Evolution of Grenville massifs in the Blue Ridge geologic province, southern and central Appalachians

The Grenville orogenic cycle of southern Laurentia: Unraveling sutures, rifts, and shear zones as potential piercing points for Amazonia

“…Thus the differences between the adjacent Pedlar and Lovingston massifs of Virginia (Fig. 7) noted by Bartholomew et al (1981), Bartholomew and Lewis (1984), Sinha and Bartholomew (1984), Hughes et al (1997Hughes et al ( , 2004, and Burton and Southworth (2004) are consistent with an active Rigolet magmatic arc (Lovingston massif) juxtaposed over an older magmatic arc (Pedlar massif), which was primarily active during the Shawinigan and Ottawan phases of the Grenville orogeny. Bailey and Simpson (1993) described the Rockfish Valley ductile shear zone (between the Pedlar and Lovingston massifs) as a Paleozoic thrust zone with no fabrics indicative of Iapetan extension, although in other papers these authors recognize similarly oriented shear zones as Iapetan normal faults.…”

“…Blue arrows show extension along the Carthage-Colton shear zone (CCSZ) (Johnson et al, 2004) and Robertson Lake shear zone (RLSZ) (e.g., Streepey et al, 2002Streepey et al, , 2004, along the Ramapo fault in New Jersey (e.g., Costa and Gates, 1993;Gates and Costa, 2006), and inferred from seismic lines across both Ohio (Pratt et al, 1989), and eastern Tennessee (Hopkins, 1995). BG -biotite gneiss (Tollo et al, 2006); AMS -Archer Mountain Suite (e.g., Hughes et al, 2004;unpublished preliminary age: B.V. Miller and M.J. Bartholomew); LA -Labrieville Anorthosite (e.g., Owens and Dymek, 1992;Owens et al, 1994); LAMLac Michel Complex Erdmer, 1990, 1986;Heaman et al, 2002); AMCG -anorthosite-mangerite-charnockite-granite suite; LM -Lovingston massif (Bartholomew and Lewis, 1984); MA -Montpelier Anorthosite (Owens and Samson, 2004;Aleinikoff et al, 1996); MEG -Mount Eve granite (Gorring et al, 2004); PM -Pedlar massif (Bartholomew and Lewis, 1984); RA and RMP -Roseland Anorthosite and Roses Mill pluton (e.g., Herz and Force, 1987; unpublished preliminary ages: B.V. Miller and M.J. Bartholomew); Oaxaquia metamorphism (m) (e.g., Cameron et al, 2004;Keppie et al, 2003Keppie et al, , 2004 widespread and associated with the rapid rise of hot, metamorphic cores (e.g., the Adirondacks) -again analogous to the Basin and Range province and associated metamorphic core-complexes. AMCG magmatism and metamorphism in Oaxaquia during the Rigolet phase (e.g., Mora et al, 1986;Cameron et al, 2004;Keppie et al, 2003Keppie et al, , 2004 suggest similar extension there, although Oaxaquia's location relative to Laurentia at that time is unknown and is only diagrammatically depicted in Fig.…”

A Gallium Anomaly Utilized in Palaeogeographic Reconstruction of Battle Mountain, Rappahannock County, Virginia

“…Nevertheless, a variety of geologic data support the original proposal of Rankin (1975Rankin ( , 1976) that the Robertson River Igneous Suite was emplaced within an anorogenic, actively rifting continental setting. Data supporting this interpretation include: (1) the lack of evidence for any major erogenic event in the central and southern Appalachian orogen during the Late Proterozoic, (2) the temporal and spatial association of the Robertson River Igneous Suite with sedimentary deposits of terrestrial clastic origin correlated with the rift-related Mechum River Formation (Hutson and Tollo, 1991), (3) the occurrence of large-scale faults that may be similar in age to the Robertson River Igneous Suite and which have been related to regional extension (Simpson and Kalaghan, 1989), (4) the association of the Robertson River Igneous Suite with bimodal volcanic sequences and dike swarms of Late Proterozoic age, and (5) the inclusion of the Robertson River Igneous Suite within a larger province of geochemically simi'ar plutonic bodies that occur throughout the Laurentian terranes from New York to North Carolina (Rankin and others, 1983;Bartholomew and Lewis, 1984) and which, in North Carolina and southern Virginia, have been shown to be consanguineous with rift-related volcanic rocks (Rankin, 1975;. Like many other A-type suites, such as the Topsails Igneous Suite (Newfoundland), the Malani Igneous Suite (India), the White Mountains Plutonic-Volcanic Suite (New Hampshire), and Saudi Arabian granites (Eby, 1990;Whalen and Currie, 1990), the Robertson River Igneous Suite includes both metaluminous and 1,000' (Whalen and others, 1987).…”

“…These bodies include rock types ranging from syenite to alkali feldspar granite to granite and are typically metaluminous to weakly peralkaline in composition with high Ga/AI ra*ios (Bartholomew and Lewis, 1984;Tollo and others, unpub. data).…”

“…The main batholith forms an elongate, narrow belt encompassing an area of more than 380 km2 (137 mi2) stretching from near Ashby Gap in northern Virginia southward nearly 120 km (72 mi) to the vicinity of Charlottesville. As such, the main batholith of the Robertson River Igneous Suite constitutes the largest body of Late Proterozoic anorogenic intrusive rocks in the Appalachian orogen (Bartholomew and Lewis, 1984;Rankin and others, 1990). Emplacement of the suite into Grenville-age orthogneisses and other metamorphic rocks of the Blue Ridge core zone occurred during an extended period of magmatic activity that coincided with the initial stages of the Late Proterozoic rifting of Laurentia (Rankin, 1975;Tollo and Aleinikoff, 1992).…”