重矿物组合及单颗粒化学组分特征的物源指示意义OACHSSCD

To determine the provenance compositions and source-to-sink processes of the Early-Middle Triassic turbidites in the Napo Basin,southern margin of the South China block,heavy mineral assemblage analyses were performed on sandstone samples,and single-grain chemical compositions of detrital pyroxenes,chromian spinels,garnets and tourmalines were determined by electron microprobe analysis.The results show that the heavy minerals in the Napo Basin sandstones are dominated by stable to ultrastable minerals,including zircon,TiO2 polymorphs,tourmaline,pyrite,chromian spinel and garnet,indicating a mixed provenance signature.Detrital pyroxenes are all clinopyroxenes and plot in the subalkaline volcanic-arc basalt field on tectonic discrimination diagrams,consistent with the pyroxene phenocrysts from the arc volcanic rocks north of the basin.Chromian spinels are characterised by high Cr#,low TiO2 and low Fe3+/Fe2+ratios,and mostly fall within the island-arc volcanic field,with a few grains showing affinities to MORB-type ophiolites and ocean-island basalts.Garnets are dominated by the almandine end-member,with low pyrope and grossular contents,whereas tourmalines are exclusively magnesian and ferrous varieties(dravite and schorl).The provenance of these two mineral types points to Li-poor granites and metasedimentary rocks from the Neoproterozoic-Early Paleozoic orogenic belt and their relatively good roundness also suggests long-distance transport or sedimentary recycling.Collectively,these results provide heavy-mineral assemblage and geochemical constraints on the source-rock types and sedimentary evolution of the basin fill in the Napo Basin.