The Madong Early Paleozoic fold–thrust belt in southern Tarim Basin

Abstract

The Madong fold–thrust belt, which strikes NE–SW and thrusts southeastward, locates in the southern Tarim Basin. It is a part of the Kunlun Early Paleozoic foreland fold–thrust belt, and so is the Tangnan fold–thrust belt on the southeast of Madong. The Madong and Tangnan fold–thrust belts developed in Cambrian–Ordovician strata, and the Middle Cambrian gypsum–salt layer serves as the main décollement surface. The Middle Silurian and above strata unconformably overlie Madong while the upper Lower Silurian unconformably overlie Tangnan. On the basis of the facts that: (1) the Upper Ordovician is the youngest strata involved in the fold–thrust deformation, (2) the upper–Lower to Middle Silurian is the oldest strata unconformably overlying the foreland fold–thrust belt (including Madong and Tangnan), and growth strata exist in the upper part of the Upper Ordovician, we infer that the deformation time of the Kunlun Early Paleozoic foreland fold–thrust belt (including Madong and Tangnan) was during the Late Ordovician–Early Silurian. Tangnan is the residual of the major part of the foreland fold–thrust belt. Its northwestward thrust direction represents the main thrust direction of the foreland fold–thrust belt. Madong is the front belt of the foreland fold–thrust belt. It mainly thrusts southeastward and serves as the back-thrust belt of the Kunlun Early Paleozoic foreland fold–thrust belt. It is a triangle zone between Madong and Tangnan. The Madong fold–thrust belt is the best-preserved section of the Kunlun Early Paleozoic collisional orogenic belt, and thus is an important geological record of the Kunlun Early Paleozoic orogeny.