Abstract

Total-field magnetic and gravity data were collected between the northwestern tip of the earliest Jurassic age Palisades sill, near Mount Ivy, New York, and the Ladentown basalts, 1.3 km to the west, to determine if a subsurface connection exists between the two bodies. The magnetics measurements show a large, negative, total-field anomaly, suggesting that a subsurface body trends from the sill to the basalts. Gravity measurements also indicate that a dense subsurface body connects the flows and the sill. Two-dimensional magnetic modeling of the gravity and magnetic data suggest that the northern edge of a magnetic, dense slab cuts east-west across the field area. The base of the slab dips ∼ 10° to 15° to the south in the eastern part of the study area and is nearly horizontal in the western part. The existence of this connecting body suggests convincingly that the Ladentown basalts were formed by the eruption of Palisades magma onto the surface of the Newark Basin. The geometry of the body derived from the modeling may also indicate that the connecting body has been vertically offset 150 to 200 m from the Palisades sill to the east by a north-south-trending normal fault at the western tip of the Palisades sill. A fifth magnetics line trending east-west along the southern margin of the field area has a very small magnetic positive, suggesting that if an igneous connection exists between the Ladentown basalts and the New City Park magnetic anomaly, it is a minor feature.

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