Source-to-sink dynamics in the Kyrgyz Tien Shan from the Jurassic to the Paleogene: Insights from sedimentological and detrital zircon U-Pb analyses

Abstract

New insights in the Mesozoic geodynamic evolution and related basin-range interactions in the Kyrgyz Tien Shan were obtained based on new sedimentological and detrital zircon U-Pb (LA-ICP-MS) results from Jurassic to Paleogene sedimentary sequences. Studied sedimentary sections are located in the Fergana and Yarkand-Fergana basins to the west of the Talas-Fergana Fault (TFF) and in the Issyk-Kul and Ming-Kush-Kökömeren basins to the east. The ages of the Phanerozoic zircon grains found in 18 Jurassic to Paleogene sandstones can be divided into four groups: Caledonian (470–390Ma), Hercynian (315–260Ma), Triassic (250–210Ma) and Jurassic (190–160Ma) ages. The differences in sedimentation pattern and zircon U-Pb results suggest that the TFF played an important role in the distribution of the sedimentary deposits in the Mesozoic. During the Early - Middle Jurassic, the TFF was active and the strongest subsidence occurred in the Yarkand-Fergana Basin. The provenance of its sediments can be explained both by local sources close to the TFF and by more distal sources to the (south)west, probably stretching into the present-day Pamir. During the Late Jurassic – Early Cretaceous, renewed compression led to the inversion of the Yarkand-Fergana Basin. Around the Jurassic – Cretaceous transition, large alluvial fans developing in a semi-arid to arid climate traceable around the whole Tien Shan were also deposited in the Fergana Basin. A mafic sill intruded within these alluvial fans provides an emplacement age of 144±8Ma (apatite U-Pb) indicating (sub)volcanic activity during the Early Cretaceous. During the Late Cretaceous to early Paleogene, the area to the west of the TFF experienced marine incursions related to the proto-Paratethys Sea. The dominance of Caledonian ages in the Upper Cretaceous – lower Paleogene detrital samples indicates a change in provenance whereby the drainage areas became larger towards low-relief land area east of the TFF.