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New U-Pb sensitive high-resolution ion microprobe (SHRIMP) ages from zircon and monazite document a 350 m.y. geologic evolution for the New Jersey Highlands. Two pulses of calc-alkaline magmatism that include the Wanaque tonalitic gneiss (1366 ± 9 Ma and 1363 ± 17 Ma) and Losee Suite tonalitic gneiss (1282 ± 7 Ma), dacitic gneiss (1254 ± 5 Ma), and dioritic gneiss (1248 ± 12 Ma) represent the southern continuation of eastern Laurentian margin arc activity.

Supracrustal paragneisses, marble, and cogenetic metavolcanic rocks were deposited in a backarc basin inboard of the Losee arc. Ages of 1299 ± 8 Ma to 1240 ± 17 Ma for rhyolitic gneisses provide lower and upper limits, respectively, for the age of the supracrustal succession. Inherited cores in zircon grains from supracrustal rhyolitic gneiss and from Losee Suite rocks yield overlapping ages of 1.39–1.30 Ga and indicate proximity to an older arc source temporally equivalent to the Wanaque tonalitic gneiss. Location of the backarc inboard of the Losee arc implies a northwest-dipping subduction zone at this time beneath the eastern Laurentian margin.

A-type granite magmatism of the Byram and Lake Hopatcong intrusive suites at 1188 ± 6 Ma to 1182 ± 11 Ma followed termination of arc and backarc magmatism and documents a change to decompression melting of delaminated lithospheric mantle by upwelling asthenospheric mantle. Waning stages of A-type granite magmatism include clinopyroxene granite (1027 ± 6 Ma) and postorogenic Mount Eve Granite (1019 ± 4 Ma).

Overgrowths on zircon and monazite give ages of 1045–1024 Ma, fixing the timing of granulite-facies metamorphism in the New Jersey Highlands; other overgrowth ages of 996–989 Ma reflect the thermal effects of postorogenic felsic magmatism and hydrothermal activity associated with regional U–Th–rare earth element (REE) mineralization.

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