Pressure-temperature paths and exhumation of Late Ordovician-Early Silurian blueschists and associated metamorphic nappes of the Salinic Brunswick subduction complex, northern Appalachians

Abstract

Research Article| November 01, 2008 Pressure-temperature paths and exhumation of Late Ordovician–Early Silurian blueschists and associated metamorphic nappes of the Salinic Brunswick subduction complex, northern Appalachians C.R. van Staal; C.R. van Staal † 1Geological Survey of Canada, 625 Robson Street, Vancouver, British Columbia V6B 5J3, Canada †E-mail: [e-mail] Search for other works by this author on: GSW Google Scholar K.L. Currie; K.L. Currie 2Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada *Retired. Search for other works by this author on: GSW Google Scholar G. Rowbotham; G. Rowbotham 3Department of Earth Sciences, University of Keele, Keele, Staffordshire ST5 5BG, UK *Retired. Search for other works by this author on: GSW Google Scholar N. Rogers; N. Rogers 4Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada Search for other works by this author on: GSW Google Scholar W. Goodfellow W. Goodfellow 4Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information C.R. van Staal † 1Geological Survey of Canada, 625 Robson Street, Vancouver, British Columbia V6B 5J3, Canada K.L. Currie *Retired. 2Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada G. Rowbotham *Retired. 3Department of Earth Sciences, University of Keele, Keele, Staffordshire ST5 5BG, UK N. Rogers 4Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada W. Goodfellow 4Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada †E-mail: [e-mail] Publisher: Geological Society of America Received: 04 Sep 2007 Revision Received: 21 Feb 2008 Accepted: 16 Mar 2008 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2008 Geological Society of America GSA Bulletin (2008) 120 (11-12): 1455–1477. https://doi.org/10.1130/B26324.1 Article history Received: 04 Sep 2007 Revision Received: 21 Feb 2008 Accepted: 16 Mar 2008 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation C.R. van Staal, K.L. Currie, G. Rowbotham, N. Rogers, W. Goodfellow; Pressure-temperature paths and exhumation of Late Ordovician–Early Silurian blueschists and associated metamorphic nappes of the Salinic Brunswick subduction complex, northern Appalachians. GSA Bulletin 2008;; 120 (11-12): 1455–1477. doi: https://doi.org/10.1130/B26324.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Late Ordovician–Early Silurian Brunswick subduction complex in northern New Brunswick preserves a nearly intact southeast-facing forearc terrane with clear links among Silurian subduction, under-plating, exhumation, and forearc sedimentation. The forearc terrane grew over time due to successive accretion and underplating of seamounts and isolated ribbons made up of continental and transitional crust concomitant with foreland migration of the trench. A sliver of strongly deformed epidote-blueschists derived from an accreted seamount was stacked together with slightly lower-pressure winchite-bearing tectonites and medium- to high-pressure greenschists of the Fournier, California Lake, and Tetagouche blocks into a series of D1 metamorphic nappes during Salinic closure of the Tetagouche-Exploits backarc basin. The blueschists (~375 °C, 7.2 kbar) locally preserve mineralogical (zoning from actinolite or barroisite core to a rim of glaucophane) and microstructural evidence for a counterclockwise pressure-temperature (P-T) path ascribed to underthrusting beneath the young oceanic lithosphere of the Fournier block shortly after the inception of subduction at ca. 450 Ma. The next phase of accretion is represented by underplating of the California Lake block at ca. 442 Ma. This may have caused emplacement of the blueschists above the slightly lower metamorphic grade Canoe Landing Lake winchite-bearing nappe (350 °C, 6.5 kbar). Underplating of the Tetagouche block at ca. 435 Ma extruded the blueschist sliver and underlying nappes of the California Lake block immediately above greenschist-facies nappes (~5.8 kbar) and beneath lower-pressure (4–5 kbar) greenschist-facies basalt and gabbro of the ophiolitic Fournier block, which was deformed and imbricated earlier, probably during accretion of the California Lake block. Shear sense indicators confirm that the hanging-wall shear zone of the blue-schist sliver accommodated Early Silurian normal motion. D1 is generally time-trans-gressive due to down-stepping of the under-plating-related deformation. Metamorphic relicts, as well as zoning in amphibole and epidote, indicate that the Canoe Landing Lake and other nappes underwent clockwise P-T paths related to subduction of the cool oceanic lithosphere and/or accretion of the California Lake and Tetagouche blocks. 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