序号：01

       Location (geographical coordinates): E102° 32' 10.111", N31° 1' 48.544"

       Geological period: Late Triassic Carnian

       Type of geological interests: Structural geology

       Level of significance: International

       Geological description: Located on the valley slopes at the mouth of Jiesi Valley, the fold morphology is clear, abundant, and diverse. It includes sharp-edged folds, tight upright folds, overturned folds, recumbent folds, and stacked folds. Additionally, lineation structures, planar structures, and rod structures are visible, making it a “natural fold structure museum”. This site is the type locality where Xu Zhiqin, an academician with the Chinese Academy of Sciences studied and named the “Xikang-type” folds.

       The “Xikang-type” folds are upright folds with cleavage parallelism, widely developed in the “Xikang Group” flysch sequence composed of thick sandstones and slates. These folds are estimated to have formed at a depth of 10-15 km. Notable features include variable fold hinge plunge angles and variable dip directions; various composite fold forms such as smooth-concentric folds, sharp-edged folds, and transitional folds; complex refracted cleavage patterns formed by different types of cleavage; and vertical stretching lineations developed on flow cleavage planes.

       The deformation structure profile of the Triassic Jiuwo Formation sandstones in Jiesi Valley indicates stable cleavage plane trends (NWW290°–304°) but significant variation in fold hinge plunge angles, suggesting a stacked fold structure that required a planar (stratigraphic or cleavage) base with varying dip angles, resulting from complex stress within the orogenic belt.

       Justification for international significance: The geopark is the type locality for the “Xikang-type” folds. The “Xikang-type” folds are a product of intracontinental orogeny in the Songpan-Garzê Orogenic Belt. The Songpan-Garzê Orogenic Belt lies between the Yangtze Block, North China Block, Qaidam Block, and Qiangtang Block, bordered to the east by the Sichuan Basin, to the north by the Kunlun-Animaqing Suture Zone, to the south by the Garzê-Litang Suture Zone and the Jinsha Suture Zone, and to the east by the Longmenshan Thrust Belt. Unlike most linear orogenic belts in the world, the Songpan-Garzê Orogenic Belt is wedge-shaped, exemplifying bidirectional compressional continent-continent collision orogeny and represents a novel type of orogenic belt. The scientific value is detailed in the paper Orogenic Processes of the Songpan-Garzê Orogenic Belt in China by Academician Xu Zhiqin. The “Xikang-type” folds in the Songpan-Garzê Orogenic Belt are upright stacked folds with cleavage parallelism. They are comparable in tectonic features, formation mechanisms, and magnificence to the world-famous “Jura-type” and “Pennine-type” folds, representing a unique fold type within orogenic belts.

A  “Xikang-Type” Folds

B  Fan-shaped cleavage

C  Refracted cleavage

D  3D diagram of folds

Representative literature：

a) Yuan, C., Zhou, M. F., Sun, M., Zhao, Y., Wilde, S., Long, X., & Yan, D. (2010). Triassic granitoids in the eastern Songpan Ganzi Fold Belt, SW China: Magmatic response to geodynamics of the deep lithosphere. Earth and Planetary Science Letters, 290(3-4), 481-492.

b) Zhang, H. F., Zhang, L., Harris, N., Jin, L. L., & Yuan, H. (2006). U–Pb zircon ages, geochemical and isotopic compositions of granitoids in Songpan-Garze fold belt, eastern Tibetan Plateau: constraints on petrogenesis and tectonic evolution of the basement. Contributions to Mineralogy and Petrology, 152, 75-88.

c) Huang, M. H., Buick, I. S., & Hou, L. W. (2003). Tectonometamorphic evolution of the eastern Tibet plateau: Evidence from the central Songpan–Garzê orogenic belt, Western China. Journal of Petrology, 44(2), 255-278.

d) Harrowfield, M., & Wilson, C.J. (2005). Indosinian deformation of the Songpan Garzê Fold Belt, northeast Tibetan Plateau. Journal of Structural Geology, 27, 101-117. 3.1

e) Haoyu Yan, Zhiqin Xu, Guangwei Li, Bihai Zheng, Jianguo Gao, Xiaoping Long; Whole-Rock and Apatite Geochemistry of Late Triassic Plutonic Rocks in the Eastern Songpan-Ganzi Orogenic Belt: Petrogenesis and Implications for Tectonic Evolution.

f) Danping YAN, Meifu ZHOU, Guoqin WEI, He LIU, Tiezhu DONG, Weichen ZHANG, Zhelong JIN, Collapse of Songpan-Garzê orogenic belt by a Mesozoic middle-crustal ductile channel flow: evidences from deformation and metamorphism within the Sinian-Paleozoic strata in the hinterland of Longmenshan foreland thrust belt, Earth Science Frontiers,Volume 15, Issue 3, 2008,Pages 186-198.

g) Liu, S., & Wang, Y. (2023). Origin of the Songpan-Garze Terrane on the northeastern Tibetan Plateau, eastern segment of the Tethyan tectonic domain: A Middle Permian–Early Triassic intracontinental rifting system. Bulletin, 135(7-8), 1993-2014.

h) Roger, F., Jolivet, M., & Malavieille, J. (2010). The tectonic evolution of the Songpan-Garzê (North Tibet) and adjacent areas from Proterozoic to Present: A synthesis. Journal of Asian Earth Sciences, 39(4), 254-269.

i) Roger, F., Malavieille, J., Leloup, P. H., Calassou, S., & Xu, Z. (2004). Timing of granite emplacement and cooling in the Songpan–Garzê Fold Belt (eastern Tibetan Plateau) with tectonic implications. Journal of Asian Earth Sciences, 22(5), 465-481.

j) Xu, Z.-q., Hou, L.-w., Wang, D.-k., & Wang, Z.-x. (1991). “Xikang-type” folds and their deformation mechanism: A new fold type in orogenic belts. Geological Bulletin of China, (1), 1-9.