Calc-silicate isograds in the Riondel area, southeastern British Columbia

1976 ◽  
Vol 13 (8) ◽  
pp. 1093-1104 ◽  
Author(s):  
Trygve Höy
Keyword(s):  
British Columbia ◽  
Regional Metamorphism ◽  
Fluid Phase ◽  
Lower Grade ◽  
Binary Fluid ◽  
Physical Conditions ◽  
Mineral Assemblages ◽  
Maximum Temperatures ◽  
Wide Zone ◽  
Model Reactions

Five metamorphic isograds have been mapped in the calc-schists of the Riondel area, British Columbia. These isograds are based on the following model reactions:[Formula: see text]The first four of these isograds represent discontinuities in the observed mineral assemblages and are located by plotting all occurrences of the complete reactant and product assemblages. The fifth isograd occurs over a wide zone in which the anorthite component of the plagioclase in the assemblage Ep–Ac–Q–Di–Pl increases with increasing metamorphic grade, from approximately An30 in the lower grade eastern part of the area to approximately An60 in the western part.The distribution of isograds and the systematic variation in plagioclase compositions in the Ep–Ac–Q–Di–Pl assemblage is modelled using [Formula: see text]diagrams that have been calculated at 5000 bars pressure under the simplifying constraint that[Formula: see text]. These diagrams provide a basis for estimating the physical conditions of regional metamorphism in the Riondel area. Maximum temperatures exceeded 600 °C in the highest grade part of the area and the composition of the hypothetical binary fluid phase varied from approximately [Formula: see text]in the lower grade to 0.5 or 0.6 in the higher grade areas.

Metamorphism of the Settler Schist, southwest of Yale, British Columbia

1976 ◽  
Vol 13 (3) ◽  
pp. 405-421 ◽  
Author(s):  
Lee C. Pigage
Keyword(s):  
British Columbia ◽  
Linear Regression ◽  
Microprobe Analysis ◽  
Regional Metamorphism ◽  
Fluid Phase ◽  
Contact Metamorphism ◽  
Major Constituent ◽  
Minor Components ◽  
Mineral Assemblages ◽  
Regression Techniques

Pelitic metasediments immediately southwest of Yale, British Columbia contain mineral assemblages characteristic of staurolite through sillimanite zones of the Barrovian facies series. Microprobe analyses of major constituent phases in the pelites are combined with linear regression techniques to formulate probable kyanite- and sillimanite-forming reactions.A zone some 3 km wide contains the assemblage staurolite–kyanite–garnet–biotite–muscovite–quartz–plagioclase-ilmenite-rutile, which is univariant in AFM projection. Within precision limits of microprobe analysis, this assemblage is also univariant using linear regression techniques. Univariant relations are possible if [Formula: see text] with the composition of the fluid phase being buffered by the progressing reaction. This assemblage emphasizes the need for precise analyses when using the regression method, since minor components are often within permissible error limits rather than being balanced.Pelitic and calc-silicate assemblages from the metasediments restrict estimates of pressure–temperature conditions during regional metamorphism to 6–8 kbar and 550–770 °C. Pseudomorphs after andalusite indicate that contact metamorphism preceded regional upgrading of the pelites.

scholarly journals Magnitude and frequency of landslides triggered by a storm event, Loughborough Inlet, British Columbia

2004 ◽  
Vol 4 (3) ◽  
pp. 475-483 ◽  
Author(s):  
R. H. Guthrie ◽  
S. G. Evans
Keyword(s):  
British Columbia ◽  
Power Law ◽  
Storm Event ◽  
Data Sets ◽  
Landslide Occurrence ◽  
Physical Conditions ◽  
Pareto Model ◽  
Order Of Magnitude ◽  
Storm Cells ◽  
Coastal British Columbia

Abstract. One hundred and one landslides were documented across 370km2 following a rainstorm that swept the British Columbia coastline on 18 November 2001. Despite the regional nature of the storm, the landslides were spaced close together, even within the study area. Landslide clustering is attributed to high intensity storm cells too small to be recorded by the general hydrometric network. The evidence nicely corroborates previous historical studies that reached similar conclusions, but against which there was no modern analog analyzed for coastal British Columbia. Magnitude-cumulative frequency data plotted well on a power law curve for landslides greater than 10000m2, however, below that size several curves would fit. The rollover effect, a point where the data is no longer represented by the power law, therefore occurs at about 1.5 orders of magnitude higher than the smallest landslide. Additional work on Vancouver Island has provided evidence for rollovers at similar values. We propose that the rollover is a manifestation of the physical conditions of landslide occurrence and process uniformity. The data was fit to a double Pareto distribution and P-P plots were generated for several data sets to examine the fit of that model. The double Pareto model describes the bulk of the data well, however, less well at the tails. For small landslides (<650m2) this may still be a product of censoring. Landscape denudation from the storm was averaged over the study area and equal to 2mm of erosion. This is more than an order of magnitude larger than the annual rate of denudation reported by other authors for coastal British Columbia, but substantially less than New Zealand. The number is somewhat affected by the rather arbitrary choice of a study area boundary.

Nature of the Quetico–Wabigoon boundary in the de Courcey – Smiley Lakes area, northwestern Ontario

1976 ◽  
Vol 13 (6) ◽  
pp. 737-748 ◽  
Author(s):  
Manfred M. Kehlenbeck
Keyword(s):  
Regional Metamorphism ◽  
Sedimentary Rocks ◽  
Metamorphic Grade ◽  
Boundary Zone ◽  
Present Level ◽  
Metasedimentary Rocks ◽  
The North ◽  
Northwestern Ontario ◽  
Multiple Phase ◽  
Mineral Assemblages

In the de Courcey – Smiley Lakes Area, the boundary between the Quetico and Wabigoon Belts is expressed by a sequence of pelitic to semi-pelitic schists and gneisses. At the present level of erosion, these metasedimentary rocks are in contact with granodioritic gneisses, granites, and pegmatites, which are exposed to the south.To the north of this area, regional metamorphism of volcanic and sedimentary rocks has resulted in greenschist facies assemblages, which characterize the Wabigoon Belt in general. In the boundary zone, the metamorphic grade increases southward toward de Courcey and Smiley Lakes.Formation of three distinct foliation surfaces was accompanied by syn-tectonic as well as post-tectonic recrystallization, producing polymetamorphic schists.In the boundary zone, mineral assemblages comprising andalusile, sillimanite, cordierite, garnet. biotite, and muscovite form a facies series of the Abukuma type.The boundary between the Quetico and Wabigoon Belts in this area is a complex zone in which rocks of both belts have been reconstituted by multiple-phase metamorphism and partial melting.

Concluding remarks

1987 ◽  
Vol 321 (1557) ◽  
pp. 275-276 ◽  
Keyword(s):  
Regional Metamorphism ◽  
Physical Conditions ◽  
New Period ◽  
Strongly Connected ◽  
History Of ◽  
Critical Problems ◽  
Stable Continental Regions ◽  
Actual Plate ◽  
Moho Depths ◽  
Metamorphic Terranes

The focus of this discussion meeting is strongly connected to that of the history of continental crust. I was reminded of G. K. Gilbert (1893), who said that 'the permanence of the continental plateau, though highly probable, is not yet fully established; and the doctrine of continental growth, though generally accepted, has not been placed beyond the field of profitable discussion’. Recently, Kerr (1985) remarked that we increasingly see continents as a ‘collage of wandering fragments’, and this present discussion has been most concerned with processes associated with this model. I think we are sometimes confused by what is formed, when we observe what is preserved. Continental metamorphism presents us with a great puzzle. Given the present heat flow, stable continental regions have temperatures little above 400 °C at Moho depths; the continents should be dominated by facies of the lowest grades. Yet continental rocks show an amazing diversity of P—T regimes, far exceeding any normal range. Verhoogen (1980) wrote ‘as deformation and orogeny are commonly associated with regional metamorphism, orogeny should perhaps be described as a thermal disturbance, rather than a mechanical one’. Modern metamorphic studies involve the central theme of tracking the convective style of the earth through time. We are now entering a new period of observation, where deep continental structure is being refined by seismic and electrical methods, while actual plate motions can be observed by satellites. Many of the metamorphic terranes discussed at this meeting involve subduction and collision-related phenomena. Recent studies of the subduction process (Uyeda 1983; Yorath et al. 1985; Kaiko Staff 1985) are beginning to elucidate the critical problems of the mechanics of subduction and the materials involved (even serpentine and diamonds; see, for example, Schulz 1986; Ozima et al. 1985). Such studies feed back to the complex paths now being revealed by the metamorphic record. Rocks show us the range of physical conditions, and place some constraints on time, while modern geophysics can show the mechanisms. We are reaching the point where petrology and geophysics are joining to produce sound models of dynamics and thermal history.

Feldspars from Adamant pluton, British Columbia

1969 ◽  
Vol 6 (5) ◽  
pp. 1199-1209 ◽  
Author(s):  
Peter E. Fox ◽  
John M. Moore Jr.
Keyword(s):  
British Columbia ◽  
Distribution Coefficient ◽  
Structural State ◽  
Regional Metamorphism ◽  
Approach To Equilibrium ◽  
The Core ◽  
Igneous Origin ◽  
Quartz Monzonite ◽  
Textural Evidence ◽  
Alkali Feldspars

Adamant pluton is a zoned body of igneous origin, with a core of pyroxene monzonite transitional outward to hornblende quartz monzonite and biotite-hornblende granodiorite. On chemical and textural evidence, the lithologic zoning resulted from reaction with introduced water and oxygen during regional metamorphism to upper amphibolite facies. Feldspars in the monzonite are orthoclase and andesine of intermediate structural state. During transformation of the pluton, systematic changes in the feldspars comprised: (1) ordering of alkali feldspars toward intermediate microcline, with increase of 2V, decrease of Na and Ca content, and appearance of grid twins; (2) ordering and increase in Na content of plagioclase. The most ordered feldspars, with highest Na distribution coefficient, are found in peripheral granodiorite and in pegmatite cutting the quartz monzonite. The feldspar data support the model proposed for the evolution of the pluton, indicating approach to equilibrium in the peripheral rocks at lower temperatures than that attendant to the formation of the core.

Accretion-related metamorphism of the Metchosin Igneous Complex, southern Vancouver Island, British Columbia

2005 ◽  
Vol 42 (8) ◽  
pp. 1467-1479 ◽  
Author(s):  
Sean Timpa ◽  
Kathryn M Gillis ◽  
Dante Canil
Keyword(s):  
British Columbia ◽  
Regional Metamorphism ◽  
Vancouver Island ◽  
Island Arcs ◽  
The West ◽  
Volcanic Stratigraphy ◽  
Igneous Complex ◽  
Orographic Effects ◽  
Metamorphic History ◽  
Metamorphic Facies

The metamorphic history of the volcanic sequence of the Metchosin Igneous Complex (MIC), an Eocene ophiolite exposed on southern Vancouver Island, British Columbia, Canada, was studied to examine the roles of seafloor and accretion-related processes. Metamorphic facies in the volcanics vary from prehnite–actinolite assemblages in the east to greenschist and amphibolite assemblages in the west. In the east, metamorphism is typified by chlorite ± prehnite ± epidote ± actinolite assemblages that fill vesicles and replace interstitial material; plagioclase is variably albitized, and clinopyroxene is relatively fresh. In the west, the common groundmass assemblage is amphibole + epidote ± chlorite. These assemblages and chlorite geothermometry show a regional east–west gradient of ∼5–10 °C/km that is oblique to the volcanic stratigraphy. The regional metamorphic facies distribution for the MIC volcanics is not consistent with seafloor hydrothermal metamorphism documented for ocean crust from mid-ocean ridges, ocean islands, or island arcs. We speculate that underthrusting of the MIC beneath the Pacific Rim Terrane led to the regional metamorphism of the MIC, and that the change in metamorphic grade from east to west results from regional tilting of the complex, perhaps by orographic effects, during or after accretion.

Compositional variation in högbomites from north Connemara, Ireland

1985 ◽  
Vol 49 (354) ◽  
pp. 649-654 ◽  
Author(s):  
N. S. Angus ◽  
R. Middleton
Keyword(s):  
Chemical Composition ◽  
Regional Metamorphism ◽  
The Other ◽  
Partial Substitution ◽  
Compositional Variation ◽  
Physical Parameters ◽  
Chemical Heterogeneity ◽  
High Grade ◽  
Thermal Metamorphism ◽  
Mineral Assemblages

AbstractHögbomite occurs in two contrasting mineral assemblages within the Currywongaun-Dough-ruagh intrusion of north Connemara: a cordierite-rich pelitic xenolith and an orthopyroxenite. In the latter, högbomite and green spinel form blebs within magnetite-ilmenite grains. The högbomite displays significant compositional variation from grain to grain: TiO2 (3.0–6.3%), FeO (21.6–21.3%), MgO (10.0–7.5%), ZnO (3.6–2.4%). This chemical heterogeneity appears to represent variable degrees of partial substitution of Mg and Zn by Ti, in the replacement of spinel by högbomite. By contrast, in the cordierite-hornfels, the högbomite compositions are more notably enriched in iron: TiO2 (4.7–7.0%), FeO (29.6–24.3%), MgO (4.2–6.2%), ZnO (2.7–2.1%). This iron-rich högbomite appears to have formed primarily by interaction between opaque ore and adjacent cordierite, rather than by replacement of spinel.Two high-grade metamorphic episodes appear to be necessary for högbomite growth, one determining chemical composition and the other appropriate physical parameters. In the Connemara occurrences thermal metamorphism and partial melting, coupled with contamination of the surrounding magma, controlled the formation of mineral assemblages rich in Fe, Mg, Al, Ti, and Zn. Emplacement of the intrusion was accompanied by amphibolite facies regional metamorphism and it is to this metamorphic event that the growth of högbomite may be attributed.

Petrochemistry of metamorphosed pillows, and the geochemical status of the amphibolites (Proterozoic) from the Sirohi district, Rajasthan, India

1984 ◽  
Vol 121 (5) ◽  
pp. 465-473 ◽  
Author(s):  
P. K. Bhattacharyya ◽  
A. D. Mukherjee
Keyword(s):  
Regional Metamorphism ◽  
Element Distribution ◽  
Island Arcs ◽  
Oceanic Sediments ◽  
Crystalline Core ◽  
Mineral Assemblages ◽  
Trace Element Contents ◽  
Closed Systems ◽  
Low K ◽  
Middle Proterozoic

AbstractRelic pillows in the middle Proterozoic amphibolites, occurring in the Sirohi Road–Abu Road tract of Rajasthan, India exhibit contrasted mineral assemblages from core to rim – mimetic after the crystalline core, the zone of incipient crystallization, and the rim of the original pillows. The major element distribution pattern across the pillows indicates exchange of Na–Al for Ca (Mg, Fe) in an inner reaction zone, surrounding the core and in the inner margin of the rim, and Fe–Al exchange for Ca–Si at the outer margin of the rim.Despite such exchanges around the rims, these pillows have retained their initial geochemical characteristics internally and thus have largely acted as closed systems during post-emplacement metamorphism. Mineral parageneses indicate that the contrasted mineral assemblages could evolve from domainal characters of the co-existing fluids, the compositions of which were only buffered by the reacting minerals during regional metamorphism.The major, minor and trace element contents of the pillows and of amphibolites of diverse petrographic character in the region further establish that the pillow interiors and the massive amphibolites were least modified during metamorphism(s), and represent oceanic tholeiites. Their average 2300 ppm K, 4.5 ppm Rb, 150 ppm Sr, along with the K/Rb and K/Sr ratios of 510 and 15 respectively resemble that of the low K-tholeiites, occurring nearest to the trenches in modern island arcs. On the other hand, the higher values of 17300 ppm K, 4.9 ppm Rb, and 210 ppm Sr of the banded and the schistose amphibolites indicate that they were contaminated in various magnitudes by oceanic sediments.

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