Geochemistry and Geochronology of High-Grade Metamorphic Rocks

Dear Colleagues,

It is a common perception that high-grade metamorphism typifies rocks of early Precambrian ages. While many large granulite complexes are indeed Archean, there also exist many well-preserved upper amphibolite–granulite facies metamorphic rocks in the Phanerozoic orogens all around the world, e.g., the Central Asian orogenic belt, the Alpine-Himalayan orogenic belt, etc., implying a range in the spatio-temporal distribution of the high-grade metamorphism. At higher temperatures, rocks tend to melt, and dealing with silicate melts is the subject of igneous petrology. However, partial melting has always been both a metamorphic and an igneous aspect. Crustal rocks that are characteristically produced via partial melting, so-called migmatites, are made up of a residual metamorphic rock and an igneous rock component, which serves as a key for linking metamorphism and magmatism. Nevertheless, the melting temperatures of rocks define the high-temperature limit of metamorphism. Melting temperatures are strongly dependent on pressure, rock composition, and the amount of water present. Geochemistry (e.g., major minerals, trace elements, and multisotope studies) and geochronology (e.g., U–Pb dating of zircon, monazite, rutile, or titanite) of the high-grade metamorphic rocks in the middle and lower crust can reconstruct the scenery of structure and composition of the lower crust and crust–mantle interaction, let alone the benefits from deciphering high-temperature processes, including migmatite and granulite formation, crustal anatexis, melt extraction, and transfer. Hence, we are planning to publish a Special Issue, titled Geochemistry and Geochronology of High-Grade Metamorphic Rocks, which aims to present contributions related to high-grade metamorphic rocks, including but not limited to high-temperature processes of migmatites.

Dr. Zhuang Li
Dr. Zhanzhan Duan
Dr. Ting Liu
Dr. Hafiz U. Rehman
Guest Editors

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• high-grade metamorphism
• geochemistry
• geochronology
• granulite
• migmatite
• partial melting

Title: From source to sink: U-Pb Geochronology and lithochemistry unraveling the missing link between Mesoarchean anatexis and magmatism in the Carajás Province, Brazil
Authors: Delinardo-Silva, M.A. (1); Monteiro, L.V.S. (2); Moreto, C.P.N. (3), Faustinoni, J.M. (3), Santos, T.J.S. (3); Sousa, S.D. (4); Xavier, R.P. (3,5),
Affiliation: 1 Geography, Geosciences and Collective Health Institute, University of Uberlândia 2 Geoscience Institute, University of São Paulo 3 Geoscience Institute, University of Campinas 4 National Institute of Industrial Property 5 Agency for the Development and Innovation of the Brazilian Mineral Sector
Abstract: The interplay between crustal anatexis and magmatism is crucial for comprehending the evolution of the continental crust. The field evidence of their connection is often obliterated by deformation in high-grade terrains. Hence, isotope geology and lithogeochemistry are important tools for reconstructing the link between these processes. This study proposes new insights into the relationships among the Mesoarchean regional metamorphism, crustal anatexis, and plutonism in the northern sector of the Carajás Province (i.e., Carajás Domain), around 2.89 to 2.83 Ga. The widespread crustal anatexis in the Carajás Domain involved water-fluxed melting of banded hornblende- and biotite-bearing orthogneisses (Xingu Complex and Xicrim-Cateté Orthogranulite; crystallization age at ca. 3.06–2.93 Ga), producing metatexites and diatexites with stromatic, net, schollen and schlieren morphologies and coeval syn-tectonic tonalitic, trondhjemitic, and granitic leucosomes. These leucosomes yielded crystallization ages of 2856 ±2 Ma (MSWD: 1.5), 2863 ±6 Ma (MSWD: 0.2), and 2877 ±4 Ma (MSWD: 0.8). The lithochemical data of these rocks is similar to those of several diachronous Mesoarchean granitoids of the Carajás Domain in terms of major, minor and trace elements and magmatic affinity. In addition, binary log-log vector diagrams (e.g., La vs. Yb; Rb vs. Yb), Sr/Y vs. Y and Eu/Eu* vs. Yb plots indicate that plagioclase fractionation preceded melt extraction, establishing evolving source-to-sink trends between leucosomes and granites. Thus, these results show that the synergy between high-grade metamorphism, crustal anatexis, and magmatism may have shaped the evolution of the Mesoarchean continental crust in the Carajás Province, exemplifying a typical petrotectonic assemblage associated with collisional orogenesis. The Mesoarchean geodynamic setting played a critical role in the development of coeval 2.89 Ga magmatic-hydrothermal copper deposits, as well as Neoarchean world-class iron oxide-copper-gold deposits linked to post-orogenic extensional rebound.