TECTONIC SETTING OF DEVONIAN SEDIMENTS IN THE QINLING OROGEN: CONSTRAINTS FROM DETRITAL MODES AND GEOCHEMISTRY OF CLASTIC ROCKS

Abstract

Devonian sediments in the Qinling orogen predominantly crop out between the Shandan and Mianlue sutures. Abundant Au, Ag and Pb-Zn deposits in the Devonian strata have attracted considerable interest since the late 1960s, but provenance and tectonic setting of these sediments are controversial. Sandstone detrital fragments, detrital heavy mineral assemblage, geochemistry of siltstone and mudstone, composition of conglomerate and paleocurrent data demonstrate that the North Qinling was the major source area of the Devonian sediments, and basement uplift should be another important source area. Detrital fragment and heavy mineral assemblage of sandstone and fragments of conglomerate indicate that arc-related igneous rocks, granitoids, metamorphic rocks and some sedimentary and ultramafic rocks should out crop in the source area. Geochemistry of siltstone/mudstone and detrital model of sandstones suggest that the Devonian sediments in the Qinling orogen mainly deposited in an active continental margin, and they derived from the rocks with different tectonic settings.