Single quartz δ18O: a new proxy in sediment provenance studies (Bengal Fan, IODP Expedition 354).

Quartz is the most stable and abundant mineral in sedimentary rocks and remains stable during weathering and diagenetic processes [1], thus being a good provenance tracer. Traditional and advanced techniques to determine quartz origin, such as petrography and cathodo-luminescence and laser ablation spectrometry have obtained limited success.

The aim of the study is to implement a new protocol to analyze the oxygen isotopic signatures of single detrital grains of quartz, with primary application in source-to-sink studies, and to assess their role as a provenance fingerprint of different magmatic, metamorphic and sedimentary domains. While single grain approach is standard in detrital thermochronology [e.g. 2,3], it has not been applied on major minerals using classic isotopic tracers.

This new protocol is tested on modern sediments of Ganga-Brahmaputra rivers and turbidites from the Bengal Fan (IODP Expedition 354). Single grain isotopic fingerprint allows us to define oxygen isotopic signature of magmatic and metamorphic source rocks of different Himalayan tectonic domains (Greater Himalaya, Lesser Himalaya, Tethys Himalaya and Trans-Himalayan Batholiths) and to detect and quantify their relative contribution in Bengal turbidites and to highlight sediment mixing from specific sources thus enhancing provenance resolution with respect to bulk approaches.

Around 200 quartz grains in each sand sample from rivers draining exclusively a single Himalayan tectonic domain have been analyzed by ion microprobe LG-SIMS to better characterize their oxygen isotopic variability, thus providing a good fingerprint of the source rocks in the detrital record. Around 150 quartz grains from each Bengal Fan turbiditic sample have been analyzed to quantify the contribution of different Himalayan tectonic domains in Bengal Fan turbidites through time.

The new data, combined with data obtained with other bulk-sediment to single-mineral approaches, allow us to enhance provenance resolution and highlight the erosional evolution of the Himalayan-Tibetan orogen through time.

This new method can be profitably applied in any sediment-provenance study as a precious complement to traditional methods applied to the same quartz grains (luminescence, OH-defects, and petrographic characteristics) as well as classic techniques (e.g., petrography, heavy minerals, elemental geochemistry, isotope geochemistry) to discriminate detrital quartz derived from felsic igneous, metamorphic, or sedimentary sources.

Key words: Oxygen isotopes, Ion Probe LG-SIMS, Provenance analysis, Single-grain techniques, Himalayan orogen, Bengal fan

[1] Clayton, Jackson & Sridhar (1978), Geochimica et Cosmochimica Acta 42(10), 1517-1522.

[2] Blum, Rogers, Gleason, Najman, Cruz & Fox (2018), Scientific Reports 8(1), 7973.

[3] Chew, Najman, Mark, Barfod, Carter, Parrish, & Gemignani (2019), Bulletin of the Geological Society of America 131; 9-10.