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Distinguished Lecture

Distinguished Lecture - SE

Wenjiao XIAO
Chinese Academy of Sciences

"Late Paleozoic Multiple Accretionary and Collisional Processes in Southern Altaids and their Implications for Metallogeny"

Abstract
The formation and development of the southern Altaids is controversial with regard to its accretionary orogenesis and mineral deposits. The Altay-East Junggar-Tianshan collages of North Xinjiang, China, offer a special natural laboratory to resolve this puzzle. Several NWW-SEE-trending linear tectonic units were juxtaposed, roughly from North to South, in the study area.

The Chinese Altai and East Junggar collages occupy the northern part. The Chinese Altay collage, composed of variably deformed and metamorphosed Paleozoic sedimentary, volcanic, and granitic rocks, is interpreted as a Japan-type island arc of Paleozoic to Carboniferous-Permian age. The Erqis unit, which occurs immediately south of the Chinese Altai unit and consists of ophiolitic mélanges and coherent assemblages, contains fragments of Paleozoic accretionary complexes, mostly associated with a major north-dipping subduction zone. The East Junggar collage, characterized by imbricated ophiolitic mélanges, Nb-enriched basalts, adakitic rocks and volcanic rocks, is regarded as a Devonian-Carboniferous intra-oceanic island arc with some Paleozoic ophiolites, superimposed by Permian arc volcanism. A southerly-distributed forearc accretionary complex of the East Junggar collage suggests a general north-ward subduction polarity for the East Junggar collage. The southern part of the study area is the Chinese Eastern Tianshan collage that was characterized by (a) the Harlik-Dananhu subduction system with a S-dipping polarity in the north; (b) a southerly N-dipping subduction system beneath the Yamansu-Central Tianshan arc in the middle; and (c) the north subduction of the South Tianshan ocean against Tarim in the south.

During the Early Paleozoic several intra-oceanic arcs and Japan-type arcs were formed. In the Devonian to Early Carboniferous, N-dipping subductions led to the enlargement of these arcs and their accretionary complexes with general southward growth, which were attached northwards to the Angaran margin, resulting in lateral enlargement of the Angaran continent in the latest Carboniferous to Permian. Final amalgamation of all these collages may have occurred in the Permian to mid-Triassic. During these long-lived, complicated geodynamic processes with multiple subduction systems in this part of the Paloasian Ocean in the Paleozoic, several metallogenic belts were formed.

The Chinese Altai–East Junggar collages are composed of five major types of Middle to Late Paleozoic metal deposits: (1) VMS Cu–Pb–Zn, (2) porphyry Cu–Au, (3) magmatic Cu–Ni-sulfide, (4) skarn Cu–Mo–Fe and (5) orogenic Au. Tectonically, the development of these metal deposits was closely associated with accretionary and convergent processes. The formation of the deposits involved three main stages, including: (i) Late Devonian to Early Carboniferous polymetallic volcanogenic massive sulfide deposits, together with some broadly contemporaneous Fe–Cu skarns, located in the accreted Qiongkuer-Talate Terrane in the western Altai, formed during back-arc extension along the the Chinese Altai–East Junggar collages. (ii) Widespread metalliferous ores of different types such as copper-bearing porphyries and Alaskan-type Cu–Ni–PGE zoned ultramafic bodies developed in arcs in the Buerjin-Ertai and Erqis terranes, and Cu–Fe skarns formed in the Erqis flysch basin, formed in the Carboniferous to Permian terrane accretion and arc magmatism. (iii) Cu–Mo skarns and orogenic-type gold vein systems formed during continuing accretion in the Permian with the development of the Dulate arc in the southern Altai. The Chinese Altai–East Junggar collage typically demonstrates the various classic metalliferous ores formed during the processes of subduction-accretion and arc generation.

The mineralization processes in the Chinese Eastern Tianshan collage were mainly related to an island arc stage (360–320 Ma) with porphyry-type and volcano-sedimentary copper deposits, an accretionary stage (300–280 Ma) with orogenic-type gold deposits, an accretionary to post-accretional stage (280–245 Ma) with mafic–ultramafic copper–nickel and epithermal gold deposits, and a post-tectonic extensional stage (240–220 Ma) that gave rise to the Jinwuozi gold deposits, Xiaobaishitou skarn W–Mo deposits, and Baishan porphyry Mo–Re deposits.

Biography
Prof Wenjiao Xiao is Vice Director and professor at the Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences (CAS) and professor at the Institute of Geology and Geophysics, CAS. He got his PhD from the Institute of Geology, CAS, in 1995. He is now a GSA fellow and Foreign member of the Leibniz Society of Sciences (Berlin), Germany. Wenjiao is Editor of Geological Society of America Bulletin, and is/was subject editor/associate editor/editorial board member of Heliyon, Journal of the Geological Society, Episodes, International Journal of Earth Sciences, Journal of Asian Earth Sciences, Gondwana Research, Ore Geology Reviews, Terra Nova, Acta Geologica Sinica, Geoscience Frontiers, National Science Review, and Science Bulletin. Among other domestic journals, he is Editor-in-Chief of Chinese Journal of Geology and Associate Editor of Geotectonica et Matellogenia. He has been invited as reviewers for international funding bodies/positions including the National Science Foundation of the United States of America, Czech Science Foundation, Chilean National Science and Technology Commission, and European Council. Wenjiao got The Second Award of National Natural Science Award of China in 2012, The First Award of Science and Technology Award of Xinjiang Uyghur Autonomous Region, China in 2012, and the Huang Jiqing Award of the Geological Society of China in 2010. Wenjiao was/is a Co-chief of IGCP 592 and IGCP 662. His research interests include tectonic evolution of the orogenic belts and continental growth and their metallogeny. Wenjiao has published more than 300 papers with 13479 Web of Science citations (H-index 56) and 20023 Google Scholar Citations (H-index 66).