Geochronology of the Belmont Lake Metavolcanic Complex and implications for crustal development in the Central Metasedimentary Belt, Grenville Province, Ontario

1988 ◽  
Vol 25 (11) ◽  
pp. 1751-1759 ◽  
Author(s):  
D. W. Davis ◽  
J. R. Bartlett
Keyword(s):  
Low Temperature ◽  
Lower Estimate ◽  
Regional Metamorphism ◽  
Sedimentary Sequence ◽  
Slow Cooling ◽  
Grenville Province ◽  
Zircon Growth ◽  
Metamorphic Fluids ◽  
Single Zircon ◽  
Unit Formula

U–Pb analyses of zircon and titanite were carried out on eight rocks from the Belmont Lake Metavolcanic Complex, a volcano-sedimentary sequence in the Central Metasedimentary Belt of the Grenville Province of southeastern Ontario. The ages of concordant supracrustal rocks within the complex do not accord with stratigraphic position.The youngest volcanic age is [Formula: see text] from a rhyolite near the base of the sequence. The oldest age, [Formula: see text], is from a dacite in the middle. This is overlain by a rhyolite [Formula: see text] in age. A rhyolite at the top of the sequence appears to contain zircon inherited from a source about 1870 Ma old. The complex is therefore interpreted as comprising a lithotectonic sequence composed of structurally interleaved segments of contrasting age. Tectonic emplacement of these segments was most likely along previously unrecognized thrust faults.The supracrustal rocks were subjected to at least two major deformational events as well as a late metamorphism. The earliest event was probably associated with thrusting. The age of the youngest volcanic unit, [Formula: see text], is an upper age estimate for this event. A lower estimate is probably given by the age of the Cordova Gabbro, 1242 ± 3 Ma. The later event, including peak regional metamorphism, should be younger than [Formula: see text], the age of a sheared, recrystallized felsic sill intruded into the supracrustal rocks, and older than [Formula: see text], the age of the undeformed and unmetamorphosed Belmont Granite.Titanite fractions in the Belmont Granite and a volcanic andesite both give an age of 1071 ± 5 Ma. The age from titanite in the Belmont Granite may be due to thermal resetting during slow cooling. Titanite in the andesite is secondary and may have grown as a result of late metamorphic reactions.The youngest age measured, 1039 ± 5 Ma, is from a concordant analysis of a single zircon grain found within the oldest rhyolite. This may be an example of zircon growth from low-temperature, late-metamorphic fluids.

Paleomagnetism of the Whitestone Anorthosite and Diorite, the Grenville Polar Track, and Relative Motions of the Laurentian and Baltic Shields

1975 ◽  
Vol 12 (2) ◽  
pp. 209-226 ◽  
Author(s):  
H. Ueno ◽  
E. Irving ◽  
R. H. McNutt
Keyword(s):  
Regional Metamorphism ◽  
Domain Theory ◽  
Slow Cooling ◽  
Grenville Province ◽  
The Third ◽  
Significant Difference ◽  
Before And After ◽  
Caledonian Orogeny ◽  
The Baltic ◽  
Cooling Model

The Whitestone anorthosite and diorite are situated in the Grenville Structural Province north of Parry Sound, Ontario. They are intruded into sediments and igneous rocks, the whole being metamorphosed to amphibolite facies. Aside from soft magnetizations due to the present field four magnetizations are present, two owing to hematite, the third mainly to magnetite, and a fourth of uncertain source. It is argued that these are thermoremanent magnetizations acquired during very slow cooling following regional metamorphism in the interval 1100 to 1000 m.y. A single-stage cooling model based on Neel's single domain theory is developed, which suggests that the hematite magnetizations were acquired during slow cooling at about 240 °C and the magnetite magnetizations at about 200 °C. The poles from Whitestone rocks fall among a group of poles from elsewhere in the Grenville Province. There are serious problems in integrating these Grenville poles with those from other parts of the Canadian Shield, and three possible ways of relating them are evaluated. Poles from Grenville-type rocks from the Baltic Shield are near to the Grenville poles after correction is made for the late Phanerozoic opening of the Atlantic, showing that the relative positions of Laurentian and Baltic Shields before and after the Caledonian orogeny were very similar. There is however a small but significant difference, and this is attributed to Caledonian diastrophism.

New age data on the low-temperature regional metamorphism of Mt. Medvednica (Croatia)

2006 ◽  
Vol 49 (3) ◽  
pp. 207-221 ◽  
Author(s):  
Katalin Judik ◽  
Kadosa Balogh ◽  
Darko Tibljaš ◽  
Péter Árkai
Keyword(s):  
Low Temperature ◽  
Regional Metamorphism ◽  
New Age

New insights into the geologic evolution of the Grenvillian Trenton Prong inlier, Central Appalachian Piedmont, USA

2020 ◽  
Vol 57 (7) ◽  
pp. 840-854
Author(s):  
Richard A. Volkert
Keyword(s):  
Tectonic Setting ◽  
Hanging Wall ◽  
Sediment Source ◽  
Slow Cooling ◽  
Grenville Province ◽  
Magmatic Arc ◽  
Metamorphic History ◽  
Arc Setting ◽  
Appalachian Piedmont ◽  
Back Arc

New geochemical and 40Ar/39Ar hornblende and biotite data from the Grenvillian Trenton Prong inlier provide the first constraints for the identification of lithotectonic units, their tectonic setting, and their metamorphic to post-metamorphic history. Gneissic tonalite, diorite, and gabbro compose the Colonial Lake Suite magmatic arc that developed along eastern Laurentia prior to 1.2 Ga. Spatially associated low- and high-TiO2 amphibolites were formed from island-arc basalt proximal to the arc front and mid-ocean ridge basalt-like basalt in a back-arc setting, respectively. Supracrustal paragneisses include meta-arkose derived from a continental sediment source of Laurentian affinity and metagraywacke and metapelite from an arc-like sediment source deposited in a back-arc basin, inboard of the Colonial Lake arc. The Assunpink Creek Granite was emplaced post-tectonically as small bodies of peraluminous syenogranite produced through partial melting of a subduction-modified felsic crustal source. Prograde mineral assemblages reached granulite- to amphibolite-facies metamorphic conditions during the Ottawan phase of the Grenvillian Orogeny. Hornblende 40Ar/39Ar ages of 935–923 Ma and a biotite age of 868 Ma record slow cooling in the northern part of the inlier following the metamorphic peak. Elsewhere in the inlier, biotite 40Ar/39Ar ages of 440 Ma and 377–341 Ma record partial to complete thermal resetting or new growth during the Taconian and Acadian orogens. The results of this study are consistent with the Trenton Prong being the down-dropped continuation of the Grenvillian New Jersey Highlands on the hanging wall of a major detachment fault. The Trenton Prong therefore correlates to other central and northern Appalachian Grenvillian inliers and to parts of the Grenville Province proper.

The Flinton Group: a late Precambrian metasedimentary succession in the Grenville Province of eastern Ontario

1980 ◽  
Vol 17 (12) ◽  
pp. 1685-1707 ◽  
Author(s):  
John M. Moore Jr. ◽  
Peter H. Thompson
Keyword(s):  
Regional Metamorphism ◽  
Grenville Province ◽  
Arc Volcanism ◽  
Late Precambrian ◽  
Granitic Intrusions ◽  
Group A ◽  
Eastern Ontario ◽  
Orogenic Cycle ◽  
Uplift And Erosion ◽  
Block Faulting

Clastic and carbonate metasediments, preserved in narrow synclines, have been correlated over an area of 2000 km2. These strata, the Flinton Group, lie unconformably on metamorphosed volcanic, clastic, and carbonate rocks, and on large granitic intrusions. The group, which comprises six formations, has undergone at least two major folding episodes and one main regional metamorphism of varying grade. The only post-Flinton intrusions are pegmatites at high grade and one tectonically emplaced ultramafic slice.Depositional environment ranged from fluvial to moderate-depth marine. Rapid facies changes, coupled with persistence of some units along strike and close relationships between facies and underlying lithology, point to local sources and local tectonic control of deposition basins. At the onset of sedimentation, a deeply weathered source terrain yielded mature basal redbeds, which were succeeded by less mature clastics as block faulting caused increase of relief between sources and basins. These facies passed offshore into finer, more reduced sediments. Deposition took place between 1050 and 1080 (±25) Ma ago, after arc volcanism, plutonism, uplift, and erosion, and before major regional metamorphism. All these events can be grouped within the Grenvillian orogenic cycle, spanning at least the interval 1300–1000 Ma and including, in eastern Ontario, the pre-Flinton Elzevirian Orogeny and post-Flinton Ottawan Orogeny.

Compositional range of P2/n omphacite from the eclogitic rocks of central Shikoku, Japan

1976 ◽  
Vol 40 (315) ◽  
pp. 773-779 ◽  
Author(s):  
Kazumi Yokoyama ◽  
Shohei Banno ◽  
Takeo Matsumoto
Keyword(s):  
Electron Microscope ◽  
South African ◽  
Lattice Structure ◽  
Regional Metamorphism ◽  
Ordered Structure ◽  
The South ◽  
Slow Cooling ◽  
Compositional Range ◽  
Lattice Symmetry

SummaryThe lattice types of omphacite-diopside series clinopyroxenes were determined for 9 Japanese, 2 Norwegian, and 1 South African samples. The boundary between the compositional ranges of P and C lattice clinopyroxenes lies at about 14·5 wt. % CaO in Japanese and Norwegian samples, and the compositional gap between them is very small, if it exists. The South African omphacite has C-lattice in the compositional range of P lattice omphacite in metamorphic eclogites. These data combined with the reported electron microscope studies suggest that the omphacite—diopside series clinopyroxene has a C lattice structure above 3 to 400°C and very slow cooling after regional metamorphism is responsible for the transition to the ordered structure with P lattice symmetry.

scholarly journals Low-temperature zircon growth related to hydrothermal alteration of siderite concretions in Mississippian shales, Scotland

2012 ◽  
Vol 164 (2) ◽  
pp. 245-259 ◽  
Author(s):  
Maciej J. Bojanowski ◽  
Bogusław Bagiński ◽  
Euan Clarkson ◽  
Ray Macdonald ◽  
Leszek Marynowski
Keyword(s):  
Low Temperature ◽  
Hydrothermal Alteration ◽  
Zircon Growth

scholarly journals The tectono-metamorphic evolution of a dismembered ophiolite (Tinos, Cyclades, Greece)

1996 ◽  
Vol 133 (3) ◽  
pp. 237-254 ◽  
Author(s):  
Yaron Katzir ◽  
Alan Matthews ◽  
Zvi Garfunkel ◽  
Manfred Schliestedt ◽  
Dov Avigad
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Subduction Zone ◽  
Sea Water ◽  
Regional Metamorphism ◽  
Greenschist Facies ◽  
Normal Faults ◽  
Model Calculations ◽  
Facies Metamorphism ◽  
Greenschist Facies Metamorphism

AbstractThe six exposures of the Upper tectonic Unit of the Cycladic Massif occurring on the island of Tinos are shown to comprise a metamorphosed dismembered ophiolite complex. The common stratigraphic section consisting of tens-of-metres- thick tectonic slices of mafic phyllites overlain by serpentinites and gabbros is considered to have been derived by a combination of thrusting during obduction and subsequent attenuation by low-angle normal faults. All rock types show evidence of a phase of regional greenschist-facies metamorphism, which in the case of the phyllites is accompanied by penetrative deformation. The greenschist-facies metamorphism in gabbros is preceded by high temperature sea-floor amphibolite-facies alteration, whereas in the serpentinites, the antigorite + forsterite greenschist-facies assemblage overprinted an earlier low temperature lizardite serpentinite. Trace element patterns of the mafic phyllites and a harzburgitic origin of meta-serpentinites suggest a supra subduction zone (SSZ) affinity for the ophiolitic suite. ρ18O values of phyllites, gabbros and serpentinites range from 6 to 15%o. Model calculations indicate that such values are consistent with low temperature (50–200°C) alteration of parent rocks by sea-water at varying water/rock ratios. This would agree with the early low temperature mineralogy of the serpentinites, but the early high temperature alteration of the gabbros would require the presence of 18O-enriched sea-water.The following overall history is suggested for Tinos ophiolitic slices. (1) Oceanic crust was generated at a supra-subduction zone spreading centre with high temperature alteration of gabbros. (2) Tectonic disturbance (its early hot stages recorded in an amphibolitic shear zone at the base of serpentinites) brought the already cooled ultramafics into direct contact with sea-water and caused low-T serpentinization. (3) Tectonism after cooling involved thrusting which caused repetition and inversion of the original order of the oceanic suite. (4) Regional metamorphism of all the ophiolite components at greenschist-facies conditions (−450°C) overprinted the early alteration mineralogy. It was probably induced by continued thrusting and piling up of nappes. The Tinos ophiolite, dated as late Cretaceous and genetically related to other low pressure rock-units of the same age in the Aegean, differs in age and degree of dismemberment and metamorphism from ophiolites in mainland Greece.

High-Ti magnetite in some fine-grained carbonatites and the magmatic implications

2002 ◽  
Vol 66 (3) ◽  
pp. 379-384 ◽  
Author(s):  
D. K. Bailey ◽  
S. Kearns
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Composition Range ◽  
Volcanic Rocks ◽  
Coarse Grained ◽  
Slow Cooling ◽  
Fine Grained ◽  
Narrow Composition Range ◽  
Fast Quenching ◽  
Temperature Crystallization

AbstractMagnetite is present in most carbonatites, and in the most abundant and best-known form of carbonatite, coarse-grained intrusions, it typically falls in a narrow composition range close to Fe3O4. A fine-grained carbonatite from Zambia contains magnetites with an extraordinary array of compositions (from 18–1% TiO2, 10–2% Al2O3, and 16–4% MgO) outranging previously-reported examples. Zoning trends are from high TiO2 to high Al2O3 and MgO. No signs of exsolution are seen. Checks on similar rocks from Germany, Uganda and Tanzania reveal magnetites with comparable compositions, ranges, and zoning. Magnetites from alkaline and alkaline ultramafic silicate volcanic rocks cover only parts of this array. Magnetite analyses from some other fine-grained carbonatites, reported in the literature, fall in the same composition field, suggesting that this form of carbonatite may be distinctive. The chemistry and zoning would be consonant with rapid high-temperature crystallization in the carbonatite melts, with the lack of exsolution pointing to fast quenching: this contrasts with coarse-grained intrusive carbonatites, in which the magnetite compositions are attributed to slow cooling, with final equilibration at low temperature. In some complexes, both forms of carbonatite, with their different magnetite compositions, are represented.

Paleomagnetism of the Lac St-Jean anorthosite and related rocks, Grenville Province, Quebec

1983 ◽  
Vol 20 (2) ◽  
pp. 246-258 ◽  
Author(s):  
K. L. Buchan ◽  
W. F. Fahrig ◽  
G. N. Freda ◽  
R. A. Frith
Keyword(s):  
North American ◽  
Regional Metamorphism ◽  
The Other ◽  
Central Portion ◽  
Grenville Province ◽  
Polar Wander ◽  
Thermal Demagnetization ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Normal Polarity

Alternating field and thermal demagnetization study of the Lac St-Jean anorthosite and related rock units in the central portion of the exposed Grenville Province reveals two components of magnetization, one of reversed and the other of normal polarity. Both components are thought to have been acquired during the last regional metamorphism, which was sufficiently intense in this area (mostly amphibolite grade) to reset any earlier magnetization. Corresponding paleopoles at 193°W, 8°S (dm = 7.3°, dp = 4.6°) and 213°W, 19°S (dm = 10.5°, dp = 8.5°) lie along the 950–900 Ma segment of the recently calibrated Grenville track of the North American apparent polar wander path, a track that has thus far been defined largely by results from rock units of the western Grenville.

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