Cenozoic Development of the Nonmarine Mula Basin in the Southern Yidun Terrane: Deposition and Deformation in the Eastern Tibetan Plateau Associated with the India-Asia Collision

Abstract

To advance tectonic models of plateau growth in response to the India-Asia collision, parameters such as the timing, mechanism (s), and extent of Cenozoic deposition and deformation throughout the eastern Tibetan Plateau need to be determined. To better understand these parameters, we examine the Mula basin, located in the southern Yidun terrane, using field data, detrital zircon geochronology, εHf zircon isotopic values, and thin section petrology. The Mula basin is a NW-SE elongate (~28 km long and 5–8 km wide) exposure of nonmarine strata ~1,000 m thick, deposited in alluvial environments. The basin is bound to the northeast by a thrust fault (327, 34°NE) that places Triassic Daocheng Pluton and Triassic Yidun Group rocks on top of the nonmarine strata. The western boundary is defined by an unconformable contact between the overlying nonmarine strata and Triassic Daocheng Pluton and Yidun Group rock. An intrabasin thrust fault, parallel to the basin-bounding fault, places older nonmarine strata on top of younger nonmarine strata, illustrating postdepositional deformation. Provenance results indicate that sediment influx originated primarily from localized drainage catchments and lacked major, well-organized throughgoing systems. A maximum depositional age of 45.5 ± 0.5 Ma, based on the weighted mean average of the youngest detrital zircon population (s), demonstrates an Eocene or younger age for strata. We interpret the Mula basin to have developed in a contractional deformational regime driven by a far-field, upper-crustal response associated with the transition from an Andean style margin to a continent-continent collisional margin as India impinged upon Eurasia.