A Discussion on the evolution of the Precambrian crust - A plate tectonic model for the Archaean crust

1973 ◽  
Vol 273 (1235) ◽  
pp. 413-427 ◽  
Keyword(s):  
Greenstone Belt ◽  
Plate Boundary ◽  
Granulite Facies ◽  
Plate Tectonic ◽  
Granulite Facies Metamorphism ◽  
Sialic Crust ◽  
Tectonic Model ◽  
Lithospheric Plates ◽  
Greenstone Belts ◽  
Relative Motions

The characteristics of Archaean greenstone belt terrains are briefly summarized together with some of the models which have been used to account for their genesis. Crystalline sialic crust is interpreted as having increased with time by separation from the mantle. Many of the problems posed by Archaean greenstone belt terrains may be eased if the first sialic crust is assumed to have consisted of small masses concentrated by plate tectonic processes similar to those still in operation. Even if Archaean plates were of similar size, and were formed and lost at rates similar to those since the Mesozoic, there would be differences in the manner in which the sialic crust was concentrated because so little had separated from the mantle during Archaean times. The original formation of the rocks now forming the earliest tonalite gneisses and migmatites is attributed to very early Archaean times when no large sialic concentrations are likely to have existed on subduced lithospheric plates and the only form of orogeny was of the Island Arc type. Even after sialic concentrations did become incorporated in subduced plates they may for a long time have been too small for significant areas to survive extensive remobilization and addition of magmas from below whenever they were associated with plate boundary zones. Sets of greenstone belts are interpreted as vestiges of former oceans. By the end of Archaean times the sialic crustal concentrations, despite possible fragmentation and periods of independent development, became sufficiently extensive for large areas to survive ocean closure without significant remobilization. This model implies that there is no need for orogeny to have been any more extensive in Archaean times than now; it could merely have been more extensive compared to the area of the sialic crust in existence at the time. Plate tectonic models of Archaean tectonics are distinguished from the alternatives by their implication that large relative motions occurred between the oldest parts of the granitoid masses now on either side of the greenstone belts. Palaeomagnetism may be able to distinguish the relative usefulness of the models if any such relative motions can be recognized through the effects of remobilization of most, if not all, the sialic crust in Archaean times. Other tests are possible but the most useful might be the necessity for any model of the formation of the greenstone belts being adaptable enough to account for the relationships emerging from studies of the Archaean crustal remnants characterized by granulite facies metamorphism and anorthosites.

scholarly journals U-Pb evidence for late Neoarchean crustal reworking in the Southern São Francisco Craton (Minas Gerais, Brazil)

2003 ◽  
Vol 75 (4) ◽  
pp. 497-511 ◽  
Author(s):  
José C.S. Campos ◽  
Maurício A. Carneiro ◽  
Miguel A.S. Basei
Keyword(s):  
Granulite Facies ◽  
Minas Gerais ◽  
Metamorphic Complex ◽  
Granulite Facies Metamorphism ◽  
Sialic Crust ◽  
Facies Metamorphism ◽  
Minimum Age ◽  
Crustal Reworking ◽  
Metamorphic Complexes

The Passa Tempo Metamorphic Complex is one of several metamorphic complexes that form the Archean sialic crust of the southern São Francisco Craton. It encompasses hypersthene-bearing gneissic rocks, with subordinateNW- or EW-trending mafic-ultramafic bodies and granodioritic to alkali-granitic, weakly foliated, and light-colored granitoids. These granitoids are the product of generalized migmatization that followed granulite-facies metamorphism. To determine the ages of the granulite-facies metamorphism and granitoid genesis, we obtained U-Pb ages on zircon extracted from the mesosome and leucosome of the migmatitic gneisses. For the mesosome, a discordia that intercepts Concordia at 2622 ± 18 Ma is interpreted as a minimum age for granulite-facies metamorphism. For the leucosome, the upper intercept of discordia at 2599 ± 45 Ma corresponds to migmatization and granitoid genesis. Contemporaneous metamorphism and magmatism have been documented elsewhere in the São Francisco Craton, especially in the southern portion, demonstrating vast and vigorous reworking of sialic crust by the end of the Neoarchean.

Rocks of unusual chemistry in the charnockitic terrains of India, and their geological significance

1975 ◽  
Vol 112 (1) ◽  
pp. 63-69
Author(s):  
S. Viswanathan
Keyword(s):  
Southern Africa ◽  
Greenstone Belt ◽  
Granulite Facies ◽  
Southern India ◽  
Metamorphic Evolution ◽  
Geological Significance ◽  
Barberton Greenstone Belt ◽  
Granulite Belt ◽  
Greenstone Belts

SummaryThe paper reports the occurrence in the 2.9–3.1 B.Y. old charnockitic terrains of Southern India of some basic charnockites that are strikingly similar, chemically, to basaltic komatiite from the 3.4 B.Y. old Barberton greenstone belt of Southern Africa, and suggests that the pre-metamorphic evolution of Archaean charnockitic terrains followed the same trends that characterized the development of Archaean greenstone belts. The main events in the evolution of one such terrain, the ‘Madras granulite belt’, before it was subjected to granulite facies meamorphism some 2.6 B.Y. ago, is outlined in Table 2.

Geochronological studies of the Bohemian massif, Czechoslovakia, and their significance in the evolution of Central Europe

1982 ◽  
Vol 73 (2) ◽  
pp. 89-108 ◽  
Author(s):  
O. van Breemen ◽  
M. Aftalion ◽  
D. R. Bowes ◽  
A. Dudek ◽  
Z. Mísař ◽  
...  
Keyword(s):  
Central Europe ◽  
Granulite Facies ◽  
Temporal Separation ◽  
European Continent ◽  
Granulite Facies Metamorphism ◽  
Moldanubian Zone ◽  
Tectonic Model ◽  
Field Evidence ◽  
Early Palaeozoic ◽  
Tectonic Style

ABSTRACTU–Pb zircon and Rb–Sr whole-rock analyses from various gneisses and plutonie rocks of the Moldanubian and Moravo-Silesian zones and the stable foreland of the Hercynian (Variscan) orogenic belt indicate that most of the crust in Central Europe was first formed during the Cadomian orogeny which straddles the Precambrian–Cambrian boundary. Zircons, however, have a memory of older ages which correspond with those of events known in Fennoscandia. The new radiometrie data are consistent with the stratigraphie record in that they do not provide any evidence for a major early Palaeozoic tectonothermal event between the Cadomian and Hercynian orogenies.Granulites from two localities in the Moldanubian zone yield U–Pb zircon ages of 345 ± 5 Ma; discordant zircon data points indicate that the granulite facies metamorphism was not of long duration. Tectonic units containing these high grade rocks were emplaced amongst amphibolite facies rocks during an event of widespread shearing which has been dated at 341 ± 4 Ma on the basis of a lower U–Pb zircon intercept age from one of the sheared gneisses and 338 ± 3 Ma U–Pb ages from monazites. Rb–Sr muscovite ages of 331 ± 5 Ma from pegmatites axial planar to asymmetrical folds date the last stage of SE-directed simple shear. A Rb–Sr whole-rock isochron of 331 ± 4 Ma from a principal magmatic type of the Central Bohemian pluton confirms the field evidence that the large NE-trending plutons of the Moldanubian zone were emplaced during a late stage of the deformation. The strong disturbance of the U–Pb zircon isotopic system in the sheared gneisses suggests U loss while a high U/Th ratio in monazite from one of these tectonised rocks suggests the simultaneous passage of hydrothermal fluids. Thus a crustal source is indicated for the uranium deposits of the Moldanubian zone.Critical to any plate tectonic model for the development of the Middle European Hercynides was the existence of an ocean in Early Devonian times which separated a North European continent from a South European continent(s). The northward movement of the South European continent over a shallowly-dipping subduction zone and subsequent continental collision can explain the high T–low P metamorphism and the imbricated tectonic style of the Moldanubian zone and adjacent Moravo-Silesian zone along the southeastern Hercynian foreland. The temporal separation of granulites and granites implies distinct conditions of formation and it has been suggested that the plutonism, following on from the imbrication of the Cadomian crust, was initiated by the subduction of wet oceanic sediments.

scholarly journals Geochemistry of greenstones in the Tasiusarsuaq terrane, southern West Greenland

2008 ◽  
Vol 15 ◽  
pp. 69-72 ◽  
Author(s):  
Anders Scherstén ◽  
Henrik Stendal ◽  
Tomas Næraa
Keyword(s):  
Spatial Association ◽  
Granulite Facies ◽  
Mineral Deposits ◽  
Base Metals ◽  
Layered Intrusions ◽  
Granulite Facies Metamorphism ◽  
West Greenland ◽  
Facies Metamorphism ◽  
Greenstone Belts ◽  
Green Land

Tonalite-trondhjemite–granodiorite (TTG) gneisses and mela nocratic to ultramafic greenstones dominate the Arc haean basement of southern West Greenland. The greenstones are likely to represent different original environments, which is important as the mineral deposits they may host depend on this. For example, massive sulphide deposits associated with gold and base metals are commonly volcan og enic, while chrome, nickel and platinum group elements are more commonly associated with layered intrusions (Robb 2005). Cur rent investigations by the Geological Survey of Denmark and Greenland (GEUS) in southern West Greenl and are therefore focused on the origin of greenstones and their relationship to associated TTG gneisses. Here, we report on work in progress on greenstones within the Tasiusarsuaq terrane (Fig. 1; Friend et al. 1996). They differ from many other greenstone belts in southern West Green land in their spatial association with the TTG gneisses. Unlike the Isua, Ivisârtoq and Storø greenstone belts in the central and northern Nuuk region, the Tasiusarsuaq greenstones are not proximal to terrane boundaries but form dismembered blocks and slivers within the terrane (Fig. 1). Contact relationships to the gneisses are almost exclusively tectonic, and primary textures are, with rare exceptions, ob literated by amphibolite to granulite facies metamorphism.

Pétrologie des niveaux trondhjémitiques de haute pression associés aux éclogites et amphibolites des complexes leptyno-amphiboliques du Massif Central français

1978 ◽  
Vol 15 (5) ◽  
pp. 696-707 ◽  
Author(s):  
C. Nicollet ◽  
A. Leyreloup
Keyword(s):  
High Pressure ◽  
Partial Melting ◽  
Granulite Facies ◽  
Massif Central ◽  
Granulite Facies Metamorphism ◽  
High Pressure Granulite ◽  
Greenstone Belts ◽  
Metamorphic Terranes ◽  
Archean Greenstone Belts ◽  
Initial Mineral

High pressure trondhjemitic rocks interbedded with eclogites and high pressure amphibolites have been recognized in the leptyno-amphibolitic series of the Rouergue and Marvejols metamorphic terranes. These rocks appear to have been derived by partial melting of the surrounding amphibolites (or amphibole-gabbro) at [Formula: see text] (<7 × 105 kPa). The initial mineral assemblage of these layers (Q, Pl, Ky, Ga, Zo, etc.) is suggested by microstructural evidence to have crystallized directly under high pressure granulite facies conditions (12.5 kbar <PT <20 kbar (12.5 × 105 kPa < PT <20 × 105 kPa); 750 °C<T<840 °C) from the trondhjemitic liquid. The partial melting has taken place before the well-known Barrovian metamorphism that has affected the whole crystalline basement of the French Massif Central. This older metamorphic event is considered to be equivalent to the high pressure granulite facies metamorphism recognized in the Variscan of Europe. This acid–basic high pressure bimodal association argues for a close similarity between Archean greenstone belts and the leptyno-amphibolitic series.

Contrasting styles of Proterozoic crustal evolution: A hot-plate tectonic model for Australian terranes

Geology ◽  
2005 ◽  
Vol 33 (8) ◽  
pp. 673-676 ◽  
Author(s):  
Sandra McLaren ◽  
Mike Sandiford ◽  
Roger Powell
Keyword(s):  
Plate Boundary ◽  
Sedimentary Basins ◽  
Crustal Evolution ◽  
Crustal Growth ◽  
Plate Tectonic ◽  
Large Aspect Ratio ◽  
Hot Plate ◽  
Tectonic Model ◽  
Orogenic Belts

Abstract Proterozoic terranes in Australia record complex tectonic histories in the interval 1900– 1400 Ma that have previously been interpreted by means of simple intracratonic or plate-tectonic models. However, these models do not fully account for (1) repeated tectonic reactivation (both orogenesis and rifting), (2) mainly high-temperature–low-pressure metamorphism, (3) rifting and sag creating thick sedimentary basins, (4) the nature and timing of voluminous felsic magmatism, (5) relatively large aspect ratio orogenic belts, and (6) a general paucity of diagnostic plate-boundary features. A key to understanding these histories is the observation that Australian Proterozoic terranes are characterized by an extraordinary, but heterogeneous, enrichment of the heat-producing elements. This enrichment must contribute to long-term lithospheric weakening, and thus we advocate a hybrid lithospheric evolution model with two tectonic switches: plate-boundary–derived stresses and heat-producing-element–related lithospheric weakening. The Australian Proterozoic crustal growth record is therefore a function of the magnitude of these stresses, the way in which the heat-producing elements are distributed, and how both of these change with time.

Rubidium–strontium ages from the Oxford Lake – Knee Lake greenstone belt, northern Manitoba

1980 ◽  
Vol 17 (5) ◽  
pp. 560-568 ◽  
Author(s):  
G. S. Clark ◽  
S.-P. Cheung
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Superior Province ◽  
Granitic Intrusion ◽  
Greenstone Belts ◽  
Archean Greenstone Belts

Rb–Sr whole-rock ages have been determined for rocks from the Oxford Lake – Knee Lake – Gods Lake greenstone belt, in the Superior Province of northeastern Manitoba.The age of the Magill Lake Pluton is 2455 ± 35 Ma (λ87Rb = 1.42 × 10−11 yr−1), with an initial 87Sr/86Sr ratio of 0.7078 ± 0.0043. This granitic stock intrudes the Oxford Lake Group, so it is post-tectonic and probably related to the second, weaker stage of metamorphism.The age of the Bayly Lake Pluton is 2424 ± 74 Ma, with an initial 87Sr/86Sr ratio of 0.7029 ± 0.0001. This granodioritic batholith complex does not intrude the Oxford Lake Group. It is syn-tectonic and metamorphosed.The age of volcanic rocks of the Hayes River Group, from Goose Lake (30 km south of Gods Lake Narrows), is 2680 ± 125 Ma, with an initial 87Sr/86Sr ratio of 0.7014 ± 0.0009.The age for the Magill Lake and Bayly Lake Plutons can be interpreted as the minimum ages of granitic intrusion in the area.The age for the Hayes River Group volcanic rocks is consistent with Rb–Sr ages of volcanic rocks from other Archean greenstone belts within the northwestern Superior Province.

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