Geochemistry of the Late Mesoproterozoic Mount Eve Granite Suite: Implications for Late to Post-Ottawan Tectonics in the New Jersey-Hudson Highlands

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The Mount Eve granite suite is a postorogenic, A-type granitoid suite that consists of several small plutonic bodies occurring in the northwestern New Jersey-Hudson Highlands. Mount Eve granite suite rocks are equigranular, medium- to coarsegrained, quartz monzonite to granite, consisting of quartz, microperthite, and oligoclase, with minor hornblende, biotite, and accessory zircon, apatite, titanite, magnetite, and ilmenomagnetite. Whole-rock analyses indicate that Mount Eve granite is metaluminous to slightly peraluminous (ASI or aluminum saturation index, A/CNK or Al 2 O 3 /(CaO + Na 2 O + K 2 O) = 0.62 to 1.12) and has A-type compositional affinity defined by high K 2 O/Na 2 O (1.4 to 2.8), Ba/Sr (3 to 12), FeO t /(FeO t +MgO) (0.77 to 0.87), Ba (400 to 3000 ppm), Zr (200 to 1000 ppm), Y (30 to 130 ppm), Ta (2.5 to 6 ppm), total rare earth elements or REE (300 to 1000 ppm), low MgO (<1 wt%), Cr and Ni (both <5 ppm); and relatively low Sr (200 to 700 ppm). Variably negative Eu anomalies (Eu/Eu * = 0.13 to 0.72, where Eu/Eu * is the chondrite-normalized ratio of measured Eu divided by the hypothetical Eu concentration required to produce REE pattern with no Eu anomaly) and systematic decreases in Sr, Ba, Zr, Hf, Nb, and Ta, with constant total REE content and increasing Ce/Yb and SiO 2 contents, suggest crystallization of feldspars + zircon + titanite ± apatite. Possible modes of origin include dry melting of charnockitic gneisses or Fe-rich mafic to intermediate diorites within the Mesoproterozoic basement. Two possible tectonic mechanisms for generation of Mount Eve granite include (1) residual thermal input from a major lithospheric delamination event during or immediately after peak Ottawan orogenesis (1090-1030 Ma) or (2) broad orogenic relaxation between peak Ottawan and a late (1020-1000 Ma) high-grade, right-lateral transpressional event.



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