Geological Mapping of the 1985 Chinese--British Tibetan (Xizang--Qinghai) Plateau Geotraverse Route

The 1:500,000 coloured geological map of the traverse route combines observations from the Geotraverse, previous mapping, and interpretation of orbital images. The position of all localities visited by Geotraverse participants and basic geological data collected by them along the traverse route are shown on a set of maps originally drawn at 1:100,000 scale, reproduced on microfiche for this publication. More detailed mapping, beyond a single line of section, was achieved in five separate areas. The relationships between major rock units in these areas, and their significance, are outlined in this paper. Near Gyanco, (Lhasa Terrane) an ophiolite nappe, apparently connected with outcrops of ophiolites in the Banggong Suture about 100 km to the north, was underthrust by a discontinuous slice of Carboniferous--Permian clastic rocks and limestone, contrary to a previous report of the opposite sequence. At Amdo, a compressional left-lateral strike-slip fault zone has modified relationships along the Banggong Suture. Near Wuli, (northern Qiangtang Terrane) limited truncation of Triassic strata at the angular unconformity below Eocene redbeds demonstrates that most of the folding here is of Tertiary age. The map of the nearby Erdaogou region displays strong fold and thrust-shortening of the Eocene redbeds, evidence of significant crustal shortening after the India--Asia collision began. In the Xidatan--Kunlun Pass area, blocks of contrasting Permo--Triassic rocks are separated by east-trending faults. Some of these faults are ductile and of late Triassic -- early Jurassic age, others are brittle and part of the Neogene--Quaternary Kunlun left-lateral strike-slip fault system. Some more significant remaining problems that geological mapping might help to solve are discussed briefly, including evidence for a possible additional ophiolitic suture within the Qiangtang Terrane.