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THE OTTAWAN OROGENY

THE OTTAWAN OROGENY. Himalayan style crustal channel?. GOALS. To present a Himalayan model for the development of the Grenville Orogenic Event. To apply this model to the a portion of the Canadian (Ontario) and adjacent Adirondack (New York) terrane assemblage.

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THE OTTAWAN OROGENY

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  1. THE OTTAWAN OROGENY Himalayan style crustal channel?

  2. GOALS • To present a Himalayan model for the development of the Grenville Orogenic Event. • To apply this model to the a portion of the Canadian (Ontario) and adjacent Adirondack (New York) terrane assemblage. • To examine this model with particular reference to the nature and timing of activity along the major terrane-bounding shear zones, periods of igneous intrusive activity, and timing of metamorphic events.

  3. 40km CENTRAL GNEISS BELT CMBBZ SHARBOT LAKE BSZ RLSZ BANCROFT N ELZEVIR MSZ FRONTENAC ADK. LOWLANDS ccsz MAZINAW ADK. HIGHLANDS Adapted from Davidson (1998)

  4. Terranes and shear zones Sharbot Lake-Frontenac/Adirondack lowlands Adirondack Highlands Mazinaw Elzevir Bancroft CCSZ RLSZ MSZ LL HL Anorthosite (AMCG Suite)

  5. 1300-1200Ma Igneous Events

  6. 1180-1120 Ma RLSZ MSZ AMCG etc.

  7. 1120-1095 Ma HAWKEYE

  8. 1090-1050 Ma CMBBTZ LYON MOUNTAIN

  9. Observations • There is a shift in the locus of igneous activity through time (generally W to E) reflecting the assembly of Grenvillian Terranes along eastern Laurentia. • The anorogenic/rift AMCG event magmas intrude the Adirondack (ADK) Highlands, Lowlands, Frontenac, Sharbot Lake and Mazinaw Terranes but are focused in the ADK Highlands • Post AMCG pre Ottowan Orogney; Hawkeye granitoids are primarily found in the ADK Highlands. • Lyon Mountain Granitoids rim the ADK Highlands are common along or adjacent to the CCSZ and scattered through the other terranes. (Pressure-release A-type magmas: )

  10. OTTAWANTHERMAL EVENT

  11. 1090-1050 Ma CGB SL B MAZ EL F ADK LL ADK H

  12. 1050-1020 Ma

  13. 1010-980 Ma

  14. ObservationsMetamorphic events • Adirondack Highlands and the Mazinaw terranes record the Ottawan Event. • Adirondack Lowlands record a weak Ottawan Event focused along the CCSZ • Frontenac and Sharbot Lake Terranes do not record the Ottawan Event. • Terranes west of the CMBBZ record pluses of metamorphism at a slightly later time and cool quickly. From Davidson (1998) An overview of the Grenville Province Geology, Canadian Shield.

  15. ccsz Dana Hill metagabbro ADK LL ADK HL Diana Syenite Body Hbl 39Ar/40Ar 979+/-8.6Ma Dana Hill Metagabbro (ADK highlands) Sphene U/Pb 989 +/- 1.7Ma Hbl 39Ar/40Ar 1020 Ma After (Streepey et al. 2001) Diana Syenite (ADK lowlands) Sphene U/Pb 1041.3+/-1.7Ma

  16. Lowlands Highlands • Early 30+m wide shear zones in the DHMG record recrystallization temperatures in excess of 700oC, sphene replacement of Fe-Ti Oxide minerals, and a complete lack of scapolite. • Late (sub-meter wide) shear zones in the DHMG record recrystallization temperatures ranging from 670-700oC and widespread repalcement of plagioclase by scapolite. • Shear zones (meter + and sub meter widths) in the Diana Syenite Body span a wide range of temperature conditions (sub 550oCa), and most show sphene replacement of Fe-Ti oxide minerals • Shear zones contain widespread scapolite replacement of plagioclase. CCSZ aLamb (1993) (Streepey et al. 2001: Johnson et.al (2004)).

  17. Lowlands Highlands • Large early-formed shear zones in Dana Hill Metagabbro (high temp) NO SCAPOLITE • Scapolite replacement of plagioclase in (sub meter wide shear zones) Dana Hill Metagabbro Body • Dana Hill Metagabbro (Highlands) Sphene cooling through 650oC at 1020 Ma. • 39Ar/40Ar cooling through closure for hornblende (550oC) ~1000-978 Ma • Scapolite replacement of plagioclase in shear zones (DSB) • Diana Syenite Body (DSB) Sphene-growth in shear zones at ~ 1041 Ma. • Thermal resetting/growth of sphene in DSB at 1035-1050 Ma age. Zircon records ~1150 Ma AMCG age (McLelland et al (2003). • 39Ar/40Ar cooling through closure tor hornblende (550oC) ~990-978 Ma CCSZ

  18. CCSZ Thermal Profile CCSZ ~1040Ma ~1020 Ma ~990Ma 700 500 Temperature oC H.L. L.L. 300 CCSZ 100 -3 -2 -1 0 1 2 3 4 5 distance (km)

  19. Fluid Inclusion data (syn-post orogenic)_LYON MOUNTAIN GRANITE

  20. CCSZ TEMPERATURE 800oC 900oC 700oC MOHO Channel Flow Thermal Gradients 100 km Adapted from: Beaumont, R.A. Jamieson, M.H. and Lee B. (2001) Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface denudation: Nature, 414, pp. 738-742.

  21. TECTONIC CROSS-SECTIONS A’

  22. ~ 1160-1110 Ma Old Mt Holly Arc MSZ RLSZ CCSZ LL Crustal detachment HL Trench roll back Or delamination FLINTON GROUP AMCG main phase

  23. Old Mt Holly Arc 1155-1112 Ma arc MSZ RLSZ CCSZ LL Crustal detachment HL FLINTON GROUP HAWKEYE GRANITOIDS AMCG late phase-Hawkeye intrusive suite 1110-1100 Ma

  24. CCSZ RLSZ MSZ LL HL Amazonia? FLINTON GROUP HAWKEYE GRANITOIDS 1090-1040 Ma LYON MOUNTAIN GRANITOIDS OTTAWAN PHASE

  25. Extrusion of the low viscositygranulite core of the orogen 1080-1030Ma Lyon Mtn A-type Granitoid ADK HL F.T. MAZ ADK LL SLT Granulite core Zone of active footwall deformation

  26. Lyon Mtn A-type Granitoid ADK HL F.T. MAZ ADK LL SLT Granulite core Zone of active footwall deformation

  27. Conclusions • The Shawinigan- AMCG- pre-Ottawan development for this part of the Grenville can be explained via tectonic switching and or collision along an Andean-type margin (first proposed by Hanmer et al. (2000)). • AMCG magmas intrude into an evolving back-arc basin at a time when the ADK Highlands are structurally beneath the ADK LL/Frontenac/Sharbot Lake Terranes. All of these terranes receive AMGG magmas. (Flinton Group deposited) • Continental-Continenal Collision occurs at or near to 1090Ma (Ottawan Orogeny)

  28. Conclusions • During Ottawan compression, the ADK H.L. Terrane is mobilized and extruded along a tectonic channel. • This extrusion is oblique thrust in character and focused along the CCSZ. Thermal gradients established across the CCSZ with localized heating of the adjacent ADK lowlands (resets isotopic systems in the ADK lowlands near to the CCSZ: Dahl (2002)). • Major un-named shear zones in the eastern Adirondack Highlands my represent the base of this channel. • Extrusion is aided by the formation of pressure release melts (syn-post Ottawan Lyon Mountain Granitoids). Fluid inclusion data from Lyon Mountain Granitoids adjacent to the CCSZ record nearly isothermal uplift.

  29. Conclusions • Uplift results in gravity-driven collapse of cover rocks (ADK L.L. Frontenac over Sharbot Lake Terranes) to the W- NW. Extrusion of the granulite core with deflation of the mid-lower crust, rotates the Mazinaw Terrane triggering amphibolite facies metamorphism. • Continued convergence reactivates shear zones to the west driving short tectonothermal events in terranes to the west (Central Gneiss Belt).

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