Monteregian Hills I. Petrography, Major and Trace Element Geochemistry, and Strontium Isotopic Chemistry of The Western Intrusions: Mounts Royal, St. Bruno, and Johnson

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Abstract
Predominantly silica-oversaturated tholeiitic basalts spread widely across the northern East Greenland continental margin (73–76° N) at the onset of Tertiary magmatism. These have been studied in two of the principal outcrop areas: Hold with Hope and Wollaston Forland. In Hold with Hope very minor eruption of nephelinitic magma preceded the tholeiitic phase. The early tholeiites of northern East Greenland tend to be more siliceous and aluminous and less iron and titanium rich than their more voluminous counterparts in the main East Greenland province south of 70° N. Some, notably those of Wollaston Forland, approach ‘enriched MORB’ compositions. The early flood basalts (distinguished in the Hold with Hope region as the Lower Plateau Lava Series, LPLS) show limited compositional range. Such variation as is shown is attributed to low-pressure plagioclase—olivine—augite fractionation. Intrusion of quartz dolerite sills within and beneath the LPLS may have constituted a separate but closely allied magmatic event. The sills are slightly more enriched in incompatible elements, have higher initial Sr isotopic ratios and show more pronounced Fe-enrichment trends.

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