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Using Pegmatite Geochronology to Constrain Temporal Events in the Adirondack Mountains

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Using Pegmatite Geochronology to Constrain Temporal Events in the Adirondack Mountains Using pegmatite geochronology to constrain temporal events in the Adirondack Mountains Marian V. Lupulescu1,*, Jeffrey R. Chiarenzelli2,*, Alexander T. Pullen3,*, and Jonathan D. Price4,*,† 1Research and Collections, New York State Museum, Albany, New York 12230, USA 2Department of Geology, St. Lawrence University, Canton, New York 13617, USA 3Department of Geosciences, University of Arizona, Tucson, Arizona 85719, USA 4Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York, 12180, USA ABSTRACT of the Grenville Province (Fig. 1). Our princi- 7 Ma (Selleck et al., 2005). Older U-Th-Pb dat- pal goal is to present the timing of the pegma- ing on uraninite from the McLear pegmatite in U-Pb laser ablation–multicollector–induc- tite emplacement using U-Th-Pb zircon ages the Lowlands (Shaub, 1940) yielded an age of tively coupled plasma–mass spectrometry determined by laser ablation–multicollector– 1094 Ma. In this study we report geochrono- (LA-MC-ICP-MS) ages have been determined inductively coupled plasma–mass spectrom- logical U-Th-Pb data for 11 pegmatite bodies from large zircon crystals separated from peg- etry (LA-MC-ICP-MS) and monazite ages by from the Adirondack Mountains (two from the matites of the Adirondack Mountains, New electron microprobe analysis (EMPA). These Lowlands and nine from the Highlands), and York. Emplacement and metamorphic ages new data are used to constrain the timing of the one from a pegmatitic intrusion in the Old Bed ranging from 949 ± 10 to 1222 ± 12 Ma help Adirondack igneous, metamorphic, and defor- magnetite-apatite ore from Mineville. These constrain the timing of igneous, metamorphic, mational events. We selected the pegmatites for ages are summarized in Table 1. Additional and deformational history of the region, and U-Pb geochronology because these rocks are U-Th-Pb data on monazite from two pegmatite are associated with Shawinigan, Ottawan, and suffi ciently abundant in the Adirondacks, often bodies from the southern Adirondack Highlands Rigolet orogenesis. Geologically reasonable occur as medium-size rock bodies associated are reported. ages were obtained from most zircon sepa- with important economic deposits, have syn- or rates despite large size, a limited number of post-tectonic emplacement, and contain miner- OCCURRENCES grains, high uranium and thorium contents, als that are readily observed in hand samples dark and opaque interiors, high density of that are easily manipulated under the binocular The Adirondack Mountains are part of the fractures, and widespread areas of metamicti- microscope and are capable of concentrating Grenville Province (for recent summaries, see zation and Pb loss. However, few grains show incompatible elements including U and Th. Rivers, 2008; McLelland et al., 2010). Based zoning or differences in composition when Despite their interesting petrographic fea- on the metamorphic grade, rock type, and viewed with the backscattered mode on the tures, geological location, and mineralogy, there composition, they are divided into Adirondack scanning electron microscope. Large, clear, are only a few modern studies and references Highlands and Adirondack Lowlands by a internally featureless, U-poor grains yield in the geological literature about the pegmatite deformation zone known as Colton-Carthage the best constrained ages. U-Th-Pb monazite bodies from New York (Tan, 1966; Putman and Mylonite Zone (Geraghty et al., 1981; Streepey ages, determined by electron probe, vary from Sullivan, 1979). The interest in the pegmatites et al., 2001). The juxtaposition of the Lowlands 874 ± 27 Ma to 297 ± 62; the younger age may of the Highlands commenced with the rush for against Highlands is interpreted as the result of refl ect the timing of hydrothermal fl uid infi l- high-quality feldspar and muscovite suitable for an orogenic collapse (Selleck et al., 2005). tration related to late Acadian events. This electrical applications, enamel, crushed stone The Lowlands contains supracrustal rocks that study suggests that, with appropriate care, zir- for concrete structures, chicken grit, and at a were metamorphosed to mid-upper am phib o lites cons from pegmatites are a reasonable target small scale for quartz used in glass manufactur- facies and were deformed during the Shawinigan for LA-MC-ICP-MS geochronology, widening ing and later for radioactive minerals; they were orogeny (Corrigan, 1995; Wasteneys et al., 1999; the current arsenal of sampling targets. mined between 1906 and 1934 (Newland, 1916, Rivers, 2008). The lithotectonic sequences of the 1921; Miller, 1921; Newland and Hart nagel, Lowlands start with the Lower Marble Forma- INTRODUCTION 1939; Tan, 1966). The pegmatites from the tion overlain by the Popple Hill Gneiss (Carl, Lowlands were mined for high-quality feldspar 1988) and Upper Marble Formation (de Lorraine In this paper we discuss results from initial between 1907 and 1938 (Newland, 1916; Cush- and Sangster, 1997). The composition of the attempts to date zircon and monazite from peg- ing and Newland, 1925; Shaub, 1929; Newland basement of these metasedimentary sequences matites from the Adirondack Mountain portion and Hartnagel, 1939; Tan, 1966). is not known, but Chiarenzelli et al. (2010a) New York pegmatite bodies remain largely suggested the metasedimentary rocks are either *E-mails: Lupulescu: [email protected]; undated except the U-Th-Pb zircon ages for the allochthonous or were deposited on oceanic Chiarenzelli: [email protected]; Pullen: apullen@ Lyonsdale Bridge Falls in the western Highlands crust. The marbles and gneisses were intruded email.arizona.edu; Price: [email protected]. †Present address: Department of Geosciences, at 1034 ± 10 Ma (McLelland et al., 2001) and between 1150 and 1200 Ma by varied igneous Midwestern State University, Wichita Falls, Texas pegmatitic phase of the Lyon Mountain Granite rocks (Wasteneys et al., 1999; Heumann et al., 76308, USA. at Brouse’s Corners in the Lowlands at 1044 ± 2006; Chiarenzelli et al., 2010b). The pegmatites Geosphere; February 2011; v. 7; no. 1; p. 23–39; doi: 10.1130/GES00596.1; 9 fi gures; 2 tables; 1 supplemental table fi le. For permission to copy, contact [email protected] 23 © 2011 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/7/1/23/3340619/23.pdf by guest on 27 September 2021 Lupulescu et al. 140°W 130°W 120°W 110°W 100°W 90°W 80°W 70°W 70°W 50°W 40°W 60°N 50°N n e 50°N g o r OOrogen 40°N AADIRONDACKDIRONDACK MMOUNTAINSOUNTAINS New York 40°N 30°N ille 30°N env GGrenviller 20°N N 600 Kilometers 20°N 120°W 110°W 100°W 90°W 80°W 70°W Figure 1. Location of the Adirondack Mountains within the greater Grenville Province (modifi ed after Tollo et al., 2004). from the Lowlands presented in this study, A simplifi ed geochronology of the Highlands mangerites from the northern Highlands (1080 McLear and Rossie, were both intruded into the records the oldest rocks as arc-related tonalites Ma), and the A-type Lyon Mountain granite Lower Marble Formation. of calc-alkaline affi nity with ages ranging from (1070–1040 Ma) (McLelland et al., 1996) are The Highlands contains supracrustal and 1330 to 1307 Ma (McLelland and Chiaren- recognized. These geochronological data prove igneous rocks that were metamorphosed under zelli, 1990a). Around 1155 Ma, a voluminous the presence of the Elzevirian, Shawinigan, and granulite facies conditions during the Shawin- anorthosite-charnockite-mangerite-granite Ottawan deformation and igneous activity in igan and Ottawan orogenies, although the pro- (AMCG) suite was emplaced (McLelland the Highlands. The distribution of these rocks duction of leucosome related to these events in et al., 2004; McLelland and Chiarenzelli, can be seen in Figure 2. pelitic gneisses in the Highlands appears to be 1990b); other younger igneous rocks such as The pegmatites from the Highlands, ana- geographically variable (Heumann et al., 2006). A-type Hawkeye granite (1100–1090 Ma), the lyzed in this study, were collected from the 24 Geosphere, February 2011 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/7/1/23/3340619/23.pdf by guest on 27 September 2021 on 27 September 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/7/1/23/3340619/23.pdf Geosphere, February2011 25 TABLE 1. SUMMARY OF U-PB AGES (IN MA) ON ZIRCON FROM PEGMATITES FROM THE ADIRONDACK MOUNTAINS Concordia plot Concordant age Weighted mean age Other Best age Upper Lower Weighted Weighted Upper Lower intercept intercept MSWD mean MSWD Probability mean MSWD Probability intercept intercept MSWD (2σ) Lowlands 1. McLear 1396 ± 820 1216 ± 110 0.18 1195.1 ± 7.2 0.09 0.76 1198 ± 13 0.78 0.73 1197 ± 13 250 ± 50 0.00 F 1195.1 ± 7.2 2. Rossie 1185 ± 19 215 ± 18 0.10 1195.1 ± 8.3 0.14 0.71 1193 ± 16 0.37 0.98 1217 ± 15 225 ± 17 1.40 1195.1 ± 8.3 Highlands 3. Hulls Falls #1 1180 ± 14 215 ± 100 0.31 1178 ± 12 0.26 1.00 1178 ± 12 4. Hulls Falls #2 1222 ± 15 256 ± 50 0.85 1222 ± 12 1.09 0.36 1222 ± 12 5. Batchellerville 1054 ± 110 246 ± 27 1.40 1090 ± 28 0.00 SP 1090 ± 28 Geochronology of the Adirondacks pegmatites Adirondacks ofthe Geochronology 6. Scott’s Farm 1063 ± 19 335 ± 280 0.19 1064.0 ± 6.5 0.12 0.73 1062 ± 14 0.21 1.00 1062 ± 14 7. Sugar Hill 1037 ± 31 –621 ± 3700 0.20 1021.7 ± 5.4 10.30 0.00 1048 ± 14 0.23 1.00 1052 ± 18 250 ± 50 0.20 F 1048 ± 14 8. Roe’s Spar Bed 1042 ± 42 248 ± 650 0.09 1030.7 ± 9.9 0.11 1.00 1042 ± 13 250 ± 50 0.08 F 1030.7 ± 9.9 9.
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