations of olivine and mica with perovskite, ilmenite, magnetite and apatite, as well as high concentrations of magmatic carbonate as an interstitial matrix phase or more rarely as ocelli. They also contain abundant glimmeritic nodules which form part of the Mica-Amphibole-Rutiile-Ilmenite-Diopside suite and are interpreted to be of cognate origin. The minettes and monchiquites are petrologically similar to other intrusions of these compositions and contain carbonate in the form of ocelli. -- Field, petrological and chemical data indicate that the monchiquites, kimberlites and carbonatites are genetically related and crystallized from a common parent. The minettes appear to be unrelated to the ultrabasic magmatism and were intruded prior to the above suite. -- The emplacement of the ultrabasic dykes is attributed to the initial separation of Greenland from North America during the formation of the Labrador Sea in the Mesozoic. The magma produced during this distension and rifting also gave rise to kimberlites and related rocks in Greenland.

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