SYN-AND POST-THICKENING EXTENSIONS IN THE YULONG—HABA MOUNTAIN RANGE IN SOUTHWEST CHINA

SYN-AND POST-THICKENING EXTENSIONS IN THE YULONG—HABA MOUNTAIN RANGE IN SOUTHWEST CHINA

Syn- and Post-Thickening Extensions in the Yulong-Haba Mountain Range in Southwest China

The Yulong and Haba snowcapped ranges in the southeast side of the Qinghai—Xizang (Tibet) Plateau are situated structurally in a corner between the Dianxi Block to the west, the Yangzi Landmass to the southeast and Songpan—Ganzi folded belts to the north. Deformations in this area are strongly effected by the Tethys—Himalaya movement and defined by the Jinshajiang\|Honghe fault in the west and the Xiaojinhe fault in the southeast. A Jinshajiang river cut through in the middle with about 200 meters drop height that gives an exposed cross section.The Yulong—Haba range is an N—S trending anticline (F 3/D 3) comprising a metamorphic core of unknown ages and a sedimentary cover from mid\| Devonian onwards. Contact between the metamorphic core and the cover sequence is structurally. Although there is no evidence being found for the unconformity interface, deformation in the core, dominated by mica\|quartz schists, phyllites and quartzite, and the cover rocks, dominated by marbles, are different. The core rocks underwent a metamorphism with well developed foliations (S 1/D 1) in a greenschist facies condition. Occasionally an intrafolial fold (F 1, folded S 0) present in the S 1 layering. The S1 foliation was re\|folded by recumbent folds (F 2/D 2). Orientations of the axes of F 2 recumbent folds, the crenulation and mineral lineations now are shallowly plunged to S or N with angles less than 20° since the intensity of the D 3 deformation, during which both the core and cover rocks are involved to form the regional upright F 3 fold. All of the L\|S fabrics formed during D 2 in the core rocks are cut off by a set of near E—W or SWW—NEE trending normal faults that showing a top to the SSE extensional movement occurred during the D 3 event as a result of syn\|thickening extension (D 3′). Deformations D 4 are characterized by (1) numbers of near S—N trending high\|angle normal faults, and (2) interlayer gliding in the cover rocks, and lower angle detachment zones in the contact. Movement indicators in the D 4 structures showing a NEE in the east side of the F 3 fold, and a SWW in the west side, normal sense of shear that demonstrated a post\|thickening extension in the area.