Abstract

A tertiary, alkaline, igneous complex occurs in eastern Greenland near the Atlantic coast at approximately 72 degrees N. latitude. The magma intruded a sequence of flat-lying, unmetamorphosed, arenaceous sediments ranging from Carboniferous to late Cretaceous in age. Thermal, metasomatic, and mechanical contact effects are very small. Igneous rock types range from pyroxenite and peridotite through gabbro and monzonite to calc-alkali syenite, alkali syenite, nepheline syenite, and alkali granite. The basic types show with titanaugite, titaniferous hornblende, Ti-rich biotite, and plagioclase as major constituents, and with residual alkali feldspar a clearly essexitic character. Age sequence from basic to acid types is well proved by inclusions and apophyses. Both intrusions of separate, distinct magmas as well as differentiation in situ took place. The general trend of the Niggli-values in the variation diagram and the development along the MF line in a QLM triangle (atlantic differentiation) correspond well with the genetic sequence. Various kinds of volcanic and subvolcanic breccias are genetically and spatially related to the intrusives (mainly to the syenites) and prove the hypabyssal, shallow character of the latter. Leucocratic dikes of mainly syenitic composition are considered to be comagmatic derivatives of the acid intrusions. Basic dikes and sills are extremely numerous and comprise both alkali basalts and lamprophyres, yet it is not possible to evaluate to what extent they may be related to the local alkaline intrusions or to the regional Greenlandic (Brito-Arctic) basalt cycle. Pneumatolytic-hydrothermal alteration of both intrusive and sedimentary rocks, and deposition of disseminated sulfides and oxides are conspicuous throughout the whole complex. Economic deposits of molybdenite and wolframite of this phase are associated with the granite in the western part of the complex, while galena and sphalerite-rich quartz veins were found N. and S. of it. The results of spectrochemical trace element study in minerals and rocks from the western part of the complex are discussed in detail. Facts which are true for both the Greenland and the Monteregian igneous complex and which prove their close relation are: alkaline character (essexite-syenite), mineralogical paragenesis, trend of differentiation, age sequence, comagmatic dike-swarms, formation of volcanic and subvolcanic breccia, near-surface intrusion level, small thermal, metasomatic, and mechanical effect against the wall-rock, and atectonic emplacement.

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