Abstract

The Newark Island layered intrusion (NILI), located in the Nain anorthosite complex of Labrador, developed through a complex sequence of fractional crystallization, periodic replenishment of both basic and silicic magmas, and magma mixing. It is subdivided into a lower layered series and an upper hybrid series. Three large transgressive trough structures cut these cumulate rocks at different levels. Each trough is lined by granitic rocks and filled mainly by chilled mafic pillows that grade inward to massive olivine gabbro. Each of these troughs originated as a large feeder dike of granitic magma into the NILI chamber when it was floored by basic magma. This resident basic magma collapsed downward into the granitic feeder and formed chilled pillows. These pillows preserve the compositions of basic magma existing in the chamber at the time of granite replenishment. Pillows in the lowest trough show a wide compositional range and provide a direct record of compositional stratification of a magma chamber related to a layered intrusion.

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