Tahsüe Shan

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Tahsüe Shan


(also Szechwan Alps), mountains in China. The Tahsüe Shan is an outlier of the Tibetan Highlands on the boundary of the plains and low mountains of eastern China. It measures approximately 750 km long and has widths to 400 km. Elevations decrease from west to east from 5,000–6,500 m to 1,000–1,200 m. The maximum elevation is 7,590 m, at Kungka Shan, in the south. The Tahsüe Shan consists of a series of ranges separated by the deep (up to 3,000 m), narrow valleys of the upper courses of the Salween, Mekong, and Yangtze rivers. The ranges generally have steep slopes, with pronounced rocky ridges dividing the various drainage areas.

The Tahsüe Shan is part of an ancient platform moved by Mesozoic activity and dissected by faults into a series of blocks. The uplifted blocks are composed of Archean and Proterozoic gneisses, schists, and sandstones; a dislocated mantle composed of Paleozoic limestones, schists, and sandstones has been preserved in the blocks that subsided. The peripheral ridges, which border on the Szechwan Basin, are composed of Permian basalts and Mesozoic sedimentary strata. The mountains are highly seismic. There are deposits of iron ore, gold, and copper. A rapid change in climate is observed with rising elevation, from the subtropical climate of the western edge of the Szechwan Basin to the cool, sharply continental climate of the Tibetan Highlands. The southern feet receive as much as 1,200 mm of precipitation (with maximum precipitation in summer), while the windward slopes receive approximately 2,000 mm and more. Closer to the Tibetan Highlands, annual precipitation decreases to 600 mm.

In the upper zone, at elevations of more than 4,000 m, alpine meadows and steppes are widespread; at 2,000–4,000 m there are coniferous forests, consisting primarily of fir and, more rarely, spruce, with some hemlock. Below 2,000 m (sometimes 2,500 m) grow mixed forests, which include trees of the genera Pseudotsuga, Lithocarpus, and Castanopsis and poplar and birch. Yew grows in the valleys facing south. At lower elevations these forests give way to evergreen subtropical forests of laurel and magnolia, with a large number of endemic species.