Grenville Supergroup Research Articles

Varicolored Marble in the Central Metasedimentary Belt, Grenville Supergroup. I. Circumstantial Evidence of Melting

Abstract Large expanses of granulite-facies white marble occur in the Central Metasedimentary Belt of the Grenville orogen in western Quebec and in contiguous areas of eastern Ontario and New York. Locally, the white rock is transformed into “varicolored” marble, ranging from pink, orange, yellow, green, gray to blue marble, in some cases closely juxtaposed. We have dissected specimens from three target areas in western Quebec. A powerful analytical workflow including high-resolution ZEISS Atlas 5 large-area imaging was employed in combination with detailed energy-dispersive spectroscopy analyses to create digital map-like online datasets of entire samples to display the textures and characteristics in their entirety. We describe in detail the texture and mineralogy of marble specimens collected from exposures created during the construction of Autoroute 5 near Wakefield and of Autoroute 50 near Grenville-sur-la-Rouge and two specimens collected near Bryson, Quebec. At the inferred pressure and temperature and in the presence of H2O, the white marble seems to have melted. A carbonate melt, a powerful flux, can dissolve silicate wallrocks along a mutual contact. In this way, a marble-derived melt has assimilated wallrocks ranging from peridotite to granite. This melting event may have occurred more than once in the 350-million-year lifespan of the Grenville event; the thermal event associated with the Rigolet stage, during gravitational collapse of the orogen approximately one billion years ago, was the most intense. The marble samples contain no vestiges of older deformed assemblages. Whereas the varicolored marble undoubtedly is metasedimentary, a coeval influx of mantle-derived carbonatitic melt and related fluids from a subjacent complex may have caused localized metasomatism of the marble prior to and after melting.

The Kilmar Magnesite Deposits: Evaporitic Metasediments in the Grenville Supergroup, Morin Terrane, Quebec

Mesoproterozoic magnesite deposits are found associated with dolomitic marble and intercalated with metasedimentary rocks of the Grenville Supergroup in the granulite facies Morin terrane (Grenville Province, Quebec). This study examines one of the remaining ore deposits exposed on the surface (at the Dobbie mine), and presents stable isotope and mineralogical data for a marine evaporitic origin. The magnesite ore zone has δ18O(Mag) = 25.5 ± 0.4‰ (VSMOW) and δ13C(Mag) = 1.7 ± 0.2‰ (VPDB; n = 7), while surrounding dolomitic marble has δ18O(Dol) = 24.2 ± 0.6‰ and δ13C(Dol) = −0.2 ± 0.7‰ (n = 11). These values are at the high end of the range for other Morin terrane marbles, and this and sharp transitions in stable isotope ratios between lithologies argue for preservation of evaporitic enrichment in δ18O and δ13C. Boron isotope ratios (δ11B = 15.5‰ to 22.7‰) are also consistent with a marine evaporite origin. Identifying evaporitic protoliths in metasedimentary rocks is important for determining pre-metamorphic depositional environments, and in this case links the sedimentary setting of the Morin terrane to the Adirondack Lowlands (New York, NY, USA). The identification of the Kilmar magnesite deposits as evaporitic also has implications for the formation of sedimentary exhalative base metal deposits in the Grenville Supergroup.

Detrital zircon constraints on Grenville sedimentation at the margin of Laurentia

The southern Grenville Province is made up of metaigneous and metasedimentary rocks that were formed and metamorphosed as part of the Mesoproterozoic active margin of Laurentia. Grenville Supergroup quartzites from the Adirondack Highlands (New York), the Morin terrane (Quebec), and New Jersey Highlands were analyzed to determine detrital and metamorphic zircon U-Pb ages and to help constrain Mesoproterozoic tectonics. These Grenville quartzites have broadly similar detrital age populations as each other, suggesting similar sedimentary source regions and depositional settings in back-arc basin environments at the Laurentian Margin during Geon 12. All samples contain detrital zircon with 1.45–1.25 Ga ages, consistent with proximal Grenville source regions. They also contain detrital ages that point to derivation from the Mazatzal (1.7–1.6 Ga), Yavapai (1.8–1.7 Ga), and Penokean (1.9–1.8Ga) orogens of the North American Midcontinent, and have a diverse population of Archean ages. These results and published data from Adirondack Lowlands metasediments (Chiarenzelli et al., 2015, 2017) show distinctly Laurentian sources, and the related and likely connected nature of the sedimentary histories of the Adirondack Highlands and Lowlands, Morin terrane and New Jersey Highlands. Metamorphic zircon formation is common in high-grade quartzites, and ages are variable between samples depending on the metamorphic history of each terrane and the melt productivity of different rocks (Peck et al., 2010a). Adirondack Highlands samples experienced metamorphic zircon grown during the Shawinigan orogeny and anorthosite-suite emplacement (1.19–1.14 Ga). Morin terrane samples are from the Morin Shear Zone, which was active and caused metamorphic zircon growth during the Ottawan phase of the Grenvillian orogeny (1.09–1.02 Ga). The New Jersey Highlands sample has metamorphic zircon formed during the Rigolet phase of the Grenvillian orogeny (1010–980 Ma).

Age and provenance of Grenville supergroup rocks, Trans-Adirondack Basin, constrained by detrital zircons

Research Article| February 01, 2015 Age and provenance of Grenville supergroup rocks, Trans-Adirondack Basin, constrained by detrital zircons Jeff Chiarenzelli; Jeff Chiarenzelli * 1Department of Geology, St. Lawrence University, Canton, New York 13617, USA *E-mails: jchiaren@stlawu.edu; dkratzmann@santarosa.edu; bselleck@colgate.edu; William.deLorraine@HudBayMinerals.com. Search for other works by this author on: GSW Google Scholar David Kratzmann; David Kratzmann * 2Earth and Space Science Department, Santa Rosa Junior College, PC 668, Call Hall, 680 Sonoma Mountain Parkway, Petaluma, California 94954-2522, USA *E-mails: jchiaren@stlawu.edu; dkratzmann@santarosa.edu; bselleck@colgate.edu; William.deLorraine@HudBayMinerals.com. Search for other works by this author on: GSW Google Scholar Bruce Selleck; Bruce Selleck * 3Department of Geology, 333 Ho Science Center, Colgate University, Hamilton, New York 13346, USA *E-mails: jchiaren@stlawu.edu; dkratzmann@santarosa.edu; bselleck@colgate.edu; William.deLorraine@HudBayMinerals.com. Search for other works by this author on: GSW Google Scholar William deLorraine William deLorraine * 4St. Lawrence Zinc Company, 408 Sylvia Lake Road, Gouverneur, New York 13642, USA *E-mails: jchiaren@stlawu.edu; dkratzmann@santarosa.edu; bselleck@colgate.edu; William.deLorraine@HudBayMinerals.com. Search for other works by this author on: GSW Google Scholar Author and Article Information Jeff Chiarenzelli * 1Department of Geology, St. Lawrence University, Canton, New York 13617, USA David Kratzmann * 2Earth and Space Science Department, Santa Rosa Junior College, PC 668, Call Hall, 680 Sonoma Mountain Parkway, Petaluma, California 94954-2522, USA Bruce Selleck * 3Department of Geology, 333 Ho Science Center, Colgate University, Hamilton, New York 13346, USA William deLorraine * 4St. Lawrence Zinc Company, 408 Sylvia Lake Road, Gouverneur, New York 13642, USA *E-mails: jchiaren@stlawu.edu; dkratzmann@santarosa.edu; bselleck@colgate.edu; William.deLorraine@HudBayMinerals.com. Publisher: Geological Society of America Received: 19 Oct 2014 Revision Received: 07 Dec 2014 Accepted: 08 Dec 2014 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2015 Geological Society of America Geology (2015) 43 (2): 183–186. https://doi.org/10.1130/G36372.1 Article history Received: 19 Oct 2014 Revision Received: 07 Dec 2014 Accepted: 08 Dec 2014 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jeff Chiarenzelli, David Kratzmann, Bruce Selleck, William deLorraine; Age and provenance of Grenville supergroup rocks, Trans-Adirondack Basin, constrained by detrital zircons. Geology 2015;; 43 (2): 183–186. doi: https://doi.org/10.1130/G36372.1 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 SocietyGeology Search Advanced Search Abstract Detrital zircons from quartzites constrain the timing of deposition, provenance, and basin evolution of the Grenville supergroup in the Adirondack Lowlands. Three samples from the stratigraphic succession yield maximum depositional ages of 1284 ± 16 Ma to 1257.6 ± 16 Ma. Shifts in provenance from rifting (unimodal volcanic), carbonate platform (Laurentian interior), deep-water clastics (southern Adirondack arc), to final basin fill (Laurentian interior) are documented. The Trans-Adirondack backarc basin is one of several that opened at ca. 1.30 Ga, filled with thick carbonate-dominated sequences, and closed during the Elzevirian orogeny (ca. 1245–1220 Ma), terminating widespread extension across the leading edge of southeast Laurentia. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Reconnaissance geochronology and geochemistry of the Mont-Tremblant gneiss of the Morin terrane, Grenville Province, Québec

The Mont-Tremblant gneiss is a granulite-facies quartzofeldspathic orthogneiss unit in Morin terrane of the southwestern Grenville Province. These gneisses are the oldest rocks in the Morin terrane and country rocks to intrusions of the 1.15 Ga anorthosite-mangerite-charnockite-granite (AMCG) suite. The Mont-Tremblant gneiss may also be basement to the Grenville Supergroup, but until now it has not been directly dated. Sensitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG) geochronology of zircon from two penetratively deformed samples of Mont-Tremblant gneiss yields igneous ages of 1324 ± 38 Ma and 1333 ± 32 Ma (2σ), and one sample shows metamorphic zircon growth during the Shawinigan orogeny at 1159.4 ± 15.6 Ma. Geochemically, Mont-Tremblant gneiss samples are calc-alkaline, granitic, and show hallmarks of an evolved arc environment. These characteristics are consistent with the Mont-Tremblant gneiss being correlative with the Geon 14 Lacoste and Bondy suites in the Central Metasedimentary Belt of Quebec to the west, but contrast with the more juvenile tonalitic Geon 14 calc-alkaline suites in the Adirondack Highlands and other Grenville outliers in the Appalachian Mountains. This transition may reflect differences in the lithosphere along strike of the Laurentian margin during Geon 14 subduction.

MINERAL AND FLUID EQUILIBRIA IN Mo-BEARING SKARN AT THE ZENITH DEPOSIT, SOUTHWESTERN GRENVILLE PROVINCE, RENFREW AREA, ONTARIO, CANADA

Late-tectonic pegmatitic, aplitic and graphic granites intrude metasedimentary units of the Grenville Supergroup, Composite Arc Belt, in the Renfrew area of southeastern Ontario. Zoned molybdenite-bearing skarns occur at the contact of graphic pegmatites with mixed calcite–dolomite marble, para-amphibolite and gneiss at the Zenith molybdenite deposit. Distal skarns also are found, in the form of discordant veins within foliated marble. Mineral zoning in the skarn consists of diopside–microcline endoskarn plus exoskarn that grades, away from the intrusion, from a diopside-dominant to a tremolite-dominant metasomatic rock. Textural evidence indicates that tremolite was an earlier-formed skarn mineral in the diopside zone. Diopside is absent in the tremolite zone. These patterns are repeated in other similar occurrences of skarn in the area. Apatite grains formed during metasomatism contain primary high-salinity (≥30 wt.% NaCl eq.) liquid-rich fluid inclusions coexisting, along growth zones, with vapor-rich inclusions, indicative of the trapping of an immiscible fluid. The observed parageneses are interpreted to reflect metasomatic replacement of marble by infiltration of a silica-rich orthomagmatic fluid that evolved by the crystallization of the granitic pegmatite, at approximately 600°C and 300 MPa. Such conditions are not inconsistent with phase separation of the aqueous fluid, because the salinity of the fluid is known to drastically raise the critical temperature of the H 2 O–CO 2 miscibility gap. A decrease in temperature or in the chemical potential of silica in skarn furthest from the granites (or both) may account for formation of the tremolite zone. The Mo likely was transported in the metasomatic fluid as alkali oxyacidic complexes. A decrease in f (O 2 ) along with reduction of magmatic sulfur upon interaction of the fluid with graphite-bearing marble are inferred to have triggered the precipitation of molybdenite.

The petrogenesis of metamorphosed carbonatites in the Grenville Province, Ontario

Veins and dikes of calcite-rich rocks within the Central Metasedimentary Belt boundary zone (CMBbz) in the Grenville Province of Ontario have been interpreted to be true carbonatites or to be pseudocarbonatites derived from interaction of pegmatite melts and regional Grenville marble. The putative carbonatites have been metamorphosed and consist mainly of calcite, biotite, and apatite with lesser amounts of clinopyroxene, magnetite, allanite, zircon, titanite, cerite, celestite, and barite. The rocks have high P and rare earth element (REE) contents, and calcite in carbonatite has elevated Sr, Fe, and Mn contents relative to Grenville Supergroup marble and marble mélange. Values of δ18OSMOW (9.9–13.3‰) and δ13CPDB (−4.8 to −1.9‰) for calcite are also distinct from those for marble and most marble mélange. Titanites extracted from clinopyroxene–calcite–scapolite skarns formed by metasomatic interaction of carbonatites and silicate lithologies yield U–Pb ages of 1085 to 1035 Ma. Zircon from one carbonatite body yields a U–Pb age of 1089 ± 5 Ma; zircon ages from two other bodies are 1170 ± 3 and 1143 ± 8 Ma, suggesting several carbonatite formation events or remobilization of carbonatite during deformation and metamorphism around 1080 Ma. Values of εNd(T) are 1.7–3.2 for carbonatites, −1.5–1.0 for REE-rich granite dikes intruding the CMBbz, and 1.6–1.7 for marble. The mineralogy and geochemical data are consistent with derivation of the carbonatites from a depleted mantle source. Mixing calculations indicate that interaction of REE-rich pegmatites with regional marbles cannot reproduce selected major and minor element abundances, REE contents, and O and Nd isotope compositions of the carbonatites.

Hydrothermal fluids during Mesozoic reactivation of the St. Lawrence rift system, Canada: C, O, Sr and Pb isotopic characterization

Calcite veins with accessory galena, sphalerite, barite and fluorite are abundant within the Ottawa-Bonnechère and the Charlevoix-Saguenay failed arms of the St. Lawrence rift system which developed, during early Paleozoic times, within gneisses of the Grenville Province of Canada. The mineral assemblages, paragenesis and precipitation temperatures of the veins resemble the Mississippi Valley deposits. Crosscutting relationships with carbonate rocks of the St. Lawrence Lowlands and deformed carbonate rock slivers of the Charlevoix astrobleme show that the Ottawa graben and Saguenay graben veins are younger than mid-Ordovician or post-Devonian, respectively. δ 18O and δ 13C values for vein calcite are positively correlated and range from +11 to +24‰ and −9 to +3‰, respectively. 87 Sr 86 Sr in calcite and barite range from 0.7129 to 0.7081. The fluids that precipitated calcite were part of a hydrothermal system dominated by meteoric water enriched in 18O by exchange with silicate minerals and deep-seated carbon, either from mantle outgassing, deep-seated brines of the Canadian Shield or from oxidation of reduced carbon in high-grade metamorphic rocks. Veins cutting marbles of the Grenville Supergroup have lower 87 Sr 86 Sr and higher δ 18O and δ 13C values than those hosted in quartzofeldspathic gneisses of the Grenville Province, showing that the fluids were modified by interaction at depth with the marbles. Stable and Sr isotope compositions are also correlated with La Yb ratios in calcite, supporting the fact that the veins formed within similar hydrothermal systems in both the Ottawa and Saguenay grabens. The Pb isotopic compositions of vein galena are radiogenic ( 206 Pb 204 Pb = 18.0–19.7 ; 207 Pb 204 Pb = 15.5–15.7 ; 208 Pb 204 Pb = 37.9–41.0 ) and positively correlated in conventional PbPb diagrams. Pb isotope and REE data strongly suggest that the fluids leached selectively, at the mineral scale, gneisses of the Grenville Province. The basinal fluids within the shelf sequence of the western Appalachians had 208 Pb 204 Pb ratios, in the lower Paleozoic, significantly lower than those of vein galena. This excludes the basin brine model of formation for the vein deposits, like suggested for the Mississippi Valley deposits. The veins rather formed in the Mesozoic, in response to the rifting of northeastern North America and the reactivation of the St. Lawrence rift.

Timing of Intrusion and Deformation of the Rivière-Pentecôte Anorthosite (Grenville Province)

The Riviere-Pentecote Anorthosite (Grenville Province) intruded metasedimentary rocks akin to those of the <1300 Ma old Grenville Supergroup of the western Grenville Province. Interstitial zircons from an undeformed garnetiferous leuconorite are concordant at $1354 \pm 3 Ma$, the age of crystallisation of the anorthosite. Titanite in anorthositic gneisses yields a concordant age of $1008 \pm 6 Ma$, the age of a transcurrent sinistrai deformation. The Riviere-Pentecote Anorthosite is thus a pre-Grenvillian, anorogenic pluton metamorphosed and deformed some 350 Ma after its consolidation, during the final stages of the Grenville orogeny. Metasediments intruded by the 1354 Ma old anorthosite are thus older than their western-Grenville equivalent.

The nature of groundwater flow in fractured rock: Evidence from the isotopic and chemical evolution of recrystallized fracture calcites from the Canadian Precambrian Shield

The isotope geochemistry of fracture calcites in three Precambrian plutons on the Canadian Shield has been investigated in order to understand the paleohydrogeological conditions in fractured crystalline rock. Fracture calcites of ancient hydrothermal origins in the Chalk River and East Bull Lake plutons exhibit 18O enrichment and 13C depletion trends resulting from recent low-temperature calcite recrystallization under open-system conditions for oxygen, but semiclosed for carbon, and under extremely variable time-integrated, water/rock (calcite) ratios. This process causes recycling of elements with calcite distribution coefficients > 1 (rare earths, manganese, and possibly iron) from the precursor calcite to younger calcites as well as calcite control over the 87Sr 86Sr ratio of the groundwater within the Chalk River pluton. The large but variable water/rock (calcite) mole ratios calculated from the shifts in the stable isotopic compositions of fracture calcites are compatible with fracture flow models that invoke flow channeling within single fractures that also contain regions of immobile porosity. Quantification of isotopic shifts resulting from recrystallization requires that the initial isotopic composition of the precursor hydrothermal calcite be well constrained. Unlike the Chalk River and East Bull Lake plutons, hydrothermal fracture calcites in the White Lake pluton, which intrudes marble-rich country rocks of the Grenville Supergroup, have highly variable δ 13C and δ 18O values. This is attributed to mixing of carbon from magmatic and sedimentary reservoirs, and to oxygen isotopic exchange between hydrothermal fluids and carbonate country rocks at the time of intrusion. Convective circulation of meteoric groundwater from the surrounding 13C-rich carbonate rocks (up to 6.6%.) resulted in δ 13C values as heavy as 3.0%. for the fracture calcites in the pluton.

The geochemistry and tectonic significance of pre-metamorphic minor intrusions of the Central Metasedimentary Belt, Grenville Province, Canada

More than 250 samples collected from dykes and sills intruded into the Grenville Supergroup have been analysed, by XRF techniques, for their major and trace element contents. The REE contents of 43 of the samples have been determined by INAA. Using these data, the rocks have been identified and placed in seven suites, each characterized by its own trace-element signature. There are four tholeiitic suites; the low zirconium suite, which comprises a bimodal series of basalts and minor dacites, the intermediate zirconium suite, which is made up of basalts, andesites, dacites, and rhyolites, the high zirconium suite consisting of high iron basalts, and rare highly fractionated tholeiites which comprise basalts characterized by high Mg number, high Ni and Cr contents, and with strongly fractionated trace-element patterns. In addition, a calc-alkaline suite made up of basalts and andesites, a transitional suite of andesites and trachyandesites, and an ultra-potassic suite of leucitites have been identified. On chondrite-normalized multi-element plots all of the suites show negative Nb and Ti anomalies. Similar ranges of rock types, with similar anomalies, occur within volcanic arcs and back-arc basins formed at collisional plate margins where the Nb and Ti anomalies are interpreted as subduction signatures, and also in some continental flood basalt sequences in which the anomalies are commonly suggested to result from crustal contamination. The geology of the Central Metasedimentary Belt leads us to favour an interpretation in which the minor intrusions were emplaced in supracrustal rocks deposited upon attenuated continental crust in a back-arc basin during a collisional orogeny.

Metamorphic constraints on the tectonic evolution of the allochthonous monocyclic belt of the Grenville Province, western Quebec

The tectono-metamorphic evolution of Grenvillian monocyclic terranes in western Quebec has been constrained along a northwest–southeast transect from Réservoir Cabonga to the Morin anorthosite by the study of garnet zoning and the application of geothermobarometric techniques to appropriate mineral assemblages. In all three terrenes examined (Réservoir Cabonga, Mont-Laurier, and Morin terranes), the results are consistent with Grenvillian metamorphism induced by thrusting. Additional magmatic heat may have been provided by the cooling of igneous rocks related to the Morin anorthosite complex.After the peak of the Grenvillian metamorphism, the monocyclic rocks were sliced, and three Grenvillian crustal levels, sharing some of their lithologic elements but having contrasting Grenvillian peak-metamorphic conditions, were subsequently juxtaposed. The deepest crustal level exposed in the transect (level A) comprises the Réservoir Cabonga terrene and the margins of the Mont-Laurier terrene. This level consists of metasediments of the "Grenville Supergroup," garnet amphibolites, and synmetamorphic plutonites whose emplacement predated the thrusting. Metamorphic conditions in level A are estimated at 725–875 MPa and 725–800 °C. Level C, which is exclusively in the central part of the Mont-Laurier terrene, comprises metasediments of the Grenville Supergroup that were metamorphosed at 425–600 MPa and 625–725 °C. Synmetamorphic igneous rocks of the Morin plutonic complex in the Morin terrane were metamorphosed at 600–800 MPa and 650–775 °C, probably in an intermediate crustal level B, which is missing in the Mont-Laurier terrane. It is thus suggested that juxtaposition of the Mont-Laurier terrane and the Morin terrane along the Labelle shear belt occurred after the peak of metamorphism.A comparison of the metamorphic evolution of these monocyclic terranes with that of their adjacent polycyclic counterparts suggests that (i) the Réservoir Cabonga terrane was thrust over the parautochthonous Réservoir Dozois terrane after the peak of metamorphism and (ii) level A rocks of the Mont-Laurier terrane and the Réservoir Baskatong terrane were juxtaposed during the peak of metamorphism.

New tectonic divisions of the Grenville Province, Southeast Canadian Shield

On the basis of geological, geophysical, and geochronological data, the Grenville Province has been divided into three first‐order longitudinal belts, the Parautochthonous Belt (PB), Allochthonous Polycyclic Belt (APB), and Allochthonous Monocyclic Belt (AMB). These are set apart by three first‐order tectonic boundaries, the Grenville Front (GF), Allochthon Boundary Thrust (ABT), and Monocyclic Belt Boundary Zone (MBBZ). The belts are subdivided into terranes based on internal lithological character. The GF separates the Archean to Proterozoic foreland northwest of the orogen from reworked equivalents to the southeast. Continuous at the scale of the orogen, its main characteristic is that of a crustal‐scale contraction fault. The PB, although less clearly identified along the length of the orogen, in most places represents upgraded and tectonically reworked rocks of the adjacent foreland. The boundary between the PB and the APB to the southeast, the ABT, is most clearly delineated in the eastern half of the province. It is the locus of major crustal delamination along which high‐grade, mostly middle Proterozoic, polycyclic terranes were tectonically transported northwest toward and onto the PB. The AMB comprises two separate areas underlain by the Wakeham Supergroup and what is currently known as the Grenville Supergroup, respectively; its basal contact, the MBBZ, is a décollement zone of variable kinematic significance between older polycyclic rocks and tectonically overlying monocyclic rocks. This first‐order zonation implies a tectonic polarity to the Grenville Province, superimposed on which are second‐order features evident from contrasting tectonic styles and radiometric ages. These characteristics are consistent with a diachronous or oblique collisional model for the Grenville orogen.

Geochemistry and origin of the Ore Chimney Formation, a transported paleoregolith in the Grenville Province of southeastern Ontario, Canada

The Ore Chimney Formation is a mid-Proterozoic metapelitic rock unit that separates mafic to intermediate metavolcanic rocks of the Grenville Supergroup from an overlying clastic metasedimentary succession, the Flinton Group. It has been interpreted alternatively as a paleoregolith or a product of hydrothermal alteration of the volcanic rocks, in a major shear zone. The formation is thin (<10 m), massive to poorly layered, crops out over 40 km along strike and is typically composed of alternating layers of biotite schist, muscovite-biotite schist, hornblende-biotite schist and hornblende schist. It typically contains coarse porphyroblasts of garnet and less commonly of staurolite, kyanite, epidote and/or hornblende. Thirty-five samples of the Ore Chimney Formation, fifty samples of the underlying metavolcanics and fourteen samples of the overlying clastic metasediments were analysed for major and twenty-eight trace elements (including REE). Immobile trace-element ratios (Ti/Zr, Zr/Y, Nb/Y, La/Yb) indicate that the Ore Chimney Formation is locally derived from the underlying metavolcanics. Bulk chemistry, field relations and petrographic observations strongly suggest that the Ore Chimney Formation is a locally-reworked weathering product of the metavolcanic rocks.

Chloritoid–hornblende assemblages in quartz–muscovite pelitic rocks of the Central Metasedimentary Belt, Grenville Province, Canada

Abstract Chloritoid–hornblende occurs in quartz–muscovite pelitic schist derived from sediment in a volcaniclastic sequence of the Grenville Supergroup and from reworked sedimentary and regolithic material above the unconformity at the base of the Flinton Group. Comparison of these samples with other pelitic rocks on triangular composition diagrams and in the ACNF and ACFM tetrahedra indicates that the presence of hornblende cannot be explained by unusually high CaO content. The rare assemblage is attributed to a combination of relatively low Al2O3 and high K2O with high CaO/(CaO+Na2O) and FeO/(FeO+MgO).On two qualitative reaction grids derived from AFM diagrams projected through CaO and plagioclase, respectively, the P–T stability field of chloritoid–hornblende overlaps the first appearance of staurolite–biotite in normal pelitic rocks in the kyanite field. Staurolite–hornblende overlaps chloritoid–hornblende and extends to the higher temperatures and pressures of the kyanite–hornblende field.The phase relations in these rocks provide a link between the conventional hornblende‐absent grids for pelitic rocks and those for K2O‐poor (muscovite‐absent) pelitic and mafic amphibolitic rocks.

Zinc and iron metallogeny in the Maniwaki-Gracefield District, southwestern Quebec

Zinc and iron deposits in the Grenville Supergroup metasedimentary rocks of the Maniwaki-Gracefield district, Quebec, exhibit close similarities to the economically important Balmat-Edwards district of New York State. The mineralization is stratiform, it is consistently associated with dolomitic marble units, and it has ages similar to the New York deposits ( approximately 1,200-1,300 m.y.). At least two phases of intense Grenvillian deformation affected the host rocks, and regional metamorphism reached the granulite facies. Lateral and vertical zoning of major and trace elements observed within the zinc deposits indicate that they probably had a submarine exhalative origin.Small magnetite-rich iron-formations related to Mg-rich carbonates, and minor amounts of base metal sulfides including sphalerite, occur within metasediments closely resembling those which host the zinc deposits. The iron deposits are interpreted to occur at stratigraphic positions which are laterally equivalent to the zinc mineralization, and consequently the iron-formations form an important stratigraphic guide to zinc mineralization within the complexly deformed and strongly metamorphosed strata of the Grenville Supergroup.At the regional scale, the Grenville zinc deposits of Quebec, Ontario, and New York are located along two major structural lineaments which border the Central Metasedimentary belt and define a first-order basin hosting the metasedimentary rocks of the Grenville Super-group. These basin-margin lineaments also delineate two regional metallogenic zones characterized principally by zinc and iron deposits: a western zone which encompasses the Maniwaki-Gracefield showings as well as several minor to medium-sized stratiform base metal deposits in Ontario and adjacent portions of Quebec, and an eastern zone which includes the Balmat-Edwards and East Pierrepont deposits of New York as well as the stratiform gold-zinc deposits of Montauban, Quebec. These regional aspects are consistent with current models for the origin of sediment-hosted submarine-exhalative base metal mineralization.

Metamorphism in the Adirondacks. I. Petrology, Pressure and Temperature

Grenville Supergroup sediments and suites of pre- and syn-tectonic igneous rocks have been metamorphosed to the upper amphibolite and granulite facies in the Adirondacks of northern New York during the Grenville orogeny about one billion years ago. Magnetite-ilmenite, alkali feldspar-plagioclase, calcite-dolomite and garnet-clinopyroxene thermometry indicate that metamorphic temperatures (T) increase from about 650 °C in the area west and northwest of Gouverneur to 700–750 °C near Colton and along the Lowlands-Highlands boundary to 750–800 °C in areas within and around the Marcy anorthosite massif. The presence of grossular-rich garnet + quartz without wollastonite + plagioclase in calc-silicate rocks and the apparent absence of metamorphic ferropigeonite in charnockites restrict maximum metamorphic T to less than 800–850 °C. Metamorphic pressures (P), determined from coexisting pyrite-pyrrhotite-sphalerite, garnet-rutile-sillimanite-ilmenite-quartz, fayalite-quartz-ferrosilite, fayalite-anorthite-garnet, ferrosilite-anorthite-garnet-quartz, kyanite-sillimanite, anorthite-garnet-sillimanite-quartz and the stability of akermanite, are 6·5–7·0 kb near Gouverneur and increase to 7·5–8·0 kb in the central Adirondack Highlands. The above P-T data deduced from diverse mineralogical/chemical systems are interpreted as peak or near-peak conditions for Adirondack metamorphism. The compositions of thin retrograde rims on garnets indicate a post-peak-metamorphic P-T path for the Adirondacks with appreciable cooling (200–300°) before decompression. Peak and retrograde P-T conditions inferred for the Adirondacks are similar to numerous other granulite terranes suggesting that similar tectonothermal events are necessary for the formation of many granulite belts.

High- 18O granitic plutons from the Frontenac Axis, Grenville province of ontario, Canada

18O 16O ratios have been determined for whole rock as well as coexisting minerals from nine syn- to post-tectonic monzonite and quartz monzonite plutons in the Westport-Gananoque area covering approximately 2500 km 2. The plutons fall in two distinct isotopic groups: 1. (I) Low- 18O group ( δ = 8.0–11.2): Rideau Lake, Westport and Wolfe Lake plutons and 2. (II) High- 18O group ( δ = 12.7–16.2): Lyndhurst, Perth Road, Battersea, Gananoque, South Lake and Crow Lake plutons. The 18O 16O ratios of granitic rocks from the latter group are among the highest ever reported in the literature. The isotopic compositions of samples within each pluton bear no relationship to the sample distance from the intrusive contacts nor are they affected by the types of country rocks (marbles vs. pelitic gneisses) into which they are emplaced. Oxygen isotope fractionations among coexisting quartz, feldspar, biotite and magnetite all show normal plutonic values. Thus, all lines of evidence suggest that the monzonite and quartz monzonite plutons did not acquire their characteristic 18O 16O ratios at the present level of exposure, either by isotopic exchange with the surrounding metasedimentary country rocks or by any post-crystallization low-temperature alteration processes. The distinct 18 O/ 16 O ratios observed in the high- and low- 18O groups probably reflect the difference in the isotopic compositions of the source materials. The most plausible source for the high- 18O group plutons is the Grenville Supergroup metasedimentary rocks and that for the low- 18O group plutons the Grenville basement gneisses mixed with a small amount of Grenville Supergroup metasedimentary rocks.

Evolution of P–T conditions during a high-grade metamorphic event in the Maniwaki area (Grenville Province)

Pelitic and basic rocks of the Grenville Supergroup in the Maniwaki area (100 km north of Ottawa) were selected for a detailed investigation of the metamorphic history of the Central Metasedimentary Belt of the Grenville Province.Mineral assemblages suggest metamorphic conditions of the granulite facies with local and irregular persistence of the amphibolite facies. Chemical analysis of minerals reveals a lack of equilibrium on the thin section scale. Systematic variation of mineral compositions is explained as the net result of several mineral equilibria established at different stages during the metamorphic evolution of the area. Peak temperatures obtained by biotite–garnet thermometry (cores of isolated grains) are between 760 and 860 °C, whereas clinopyroxene–garnet thermometry gives 740–820 °C. Retrograde temperatures as estimated by various thermometers range between 550 and 750 °C (biotite–garnet), 498 and 670 °C (cordierite–garnet), and 690 and 720 °C (clinopyroxene–garnet). Peak pressures were 6.5–8.5 kbar (650–850 MPa) based upon the ga–pl–sil–qtz barometer and the cpx–ga–pl–qtz barometer. Retrograde pressures of 3.5–5.5 kbar (350–550 MPa) (ga–pl–sil–qtz), 4.1–5.2 kbar (410–520 MPa) (cd–ga), and 5.7–7 kbar (570–700 MPa) (cpx–ga–pl–qtz) were determined.A compilation of results in a P–T diagram allows us to construct a retrograde gradient convex towards the T axis, with an average slope of 12 bar/°C (1.2 MPa/°C). This curve suggests fast uplift and erosion just after the peak of metamorphism followed by a long cooling stage accompanied by minor uplift.

The age and origin of Grenville Province uraniferous granites and pegmatites

Uranium mineralization in pegmatites and granites occurs widely in the Grenville Province but is especially important near Bancroft, Ontario and north of Mont Laurier and Johan Beetz in Quebec. Most investigators have concluded that these rocks were produced by anatexis of a uranium-enriched sedimentary protolith. We have used Rb–Sr isotopic methods to test this and other hypotheses and have reexamined the petrologic and structural features that led to these hypotheses.Rb–Sr whole-rock isochron ages from all three areas range from 937 to 980 Ma, some 150 Ma younger than the age of the peak of Grenville metamorphism as inferred from numerous ages from syntectonic intrusive rocks and high-grade metasediments. The ages of the pegmatites are similar to or just slightly greater than K–Ar ages from this region. The initial 87Sr/86Sr ratios range from 0.7028 to 0.7054, plus one poorly defined value of 0.709. Excluding this last one, these values are only slightly greater than mantle ratios, and calculations show that these rocks could not have been derived from the quartzofeldspafhic gneisses of these areas and certainly not from Grenville Supergroup sediments.The late timing of the emplacement of these rocks and the popularity of a continental collision model for the Grenville Province producing a very thick crust lead us to suggest an origin by deep melting due to isothermal decompression during rapid uplift. This suggestion is supported by the location of all the occurrences near zones interpreted to be paleorift systems.