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The Opatica Subprovince in the Canadian Shield is a late Archaean (2761–2702 Ma) plutonic arc formed above a north-dipping subduction zone. Anatexis (2690–2677 Ma) of leucogranodiorite and leucotonalite orthogneisses in the Opatica generated migmatites in an area of north-vergent back thrusts visible at the surface and in Lithoprobe seismic profile 48. Schollen diatexite migmatites occur in the thrusts...
Plate tectonics is a self-organizing global system driven by the negative buoyancy of the thermal boundary layer resulting in subduction. Although the signature of plate tectonics is recognized with some confidence in the Phanerozoic geological record of the continents, evidence for plate tectonics becomes less certain further back in time. To improve our understanding of plate tectonics on the Earth...
Melt-producing reactions have operated both in pelitic xenoliths and in pelitic migmatites, but melt-consuming reactions, related to in situ melt crystallization, are largely restricted to migmatites. Hence, xenolith reaction textures may provide clues on the relative roles of both reaction types in migmatites. A comparison of xenoliths and migmatites results in a catalogue of textural and chemical...
Reaction histories in xenoliths are commonly based on textural analysis alone and are often highly disputed. In this paper we propose a more rigorous approach that combines textural analysis, reaction balance calculations and quantitative P–T pseudosections using model reactions. Examples highlighting the power of this approach are: disequilibrium behaviour of plagioclase in a partial melting reaction;...
Many magmatic bodies have a hybrid isotopic signature suggesting that somewhere during genesis, transport and emplacement, magmas assimilated other rocks or mixed with other magmas. Where and how hybridization takes place is seldom documented. Here, we investigate a magmatic system in the Eastern Karakoram, Ladakh, NW India, comprising an anatectic zone, and a network of sheets, stocks and plutons...
Tube-like schlieren structures occur at the boundary between two units of the Fürstenstein Intrusive Complex, the Tittling and the Saldenburg granites. We have analysed the magnetic fabrics, petrographic variation and geochemistry of key examples of these structures in order to test the hypothesis that they originated as granitic microdiapirs. The rims of the schlieren structures have high magnetic...
The Ryoke Metamorphic Complex of the Mikawa Plateau, Central Japan, contains well-preserved geological and thermal structures formed during Cretaceous high-temperature (high-T) metamorphism. These structures can be explained by a pervasive melt migration model. However, the estimated flux of melt is much higher than that expected for compaction flow of felsic melt. An additional tectonic force and/or...
Jakob Johannes Sederholm (1863–1934) was one of the more influential pioneers in Precambrian geology having introduced some fundamental insights and concepts which are still relevant today. Towards the end of the 19th century, he demonstrated how the principle of actualism can be applied to Precambrian terranes, while during the early part of the 20th century he undertook detailed studies on deformed...
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