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Fredericton, Canada

Recently gathered stratigraphic and U–Pb geochronological data indicate that the pre-Triassic rocks of the Grand Manan Terrane on the eastern side of Grand Manan Island can be divided into: (1) Middle Neoproterozoic (late Cryogenian) quartzose and carbonate sedimentary sequences (The Thoroughfare and Kent Island formations); (2) a Late Neoproterozoic (early Ediacaran) volcanic-arc sequence (Ingalls Head Formation); and (3) Late Neoproterozioc (mid-Ediacaran) to earliest Cambrian (early Terreneuvian) sedimentary and volcanic-arc sequences (Great Duck Island, Flagg Cove, Ross Island, North Head, Priest Cove, and Long Pond Bay formations). A comparison to Precambrian terranes on the New Brunswick mainland (Brookville and New River terranes) and in adjacent Maine (Islesboro Terrane) suggests that the sedimentary and volcanic sequences of the Grand Manan Terrane were deposited on the continental margin of a Precambrian ocean basin that opened during the breakup of Rodinia in the Middle Neoproterozoic (Cryogenian) and closed by the Early Cambrian (Terreneuvian) with the final assembling of Gondwana. Rifting associated with the initial opening of the Paleozoic Iapetus Ocean began in the Late Neoproterozoic (late Ediacaran) and so overlapped in time with the closing of the Precambrian Gondwanan ocean. The southeastern margin of the Iapetus Ocean is defined by thick sequences of quartzrich Cambrian sediments (within the St. Croix and Miramichi terranes of New Brunswick) that were largely derived from recycling of Precambrian passive-margin sedimentary rocks preserved in the Grand Manan and Brookville terranes of New Brunswick and in the Islesboro Terrane of Maine. These Precambrian terranes are interpreted to represent dextrally displaced basement remnants of the Gondwanan continental margin of Iapetus, consistent with the model of a two-sided Appalachian system proposed by Hank Williams in 1964 based on his work in Newfoundland. © 2014 GAC/AGC®.

Zhang W.,University of New Brunswick | Lentz D.R.,University of New Brunswick | Thorne K.G.,Geological Surveys Branch | McFarlane C.,University of New Brunswick
Ore Geology Reviews | Year: 2016

The Sisson Brook W-Mo-Cu deposit was formed by hydrothermal fluids likely related to the Nashwaak Granites (muscovite-biotite granite, Group I; and biotite granite, Group II) and related dykes (biotite granitic dykes, Group III; and a feldspar-biotite-quartz porphyry dyke, Group IV). Chemical data obtained using EPMA and LA-ICP-MS data of primary magmatic biotites were used to investigate magmatic processes and associated hydrothermal fluids.Trace element features of biotite in the Group I two-mica granite suggest other magmatic processes along with a simple fractional crystallization. The K/Rb ratios and compatible elements (Cr, Ti, Co, V, and Ba) in biotite from Groups II, III, and IV decrease, whereas incompatible elements including Ta, Tl, Ga, Cs, Li, and Sn increase with magma fractionation. No correlation of Cu, W and Mo with K/Rb ratios is evident, suggesting that partitioning of Cu, W, and Mo into biotite may not be entirely controlled by magma fractionation.Halogen fugacity of the parental magma of the Nashwaak Granites and related dykes, calculated from zircon saturation temperature shows that Group I has high fHF/fCl ratios (broadly higher than 0), similar to the plutons at the Henderson porphyry Mo deposit. The fHF/fCl ratios of the other groups are generally lower than 0, comparable to the Santa Rita porphyry Cu deposit. The fH2O/fHCl and fH2O/fHF ratios inferred from biotite in the Nashwaak Granites and related dykes range from 3 to 5 and from 4 to 5, respectively. The inferred oxygen fugacity shows that the dyke phases (Groups III and IV) have the oxygen fugacity around the nickel-nickel oxide buffer. The plutonic phases (Groups I and II) have the oxygen fugacity around the quartz-fayalite-magnetite (QFM) buffer at high temperatures and oxidized to nickel-nickel oxide buffer at lower temperatures. This oxidation process in the plutonic phases (Groups I and II) could be caused by H2 release at or near H2O vapor saturation at high H2O/Fe2+. The magma associated with the biotite dykes (Group III) is more likely the source of the hydrothermal fluids at the Sisson Brook deposit since it has the highest differentiation degree and seems to have formed in an oxidized setting, necessary for Mo to concentrate in the late stage fluids. © 2016 Elsevier B.V.

LoDuca S.T.,Eastern Michigan University | Miller R.F.,New Brunswick Laboratory | Wilson R.A.,Geological Surveys Branch
Atlantic Geology | Year: 2013

Carbonaceous compressions from the Pridolian to middle Lochkovian Indian Point Formation in the Flatlands area of New Brunswick comprising a central axis with irregularly arranged unbranched appendages are assigned to Medusaegraptus mirabilis. This is the first report of intact thalli of this noncalcified macroalgal taxon from a locality outside of western New York. The biotic composition, stratigraphic context, and sedimentology of this occurrence suggest a shallow-marine depositional setting roughly comparable to that for the type material of Medusaegraptus mirabilis from Gasport, New York. © Atlantic Geology 2013.

The central part of the Central plutonic belt in New Brunswick is underlain by numerous plutons of calc-alkaline, foliated and unfoliated granite that intrude Cambrian to Early Ordovician metasedimentary rocks. U-Pb (zircon) dating demonstrates that granites range in age from Middle Ordovician to Late Devonian, although most are late Silurian to Early Devonian. An age of 467 ± 7 Ma has been obtained on the foliated McKiel Lake Granite, whereas unfoliated intrusions yield ages of 423.2 ± 3.2 Ma (Bogan Brook Granodiorite), 420.7 +1.8/-2.0 Ma (Nashwaak Granite), 419.0 ± 0.5 Ma (Redstone Mountain Granite), 416.1 ± 0.5 Ma (Beadle Mountain Granite), 415.8 ± 0.3 Ma (Juniper Barren Granite), 409.7 ± 0.5 Ma (Lost Lake Granite), and 380.6 ± 0.3 Ma (Burnthill Granite). All plutons exhibit mixed arc-like and within-plate geochemical signatures, although the Redstone Mountain and Burnthill granites are dominantly within-plate type. Trace element data reveal a close overall geochemical similarity between Ordovician and Silurian – Devonian plutons, indicating that all were generated by partial melting of similar crustal sources and/or share a similar petrogenesis. Late Silurian to Early Devonian plutons mainly comprise biotite and/or muscovite-bearing, peraluminous granite and are considered prospective for granophile-element mineralization. All plutons contain Sn well in excess of the granite global average abundance, and several contain average tin values comparable to productive stanniferous granites elsewhere. The Burnthill, Lost Lake, Beadle Mountain and Nashwaak granites are geochemically most evolved and enriched in Sn and W. The Burnthill Granite in particular has experienced late-stage hydrothermal processes that have resulted in local enrichments of these elements. © Atlantic Geology 2016.

Wilson R.A.,Geological Surveys Branch | Van Staal C.R.,Geological Survey of Canada | McClelland W.C.,University of Iowa
American Journal of Science | Year: 2015

Development of an Upper Ordovician to lower Silurian (Llandovery) accretionary wedge (Brunswick subduction complex) along the composite Laurentian margin accompanied subduction of the Tetagouche backarc basin and coincided with synaccretionary sedimentation in the Bathurst and Fournier supergroups in northern New Brunswick. These dominantly turbiditic synaccretionary units conformably to unconformably overlie Upper Ordovician pelagic shale and chert in the upper stratigraphic levels of several of the nappes that compose the imbricate thrust stack of the subduction complex. Local occurrences of tectonic mélange at the contacts between the turbidites and their pelagic substrate are consistent with deposition of at least some of the former during thrust-related deformation in the accretionary wedge. Detrital zircon data indicate maximum depositional ages ranging from 454 ± 3 to 459 ± 8 Ma, coeval with initiation of subduction of the Tetagouche backarc basin. In the Elmtree inlier, arc tholeiitic basalt disconformably or unconformably overlies Darriwilian MORB-type pillowed flows that constitute backarc oceanic crust of the Tetagouche basin. Sedimentary rocks immediately below and intercalated with the arc tholeiites contain detrital zircons ranging from 444 ± 6 Ma to 455 ± 10 Ma, suggesting that the tholeiites are related to backarc subduction. Detrital zircon age spectra from all sampled units exhibit a distinct Laurentian signature, indicating an abrupt change in provenance coeval with closure of the backarc basin and Ganderia - Laurentia collision. The lithology and implied ages of the Bathurst and Fournier synaccretionary sedimentary rocks support a correlation with siliciclastic and carbonate-rich turbidites of the Matapedia cover sequence, which were deposited farther west in a forearc setting (Matapedia forearc) with respect to subduction of Tetagouche backarc oceanic lithosphere. The implication of Late Ordovician influx onto the accretionary wedge and foredeep of sediments having a Laurentian affiliation (like those in the Matapedia forearc), demonstrates trenchward migration of forearc sedimentation between ca. 450 and 430 Ma. This southeastward (present coordinates) expansion occurred in concert with episodic accretion of buoyant crustal blocks that populated the Tetagouche - Exploits basin, and concomitant southeastward step-back of the subduction zone.

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