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Kinematic Evolution of the Nyakong-Manyi Shear Zone(Adamawa,Cameroon): Constraints from Field Observations and Microstructures,and Implication for Metamorphic P-T-t estimation

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Journal of Earth Science 2023年第5期34卷 1465-1487页

作者： Belmien Robinson Sobze Yemdji Jules Tcheumenak Kouémo Eric Martial Fozing Ludovic Achu Megnemo Julios Efon Awoum Agnes Blandine Kamgang Tchuifong Brice Rostant Tepi Yemele Maurice Kwékam Department of Earth Science University of DschangDschang 67Cameroon Department of Earth Science Faculty of ScienceUniversity of DoualaDouala 24157Cameroon

The Nyakong-Manyi Shear Zone(NMSZ) is a NE-SW elongated corridor found to the northwest of the Foumban-Bankim Shear Zone(FBSZ) along the Central Cameroon Shear Zone. Controversial chronology models has been proposed for the kinematic evolution of the sinistral and dextral shear phases in the Tikar Plain, thus in the FBSZ;early dextral and late sinistral shear phases for some authors and early sinistral and late dextral shear for others. Moreover, the NMSZ kinematic evolution implication on the mylonitization P-T-t path in the area seem to be problematic and the present paper aim is to clear enough those problems;since this shear zone is the main mylonitic corridor that registered the left and right lateral movement in this area. The NMSZ comprises amphibolites, protomylonites, strict sensus mylonites(garnet-kyanite-sillimanite mylonite and garnet-pyroxene mylonite), ultramylonites kyanite-sillimanite and garnet-kyanite-sillimanite gneiss. Field structures testify that the investigated area recorded three deformation phases:(i) the D1deformation phase which is marked by NW-SE to N-S trending S1metamorphic foliation with low to moderate dips(15°–45°) that was transposed during the D2phase, is responsible for a regional metamorphism whose mineral paragenesis is garnet-kyanite-sillimanite;(ii) the early sinistral NNE-SSW to NE-SW shear phase D2marked by S2metamorphic and mylonitic foliations;responsible for, L2stretching mineral lineation, F2fold axes and B2boudins structures;(iii) the late dextral NE-SW shear phase D3, characterized by F3folds, B3boudins and ductile dextral C3shear planes. Mineral paragenesis garnet + kyanite + sillimanite and microstructures within gneiss testify that this rock underwent high grade regional metamorphism whose peak conditions are estimated at 11.5–13.5 kbar/850–900 ℃. After the peak of metamorphism gneiss was overprinted by high grade pressure mylonitization during the early sinistral and late dextral shear deformations. Microstructura

关键词： structural and microstructural features pressure-temperature estimation Nyakong-Manyi Shear Zone Foumban-Bankim Shear Zone Central Cameroon ShearZone tectonics petrology

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Middle Paleozoic metamorphic and sedimentary events in the central Korean Peninsula and their geological implications

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Geoscience Frontiers 2024年第5期15卷 136-161页

作者： Byung Choon Lee Sung Won Kim Bo Young Lee Chang Whan Oh Deung-Lyong Cho Weon-Seo Kee Department of Earth and Environmental Sciences Chonnam National University77Yongbong-roBuk-guGwangju 61186Republic of Korea Geology and Space Division Korea Institute of Geoscience and Mineral ResourcesDaejeon 34132Republic of Korea Department of Earth and Environmental Sciences Jeonbuk National UniversityJeonju 561-756Republic of Korea

The Middle Paleozoic tectonic evolution of the central Korean Peninsula(Gyeonggi Massif,Hongseong-Imjingang,and Okcheon zone of Okcheon Belts)remains ***,the occurrence of high-grade metamorphism and sedimentation need further *** this study,we conducted zircon U-Pb-rare earth element analyses from in the ultramafic-mafic complex in the central Korean Peninsula(Cheonan and Gapyeong areas)and the Paleozoic metasedimentary rocks in the Okcheon Zone of the Okcheon Belt to constrain the timing of maximum depositional and metamorphic *** also examined the metamorphic P-T-t path from garnet-bearing amphibolite in the central Korean Peninsula by pseudosection modeling and *** results show that(i)some of the ultramafic-mafic complex and metasedimentary rocks in the central Korean Peninsula formed during the Middle Paleozoic(ca.450–374 Ma);(ii)garnet-bearing amphibolite underwent successive metamorphism from amphibolite facies condition(7.5–8.0 kbar and 540–630℃)at pre-peak stage to granulite facies condition(10.9–11.8 kbar and 740–820℃)at peak stage,and then retrograded into amphibolite facies condition(5.7–7.7 kbar and 530–670℃)along the clockwise P–T path during ca.403–362 *** and previous studies suggest that the central Korean Peninsula underwent subduction-related orogenic events during the Middle Paleozoic era,and it is well correlated to those of the orogenic events in the North Qinling belt.

关键词： Central Korean Peninsula Middle Paleozoic Orogenic event pressure-temperature estimation Zircon U-Pb-REE analysis

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