Journal of Earth Science  2018, Vol. 29 Issue (5): Ⅰ-Ⅱ   PDF    
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Preface
Neng-Song Chen1,2, Zeming Zhang3,4, Roger Mason1    
1. School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;
2. Center for Global Tectonics, China University of Geosciences, Wuhan 430074, China;
3. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China;
4. Institute of Geology, Chinese Academy of Geological Science, Beijing 100037, China

Zhendong You was born in 1928, in Fujian Province, eastern China in golden September. He graduated from the Department of Geology of Peking University in 1952, and has subsequently been teaching and researching in petrology and optical mineralogy at China University of Geosciences (CUG) and its predecessors, Beijing Institute of Geology and Wuhan Institute of Geology, since 1956. He taught petrology and petrogenesis of metamorphic rocks in School of Earth Sciences, CUG for nearly 50 years as a professor and doctoral supervisor and made outstanding contributions nationally to metamorphic petrology and personnel training. His contributions have been recognized by a Li Siguang Earth Science Teaching Award, the national prizes including a first prize for teaching and a national education model worker award from the former State Education Commission (now the Ministry of Education of China).

Professor You was one of the founders of metamorphic geology in China and has many innovative achievements in metamorphic petrology and metamorphic geology to his credit. In the 1980s, he became keenly aware that international studies in metamorphism had begun to shift from static classification into metamorphic facies to dynamic metamorphic process such as P-T-t paths, reflecting a strategic shift in the understanding of tectonic evolution of metamorphic terrains. He carried out research on P-T-t paths and their geodynamic causes in the metamorphic core of the eastern Qinling Mountains, leading a group who surveyed several north-south cross sections in the central part of the eastern Qinling complex that included comprehensive studies of microstructures, P-T estimates and modeling of growth zoning of garnets. Combined with preliminary geochronological dating, this led to the recognition of three regional metamorphic zones in the Shewei area (now updated with a new name 'Shuanglong', meaning "pair of dragons") in northern Xixia County, western Henan Province: a muscovite-andalusite zone in the north, a kyanite zone in the south, and a sillimanite-potassium feldspar zone in the inner portion. The latter is overprinted by a contact aureole of which the innermost margin against the contact reaches a high temperature olivine- chrondrodite zone. The study enabled reconstruction of a P-T trajectory characterized by two cycles (episodes) of metamorphism (You et al., 1994, 1993). The first occurred during a Mesoproterozoic (990-800 Ma) collisional orogeny and the second took place by contact metamorphism caused by intrusion of a granitic pluton in the Early Paleozoic (~450-400) Ma. More recent advanced high-precision in situ dating reveals that the two metamorphic events were in fact of two stages of one Early Paleozoic (450-400 Ma) tectonometamorphic process, but Prof. You's chronological sequence and associated geodynamic processes remain correct. The research results achieved were comparable to those of his international peers at that time.

Later in the 1990s he led a research team that moved to the Dabie-Sulu orogenic belt in Central China and determined the P-T-t path of the northern Dabieshan granulite, Central China blueschist belt, and Dabie-Sulu ultrahigh-pressure (UHP) metamorphic rocks. The study of granulites of the North Dabie unit in Huangtuling Village, Luotian County, northeastern Hubei Province revealed two episodes of granulite-facies metamorphism. The first occurred in the Late Paleoproterozoic; the second took place in the Triassic. The Triassic granulites display obvious decompressive microtextures (You et al., 1995). Study of the Triassic UHP eclogites also indicated a complex metamorphic history. A pre-eclogite stage grew epidote, quartz and barroisite, preserved as inclusions inside garnet porphyroblasts, followed by prograde growth up to a metamorphic peak that generated coesite and/or diamond now also preserved inside garnets. This was followed by near-isothermal decompression with growth of single or double dolomite coronas on margins of magnesites, and albite+amphibole symplectites at contacts of garnet and omphacite under amphibolite-facies conditions; and subsequent nearisobaric cooling causing growth of amphibole and epidote containing relicts of fine-grained garnets (Fig. 2). These results provided insights into the geodynamics of HP-UHP metamorphic rocks and their associated granulites generally and uplift histories of orogenic belts, and made a major contribution to the recognition and understanding of deep subduction of continental crust (You et al., 1996). Though more recent advanced high-precision in situ dating reveals that the UHP metamorphic processes all occurred during the Late Triassic (245-210 Ma) rather than in the Early Paleozoic, but the chronological sequence and associated geodynamic processes also remain correct.

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Figure 1. Metamorphic P-T path of the Qinling complex (redrawn after You et al., 1993 with simplification and modification). Al2SiO5 phase equilibrium curves of H and G are from Holdaway (1971) and Mueller and Saxena (1977), respectively. (1) Fe-St+Qtz=Al2SiO5+Alm+H2O (Richardson, 1968); (2) Ms+Qtz=Kfs+Sil+H2O (Day, 1973). D2, D3 and D4 are episodes of deformation, M1 and M2 are metamorphic cycles.
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Figure 2. P-T-t paths for diamond- and quartz-bearing eclogites from Dabieshan (You et al., 1996). Multiple metamorphic stages of a. pre-eclogite; d. peak UHP; c-f. amphibolite facies (AM) followed by c-b. epidote-blueschist facies retrograde metamorphism (redrawn from You et al., 1996).

His decades of research indicate that Prof. You has characteristically pursued cutting-edge ideas, inspired continuous innovation and encouraged careful record-keeping and presentation. His upright character and sympathetic attitude combined with rigorous scholarship in his approach to scientific research, his innovations and exploration of ideas have encouraged a stream of young academics to enter the field of metamorphic rock studies. He has made many friends and admirers among his Chinese and foreign colleagues and students over the years. He has persisted with international cooperation and helped many foreign researchers visiting China by introducing them to Chinese metamorphic terrains and supporting their accounts of their research.

This special issue of Journal of Earth Science (JES) is a festschrift in celebration of Prof. You's 90th birthday and focuses on the theme "Metamorphic Processes and Geodynamics". It contains 21 contributions that report new advances in metamorphic geology in both China and abroad. Most contributions cover metamorphic and magmatic processes and orogeny in the Qinghai-Tibetan Plateau (Zhang Z M et al.; Sun et al.; Zhang Li et al.), Tianshan Orogen (Su et al.; Xia et al.), Central China orogenic belt, including Kunlun (Zhang Lu et al.), Qilian (Wang Q Y et al.; Li Y L et al.), Qinling (Liu et al.; Zhu et al., 2018), Tongbai-Dabie Mountains (Xiang et al.; Ahmed et al.; Li Z Y et al.). Others focus on metamorphism, magmatism and tectonics of the North China Craton in the Neoarchean and Late Paleoproterozoic, and of the Pan-African Jiamusi terrane in northeastern China (Zhong et al.; Nie et al.; Chen et al.; Xu et al.). Additional themes are progress in conventional geothermometry (Wu) and chemistry and physics of minerals (Schertl et al.), general aspects of contact metamorphism (Mason and Liu). A review of ultrahigh-temperature (UHT) metamorphism (Lei and Xu) is also included.

The 21 contributions in this volume cover a selection of the important issues to which Prof. You made pioneering contributions, such as the metamorphic P-T paths of the eastern Qinling complex and burial and uplift processes of the Dabie UHP rocks. We thank all the contributors to this volume for their support and the referees who spared valuable time and effort to offer scholarly reviews in a limited time. We dedicate this special issue to the 90th birthday of Zhendong You and believe that these works should further promote investigations in topics related to metamorphic geology that Prof. You has researched, leading to further progress in the study of metamorphic rocks in China. The final publication is available at Springer via https://doi.org/10.1007/s12583-018-0890-5.


REFERENCES CITED
Day, H. W., 1973. The High Temperature Stability of Muscovite Plus Quartz. American Mineralogicat, 58: 255-262.
Holdaway, M. J., 1971. Stability of Andalusite and the Aluminum Silicate Phase Diagram. American Journal of Science, 271(2): 97-131. DOI:10.2475/ajs.271.2.97
Mueller, R. F., Saxena, S. K., 1977. Chemical Petrology. Springer Verlag, New York.
Richardson, S. W., 1968. Staurolite Stability in a Part of the System Fe-Al-Si-O-H. Journal of Petrology, 9(3): 467-488. DOI:10.1093/petrology/9.3.467
You, Z. D., Chen, N. S., Chalokwu, C. I., 1995. The Metamorphism of Deeper Crust in the Dabie Mountains:As Evidenced by the Study of Granulites near Huilanshan, Luotian. Acta Petrologica Sinica, 11(2): 137-147.
You, Z. D., Han, Y. J., Suo, S. T., et al., 1993. Metamorphic History and Tectonic Evolution of the Qinling Complex, Eastern Qinling Mountains, China. Journal of Metamorphic Geology, 11(4): 549-560. DOI:10.1111/jmg.1993.11.issue-4
You, Z. D., Han, Y. J., Zhang, Z. M., 1996. The Petrological Evidence for the Uplift of Ultrahigh-Pressure Metamorphic Rocks in Root Zone of the Qinling-Dabie Orogenic Belt. Science in China (Series D), 39(Suppl.): 93-101.
You, Z. D., Suo, S. T., Han, Y. J., et al., 1994. Metamorphic Evolution of the East Qinling and Dabieshan Tectonic Belt, Central China. Journal of Asian Earth Sciences, 9(4): 397-403. DOI:10.1016/0743-9547(94)90051-5