COMPARISON OF NEOPROTEROZOIC AND MESOZOIC DIKES IN THE EASTERN ADIRONDACK MOUNTAINS

Numerous vertical and subvertical mafic dikes cut the 1.1-1.3 Ga metamorphic basement rocks and the early Paleozoic sedimentary cover in the eastern Adirondack Mountains. The Neoproterozoic diabase dikes that intrude the metamorphic basement are believed to have formed in the Neoproterozoic when Rodinia broke apart to form the Iapetus Ocean. The 140 Ma lamprophyre dikes that intrude the Paleozoic sediments could represent early onset of magmatism associated with the 124 Ma Monteregian Hills intrusions. Here we present new major and trace element analyses of eastern Adirondack lamprophyre and diabase dikes. We compare the lamprophyres intruding the metamorphic basement of the High Peaks region to those of cutting Paleozoic sediments. Trace element ratios suggest that they are derived from a similar, geochemically-enriched mantle source. Also explored in this presentation is the petrogenetic relationships of the 640 Ma Rand Hill and Dannemora dike swarms. The existence of range of differentiated magmas in these swarms suggest the existence of magma chambers during the Neoproterozoic while the high MgO lamprophyres suggest a lack of differentiation and magma storage during Mesozoic magmatism.