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Review of the Proterozoic Evolution of the Grenville Province, Its Adirondack Outlier, and the Mesoproterozoic Inliers of the Appalachians

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Review of the Proterozoic Evolution of the Grenville Province, Its Adirondack Outlier, and the Mesoproterozoic Inliers of the Appalachians mwr206-02 page 1 The Geological Society of America Memoir 206 2010 Review of the Proterozoic evolution of the Grenville Province, its Adirondack outlier, and the Mesoproterozoic inliers of the Appalachians James M. McLelland Bruce W. Selleck Department of Geology, Colgate University, Hamilton, New York 13346, USA M.E. Bickford Department of Earth Sciences, Syracuse University, Syracuse, New York 13244, USA ABSTRACT In recent years, a rapidly expanding database, especially in sensitive high-resolution ion microprobe (SHRIMP) geochronology, has led to signifi cant advances in understanding of the Precambrian tectonic evolution of the Grenville Province, including its Adirondack outlier, and the Mesoproterozoic inliers of the Appalachians. Based upon this information, we review the geochronology and tec- tonic evolution of these regions and signifi cant similarities and differences between them. Isotopic data, including Pb isotopic mapping, suggest that a complex belt of marginal arcs and orogens existed from Labrador through the Adirondacks, the midcontinent, and into the southwest during the interval ca. 1.8–1.3 Ga. Other data indicate that Mesoproterozoic inliers of the Appalachians, extending from Vermont to at least as far south as the New Jersey Highlands, are, in part, similar in com- position and age to rocks in the southwestern Grenville Province. Mesoproterozoic inliers of the Appalachian Blue Ridge likewise contain some lithologies similar to northern terranes but exhibit Nd and Pb isotopic characteristics suggesting non- Laurentian, and perhaps Amazonian, affi nities. Models invoking an oblique colli- sion of eastern Laurentia with Amazonia are consistent with paleomagnetic results, and collision is inferred to have begun at ca. 1.2 Ga. The collision resulted in both the ca. 1190–1140 Ma Shawinigan orogeny and the ca. 1090–980 Ma Grenvillian orogeny, which are well represented in the Appalachians. Several investigators have proposed that some Amazonian Mesoproterozoic crust may have been tectonically transferred to Laurentia at ca. 1.2 Ga. Data that potentially support or contradict this model are presented. McLelland, J.M., Selleck, B.W., and Bickford, M.E., 2010, Review of the Proterozoic evolution of the Grenville Province, its Adirondack outlier, and the Meso- proterozoic inliers of the Appalachians, in Tollo, R.P., Bartholomew, M.J., Hibbard, J.P., and Karabinos, P.M., eds., From Rodinia to Pangea: The Lithotectonic Record of the Appalachian Region: Geological Society of America Memoir 206, p. 1–29, doi: 10.1130/2010.1206(02). For permission to copy, contact editing@ geosociety.org. ©2010 The Geological Society of America. All rights reserved. 1 mwr206-02 page 2 2 McLelland et al. INTRODUCTION thonous Polycyclic Belt along the Allochthon Boundary thrust at ca. 1050 Ma, followed by orogen collapse at ca. 1020 Ma. A fi nal A schematic map of the surface and subsurface extent of the contractional pulse (ca. 1010–980 Ma) ending with extensional Grenville orogen is shown in Figure 1, including the Grenville collapse gave rise to the Grenville Front thrust. The Allochthonous Province, as well as the ca. 1.2–0.98 Ga Mesoproterozoic inliers Monocyclic Belt consists of rocks younger than ca. 1.35 Ga. De- of the Appalachians (Rankin et al., 1993, their Plate 5B). Addi- tails of these belts and the orogenic sequence of events preserved tional exposures of the Grenville orogen exist in the Mesoprotero- in them will be discussed in later sections. The subsurface distribu- zoic inliers of Texas, lying to the west in Figure 1 (Rankin et al., tion of the Grenville orogen in Figure 1 has been approximated 1993). Rivers et al. (1989) divided the exposed Grenville Province from drill-core samples and geophysical data (Rankin et al., 1993) into three principal tectonic segments (Fig. 1): (1) the Parautoch- and is especially uncertain below the complexities of the north- thonous Belt, (2) the Allochthonous Polycyclic Belt, and (3) the eastern Appalachian orogen. However, a small outcropping of Alloch thonous Monocyclic Belt. The Parautochthonous Belt Mesoproterozoic basement at Cape Breton (Fig. 1) suggests the consists of reworked Archean and Paleoproterozoic rocks of the existence of Mesoproterozoic basement to the west. Superior Province foreland that were deformed by northwestward Figure 1 underscores the continental scale of the Grenville thrusting of the multiply metamorphosed ca. 1.7–0.98 Ga Alloch- orogen and inevitably leads to questions regarding relationships I I I 90°W 80°W 70°W Grenville Front thrust LRI Allochthon boundary thrust PB ABT I (ABT, Fig. 3) 50°N APB ? N FRONT Cape Figure 1. The extent of the Grenville SUPERIOR PROVINCE Breton orogen in eastern North America. The Grenville Province, its tectonic divi- AMB sions, and major anorthosite massifs are ? shown in shades of gray identifi ed in the F ? legend. Mesoproterozoic inliers of the AD Appalachians are designated in black. The subsurface distribution of Grenville basement as determined from drill-hole Appalachian and geophysical data is represented by Mesoproterozoic I diagonal ruling. The New York–Alabama inliers (Fig. 4) 40°N Lineament (King and Zeitz, 1978) marks the trend of a large magnetic anomaly Allochthonous that may have tectonic implications. APB polycyclic belt (Fig. 3) BFZ—Bahamas fracture zone; EGRP— EGRP GRENVILLE Parautochthonous Eastern granite-rhyolite province. (Fig- PB ure was modified after Rivers et al., belt (Fig. 3) 1989; Tollo et al., 2004.) Allochthonous AMB monocyclic belt Major anorthosite Grenville Province Grenville plutons (Fig. 3) NEW YORK- ALABAMA LINEAMENT Region of subsurface Grenville Province BFZ I 0 400 800 km 30°N mwr206-02 page 3 Review of the Proterozoic evolution of the Grenville Province 3 between its various components and their plate-tectonic evolu- MH, ATH HH HB,BG FBM, CGP ADK SHEN tion. In recent years, an expanding database derived from modern CH,BRK NJH GOOCH WC - granite geophysics, petrology, tectonics, numerical modeling, fi eld inves- - dikes R 1000 - R tigations, and geochronology has led to substantial clarifi cation of - these issues. Most geochronological studies performed prior to the - pegmatites OT - OT OT OT last decade involved variations of thermal ionization mass spec- - OT OT trometry (TIMS), which offers greater analytical precision but less 1100 - H - M spatial resolution than sensitive high-resolution ion microprobe - HL ONLY M (SHRIMP) techniques. As a result, with TIMS, it is much more - S S S - S S S diffi cult to date and analyze the small and intricately intergrown 1200 - - domains and zones that characterize zircons in polymetamorphic Age (Ma) - E E E rocks. We suggest that some current disparities in ages cited in the - E E - literature are the result of comparisons between SHRIMP- and 1300 - TIMS-derived data. Based on experience and reading of pertinent - - DY-MH DY-MH DY-MH geologic literature, we have found that SHRIMP-derived ages are - DY-MH generally more reliable in deciphering complex metamorphic and - 1400 - igneous histories. Our results indicate that in the Adirondacks, - as well as in the southern Appalachians (e.g., Tollo et al., 2006; - - Southworth et al., this volume; Volkert et al., this volume), gran- - itoids originally dated by TIMS techniques, and subsequently re- dated by SHRIMP, commonly yield ages that differ by 10–50 m.y. Figure 2. Time scale for Mesoproterozoic events in eastern North Table DR1 (in the GSA Data Repository1) presents a summary America. Orogenies: R—Rigolet, OT—Ottawan, S—Shawinigan, and E—Elzevirian. Symbols: Black dots—anorthosite-mangerite- of both SHRIMP and TIMS U-Pb geochronological data for the charnockite-granite magmatism; white dots— mangerite-charnockite- Adirondacks, and similar data for the Appalachians can be found granite magmatism; black—precollision calc-alkaline magmatism. in other papers in this volume (e.g., Southworth et al., Tollo et al., Abbreviations: CGP—Grenville Province of Canada (Rivers, 2008); Volkert et al., this volume). Rivers (1997, 2008) has summarized ADK—Adirondack outlier (McLelland, this volume). References for geochronological data for the entire Grenville Province, and Fig- geochronology in the following abbreviated localities may be found in the text (under Mesoproterozoic Inliers of the Appalachians): ure 2, which is consistent with his orogenic defi nitions, provides a AH—Adirondack Highlands; ATH—Athens Dome, CH—Cheshire time scale for events in the Grenville orogen and illustrates some Dome, BRK—Berkshire Mountains; DY-MH—Dysart–Mount Holly of the important geochronological links that exist across much of suite; FBM—French Broad massif; HH—Hudson Highlands; M— the region. In addition to U-Pb zircon igneous crystallization ages Mars Hill; MH—Mount Holly complex; NJH—New Jersey High- for plutons, whole-rock Nd model ages (e.g., Dickin, 2000; Daly lands; HB—Honey Brook uplands; BG—Baltimore Gneiss Domes; Gooch—Goochland terrane; H—Hawkeye granite; HL—Highlands; and McLelland, 1991) provide estimates for the time of extraction SHEN—Shenandoah massif; M—Marshall granite; TR—Trimont of magma from the mantle and the extent to which plutons intrud- Ridge; WC—Wolf Creek. ing the crust may be juvenile. Zircon, titanite, and monazite (e.g., Mezger et al., 1991, 1992; Heumann et al., 2006) ages have been used to constrain the timing of metamorphic events and, together GEOLOGICAL OVERVIEW OF THE GRENVILLE with 40Ar/39Ar ages, have facilitated the determination of cooling PROVINCE AND ITS ADIRONDACK OUTLIER histories (e.g., Cosca et al., 1991; Busch et al., 1996; Dahl et al., 2004; Streepey et al., 2000, 2001; Rivers, 2008). Equally signifi - Introduction cant data are Pb-Pb whole-rock isotopic ages that serve to estab- lish the age and nature of crustal Pb reservoirs (Sinha et al., 1986; The Grenville Province (Figs. 1 and 3) consists primarily Sinha and McLelland, 1999; Loewy et al., 2003). All of these will of reworked amphibolite- to granulite-facies crust ranging in be discussed in the main body of the text and will be utilized to age from Archean to ca.
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