02845nas a2200265 4500008004100000022001300041245012700054210006900181300001100250490000700261520199600268653002202264653001802286653001702304653002402321653002002345653002802365100001702393700002202410700002302432700001702455700001802472700001702490856007202507 2023 eng d a2666277900aAge and origin of the Cortlandt intrusive complex, New York State: A detailed look at the Stony Point and Rosetown plutons0 aAge and origin of the Cortlandt intrusive complex New York State a1000240 v103 a

The Cortlandt Complex is a classic alkaline intrusive complex exposed along the Hudson River in southeastern New York. Early work by James Dana in the 1880s set the stage for over 100 additional studies over the next century. Studies in the past few decades have focused on constraining the genetic relationships between phases of the intrusive complex and the timing of emplacement relative to peak metamorphism and deformation during the Taconic orogeny.

LA-MC-ICP-MS U/Pb zircon emplacement ages were obtained on five samples from the Cortlandt Complex. The five samples yielded dates ranging from 443 to 454 Ma, with an overall weighted mean emplacement age of 447.1 +/- 4.5 Ma. Three of the five samples contained inherited zircons, nearly all of Mesoproterozoic age. A sample of the adjacent Annsville Phyllite contained a diverse population of detrital zircons. The most common ages are between 1.25 and 1.85 Ga, although zircons of Neoarchean age are also present.

The westernmost and relatively small Rosetown and Stony Point plutons are lithologically and compositionally diverse. Major and trace element trends indicate a complex petrogenesis, which is supported by variable initial isotope ratios. The geochemical data indicate that the mafic magmas were derived primarily from an asthenospheric mantle source, while the inherited zircons and more radiogenic isotope ratios of the silicic units imply a significant crustal component was involved in their formation.

The timing and composition of intrusions in the Cortlandt Complex indicate that they are not the result of subduction related to the Taconic Orogeny. We suggest that the mafic units are the result of post-collisional, slab-failure induced asthenospheric upwelling, while the silicic units are primarily partial melts of Grenville-age, garnet amphibolites in the lower crust.

10aCortlandt Complex10ageochronology10aPetrogenesis10aRadiogenic isotopes10aTaconic Orogeny10aWhole-rock geochemistry1 aBailey, D.G.1 aLupulescu, M., V.1 aChiarenzelli, J.R.1 aConrey, R.M.1 aWuebber, J.W.1 aAnders, M.H. uhttps://www.sciencedirect.com/science/article/pii/S266627792300002301918nas a2200193 4500008004100000245009100041210006900132300001000201490000600211520132500217653002501542653001801567653001401585100002201599700002501621700001901646700001801665856004101683 2011 eng d00aUsing Pegmatite Geochronology to Constrain Temporal Events in the Adirondack Mountains0 aUsing Pegmatite Geochronology to Constrain Temporal Events in th a23-290 v73 a

U-Pb laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) ages have been determined from large zircon crystals separated from pegmatites of the Adirondack Mountains, New York. Emplacement and metamorphic ages ranging from 949 ± 10 to 1222 ± 12 Ma help constrain the timing of igneous, metamorphic, and deformational history of the region, and are associated with Shawinigan, Ottawan, and Rigolet orogenesis. Geologically reasonable ages were obtained from most zircon separates despite large size, a limited number of grains, high uranium and thorium contents, dark and opaque interiors, high density of fractures, and widespread areas of metamictization and Pb loss. However, few grains show zoning or differences in composition when viewed with the backscattered mode on the scanning electron microscope. Large, clear, internally featureless, U-poor grains yield the best constrained ages. U-Th-Pb monazite ages, determined by electron probe, vary from 874 ± 27 Ma to 297 ± 62; the younger age may reflect the timing of hydrothermal fluid infiltration related to late Acadian events. This study suggests that, with appropriate care, zircons from pegmatites are a reasonable target for LA-MC-ICP-MS geochronology, widening the current arsenal of sampling targets.

10aAdirondack Mountains10ageochronology10aPegmatite1 aLupulescu, M., V.1 aChiarenzelli, J., R.1 aPullen, A., T.1 aPrice, J., D. uhttp://dx.doi.org/10.1130/GES00596.101810nas a2200229 4500008004100000245010500041210006900146300001200215490000700227520110000234653002401334653001701358653001801375653002401393100002501417700002201442700001601464700001401480700001501494700001401509856005701523 2010 eng d00aEnriched Grenvillian Lithospheric Mantle as a Consequence of Long-lived Subduction Beneath Laurentia0 aEnriched Grenvillian Lithospheric Mantle as a Consequence of Lon a151-1540 v383 a

Geochemical and Nd isotopic data from mafic and newly discovered ultramafic rocks in the Adirondack Lowlands suggest widespread enrichment of the lithospheric mantle under the Grenville Province. Incompatible element abundances and previously published Hf TDM (zircon) (depleted mantle model age) and Nd TDM ages from rocks of the anorthosite-mangerite-charnockite-granite suite in the Adirondack Highlands document similar enrichment in the lower crust and its strong influence on subsequent magmatic events throughout the Ontario-Quebec-Adirondack segment of the Grenville Province. Likely the consequence of long-lived (ca. 1.4–1.2 Ga) northwest-directed subduction along the southeast edge of Laurentia (previously proposed Andean margin), this enrichment is similar to that associated with the vast (>240,000 km2) ultrapotassic province of the western Churchill Province. Enrichment of the lithospheric mantle beneath orogenic belts is a predictable and important differentiation process that has operated on Earth for at least the past 3 b.y.

10aAdirondack Lowlands10aGeochemistry10ageochronology10alithospheric mantle1 aChiarenzelli, J., R.1 aLupulescu, M., V.1 aCousens, B.1 aThern, E.1 aCoffin, L.1 aRegan, S. uhttp://geology.gsapubs.org/content/38/2/151.abstract