Type and genesis of amphibole in the Huanghe River and Changjiang River estuaries and significance of its provenance

Abstract

Electronic probe analyses were performed on 343 and 406 sedimentary amphibole single-mineral samples extracted from five sampling points in the Huanghe River estuary and six in the Changjiang River estuary. The profiles of amphibole single-mineral major elements were determined for the two rivers using these samples. The cation coefficients and related parameters of 749 amphiboles were calculated based on 23 oxygen standards, and their crystal structure molecular formulae and related characteristic crystallochemical values were determined. The results show that the sedimentary amphiboles of the two estuaries belong to the calcic amphibole subgroup, where the majority is Magnesiohornblende, accounting for more than 70%, followed by Tschermakite. A genetic mineralogical analysis was carried out on the genesis type, magmatic source, and crystallization temperature and pressure environment of the amphiboles in the Huanghe River and Changjiang River estuaries, showing that most of the calcic amphiboles in these estuaries originated from metamorphic rocks, followed by magmatic rocks. Amphiboles of magmatic genesis in the Huanghe River and Changjiang River estuaries were largely crust-mantle type. Most of the metamorphic amphiboles originated in a metamorphic environment below moderate temperature and pressure. The amphiboles of the Huanghe River estuary mainly originate from the orogenic belt in the Northern Loess Plateau. The amphiboles of the Changjiang River estuary mainly originate from the middle and upper reaches of the Changjiang River, where the amphiboles mainly form as a result of magmatic and hydrothermal activity, as well as metamorphism. The chemical composition and characteristic values of sedimentary amphiboles in the Huanghe River and Changjiang River estuaries are stable, and can be used as standardized substances for terrestrial sediments.