The structural and metamorphic history of the Taconic unconformity in western Massachusetts

Evidence from detailed structural and petrographic studies in western Massachusetts shows that the Cambro-Ordovician Rowe Schist and the Middle Ordovician Moretown Formation have different depositional, structural, and metamorphic histories and are separated by a pre-Taconic angular unconformity. The Rowe Schist (pelitic and semi-pelitic schists and minor lenticular amphibolites) underwent multiple periods of deformation and amphibolite facies grade of metamorphism before the deposition of the Moretown Formation. The latter is composed of the Chester Amphibolite, chlorite–muscovite schist, and staurolite–garnet–biotite schists. The predominant structures and metamorphism in the Moretown Formation are those of the Acadian Orogeny. Both the Rowe Schist and the Moretown Formation are transected by a foliated pegmatitic granite (Middlefield – Blair Pond Pluton). A dyke of the granite cuts the composite tectonic fabric in the Rowe Schist (which it post-dates), but it is generally deformed by the earliest and regional schistosities found in the Moretown Formation (which it pre-dates). The base of the Moretown Formation is defined by the Chester Amphibolite. It represents a recrystallized basic volcanic rock associated with an island arc system.

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A retrogressive sapphirine-cordierite-talc paragenesis in a spinel-orthopyroxenite from southern Karnataka, India

Mineralogical Magazine ◽

10.1180/minmag.1993.057.387.10 ◽

1993 ◽

Vol 57 (387) ◽

pp. 273-288 ◽

Cited By ~ 4

Author(s):

C. R. L. Friend ◽

A. S. Janardhan ◽

N. Shadakshara Swamy

Keyword(s):

Dharwar Craton ◽

Amphibolite Facies ◽

Coarse Grained ◽

Cooling History ◽

Metamorphic History ◽

Gneiss Complex ◽

Igneous Origin ◽

Mineral Assemblages ◽

History Of ◽

Granoblastic Texture

AbstractWithin amphibolite facies Peninsular gneisses in the south of the Dharwar craton, units of Sargur supracrustal rocks contain ultrabasic enclaves. One of these enclaves is an orthopyroxenite which comprises bronzite, spinel and minor phlogopite preserving coarse-grained, relic textures of probable igneous origin. After incorporation into the gneisses the enclave evolved through several distinct stages, elucidation of which allow an assessment of its metamorphic history.Firstly, deformation during closed system, anhydrous recrystallisation caused the coarse-grained textures to be partially overprinted by similar mineral assemblages but with a granoblastic texture. Secondly, open system hydration caused retrogression of the bronzite to alumino-gedrite at the margins of the enclave. Subsequently, the penetration of these fluids along grain boundaries caused reactions between spinel and bronzite to produce reaction pockets carrying assemblages of peraluminous sapphirine associated with cordierite and talc. The differences in the mineral assemblages in each pocket coupled with slight variations in their chemistry, suggest that equilibrium did not develop over the outcrop. Because sapphirine + magnesite is present in some pockets, it is evident that CO2 was also a component of the fluid.Phase relations from the MASH portion of the FMASH system, to which the chemistry of the reaction pockets approximates, suggest that the hydrous metamorphism causing the changes depended upon the assemblage enstatite + spinel + vapour which exists at PT conditions above the position of I16, ∼760°C at 3 kbar and below I21 at ∼765°C at 5.6 kbar (Seifert, 1974, 1975), where sapphirine is replaced by kornerupine. The suggested path of reaction occurred between I18 and I21. Subsequent reactions related to I20 cause the formation of cordierite. Talc formation has to be modelled in a different reaction grid.The metamorphism recorded by these reactions is thus at a maximum of amphibolite facies and is interpreted to have formed during the uplift and cooling history of the gneiss complex when hydrous fluids were free to migrate. Given the complex high-grade metamorphic history of this part of the Dharwar craton this event is likely to be late Archaean or Palaeoproterozoic in age.

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An application of factor analysis to basic volcanic rock geochemistry

Bulletin of Volcanology ◽

10.1007/bf02597106 ◽

1974 ◽

Vol 38 (3) ◽

pp. 1070-1089 ◽

Cited By ~ 6

Author(s):

D. M. Shaw ◽

C. Dupuy ◽

M. Fratta ◽

J. Helsen

Keyword(s):

Factor Analysis ◽

Volcanic Rock ◽

Basic Volcanic Rock ◽

Basic Volcanic

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The tectonics and depositional history of the Ordovician and Silurian rocks of Notre Dame Bay, Newfoundland

Canadian Journal of Earth Sciences ◽

10.1139/e85-060 ◽

1985 ◽

Vol 22 (4) ◽

pp. 607-618 ◽

Cited By ~ 27

Author(s):

R. J. Arnott ◽

W. S. McKerrow ◽

L. R. M. Cocks

Keyword(s):

Strike Slip ◽

Late Ordovician ◽

Island Arc ◽

The West ◽

Depositional History ◽

Middle Ordovician ◽

The North ◽

Lower Ordovician ◽

History Of ◽

Ophiolitic Rocks

In the Notre Dame Bay region, ophiolitic rocks underlie a thick sequence of Lower Ordovician volcanic-arc rocks to the north of the Lobster Cove – Chanceport Fault. Neither this fault nor the Lukes Arm – Sops Head Fault shows evidence of very large strike-slip movements, as parts of the same arc, together with much arc-derived detritus, straddle both faults. Towards the east, this arc-derived detritus becomes more distal in aspect and passes laterally into the Dunnage Mélange. During the Middle Ordovician Epoch (late Llandeilo and early Caradoc), most areas show a marked decrease in volcanic activity and in the amount of coarse detritus deposited. Coarse turbidites reappear, at different times in different areas, during the Late Ordovician. These are related to several fault-bounded basins and to movements on the Lukes Arm – Sops Head Fault. Many of these faults, particularly in the east, are marked by olistostromes, several of which can be dated by fossils as Late Ordovician and Early Silurian. The whole region, between the Reach Fault on the east and the Baie Verte – Brompton Line on the west, has a stratigraphic unity. If it has been moved by strike slip relative to the Long Range, then any such fault must lie to the west of the Baie Verte – Brompton Line. The interpretation of an Early Ordovician island arc moving above an easterly directed subduction zone is in accord with both the geochemical and palaeontological evidence. The Notre Dame Bay region may have been converted into a transform-dominated margin in the Late Ordovician and Early Silurian in a manner analogous to the oblique slip tectonic regimes of the Californian and New Zealand margins during the Tertiary, with a precursor of the Reach Fault marking the edge of the continent after the Notre Dame island arc had collided with North America.

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Sur la structure en coussins des volcanites basiques de la region de Cumbres-Mayores (Huelva, Espagne)

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.s7-vii.1.80 ◽

1965 ◽

Vol S7-VII (1) ◽

pp. 80-84

Author(s):

Jean Pierre Bard

Keyword(s):

Volcanic Rock ◽

Open Water ◽

Sea Floor ◽

Basic Volcanic Rock ◽

Pillow Lavas ◽

Rock Types ◽

Basic Volcanic

Abstract Petrographic and structural analyses of the pillow lavas in the Cumbres-Mayores spilitic complex show that they belong to two different basic volcanic rock types representing different conditions of emplacement. The first type exhibits decreasing crystallinity toward the center of the mass, radial disposition of amygdules, a clastic envelope, and a clay-sand cement between the pillows. This suggests that this type of pillow structure was formed in an unconsolidated mud. The second type has fluid structures parallel to the contours of the pillows, ovoid lithophysae, clastic aureoles and very little or no cement. These pillows were probably formed in open water, rolled on the sea floor, and massed in piles.

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Anatomy and orogenic history of a Paleoproterozoic accretionary belt: the Makkovik Province, Labrador, Canada

Canadian Journal of Earth Sciences ◽

10.1139/e01-099 ◽

2002 ◽

Vol 39 (5) ◽

pp. 711-730 ◽

Cited By ~ 33

Author(s):

John W.F Ketchum ◽

Nicholas G Culshaw ◽

Sandra M Barr

Keyword(s):

Island Arc ◽

Amphibolite Facies ◽

Mobile Belt ◽

Localized Deformation ◽

Facies Metamorphism ◽

History Of ◽

Archean Crust ◽

Arc Setting ◽

Back Arc ◽

Over Time

The Makkovik Province is a segment of a Paleoproterozoic accretionary belt (the MakkovikKetilidian orogen) that developed on the southern margin of Laurentia at 1.91.7 Ga. In contrast to coeval Laurentian orogenic belts that mainly resulted from collision of Archean plates, MakkovikianKetilidian orogenesis was dominated by active-margin processes including continental margin arc plutonism and juvenile terrane accretion, both of which were accompanied by regional transpression. In the Makkovik Province, earliest deformation and amphibolite-facies metamorphism of Paleoproterozoic riftdrift assemblages (Post Hill and Moran Lake groups) and the Archean foreland (Nain Province) occurred at 1.9 Ga in response to accretion of a Paleoproterozoic island arc. Following this collision, cratonward-dipping subduction was established, resulting in the formation of the 18951870 Ma Island Harbour Bay Plutonic Suite, a calc-alkaline magmatic arc built on reworked Archean crust. Crust formation continued between ca. 1860 and 1850 Ma with deposition of the Aillik Group on a largely juvenile basement in a rifted-arc or back-arc setting. Sometime before 1802 Ma this depositional basin was tectonically inverted, with resultant northwestward thrusting of the Aillik Group over reworked Archean crust. This phase of deformation may have been driven by accretion of a second island arc potentially represented by the Cape Harrison Metamorphic Suite. Regional transpression and amphibolite-facies metamorphism at ca. 18151780 Ma were accompanied by widespread granitoid plutonism. These events were mainly concentrated in the juvenile domains and are thought to reflect processes in a broad continental back-arc setting. A final orogenic pulse, marked by regional greenschist-facies transpression and emplacement of A-type granitoid plutons, occurred between 1740 and 1700 Ma, with deformation and plutonism potentially linked to crustmantle detachment and incursion of mafic magmas at the base of the crust, respectively. The record of crustal development suggests that the coeval themes of spatially and temporally linked structural and plutonic activity, oceanward migration of this activity over time, and a trend toward increasingly more localized deformation occurred throughout the orogenic history of the Makkovik Province. These characteristics are thought to broadly reflect oceanward crustal growth of the orogen over time. In the correlative Ketilidian mobile belt of southern Greenland, these themes were also operative but appear to have been less pronounced, most likely due to minimal or a complete absence of accretion of island-arc material.

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Timing of deformation, metamorphism and leucogranite intrusion in the lower part of the Seve Nappe Complex in central Jämtland, Swedish Caledonides

10.5194/egusphere-egu21-13097 ◽

2021 ◽

Author(s):

Iwona Klonowska ◽

Anna Ladenberger ◽

David G. Gee ◽

Pauline Jeanneret ◽

Yuan Li

Keyword(s):

High Pressure ◽

White Mica ◽

Detrital Zircons ◽

Amphibolite Facies ◽

Foreland Basins ◽

Middle Ordovician ◽

Metamorphic History ◽

Icp Ms ◽

Nappe Complex ◽

Seve Nappe Complex

The new LA-ICP-MS zircon isotope age data from paragneiss, amphibolite and two leucogranite intrusions in the Lower Seve Nappe of the &#197;re synform in the Caledonides of central J&#228;mtland provide evidence of both Silurian and Ordovician tectonothermal histories. Well established concordant c. 468 and c. 470 Ma magmatic ages for the S&#229; quarry leucogranite, which cut earlier foliations and folds in the host-rock amphibolites and paragneisses, imply a tectonothermal history prior to the Middle Ordovician (c. 469 Ma), perhaps synchronous with what has been previously recognized in the Seve Nappe Complex of Norrbotten (e.g. Root & Corfu, 2012), 400 km farther north in the Swedish Caledonides, and very recently also in the Middle Seve Nappe in central J&#228;mtland (Walczak et al. 2020).The field relationships and data presented here show that magmatic activity occurred during the early Silurian (c. 443 Ma) and earlier during the Early to Middle Ordovician (c. 469 Ma), and that deformation and metamorphism took place both prior to and after c. 469 Ma. The Lower Seve rocks from the nearby COSC-1 drill core have been metamorphosed in the upper amphibolite facies, however, the remnants of the high-pressure metamorphic history are preserved in the relic minerals, including high-silica white mica, in the garnet-bearing mica schists. The exact age of the high-pressure metamorphism is not known so far; however, it predates the 460-430 Ma amphibolite facies deformation recorded by titanites in the amphibolites (Giuntoli et al. 2020). &#160;&#160;&#160;Zircons in an amphibolite proved to be highly discordant but indicate Early Silurian metamorphism during isoclinal folding. Detrital zircons in a paragneiss are dominated by Sveconorwegian populations, but also include a range of younger Neoproterozoic grains down to the Early Ediacaran (c. 600 Ma).This new evidence of early Caledonian deformation and metamorphism indicates that the Seve tectonothermal history in central J&#228;mtland probably started early in the Ordovician, or before. Subduction and accretion along the Baltoscandian outer margin occurred prior to the Scandian continent-continent collision, with Siluro-Devonian emplacement of the Seve Nappe Complex across the foreland basins onto the Baltoscandian platform.References:Giuntoli, F., Menegon, L., Warren, C.J., Darling, J., Anderson, M.W. 2020. Tectonics, 39, e2020TC006267, https://doi.org/10.1029/2020TC006267.Root, D., Corfu, F. 2012. Contributions to Mineralogy and Petrology, 163, 769-788, https://doi.org/10.1007/s00410-011-0698-0.Walczak, K., Barnes, C.J., Majka, J., Gee, D.G. Klonowska, I., 2020. Geoscience Frontiers (in press), https://doi.org/10.1016/j.gsf.2020.11.009.This work is financially supported by the National Science Centre (Poland) research project no. 2018/29/B/ST10/02315 and is part of the ICDP project &#8220;Collisional Orogeny of the Scandinavian Caledonides.&#8221;

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