Magmatism in the southern Grenville Province records a collisional and postcollisional history during the period 1.20–1.15 Ga in the Adirondack Lowlands (New York State, USA) and the Frontenac terrane (Ontario, Canada). The 1.20 Ga bimodal Antwerp-Rossie suite of the Adirondack Lowlands was produced by subduction in the Trans-Adirondack backarc basin. This was followed by intrusion of the 1.18 Ga alkalic to calc-alkalic Hermon granite, which may have been generated by melting of metasomatized mantle during collision of the Adirondack Lowlands and Frontenac terrane during the Shawinigan orogeny. The Hyde School gneiss plutons intruded the Adirondack Lowlands at 1.17 Ga, and Rockport granite intruded into the Adirondack Lowlands and Frontenac terrane, stitching the Black Lake shear zone, which marks the boundary between these terranes. Subsequent extensional collapse and lithospheric delamination caused voluminous anorthosite-mangerite-charnockite-granite plutonism. In the Frontenac terrane, this event is represented by the 1.18–1.15 Ga Frontenac suite, which is composed predominately of ferroan granitoids produced from melting of the lower crust by underplating mafic magmas. The Edwardsville, Honey Hill, and Beaver Creek plutons are newly recognized members of this suite in the Adirondack Lowlands. High oxygen isotope ratios of this suite in the central Frontenac terrane and western Adirondack Lowlands point to the presence of underthrust altered oceanic rocks in the lower crust. Oxygen isotopes of the Frontenac suite in both terranes preclude its derivation from mantle melts alone.

Monazite crystals, intergrown with allanite, fluorapatite, and quartz from the Cheever Mine iron oxide-apatite (IOA-type) deposit in Essex County, New York, USA, display rare symplectite textures. Electron probe wavelength-dispersive spectrometry (WDS) mapping and major and trace element characterization of these features reveal a natural experiment in fluid-mediated monazite recrystallization. Two types of monazite with symplectite intergrowths have been recognized (Type I and II). Both types of symplectite development are associated with a decrease in HREE, Si, Ca, Th, and Y, but an increase in both La and Ce in monazite. Electron microprobe Th-U-total Pb analysis of Type I monazite with suitable ThO₂ concentrations yielded a weighted mean age of 980 ± 5.8 Ma (MSWD: 3.3), which is interpreted as the age of monazite formation and the onset of symplectite development. Both types of monazite formed during a series of reactions from fluorapatite, and possibly britholite, to produce the final assemblage of monazite, allanite, and fluorapatite. Monazite formation was likely a response to evolving fluid conditions, which favored monazite stability over fluorapatite at ca. 980 Ma, possibly a NaCl brine. A subsequent transition to a Ca-dominated fluid may have then promoted the consumption of monazite to produce another generation of allanite and fluorapatite. Our results indicate that recrystallized monazite formed during fluid-mediated processes that, over time, trended towards an increasingly pure end-member composition. Regionally, these data are consistent with a magmatic-origin followed by fluid-mediated remobilization of select phases at subsolidus conditions for the Adirondack IOA deposits.

Columbite crystals from niobium-yttrium-fluorine (NYF) pegmatites lacking zircon or containing metamict cyrtolite were analyzed for major and minor elements (Electron Microprobe (EMP)), trace elements (Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)), and U-Pb geochronology (Laser AblationMulti-Collector-Inductively Coupled Plasma-Mass Spectrometry (LA-MC-ICP-MS)). All four pegmatite localities sampled are hosted by the Proterozoic Fordham gneiss and/or Paleozoic Bedford gneiss (Columbite-(Fe); Kinkel and Baylis localities) and the Manhattan Schist of Lower Paleozoic age (Columbite-(Mn); Fort George and Harlem River Drive localities) and yield Neoacadian ages. The weighted average U-Pb ages are 372.2 ± 8.2 Ma (Baylis Quarry), 371.3 ± 7.3 and 383.4 ± 8.9 Ma (Kinkel Quarry); 383 ± 15 Ma (185th St. and Harlem River Drive); and 372 ± 10 Ma (Fort George). A partial metamict zircon (“cyrtolite”) from the Kinkel Quarry yielded a weighted average U-Pb age of 376.9 ± 4.3 Ma. The Neoacadian ages obtained agree with those determined by thermal ionization mass spectrometry (TIMS) for zircon from Lithium-Cesium-Tantalum (LCT) pegmatites from Connecticut and Maine. No pegmatites temporally associated with the Taconic orogeny were found. The size, lack of common Pb, uniform U concentrations across crystal cross-sections, sufficient but moderate uranium concentrations, lack of metamictization, and consistency in U-Pb isotopic ratios for columbite samples BCB-COL, NYSM #25232, and NYSM #525.8 suggests they show promise as potential standards for oxide mineral LA-MC-ICP-MS geochronological analyses, however, additional characterization using ID-TIMS would be necessary to develop as such.

(2018). The Rose Road Localities, Town of Pitcairn, St. Lawrence County, New York: Part 1—History. Rocks & Minerals: Vol. 93, No. 5, pp. 442-453.

(2019). Rose Road Localities: Town of Pitcairn, St. Lawrence County, New York Part 2—Geology. Rocks & Minerals: Vol. 94, No. 6, pp. 540-554.