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_Journal of Structural Geology 33 (2011) 312-328_ Contents lists available at ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com/locate/jsg Minas Fault Zone: Late Paleozoic history of an intra-continental orogenic transform fault in the Canadian Appalachians J. Brendan Murphy a,*, John W.F. Waldron b, Daniel J. Kontak c, Georgia Pe-Piper d, David J.W. Piper e a Department of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia, B2G 2W5 Canada b Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3 Canada c Department of Earth Sciences, Laurentian University, Sudbury, Ontario, P3E 2C6 Canada d Department of Geology, Saint Mary’s University, Halifax, Nova Scotia, B3H 3C3 Canada e Geological Survey of Canada (Atlantic), Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia, B2Y 4A2 Canada Article info Article history: Received 12 March 2010; Received in revised form 29 September 2010; Accepted 21 November 2010; Available online 2 December 2010 Keywords: Minas Fault Zone, Appalachian orogen, Avalon terrane, Meguma terrane Abstract The Minas Fault Zone (MFZ) defines the boundary between the Avalon and Meguma terranes in the Canadian Appalachians and is exposed in mainland Nova Scotia and southern New Brunswick. These terranes originated along the Gondwanan margin but had accreted to Laurentia by the middle Devonian. The surface trace of the MFZ is adjacent to the southern margin of the Late-Devonian-Late Carboniferous Maritimes Basin. The Late Devonian-Late Carboniferous evolution of the MFZ involves several episodes of oblique dextral shear that resulted in basin formation and inversion, and at various times the zone was the focus of magmatism, regional fluid flow and mineralization. In the Late Devonian-Early Carboniferous, asymmetric rifting accompanied by dextral shear produced two coeval sequences: the Horton Group, which is dominated by continental clastic strata, and the Fountain Lake Group, which consists predominantly of bimodal volcanic rocks that overlie high-level plutons emplaced along active shear zones. The overall tectonic environment may have been dominated by dextral transtension along the southern margin of Laurentia, which corresponded with the northern flank of the Rheic Ocean. A major change in the evolution of the Minas Fault Zone occurred in the Late Mississippian-Early Pennsylvanian and produced the E-W Chedabucto Fault, clockwise rotation of pre-existing structures, local zones of transtension and transpression, as well as regional fluid flow and extensive mineralization. This major change may reflect the onset of Laurentia-Gondwana oblique collision, the effects of which continued into the latest Carboniferous with coeval development of flower structures and pull-apart basins in zones of local transpression and transtension. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction Accreted terranes are typically bounded by complex long-lived fault zones that focus and accommodate relative crustal movements during their initial docking and subsequent post-accretionary histories (e.g., Teyssier et al., 1995). The long-lived fault zones are also commonly the locus of mineralization, the structure having been the focus of magmas, heat and fluids (e.g., Goldfarb et al., 2005). Fabrics developed within these fault zones are difficult to interpret, as later movements commonly obliterate earlier fabrics and therefore obscure evidence of earlier movement (e.g., Holdsworth et al., 2001). * Corresponding author. E-mail address: bmurphy@stfx.ca (J.B. Murphy). 0191-8141 $ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsg.2010.11.012 The Minas Fault Zone (MFZ) of Maritime Canada (Fig. 1) is exposed in various localities in mainland Nova Scotia over a length of ca. 300 km and separates the Avalon terrane to the north from the Meguma terrane to the south (Williams, 1979; Keppie, 1982). Its northern margin is also exposed in southern New Brunswick along the southern flank of Avalonia. It terminates westward in an unclear manner in the Gulf of Maine. Its eastward continuation in the late Paleozoic has been correlated to the Collector Anomaly across the central Grand Banks (Haworth and Lefort, 1979), and it appears to have affected deposition and deformation of Late Devonian-Late Carboniferous strata in southernmost Cape Breton Island (Force and Barr, 2006). Since the pioneering work of Eisbacher (1969, 1970), the MFZ has been recognized as a predominantly dextral shear zone in the Late Paleozoic reflecting relative motion between the Avalon and Meguma terranes (e.g., Webb, 1969; Keppie, 1982; Mawer and White, 1987; Hibbard and Waldron, 2009). It is now almost three decades since the last comprehensive overview of the MFZ (Keppie, 1982). Since that time, however, the knowledge of structural evolution, stratigraphy, geochronology and mineralization of rocks along the MFZ has advanced and a wide variety of geological features have been attributed to Late Paleozoic tectonic activity along the fault zone. Many recent studies, however, document only a portion of the history of the MFZ in a particular area. The purpose of this article is to provide a comprehensive overview of the evolution of the MFZ in the Late Paleozoic during Laurentia-Gondwana interaction. We review the various lines of evidence for the Late Paleozoic history of the Meguma-Avalon boundary zone, integrate these data into a chronological account of the MFZ, and attempt a kinematic interpretation. We show that there are several discrete episodes of movement during the Late Devonian and Carboniferous, that resulted in several phases of basin formation and deformation, and provided structural controls for magmatism. We also show that one episode in particular involved regional scale fluid flow, with implications for mineralization. 2. Geological setting On the basis of faunal, paleomagnetic, lithostratigraphic and geochronological data, there is a consensus that both the Meguma and Avalon terranes originated along the northern margin of Gondwana (Amazoniae-West Africa) in the Neoproterozoic, subsequently separated from Gondwana some time between the Late Cambrian and Early Silurian, and were later accreted to Laurentia in the Late Silurian during the development of the Appalachian orogen (e.g., Williams and Hatcher, 1982; Keppie, 1985; van Staal et al., 1998, 2009; Murphy et al., 2004, 2006; Hibbard et al., 2007). Waldron et al., 2009). The oldest rocks in common to both terranes are Late Devonian-Early Carboniferous in age (Horton Group, Fig. 1) and the relationship between the terranes prior to that time is controversial. Avalonia in mainland Nova Scotia is characterized by Neoproterozoic (635-570 Ma) arc-related sequences (Murphy and Nance, 2002), unconformably overlain by Cambrian-Early Ordovician platformal successions with minor, localized volcanic rocks (Landing, 1996); these are followed by ca. 460 Ma bimodal volcanic rocks (Hamilton and Murphy, 2004) that are overlain by Early Silurian-Early Devonian predominantly siliciclastic rocks (Boucot et al., 1974). The basement to the Avalon terrane is not exposed, but Sm-Nd isotopic data from Neoproterozoic and Paleozoic crustally-derived felsic rocks mostly indicated derivation from crustal sources with depleted mantle model ages (TDM) between 0.95 and 1.2 Ga (Nance and Murphy, 1994; Murphy and Nance, 2002). The Meguma terrane is underlain by a ca. 10 km thick succession of Cambrian (possibly Ediacaran) to Ordovician metaturbiditic rocks of the Meguma Supergroup (White, 2008; Waldron et al., 2009) that are unconformably overlain by a mainly Silurian to Early Devonian succession of bimodal volcanic and shallow marine to continental clastic rocks (e.g., Schenk, 1997; MacDonald et al., 2002). These rocks were deformed and metamorphosed beginning at ca. 400 Ma (Reynolds and Muecke, 1978; Hicks et al., 1999), and were intruded by late syntectonic Late Devonian (ca. 380-372 Ma) granitoids (Kontak et al., 2003, 2004). The basement to the Meguma terrane is not exposed, but Sm-Nd isotopic data from Early Silurian and Devonian crustally-derived felsic rocks indicated derivation from crustal sources with depleted mantle model ages (TDM) between 0.9 and 1.9 Ga (Keppie et al., 1997; Clarke et al., 1997; MacDonald et al., 2002). As the Early Silurian volcanic rocks (White Rock Formation) predate all metamorphic and structural events recorded in the Meguma terrane, these data may be representative of the Sm-Nd isotopic composition of the Meguma basement during, and immediately prior to the deposition of the Meguma Supergroup. The surface trace of the MFZ is located close to Avalon-Meguma terrane boundary and to the southern flank of the Maritimes (or Magdalen) Basin (Fig. 1). The formation and evolution of the intracontinental Maritimes Basin dominates the Late Paleozoic geology of Atlantic Canada (e.g., Williams, 1979). Recent syntheses (Gibling et al., 2008; Hibbard and Waldron, 2009) indicate that basin formation recorded continued deformation after Laurentia-Gondwana collision in which predominantly dextral motion on strike-slip faults was accompanied by basin formation, as well as by localized zones of transtension and transpression. 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