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Metamorphism
About: Metamorphism is a research topic. Over the lifetime, 18308 publications have been published within this topic receiving 655859 citations.
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TL;DR: In this article, an ion microprobe U-Th-Pb analysis of residual cores and metamorphic mantles of zircons from three high grade paragneisses from the Seve Nappe Complex, north-western Sweden, showed that the sediments comprising the protolith of the gneisses over a distance of 250 km were probably derived from similarly-aged source terranes.
Abstract: Ion microprobe U-Th-Pb analyses of residual cores and metamorphic mantles of zircons from three high grade paragneisses from the Seve Nappe Complex, north-western Sweden, show that: 1) The sediments comprising the protolith of the Seve Nappes gneisses over a distance of 250 km were probably derived from similarly-aged source terranes. 2) Those source terranes were dominated by rocks with ages in the range 1400 to 1730 Ma, with minor components at least as young as 1000 Ma. The oldest component identified is 1730±12 Ma old. 3) Those rocks had U and Th contents normal for felsic igneous rocks. 4) The gneiss protolith was metamorphosed to granulite grade during the Caledonian. There is evidence to suggest that the peak of metamorphism may not have been synchronous throughout the Nappes. 5) The metamorphism probably included a reduction of about a factor of ten in the gneisses' Th/U.
885 citations
TL;DR: Several types of growth morphologies and alteration mechanisms of zircon crystals in the high-grade metamorphic Ivrea Zone (IZ) are distinguished and attributed to magmatic, metamorphics and fluid-related events as mentioned in this paper.
Abstract: Several types of growth morphologies and alteration mechanisms of zircon crystals in the high-grade metamorphic Ivrea Zone (IZ) are distinguished and attributed to magmatic, metamorphic and fluid-related events. Anatexis of pelitic metasediments in the IZ produced prograde zircon overgrowths on detrital cores in the restites and new crystallization of magmatic zircons in the associated leucosomes. The primary morphology and Th-U chemistry of the zircon overgrowth in the restites show a systematic variation apparently corresponding to the metamorphic grade: prismatic (prism-blocked) low-Th/U types in the upper amphibolite facies, stubby (fir-tree zoned) medium-Th/U types in the transitional facies and isometric (roundly zoned) high-Th/U types in the granulite facies. The primary crystallization ages of prograde zircons in the restites and magmatic zircons in the leucosomes cannot be resolved from each other, indicating that anatexis in large parts of the IZ was a single and short lived event at 299 ± 5 Ma (95% c. l.). Identical U/Pb ages of magmatic zircons from a metagabbro (293 ± 6 Ma) and a metaperidotite (300 ± 6 Ma) from the Mafic Formation confirm the genetic context of magmatic underplating and granulite facies anatexis in the IZ. The U-Pb age of 299 ± 5 Ma from prograde zircon overgrowths in the metasediments also shows that high-grade metamorphic (anatectic) conditions in the IZ did not start earlier than 20 Ma after the Variscan amphibolite facies metamorphism in the adjacent Strona–Ceneri Zone (SCZ). This makes it clear that the SCZ cannot represent the middle to upper crustal continuation of the IZ. Most parts of zircon crystals that have grown during the granulite facies metamorphism became affected by alteration and Pb-loss. Two types of alteration and Pb-loss mechanisms can be distinguished by cathodoluminescence imaging: zoning-controlled alteration (ZCA) and surface-controlled alteration (SCA). The ZCA is attributed to thermal and/or decompression pulses during extensional unroofing in the Permian, at or earlier than 249 ± 7 Ma. The SCA is attributed to the ingression of fluids at 210 ± 12 Ma, related to hydrothermal activity during the breakup of the Pangaea supercontinent in the Upper Triassic/Lower Jurassic.
815 citations
TL;DR: In this article, the authors show that the 2.6-2.5 Ga basement rocks in the eastern and western parts of the NCC formed under different tectonic settings from those in the central part, consistent with subduction and continent-continent collisional belts.
804 citations
TL;DR: In this article, the authors presented an overview of key geological observations in the South China Block with respect to its Phanerozoic tectonics, and proposed a geodynamic model for the Mesozoic evolution of the SCB, which is characterized by strong thrusting/transpression, anatexic granitic magmatism, high-grade metamorphism and the poor involvement of the juvenile mantle derived rocks.
799 citations
TL;DR: In this article, five minor and trace elements, known to be chemically stable during alteration and metamorphism, have been combined in a set of binary diagrams that distinguish fresh tholeiites from alkali basalts.
793 citations