Abstract:

On the basis of the systematic geochemical testing and analysis on 27 collected glutenite samples from northeastern Qaidam margin, combined with the existing research results, the tectonic environment and prototype basin of northeastern Qaidam area during the Late Paleozoic Era are discussed in this paper. Interrelated analyses conclude that, in contrast to the upper continental crust, the Upper Paleozoic detrital rocks from the northeastern Qaidam margin have the characteristics of the enrichment of SiO2 and the loss of the rest main oxides. All the rare earth elements contents are low, but have very similar distribution pattern to the UCCnormalized. The conglomerates contain variable contents of trace elements, but generally have a similar variation trend such as systematic severe depletion of incompatible trace elements, mediumdepletion of LILE, and weak depletion of HFSE. The geochemical characteristics of tested samples are very close to the passive continental margin sandstone. Interrelated tectonic environment and source rock combination discrimination diagrams also manifest that the passive continental margin basin was developed in northeastern Qaidam margin in the Late Paleozoic Era, that rock assemblage in the provenance is mainly composed of acidic rocks from the upper continental crust, scarcely any basicintermediate acidic rocks. Based on the previous statement geochemical analysis, combining existing research conclusions of petrologic feature, sedimentary facies types and sedimentary contrast, paleocurrent direction and geochronology of zircons, it is concluded that during the Late Paleozoic Era, the northeastern Qaidam area was a passive continental margin basin with northdipping slope, that its detrital material came from the north Qaidam caledonian orogenic belt, and that the transgression came from Zongwulong aulacogen.

Key words: northeastern Qaidam margin, Upper Paleozoic, sandy conglomerate, geochemistry, basinmountain framework