252 D14. Recent Advances in Mineralogy and Petrology

Wednesday, 18 October 2023
1:30 PM - 5:30 PM
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A COMPLETE SECTION THROUGH THE CENTRAL PART OF THE DIFFERENTIATED PALISADES INTRUSION HAS BEEN SAMPLED AT A DEPTH OF 1527-2006 M IN SE NEW YORK: EVIDENCE FOR MAGMA CHAMBER CONVECTION AND INTERSTITIAL MELT MIGRATION

Paper number: 252-10
Program: Technical Sessions
Time: 3:35 PM – 3:50 PM

Authors

Abstract

Surface outcrops and geophysical data indicate that the Palisades intrusion in the Newark Basin extends for >12 kms E-W and >80 kms N-S with an overall saucer shape; thicker and deeper in the center; thinner and shallower on the edges. Although previously described as a sill, the intrusion cuts across the local stratigraphy giving the intrusion more of a lopolith shape. A ~480 m section through the intrusion was sampled at depth by rotary drilling in Nanuet, NY. Washed chip samples have been analyzed by ICP-OES & ICP-MS techniques: 155 samples from the intrusion and 12 samples from the country rock above and below. In the sampled section the intrusion is strongly differentiated with a V-shaped Mg# (100*Mg/[Mg+Fe]) profile, with maximum values of 60-63 near the upper and lower contacts, and minimum values of 23-24 in a sandwich zone (SZ) ~350-400 m above the base, indicating a well-defined floor sequence (FS ~80%) and roof sequence (RS ~20%). Bulk samples show an increase in K, P, Rb, Y, Nb, Hf, U, Th, & the REEs and a decrease in Mg, Ca, Cr, & Ni upward from the base to the SZ, with reverse trends in these elements from the upper contact downward to the SZ. Enrichments in excluded elements indicate that the SZ represents >50% fractionation of the bulk magma. High concentrations of Mg, Ca, & Cr near the upper and lower contacts indicates augite was the dominant early fractionating phase in both the roof and floor sequences. Al increases upward in the FS, but decreases downward in the RS indicating plagioclase was removed from the upper part of the magma chamber and concentrated in the lower part. Maximum concentrations of Ti, Fe, V, Co, & Sc occur at 250-300 m above the base in the FS where magnetite becomes a cumulus phase. Strong depletion of V above the magnetite zone indicates that depleted interstitial melt is migrating upward from the FS into the SZ. High excluded trace element concentrations in some samples above the SZ suggest that evolved liquids have migrated upward into the RS. Previous studies from outcrops in Fort Lee, NJ, on the eastern edge of the intrusion, indicate that there was a magma recharge event 48 m above the base in the ~285 m thick Fort Lee section. The drill hole section correlates well with the Fort Lee section above the 48 m horizon, suggesting that the recharge event at this level expanded the intrusion northwestward into the Newark Basin.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-394049

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