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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...
The late-Proterozoic Allard Lake ilmenite deposit is located in the Havre-Saint-Pierre anorthosite complex, part of the allochtonous polycyclic belt of the Grenville Province. Presently the world's largest Fe–Ti oxide deposit, it had a pre-mining amount in excess of 200Mt at grades over 60wt.% hemo-ilmenite. The main ore body is a funnel-shaped intrusion, measuring 1.03×1.10km and 100–300m-thick....
U–Pb zircon geochronology, Sr–Nd isotope and bulk-rock geochemistry have been applied to meta-igneous and meta-sedimentary rocks from high-pressure metamorphic mélanges exposed on the Cycladic islands of Tinos, Syros and Andros. Ion microprobe (SHRIMP) U–Pb zircon dating of 7 samples representing meta-igneous blocks (Tinos), a blackwall zone (Tinos) and chlorite–talc schists from block-matrix contacts...
Zircon U–Pb dating, whole-rock major oxide, trace element and Sr–Nd–Hf isotopic data are presented for the Late Permian to Early Triassic Shijianfang batholith from Faku in North Liaoning Province, North China. Two main magmatic suites are documented: one, with an emplacement age of ca. 260Ma, is mafic to intermediate in composition, forming small gabbroic to monzonitic intrusions; the other is felsic...
Garnet peridotite, interlayered with lesser amounts of dunite and olivine websterite and interwoven with garnet pyroxenite dikes, makes up a 0.5km 2 massif near Lüliangshan in the North Qaidam ultrahigh-pressure (UHP) metamorphic belt, Northern Tibetan Plateau. Previous studies have suggested that the garnet peridotites represent Alaskan-style magmatic cumulates or oceanic serpentinites that...
The Hongseong area in the western Gyeonggi Massif, South Korea, is characterized by the occurrence of several isolated ultramafic lenses in close association with metabasites within the granitic gneiss. Most of these bodies suffered various degrees of serpentinization and also have been highly deformed and metamorphosed. The Bibong ultramafic rock is assumed to be a mantle section of a probable Neoproterozoic...
Granitic leucosome and pegmatite are widely distributed within biotite-bearing orthogneiss in the northern part of the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. A combined study of mineral inclusions, cathodoluminescence (CL) images, U–Pb SHRIMP dates, and in situ trace element and Lu–Hf isotope analyses of zircons provided insight into the nature and timing of partial melting...
In our Reply to the Comment by Abbott R.N., Jr., Draper, G., 2010. Comment on “Corundum-bearing garnet peridotite from northern Dominican Republic: A metamorphic product of an arc cumulate in the Caribbean subduction zone” by Hattori et al. Lithos 114 (2010) 437–450]. Lithos 117, 322–326 (this issue), we clarify several points concerning the origin of garnet (Grt)-bearing ultramafic rocks in Dominican...
Medium-grade mica schists and intercalated paragneisses and amphibolites from the basement of the Tisia Unit, Slavonian Mountains., northeastern Croatia, contain complexly zoned garnets. At the Kutjevo locality, mica schists are characterised by garnets with Mn-rich cores and Ca-rich rims. Mn decreases steadily from core to rim and Ca increases abruptly. This is in contrast to the paragneisses and...
Phonolites of Palaeogene age occur at two different localities in central Namibia, occurring as clusters of eroded monogenetic lava domes. Six phonolites at Aris collectively exhibit a narrow compositional range and represent a single magma system of highly evolved phonolite with high concentrations of Na 2 O, Rb, Th, Zr, Zn, Pb, and REE and very low abundances of MgO, P 2 O 5...
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