ON LIMITS TO DISTANCES OF MOVEMENT OF MATTER DURING REGIONAL METAMORPHISM: AN INVESTIGATION OF NINE SAMPLES FROM HIGH-GRADE METAMORPHIC TERRANES

2006 ◽  
Vol 44 (5) ◽  
pp. 985-1024 ◽  
Author(s):  
R. L. Stanton
Keyword(s):  
Regional Metamorphism ◽  
High Grade ◽  
Metamorphic Terranes

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.

XX.—The Metamorphism of the Deeside Limestone, Aberdeenshire

1933 ◽  
Vol 57 (2) ◽  
pp. 557-592 ◽  
Author(s):  
Arthur G. Hutchison
Keyword(s):  
Regional Metamorphism ◽  
High Grade ◽  
Thermal Metamorphism

The limestone to be described occurs in two separate areas (fig. 1)—one in Lower Deeside around Banchory, another in Middle Deeside around Aboyne. The whole of the Banchory and a large part of the Aboyne outcrops provide limestone types in a high grade of regional metamorphism (the associated schists contain sillimanite). In the latter outcrop the limestone has undergone thermal metamorphism at the contacts with Newer Granite intrusions. Many of the resulting hornfelses have suffered hydrothermal alterations with development of prehnite and zeolites. Newer Granite pegmatites, intruded at the time of hornfelsing, share in this hornfelsing and later hydrothermal modifications. In addition, they exercise exopneumatolytic and exohydrothermal metamorphism. Quite local metamorphisms take place at hornblende-schist and Older Granite contacts.

Gneissic Alkalic Rocks and Carbonatites in the Frenchman's Cap Gneiss Dome, Shuswap Complex, British Columbia

1974 ◽  
Vol 11 (2) ◽  
pp. 304-318 ◽  
Author(s):  
W. J. McMillan ◽  
J. M. Moore Jr.
Keyword(s):  
Regional Metamorphism ◽  
Lava Flows ◽  
High Grade ◽  
Metamorphic Complex ◽  
Sedimentary Deposits ◽  
Gneiss Domes ◽  
The Core ◽  
Igneous Origin ◽  
Eastern Border ◽  
Shuswap Metamorphic Complex

Frenchman's Cap dome is one of a series of gneiss domes along the eastern border of the high-grade Shuswap metamorphic complex. The granitic gneisses which compose the core of the dome are enclosed in an envelope of metasedimentary rocks.Before Shuswap metamorphism and deformation, the rocks of the sedimentary envelope were intruded by concordant bodies of alkalic rocks and carbonatite. Other carbonatite bodies appear to have formed at or extruded onto the surface. It is not certain whether these are exhalative sedimentary deposits, lava flows, or pyroclastic deposits.Criteria which can be used to distinguish igneous alkalic rocks from those of metasomatic origin were almost entirely destroyed by regional metamorphism. A few relict igneous textures show that at least some of the alkalic gneisses are of igneous origin.

Late Sillimanite in the Migmatites of Kildonan, Sutherland

1948 ◽  
Vol 85 (3) ◽  
pp. 149-162 ◽  
Author(s):  
Janet Watson
Keyword(s):  
Country Rock ◽  
Regional Metamorphism ◽  
High Grade ◽  
Direct Connection ◽  
North West ◽  
Feature Characteristic ◽  
History Of ◽  
The Common ◽  
The Village ◽  
Pelitic Rocks

A large part of Central Sutherland is occupied by an injection complex in which rocks of the Moine Series are associated with much granitic and pegmatitic material. These migmatitic Moinian rocks have reached a higher grade of metamorphism than those which occur outside the injection complex. One feature characteristic of the high-grade migmatites is the presence of sillimanite in many of the pelitic and semi-pelitic rocks. Near the village of Kildonan, ten miles north-west of Helmsdale, sillimanite is not only abundant in the country rock, but occurs also in many pegmatitic and aplitic veins. The field and microscopic evidence shows that this mineral was formed as a result of metasomatic activity at a late stage in the history of the injection complex, when the general metamorphism was already on the wane. The sillimanite seems to have no direct connection with the conditions of regional metamorphism. It was formed under the influence of pegmatitic solutions. In view of the common use of this mineral as an index of the grade of regional metamorphism, it is of interest to describe the evidence on which the above conclusions are based.

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.

scholarly journals U-Pb age determinations on zircons and monazites from a migmatite area on Bjørneøer, Scoresby Sund, East Greenland

1973 ◽  
Vol 58 ◽  
pp. 63-74
Author(s):  
F Oberli ◽  
R.H Steiger
Keyword(s):  
Regional Metamorphism ◽  
High Grade ◽  
Sampling Area ◽  
Accessory Minerals ◽  
East Greenland ◽  
Preliminary Results ◽  
Limited Sampling ◽  
South West ◽  
Insight Into ◽  
Age Determinations

During the 1969 geological expedition to Scoresby Sund, a small migmatite area on the south-west peninsula of island no. 1 of the Bjørneøer (71°08'44"N/25°20' 56"W - see fig. 1) was mapped and sampled in detail. More than 2000 kg of rock were collected for petrographic and isotope geochemical investigations to give an insight into the nature of rock-forming processes induced by high-grade regional metamorphism. The restriction to a very limited sampling area (700 m × 200 m) provided rock samples which were subjected to very similar P-T conditions for at least part of their history. This report presents preliminary results obtained by the comparison of U-Pb systematics of accessory minerals from various rock phases.

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