Anatomy of a mid-crustal suture: Geology of the Central Metasedimentary Belt boundary thrust zone, Grenville Province, Ontario
What: This project focuses on the geology of the Bancroft area of Ontario, which is thought to have been the margin of North America during the Mesoproterozoic. This part of the Grenville Province of Ontario is made up of two tectonic elements: (1) High-grade gneisses that were part of the 1.7-1.4 Ga continental margin and (2) a package of volcanic, plutonic, and sedimentary rocks that are thought to be a collage of arc components accreted at ca. 1.17 Ga. This Keck project focuses on this arc assemblage and its collision + suture with North America. Because these rocks have enjoyed several mountain-building events at the margin of the craton, they are now highly-deformed gneisses, amphibolites and marbles. This project will examine the petrology and structural geology of these rocks to better understand the details of continental accretion, thrusting, and metamorphism in mid-crustal rocks.
When: July 1-30
Who: William Peck (Colgate University), Steve Dunn (Mt. Holyoke College), and Michelle Markley (Mt. Holyoke College)
The Composite Arc Belt of Carr et al. (2000) is a subdivision of the southern Grenville Province that includes a number of small terranes (Fig. 1) with distinct geology. These terranes contain greenschist- and amphibolite facies metasedimentary and 1.29-1.24 Ga metavolcanic and volcanoclastic rocks that are intruded by suites of gabbroic, tonalitic, and granitic plutons (Easton 1992). The volcanic rocks have arc geochemical signatures and are dominated by mafic tholeiitic suites, but include intermediate and felsic rocks and some with calc-alkaline signatures (see Easton 1992; Carr et al. 2000; Smith et al. 2001). Terrane boundaries are generally east-dipping, tops to the west shear zones. The youngest cross-cutting plutonic rocks may constrain terrane amalgamation in the Composite Arc Belt to 1.24-1.22 Ga (Carr et al. 2000).
Figure. 1. A. Location map of the Grenville Province. B. The southern Grenville Province of Ontario, after Hanmer and McEachern (1992). CMBbtz, Central Metasedimentary Belt boundary thrust zone; the Composite Arc Belt is sub-divided into the Harvey-Cardiff (H), Belmont (B), Grimsthorpe (G), Mazinaw (M), and Sharbot Lake (S) domains after Easton (1992).
The tectonic interpretation of the Composite Arc Belt is somewhat controversial. Some workers have postulated that these arcs formed on oceanic crust offshore of Laurentia (e.g., Brown et al. 1975; Windley 1989; Carr et al. 2000), while others have assigned these rocks to rifting and back-arc environments, some underlain by continental crust, and developed at the continental margin (Pehrsson et al. 1996; Hanmer et al. 2000; Smith et al. 2001).
The Composite Arc Belt is bounded on the west by the Central Metasedimentary Belt boundary thrust zone (CMBbtz; Fig. 2): a mid-crustal deformation zone that separates metasedimentary, metavolcanic, and metaplutonic rocks of the Composite Arc belt from the Central Gneiss Belt of the foreland. The CMBbtz is made up of annealed, heterogeneously deformed mylonitic and marble mélange tectonites surrounding metaigneous thrust sheets (Hanmer 1988, Hanmer and McEachern 1992, McEachern and van Breemen 1993; see Fig. 2).
Figure 3. Map of the Central Metasedimentary Belt boundary thrust zone after Hanmer and McEachern (1992). R, Redstone thrust sheet; D, Dysart thrust sheet; GL, Glamorgan thrust sheet; G, Grace thrust sheet; P, Papineau thrust sheet; F, Foymount thrust sheet; S, Stafford thrust sheet.
The timing of accretion of the Composite Arc Belt to the Central Gneiss Belt is controversial, as there is evidence for two deformation events in the CMBbtz at ca. 1.19 and 1.08-1.06 Ga (McEachern and van Breemen 1993; Carr and McMullen 2000). The 1.08-1.06 Ga event is associated with the most pervasive deformation, and Central Gneiss Belt rocks structurally below the CMBbtz only record the 1.08 Ga metamorphism, which is interpreted by Timmermann et al. (1997) as representing docking of the Composite Arc Belt. Pehrsson et al. (1996) proposed that the Raglan gabbro belt (Fig. 2; to the east of the CMBbtz) could have provided a rheological barrier that controlled the location of the top of the thrust zone, and Hanmer (1988) and Hanmer and McEachern (1992) proposed that the location of the lower boundary of the thrust zone was controlled by a weak (and probably discontinuous) horizon of aluminous (locally cordierite+gedrite) gneisses (Peck and Valley, 2000; Peck and Smith, 2005).
Keck Project Focus
The CMBbtz provides an ideal natural laboratory in which the interplay between terrane amalgamation, thrusting, metamorphism, and fluid-flow can be examined in mid-crustal rocks. This area has been well-characterized structurally (Hanmer 1988, Hanmer and McEachern 1992; Carr and McMullen 2000) has good geochronologic control (McEachern and van Breemen 1993; Pehrsson et al. 1996; Carr and McMullen 2000), and has been mapped in detail by the Ontario Geological Survey (e.g. Armstrong and Gittins 1968; Culshaw 1986; Bright 1987a,b; 1988; Easton 1990; 1986; 1987a,b; Breaks and Thivierge 2001; Lumbers and Vertolli 2003). However, igneous and metamorphic petrologic studies in this area are for the most part reconnaissance or regional in nature (e.g., Anovitz and Essene, 1990; Lumbers et al., 1990; Carr and Berman 1997). We plan to examine several outstanding petrologic and tectonic questions in the CMBbtz, with a goal of better understanding the mid-crustal levels of major thrust systems.
Potential Student Projects
There are a host of potential projects in this area depending on student background and interests. Please contact one of the project faculty if you are interested in any of these projects or some other aspect of petrology/structural geology not mentioned!
Surprisingly little detailed metamorphic petrology has been done in the CMBbtz. Some students will focus on transects across-strike of the CMBbtz to constrain the meatamorphic field gradient in marbles. These projects will include attempts to map isograds in the field and use petrography and phase equilibria constraints on temperature and fluid evolution, possibly also using calcite-graphite carbon isotope thermometry or dating metamorphic minerals. This is important because Carr et al. (2000) have questioned the long-held assumption that the CMBbtz should be grouped with the Arc Belt in tectonic reconstructions, suggesting suggest that these metasediments were deposited on the Laurentian margin and not as part of Composite Arc Belt. Compositions, mineral assemblages, and stable isotopes of marbles across this proposed suture may help answer this question, and provide evidence for more accurate placement of the CAB-Laurentian suture zone.
Besides the constraints on mid-crustal fluid-flow from marbles, one student may examine fluid interaction between marbles and metaigneous rocks. The focus of this project will be the 40 km2 Allsaw anorthosite (larger anorthosite in Fig. 3, near the Dysart thrust sheet). This body has only been analyzed as part of geochemical reconnaissance, but is mapped in detail (see Easton, 1992). Interaction with fluids has produced spectacular vein replacement of igneous plagioclase with scapolite. This study may allow a better understanding of fluid-rock interaction and the control that rock-types exert on fluid infiltration in the CMBbtz. This project will involve field characterization of textures, petrography and petrology of metamorphic assemblages, and possibly whole-rock geochemistry to constrain igneous protoliths.
Recent tectonic interpretations of the Composite Arc Belt have argued for a back-arc or rifted arc environment (e.g. Hanmer et al. 2000). One of the lines of evidence for this model is the distribution of 1.3 Ga calc-alkaline rocks, which are thought to represent a pre-rift continental arc that became fragmented by back-arc extension. Some of these rocks occur in the Adirondacks and Green Mountains (NY and VT), which are loosely correlated with tonalities in the Dysart thrust sheet in the CMBbtz (see Fig. 3). The CMBbtz tonalities haven’t been studied in detail, and this project would focus on the geochemistry and petrology of these rocks. This study will also be one in which obtaining zircon dates may be possible and refining the age of the Dysart intrusive rocks would be a useful constraint for the timing and spatial distribution of Grenville magmatism. It would be particularly significant if these rocks are indeed contemporaneous with those in New York and Vermont.
Because this project focuses on the CMBbtz, structural geology projects will have an emphasis on deformation related to this structure and in adjacent terranes. One possible focus of study, the Bancroft shear zone, is a tectonically-late mainly marble-hosted deformation zone which has been interpreted by some as being the boundary between the CMBbtz and the Harvey-Cardiff domain of the Composite Arc Belt (e.g., Carlson et al., 1990; Cosca et al., 1992). In Carlson et al.’s tectonic reconstruction, the Bancroft shear zone represents the site of late extension after peak Grenville orogenesis, and the fundamental relationship between these adjacent terranes is one of tectonic collapse. The interpretation that this feature is a terrane boundary has been disputed by Carr and McMullen (2000) and Easton and Carr (2009). There are several field-based tests of the Carlson et al. (1990) tectonic model that can be applied, especially determining metamorphic conditions during shearing and constraining the age of deformation. This project will also bear on studies of the earlier Salerno Creek deformation zone (below).
The Salerno Creek deformation zone is the newly-proposed boundary between the CMBbtz and the Harvey-Cardiff domain of the Composite Arc Belt (Easton and Carr, 2009). This mylonite zone is well-mapped in part of the southern CMBbtz, so this project will focus on seeing if it is in fact a fundamental boundary across which rocks have experienced different histories. This zone separates two marble belts and appears to host plutonic rocks that do not appear to be present in adjacent terranes (Easton and Carr, 2009). Possible projects related to the Salerno Creek deformation zone include comparative igneous petrology of rocks within and outside of the zone and metamorphic petrology of similar lithologies astride the zone. This project includes enough questions and potential work that it could easily accommodate a second student, should that become necessary or desirable.
Field conditions and special logistics
Camping and hiking in at times moderately steep terrain. Possibility of wet + buggy conditions.
Course Preparation and special logistics
ALL STUDENTS MUST HOLD A U.S. PASSPORT FOR TRAVEL TO AND FROM CANADA!! Students must have taken Mineralogy and Petrology and/or Structural Geology. Additional coursework in tectonics, geochemistry, or geologic field methods would be helpful.
- Anovitz, LM, and Essene, EJ, 1990, Thermobarometry and pressure-temperature paths in the Grenville Province of Ontario. Journal of Petrology, 31:197-241.
- Brown, RL, Chappell, JF, Moore, JM, and Thompson, PH, 1975, An ensimatic island arc and ocean closure in the Grenville Province of southeastern Ontario, Canada. Geoscience Canada, 2:141-144.
- Carr, S, and Berman, RG, 1997, Metamorphic history of the Bancroft – Barry’s Bay area, Ontario Grenville. Geological Association of Canada/ Mineralogical Association Canada Abstracts and Programs, 22:A-23.
- Carr, S, and McMullen, S, 2000, Geologic transect through parts of the Central Metasedimentary Belt (Muskoka Domain), the central Gneiss Belt boundary thrust zone and the Bancroft shear zone in the Barry’s Bay- Bark Lake- Papineau Lake- Maynooth- Gooderham region of the Ontario Grenville. Friends of the Grenville Field Trip Guidebook, 47 p.
- Carr, SD, Easton, RM, Jamieson, RA, and Culshaw, NG, 2000, Geologic transect across the Grenville Orogen of Ontario and New York. Canadian Journal of Earth Sciences, 37:193-216.
- Carlson, KA, van der Pluijm, BA, Hanmer, S, 1990, Marble mylonites of the Bancroft shear zone: Evidence for extension in the Canadian Grenville. Geol Soc Am Bull, 102:174-181.
- Corfu, F, and Easton, RM, 1997, Sharbot Lake Terrane and its relationships to Frontenac Terrane, Central Metasedimentary Belt, Grenville Province; new insights from U-Pb geochronology. Canadian Journal of Earth Sciences, 34:1239-1257.
- Cosca, MA, Essene, EJ, Kunk, MJ, Sitter, JF. 1992. Differential unroofing within the Central Metasedimentary Belt of the Grenville orogen- constraints from Ar-40 Ar-39 thermochronology. Contributions to Mineralogy and Petrology, 10:211-225.
- Dickin, AP, 1998, Nd isotope mapping of a cryptic continental suture, Grenville Province of Ontario. Precambrian Research, 91:433-444.
- Dunn, SR, 2005, Calcite-graphite thermometry in amphibolite facies marble, Bancroft, Ontario. Journal of Metamorphic Geology, 23:813-827.
- Dunn, SR, and Valley, JW, 1996, Polymetamorphic fluid-rock interaction of the Tudor gabbro and adjacent marble, Ontario. American Journal of Science, 296:244-295.
- Dunn, SR, and Valley, JW, 1992, Calcite-graphite thermometry: a test for polymetamorphism in marble, Tudor gabbro, Ontario. Journal of Metamorphic Geology 10:487-501.
Easton, RM, 1992, The Grenville Province and the Proterozoic history of central and southern Ontario, In Geology of Ontario, Edited by PC Thurston, HR Williams, RH Sutcliffe and GM Stott. Ontario Geological Survey Special Paper, 4, pp 715-904.
- Easton, RM and Carr, SD, 2009, Field trip guidebook, Precambrian geology of Cavendish Township and environs, Grenville Province. Friends of the Grenville 38th Annual Meeting and Field Trip, Ontario Geological Survey Open File Report 6230, 59p.
- Hanmer, S, 1988, Ductile thrusting at mid-crustal level, southwestern Grenville Province, Ontario. Canadian Journal of Earth Sciences, 25:1049-1059.
- Hanmer, S, 1989, Geology, western part of the Central Metasedimentary Belt boundary zone, Grenville Province, Ontario. Geological Survey of Canada Map 1688A.
- Hanmer, S, and McEachern, S, 1992, Kinematical and rheological evolution of a crustal-scale ductile thrust zone, Central Metasedimentary Belt, Grenville Orogen, Ontario. Canadian Journal of Earth Sciences, 29:779-790.
- Hanmer, S, Corrigan, D, Pehrsson, S, and Nadeau, L, 2000, SW Grenville Province, Canada; the case against post-14 Ga accretionary tectonics. Tectonophysics, 319:33-51.
- Harnois, L, and Moore, JM, 1991, Geochemistry of two metavolcanic arc suites from the Central Metasedimentary Belt of the Grenville Province, southeastern Ontario, Canada. Canadian Journal of Earth Sciences, 28:1429-1443.
- Lumbers, SB, Heaman, LM, Vertolli, VM and Wu, TW, 1990, Nature and timing of Middle Proterozoic magmatism in the Central Metasedimentary Belt, Grenville Province, Ontario, in Mid-Proterozoic Laurentia-Baltica, edited by CF Gower, T Rivers and AB Ryan. Geological Association of Canada Special Paper 38:243-276.
- McEachern, SJ, and van Breemen, O, 1993, Age of deformation within the Central Metasedimentary Belt boundary thrust zone: constraints on the collision of the Mid-Proterozoic Elzevir terrane. Canadian Journal of Earth Sciences, 30:1155-1165.
- Pehrsson, S, Hanmer, S, and van Breemen, O, 1996, U-Pb geochronology of the Raglan gabbro belt, Central Metasedimentary Belt, Ontario: implications for an ensialic marginal basin in the Grenville Orogen. Canadian Journal of Earth Sciences, 33:691-702.
- Peck, WH, and Smith, MS, 2005, Cordierite-gedrite rocks from the Central Metasedimentary Belt boundary thrust zone (Grenville Province, Ontario): Mesoproterozoic volcanics with affinities to the Composite Arc Belt. Canadian Journal of Earth Sciences, 42:1815-1828.
- Peck, WH, and Valley, JW, 2000, Genesis of cordierite-gedrite gneisses, Central Metasedimentary Belt boundary thrust zone, Grenville Province, Ontario, Canada. Canadian Mineralogist, 38:511-524.
- Peck, WH, DeAngelis, MT, Meredith, MT, Morin, E, 2005, Polymetamorphism of marbles in the Morin terrane (Grenville Province, Quebec). Canadian Journal of Earth Sciences, 42:1949-1965.
- Peck, WH, Volkert, RA, Meredith, MT, and Rader, EL, 2006, Calcite-graphite carbon isotope thermometry of the Franklin Marble, New Jersey Highlands. Journal of Geology, 114:485-499.
- Peck, WH, Volkert, RA, Mansur, A, Doverspike, BA, 2009, Stable isotope and petrologic evidence for the origin of regional marble-hosted magnetite deposits and the zinc deposits at Franklin and Sterling Hill, New Jersey Highlands. Economic Geology, 104:1037-1054.
- Rivers, T, Martignole, J, Gower, CF, and Davidson, A, 1989, New tectonic divisions of the Grenville Province, Southeast Canadian Shield. Tectonics, 8:63-84.
- Robinson, P, Spear, FS, Schumacher, JC, Laird, J, Klein, C, Evans, BW, and
Smith, TE, Harris, MJ, Huang, CH, and Holm, PE, 2001, The geochemical nature of the igneous rocks of the Sharbot Lake Domain, Central Metasedimentary Belt, Ontario. Canadian Journal of Earth Sciences, 38:1037-1057.
- Timmermann, H, Parrish, RR, Jamieson, RA, and Culshaw, NG, 1997, Time of metamorphism beneath the Central Metasedimentary Belt boundary thrust zone, Grenville Orogen, Ontario: accretion at 1080 Ma. Canadian Journal of Earth Sciences, 34:1023-1029.
- Windley, BF, 1989, Anorogenic magmatism and the Grenvillian Orogeny. Canadian Journal of Earth Sciences, 26:479-489.
Published Maps of the CMBbtz
- Armstrong, HS, and Gittins, J, 1968. Geology of Glamorgan and Monmouth Townships, Haliburton County; Ontario Department of Mines, Geological Branch, Open File Report 5021, 210p. (includes two maps, P. 59 and P. 60, both 1 inch: ½ mile).
- Breaks, FW and Thivierge, RH, 2001. Precambrian geology, Wicklow area, Ontario Geological Survey, Report 288, 107p. (includes color Map 2550, scale 1:20,000).
- Bright, EG, 1987a. Geology of the Eels Lake Area, County of Peterborough; Ontario Geological Survey, Open File Report 5604, 190p. (including revised map P.2205 1:50,000).
- Bright, EG, 1987b. Precambrian Geology of the Centre Lake Area, Haliburton and Hastings Counties; Ontario Geological Survey, Open File Report 5658, 186p.
- Bright, EG, 1988. Precambrian Geology of the Burleigh Falls Area, Peterborough County, Southern Ontario; Ontario Geological Survey, Open File Report 5652, 131p. (including map P. 3096).
- Culshaw, NG, 1986. Geology of the Drag Lake Area, Haliburton County; Ontario Geological Survey, Open File Report 5594, 79p. (no map).
- Easton, RM, 1990. Precambrian geology, Digby-Lutterworth area; Ontario Geological Survey, Report 269, 86p. (including color map P. 2530, 1:20,000).
- Easton, RM, 1987a. Geology of the Howland area, Haliburton, Peterborough and Victoria counties; Ontario Geological Survey, Open File Report 5639, 188p. (includes map P. 2699, 1:15,840).
- Easton, RM, 1987b. Geology of the Lochlin area, County of Haliburton; Ontario Geological Survey, Open File Report 5678, 251p. (including map P. 3071, 1:15,840).
- Easton, RM, 1986. Geology of the Digby-Lutterworth Area/ Haliburton and Victoria Counties; Ontario Geological Survey, Open File Report 5601, 270p. (including color maps P.2951, P.2952, both 1:15,840).
- Hanmer, S, 1989, Geology, western part of the Central Metasedimentary Belt boundary zone, Grenville Province, Ontario Geological Survey of Canada, Map 1688A.
- Lumbers, SB and Vertolli, VM, 2003. Precambrian geology, Kawagama Lake area; Ontario Geological Survey, Preliminary Map P. 3525, scale 1:50,000.