The Tula uplift, northwestern China: Evidence for regional tectonism of the northern Tibetan Plateau during late Mesozoic–early Cenozoic time

Abstract

Geologic mapping combined with petrographic and geochronologic studies in the Tula uplift of western China provides insights into the tectonic evolution of the northern edge of the Tibetan Plateau. The Mesozoic and early Cenozoic history of the area is preserved in the Tula uplift, which includes basin strata now exposed in a large syncline, pre-Mesozoic metamorphic basement, and Cretaceous plutons. Petrographic analyses of Upper Jurassic through Paleogene syntectonic sandstones show that rocks in the area were derived from lithologically diverse source terranes consisting of sedimentary, metasedimentary, and igneous rocks. These relationships imply that uplift in the Tula area began in Late Jurassic time and that uplift of the Tibetan Plateau’s northern edge may have been initiated long before the early Tertiary IndiaAsia collision. Continued orogenic activity in the Tula area is recorded by intrusion of ca. 74 Ma granitoid bodies, latest Cretaceous to Paleogene shortening, uplift of Precambrian basement rock, the syntectonic nature of Cretaceous and Paleogene sandstones, and folding of all the basin strata into a regional north-vergent syncline. The northern range-bounding thrust of the Tula uplift has been recently active, suggesting that uplift and thickening continues in the northern Tibetan Plateau.