26Al /10Be Cosmogenic Burial Dating and Magnetostratigraphy of Growth Strata in the Western Tarim Foreland Basin, NW China

Abstract

Foreland basins adjacent to growing orogens record key information about the deformational and erosional history of the orogen. However, dating the basin fill is often challenging when other age control, such as tephrochronology, biostratigraphic markers, or magnetostratigraphy, are unavailable or ambiguous. 26Al /10Be burial dating, an emerging dating technique, relies on the decay of cosmogenic radionuclides produced in the source areas. Because the isotopes decay at different rates once buried, the 26Al /10Be ratio can be used to determine the age of deposition of the strata in question. This approach is particularly useful for dating coarse-grained strata that are typically difficult to date with more traditional methods. In this study, we present eight new 26Al/10Be cosmogenic burial ages from Plio-Pleistocene conglomerates that have been re-exhumed by growing structures in the Pamir and Tian Shan orogens in the western Tarim foreland basin in NW China. The Pamir and Tian Shan orogens formed as a result of the Indo-Eurasian collision. These two orogens are impinging on each other and gradually deforming and closing the western Tarim Basin. To determine the onset of deformation of individual structures, samples were strategically collected from growth strata and from sedimentary units beneath active faults. Where feasible, we combined our burial ages with magnetostratigraphic sections to place further constraints on the deposition of strata within the Tarim basin and the deformation of nearby structures. Because burial dating relies on the decay of cosmogenic radionuclides, additional production of the isotopes during burial in the basin and subsequent exhumation may perturb the ages. This uncertainty was constrained with several different models accounting for synburial and post-burial nuclide production. These new burial ages date the timing of deformation of individual structures. Together with previously published magnetostratigraphic sections and thermochronology, the ages document the late Neogene growth of both the Pamir and Tian Shan orogens into the adjacent foreland basin, delineating both the eastward propagation of deformation and basinward growth of both mountain belts. These data provide valuable insight into the rates and styles of deposition of coarse-grained strata near actively growing structures. In addition, the ages provide constraints on the timing of deformation that aid in developing structural restorations in foreland basins.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016