Tectono-sedimentary development of backarc continental basin in Yunnan, southern China

Abstract

Sedimentological analyses of the strata occurring in the Cretaceous-Paleogene continental basin of western and central Yunnan enabled the writers to reconstruct the sedimentary history of the basin within the framework of the regional tectonics of the Yunnan-Burma region. The sedimentary record in the basin is characterized by diachroneity within the various sedimentary facies. This diachroneity resulted from increasing uplift in the west that produced a steadily increasing drainage gradient toward the east. The record of uplift is especially reflected in the changes within the sandstones. Granitic batholiths extend north-south through the full length of the uplifting hinterland along the Yunnan-Burma border region. Sedimentation in the continental basin exhibits a close relationship with a multiphase granitic emplacement history revealed through radiometric dating. A close relationship is also evident with an ophiolite-bearing flysch basin exposed today in the Indo-Burma Ranges of western Burma. The writers interpret the Cretaceous-Paleogene sequences as follows. The Yunnan-Burma region was the site of a westward-facing continental arc-trench system with a forearc basin and a backarc basin developed above continental crust. Tectonic and sedimentologic data suggest that the development of the backarc continental basin was controlled by asymmetric arching of the continental arc, in which structural vergence was toward the west and granitic magmatism took place along its axis.