Provenance and tectonic setting of middle-upper Devonian sandstones in the Qinling Orogen (Shanyang area): New insights from geochemistry, heavy minerals and tourmaline chemistry

- The Devonian sandstones in the Shanzhou area are highly recycled.
- Detrital tourmalines correlate with protolithes of granitic and metamorphic rocks.
- The Qinling Complex is a principal source area of the Devonian sandstones.
- The Devonian sandstones are deposited in a foreland tectonic setting.

Devonian sandstones in the Shanyang area crop out in the southern part of the Qinling Orogenic Belt. Geochemical analyses show that the sandstones are enriched in Zr and have high Th/U and Rb/Sr ratios indicating the sandstones underwent repeated recycling. Zircon, tourmaline, apatite, rutile and anatase are the predominant heavy minerals while minor minerals include spinel, pyroxene, ilmenite and magnetite. The mineral compositions of detrital tourmaline grains indicate that the alkali compositional subgroup dominates; schorl and dravite are the main tourmaline species. A tourmaline composition environment discrimination diagram shows that about 70% grains are consistent with metapelite, metapsammite, and calc-silicates sources and about 30% of grains are from granitoids and associated pegmatites, and aplites. Metamorphic and granitic rocks in the Qinling Complex area are potential provenance. Overall data from geochemistry, heavy minerals and tourmaline chemistry suggests the Devonian sandstones were extensively recycled in a foreland basin setting rather than at a passive continental margin.