Quartz-Hosted Fluid Inclusions Characteristics and Their Implications for Fluvial Deposits along the Changjiang River

Abstract

The characteristics of quartz-hosted fluid inclusions in fluvial sediments from five locations in the upstream, midstream, and estuary of the Changjiang River, China, are analyzed. The sources of sediments are discussed concerning their differences in the shape, size, number, gas percentage and genetic type of quartz-hosted fluid inclusions. From upstream to downstream, the characteristics of quartz-hosted fluid inclusions in sediments are different. The fluid inclusion types in the samples from upstream to estuary are gradually enriched. The sediment influx from the tributaries of the Changjiang River makes new types of quartz-hosted fluid inclusions in the downstream and estuary. In terms of the number and size, most quartz-hosted fluid inclusions are concentrated in the range of 2–4 µm in diameters and 10–150 in number per 10−3 mm3. The number and size ranges of the fluid inclusions from different positions are also different. The fluid inclusions in the sample collected from the Shigu, upstream of the Changjiang River, are 2–18 µm in size, with the number of 2–166 per 10−3 mm3. Among the samples collected from Yibin, Yichang and Wuhan, the sizes of fluid inclusions are 2–15, 2–10, 2–12 µm, with the number of 1–270, 2–220, and 1–308 per 10−3 mm3, respectively. The proportion of primary fluid inclusions in the sample of the upstream (14%) is higher than that of the midstream (6%–8%) and the estuary (5%), suggesting that different types of source rocks have been input into the river by the tributaries. The characteristics of quartz-hosted fluid inclusions in the fluvial sediments could offer a new perspective for exploration of the source of sediments.